The relationship between marine transgression and the distribution of lacustrine organic matter has restricted shale oil and gas exploration for decades.In this study,the research objective is to analyze the sedimenta...The relationship between marine transgression and the distribution of lacustrine organic matter has restricted shale oil and gas exploration for decades.In this study,the research objective is to analyze the sedimentary environment and evaluate its influence on organic matter in transgressive lacustrine shale.The study uses various analyses including total organic carbon(TOC),Rock-Eval pyrolysis,gas chromatography-mass spectrometry(GC-MS),trace element and isotope analysis.Finally,the study proposes an enrichment model for organic matter.The lacustrine shale of the second member of the Funing Formation(E_(1)f^(2))is divided into three sequences.The results indicate that the depositional environment of the organic matter during this period was an arid and humid,reduced,closed,rift lake basin.In the first sequence,high salinity resulted from increased evaporation,leading to low primary biological productivity.At this time,the lake basin belonged to a salinized closed lake basin.Intermittent transgressions began in the second sequence,with the deep lake area still being dominated by a reducing environment.The third sequence saw the environment evolve into a closed lake basin characterized by a warm and humid freshwater environment with high primary productivity.Marine transgressions introduce a substantial amount of marine plankton,nutrient elements,as well as more CO_(2) and CO_(3)^(2−)into the lake,leading to increased primary productivity.The sedimentary model for transgressive lacustrine source rocks proposed here serves as an example for similar transgressive lake basins.展开更多
The occurrence types and controlling factors of organic matter in the sepiolite-containing successions of the first member of Mid-Permian Maokou Formation(Mao-1 Member for short)in the Eastern Sichuan Basin,SW China,h...The occurrence types and controlling factors of organic matter in the sepiolite-containing successions of the first member of Mid-Permian Maokou Formation(Mao-1 Member for short)in the Eastern Sichuan Basin,SW China,have been investigated through outcrop section measurement,core observation,thin section identification,argon ion polishing-field scanning electron microscopy,energy spectrum analysis,X-ray diffraction,total organic carbon content(TOC),major and trace element analysis.Finally,the symbiotic adsorption model of sepiolite for organic matter enrichment has been established.The results show that the sepiolite-containing successions of the Mao-1 Member are composed of the rhythmite of mudstone,argillaceous limestone and limestone,with five depositional intervals vertically and the organic matter mostly developed in the mudstone and argillaceous limestone layers within the lower three intervals.The organic matter occurrence types are mostly layered or nodular in macro to meso-scale,blocky-vein-like under a microscope,but scattered,interstitial or adsorbed at a mesoscopic scale.It underwent transition processes from lower to higher salinity,from oxygen-poor and anoxic reduction to oxygen-poor and localized oxygen enrichment on the palaeo-environment of the Mao-1 Member.The first two intervals of the early depositional phase of Mao-1 Member constitute the cyclothems of mudstone,argillaceous limestone and limestone and quantities of fibrous-feathered sepiolite settle down within the Tongjiang-Changshou sag with continuous patchy organic matter from adsorption of alginate by sepiolite in intercrystalline,bedding surfaces and interlayer pores.The third and fourth intervals in the mid-depositional phase are mostly composed of the mudstone and argillaceous limestone alternations with the continuous patchy or banded organic matter in the surface and inter-crystalline pores of fibrous,feathered and flaky sepiolite.And the fifth interval in the late depositional phase of the Mao-1 Member comprises the cyclothems of extremely thin layered argillaceous limestone and thick-layered limestone with the fibrous sepiolite depositing in the argillaceous limestone and irregular organic matter dispersing around the sepiolite.Therefore,the symbiotic adsorption between organic matter and sepiolite effectively enhances the preservation efficiency of organic matter and improves the source rock quality of the Mao-1 Member,which enhances our understanding on the enrichment model of the depositional organic matter.展开更多
Cadmium (Cd) pollution of agricultural soil is of public concern due to its high potential toxicity and mobility.This study aimed to reveal the risk of Cd accumulation in soil and wheat/maize systems,with a specific f...Cadmium (Cd) pollution of agricultural soil is of public concern due to its high potential toxicity and mobility.This study aimed to reveal the risk of Cd accumulation in soil and wheat/maize systems,with a specific focus on the source-specific ecological risk,human health risk and Cd enrichment model.For this we investigated more than 6100 paired soil and grain samples with 216 datasets including soil Cd contents,soil pH and grain Cd contents of 85 sites from China.The results showed that mining activities,sewage irrigation,industrial activities and agricultural practices were the critical factors causing Cd accumulation in wheat and maize cultivated sites.Thereinto,mining activities contributed to a higher Cd accumulation risk in the southwest China and Middle Yellow River regions;sewage irrigation influenced the Cd accumulation in the North China Plain.In addition,the investigated sites were classified into different categories by comparing their soil and grain Cd contents with the Chinese soil screening values and food safety values,respectively.Cd enrichment models were developed to predict the Cd levels in wheat and maize grains.The results showed that the models exhibited a good performance for predicting the grain Cd contents among safe and warning sites of wheat (R2=0.61 and 0.72,respectively);while the well-fitted model for maize was prone to the overestimated sites (R2=0.77).This study will provide national viewpoints for the risk assessments and prediction of Cd accumulation in soil and wheat/maize systems.展开更多
Compared with marine facies shale strata,lacustrine shale strata are more complicated in geological conditions,and thus more difficult to explore and develop.To realize economic exploration and development of lacustri...Compared with marine facies shale strata,lacustrine shale strata are more complicated in geological conditions,and thus more difficult to explore and develop.To realize economic exploration and development of lacustrine shale oil,the geological regularities of accumulation and high yield of retained movable petroleum in shale should be understood first.In this work,taking the shale strata of Kong 2 Member and Sha 3 Member in the Paleogene of Huanghua depression in the Bohai Bay Basin as examples,based on the previous joint analysis results of over ten thousand core samples and the latest oil testing,production test and geochemical data of more than 30 horizontal wells,accumulation conditions and models of retained movable petroleum in lacustrine shale were studied comprehensively.The study shows that at moderate organic matter abundance(with TOC from 2%to 4%),shale strata have the best match between oil content and brittleness,and thus are rich in oil and good in fracability.Moderate ancient lake basin size and moderate sediment supply intensity are the internal factors leading to best coupling of organic matter abundance and brittle mineral content in the shale formation.Moderate thermal evolution maturity of Ro of 0.7%–1.0%(at burial depth of 3200 to 4300 m)is the interval where oil generation from thermal evolution and oil adsorption by kerogen in shale layers match best,and retained movable petroleum is high in proportion.Moderate diagenetic evolution stage(3200 to 4300 m in the middle diagenetic stage A)is conducive to the formation of a large number of dissolved pores and organic matter pores,which provide storage space for shale oil enrichment.Moderate development degree of natural fractures(without damaging the shale oil roof and floor sealing conditions)is conducive to the storage,seepage and preservation of shale oil.The research results have overthrown the general understanding that high organic matter abundance,high maturity,and high development degree of natural fractures are conducive to shale oil enrichment,and have guided the comprehensive evaluation of shale oil and gas sweet spots and well deployment in the second member of the Kongdian Formation in the Cangdong sag and the Shahejie Formation in the Qikou sag.Industrial development of the shale oil in Kong 2 Member of the Cangdong sag has made major breakthrough,and important signs of shale oil have been found in Sha 3 Member of the Qikou sag,demonstrating huge exploration potential of lacustrine shale oil.展开更多
Based on the geochemical,seismic,logging and drilling data,the Fuyu reservoirs of the Lower Cretaceous Quantou Formation in northern Songliao Basin are systematically studied in terms of the geological characteristics...Based on the geochemical,seismic,logging and drilling data,the Fuyu reservoirs of the Lower Cretaceous Quantou Formation in northern Songliao Basin are systematically studied in terms of the geological characteristics,the tight oil enrichment model and its major controlling factors.First,the Quantou Formation is overlaid by high-quality source rocks of the Upper Cretaceous Qingshankou Formation,with the development of nose structure around sag and the broad and continuous distribution of sand bodies.The reservoirs are tight on the whole.Second,the configuration of multiple elements,such as high-quality source rocks,reservoir rocks,fault,overpressure and structure,controls the tight oil enrichment in the Fuyu reservoirs.The source-reservoir combination controls the tight oil distribution pattern.The pressure difference between source and reservoir drives the charging of tight oil.The fault-sandbody transport system determines the migration and accumulation of oil and gas.The positive structure is the favorable place for tight oil enrichment,and the fault-horst zone is the key part of syncline area for tight oil exploration.Third,based on the source-reservoir relationship,transport mode,accumulation dynamics and other elements,three tight oil enrichment models are recognized in the Fuyu reservoirs:(1)vertical or lateral migration of hydrocarbon from source rocks to adjacent reservoir rocks,that is,driven by overpressure,hydrocarbon generated is migrated vertically or laterally to and accumulates in the adjacent reservoir rocks;(2)transport of hydrocarbon through faults between separated source and reservoirs,that is,driven by overpressure,hydrocarbon migrates downward through faults to the sandbodies that are separated from the source rocks;and(3)migration of hydrocarbon through faults and sandbodies between separated source and reservoirs,that is,driven by overpressure,hydrocarbon migrates downwards through faults to the reservoir rocks that are separated from the source rocks,and then migrates laterally through sandbodies.Fourth,the differences in oil source conditions,charging drive,fault distribution,sandbody and reservoir physical properties cause the differential enrichment of tight oil in the Fuyu reservoirs.Comprehensive analysis suggests that the Fuyu reservoir in the Qijia-Gulong Sag has good conditions for tight oil enrichment and has been less explored,and it is an important new zone for tight oil exploration in the future.展开更多
The coal measure of Middle Jurassic Walloon Subgroup is the main reservoir of coalbed methane(CBM)reservoirs in the Surat Basin,Australia,and it is a set of typical low-rank,high-yield coal measure.To figure out the C...The coal measure of Middle Jurassic Walloon Subgroup is the main reservoir of coalbed methane(CBM)reservoirs in the Surat Basin,Australia,and it is a set of typical low-rank,high-yield coal measure.To figure out the CBM accumulation conditions and enrichment models of this coal measure,its distribution characteristics,source rock characteristics,reservoir characteristics and preservation conditions were inves-tigated based on mud logging,experimental and testing data.Then,based on the analysis results of gas origin and gas bearing property of this coal measure,3 CBM development areas in northeastern Surat Basin were analyzed and compared in terms of its gas enrichment model,and favorable conditions for CBM accumulation and enrichment of Walloon coal measure(WCM)was summarized.It is indicated that tectonic movements,groundwater conditions and macerals provide favorable conditions for gas generation of Walloon coal.The roof,floor and interbed of this coal measure are lithologically tight,presenting a good sealing capacity.Besides,the Walloon CBM reservoir is a mixed origin gas reservoir with the secondary biogenic methane as the dominant component formed in a monocline structure jointly sealed by hydrodynamic force and lithology.CBM enrichment is controlled by 3 factors,i.e.,local structure,methane generating capacity of coal bed and underground hydrodynamic force,and it can be divided into 3 models,i.e.,anticline model,syncline model and slope model,among which,the CBM enrichment degree of the former two models is higher.Finally,different from other CBM reservoirs,the Walloon CBM reservoir satisfies four favorable conditions in CBM accumulation and enrichment,including dual-carbon source,efficient methane generation,moderate hydrodynamic force and double sealing.展开更多
Marine shale gas in the southern Sichuan Basin is the most successful area of shale gas exploration and development in China.In order to open up new shale gas fields and search for new shale gas reserves and productio...Marine shale gas in the southern Sichuan Basin is the most successful area of shale gas exploration and development in China.In order to open up new shale gas fields and search for new shale gas reserves and production replacement blocks,it is necessary to continuously establish and complete the standards on shale gas reservoir evaluation and area selection under different structural settings.The early exploration practice shows that shale in the mountainous complex structural area along the southwestern margin of the Sichuan Basin varies greatly in the gas bearing property,so systematical analysis and study on the shale gas enrichment mechanisms in this area is of great significance to searching for new shale gas exploration areas.Based on drilling data of 5 wells in the mountainous complex structural area along the southwestern margin of the Sichuan Basin,the main factors controlling the shale gas bearing property and the shale gas enrichment model were discussed based on the systematical experiments and analysis of the outcrops,cores and cuttings of Longmaxi Formation shale from the aspects of organic geochemistry,physical property,gas content,hydrocarbon generation history and pore evolution history,so as to lay a solid geological basis for the birth of a new shale gas area.And the following research results were obtained.First,the shale of the first submember of first Member of Longmaxi Formation(S1l11)in the mountainous complex structural area along the southwestern margin of the Sichuan Basin has an average TOC of 3.02%–4.97%and Ro of 2.38%–3.37%,and the average total gas content in local enrichment zones is up to 4.62 m^(3)/t,so it is classified as quality shale.Second,the detailed studies on hydrocarbon generation history indicate that the shale has the characteristics of“low thermal evolution rate and low maturity”.It is characterized by late hydrocarbon generation,low thermal evolution rate,low current maturity and short late diffusion time,which are favorable for shale gas enrichment.Third,the pore evolution history reveals that shale pore evolution can be divided into six stages,i.e.,sharp pore reduction,pore reduction,organic pore formation,pore preservation,organic pore dissipation and karstification,and organic pore and TOC are the most direct control factors of shale gas content.Fourth,favorable shelf facies belt is conducive to the formation of large-scale reservoir space and effective pores,and diversities of preservation conditions under different structural styles and at different structural positions control different pore evolution stages.The shale gas in the mountainous complex structural area is characterized by horizontal zoning and differential enrichment.“Low thermal evolution rate and low maturity”and“slow structural uplifting”are beneficial to the long-term enrichment and preservation of shale gas.In conclusion,the mountainous complex structural area along the southwestern margin of the Sichuan Basin has a shale gas enrichment model of“sedimentation controlling source rocks,diagenesis controlling reservoirs and structure controlling preservation”.This research result provides idea and reference for searching for new shale gas areas and fields.展开更多
To understand the shale gas reservoirs in the first member of the Permian Maokou Formation(Mao 1 Member)in Nanchuan area of the Sichuan Basin,we used outcrops,cores,mineralogical and geochemical datas,thin-section ana...To understand the shale gas reservoirs in the first member of the Permian Maokou Formation(Mao 1 Member)in Nanchuan area of the Sichuan Basin,we used outcrops,cores,mineralogical and geochemical datas,thin-section analysis,and argon-ion-polishing scanning electron microscopy results with logging and seismic attribute prediction techniques to study the sedimentary facies,source rocks,reservoir properties and types.The geological characteristics and enrichment model of shale gas reservoirs of the Mao 1 Member were revealed and are summarized as follows:(1)the Maokou Formation can be divided into four members from bottom to top.The Mao 1 Member is located in the relatively deep-water gentle slope of a carbonate platform,comprising well-developed dark-gray/grayish-black carbonaceous mudstone,calcareous mudstone,argillaceous limestone,and bioclastic limestone.Carbonaceous and calcareous mudstones,with a relatively high total organic carbon content(TOC0.5-5.1%)and moderate thermal maturity(Ro:2.0-2.3%),are potentially good hydrocarbon source rocks with possibly new type of atypical shale gas reservoir;(2)organic pores,dissolution pores,grain margin fractures,and shrinkage fractures are developed in the Mao 1 Member and may form a reservoir of a complex“poreefractureenetwork,”which is beneficial to gas storage and migration;(3)the shale gas in the Mao 1 Member has the accumulation and enrichment model of“integrated source and reservoir,continuous distribution,and structurefracture dual reservoir control”with a continuous distribution area exceeding 500 km^(2)and a geological resource volume exceeding 70 billion cubic meters;therefore,it has great exploration potential for shale gas.The research results are crucial in improving the understanding of new type of shale gas geology and guide shale gas exploration in southeastern Sichuan.展开更多
Based on the analysis of Upper Paleozoic source rocks, source-reservoir-caprock assemblage, and gas accumulation characteristics in the Ordos Basin, the gas accumulation geological model of total petroleum system is d...Based on the analysis of Upper Paleozoic source rocks, source-reservoir-caprock assemblage, and gas accumulation characteristics in the Ordos Basin, the gas accumulation geological model of total petroleum system is determined. Then, taking the Carboniferous Benxi Formation and the Permian Taiyuan Formation and Shanxi Formation as examples, the main controlling factors of gas accumulation and enrichment are discussed, and the gas enrichment models of total petroleum system are established. The results show that the source rocks, faults and tight reservoirs and their mutual coupling relations control the distribution and enrichment of gas. Specifically, the distribution and hydrocarbon generation capacity of source rocks control the enrichment degree and distribution range of retained shale gas and tight gas in the source. The coupling between the hydrocarbon generation capacity of source rocks and the physical properties of tight reservoirs controls the distribution and sweet spot development of near-source tight gas in the basin center. The far-source tight gas in the basin margin is mainly controlled by the distribution of faults, and the distribution of inner-source, near-source and far-source gas is adjusted and reformed by faults. Generally, the Upper Paleozoic gas in the Ordos Basin is recognized in four enrichment models: inner-source coalbed gas and shale gas, inner-source tight sandstone gas, near-source tight gas, and far-source fault-transported gas. In the Ordos Basin, inner-source tight gas and near-source tight gas are the current focuses of exploration, and inner-source coalbed gas and shale gas and far-source gas will be important potential targets in the future.展开更多
Based on the combination of core observation,experimental analysis and testingand geological analysis,the main controlling factors of shale oil enrichment in the Lower Permian Fengcheng Formation in the Mahu Sag of th...Based on the combination of core observation,experimental analysis and testingand geological analysis,the main controlling factors of shale oil enrichment in the Lower Permian Fengcheng Formation in the Mahu Sag of the Junggar Basin are clarified,and a shale oil enrichment model is established.The results show that the enrichment of shale oil in the Fengcheng Formation in the Mahu Sag is controlled by the organic abundance,organic type,reservoir capacity and the amount of migration hydrocarbon in shale.The abundance of organic matter provides the material basis for shale oil enrichment,and the shales containing typesⅠandⅡorganic matters have good oil content.The reservoir capacity controls shale oil enrichment.Macropores are the main space for shale oil enrichment in the Fengcheng Formation,and pore size and fracture scale directly control the degree of shale oil enrichment.The migration of hydrocarbons in shale affects shale oil enrichment.The shale that has expelled hydrocarbons has poor oil content,while the shale that has received hydrocarbons migrated from other strata has good oil content.Lithofacies reflect the hydrocarbon generation and storage capacity comprehensively.The laminated felsic shale,laminated lime-dolomitic shale and thick-layered felsic shale have good oil content,and they are favorable lithofacies for shale oil enrichment.Under the control of these factors,relative migration of hydrocarbons occurred within the Fengcheng shale,which leads to the the difference in the enrichment process of shale oil.Accordingly,the enrichment mode of shale oil in Fengcheng Formation is established as"in-situ enrichment"and"migration enrichment".By superimposing favorable lithofacies and main controlling factors of enrichment,the sweet spot of shale oil in the Fengcheng Formation can be selected which has great significance for the exploration and development of shale oil.展开更多
The Middle Jurassic Xishanyao Formation in the central section of the southern Junggar Basin has substantial amounts of low-ranked coalbed methane(CBM)recourses and is typically characterized by multi superimposed coa...The Middle Jurassic Xishanyao Formation in the central section of the southern Junggar Basin has substantial amounts of low-ranked coalbed methane(CBM)recourses and is typically characterized by multi superimposed coal seams.To establish the CBM enrichment model,a series of experimental and testing methods were adopted,including coal maceral observation,proximate analysis,low temperature nitrogen adsorption(LTNA),methane carbon isotope determination,porosity/permeability simulation caused by overburden,and gas content testing.The controlling effect of sedimentary environment,geological tectonic,and hydrogeological condition on gas content was analyzed in detail.The results demonstrate that the areas with higher gas content(an average of 8.57 m3/t)are mainly located in the Urumqi River-Santun River(eastern study area),whereas gas content(an average of 3.92 m3/t)in the Manasi River-Taxi River(western study area)is relatively low.Because of the combined effects of strata temperature and pressure,the gas content in coal seam first increases and then decreases with increasing buried depth,and the critical depth of the inflection point ranges from 600 m to 850 m.Affected by the changes in topography and water head height,the direction of groundwater migration is predicted from south to north and from west to east.Based on the gas content variation,the lower and middle parts of the Xishanyao Formation can be divided into three independent coalbearing gas systems.Within a single gas-bearing system,there is a positive correlation between gas content and strata pressure,and the key mudstone layers separating each gas-bearing system are usually developed at the end of each highstand system tract.The new CBM accumulation model of the multi-coals mixed genetic gas shows that both biological and thermal origins are found in a buried depth interval between 600 m and 850 m,suggesting that the coals with those depths are the CBM enrichment horizons and favorable exploration regions in the middle section of the southern Junggar Basin.An in-depth discussion of the low-rank CBM enrichment model with multi-coal seams in the study region can provide a basis for the optimization of CBM well locations and favorable exploration horizons.展开更多
Owing to the characteristics of chemical inertness,low molecular weight,low boiling point,strong permeability and high heat conductivity,helium is extensively used in the fields of aerospace,low-temperature supercondu...Owing to the characteristics of chemical inertness,low molecular weight,low boiling point,strong permeability and high heat conductivity,helium is extensively used in the fields of aerospace,low-temperature superconductivity,medicine and high tech,and it is a kind of irreplaceable strategic rare resource.So far,however,less research has been conducted on the enrichment of helium in natural gas reservoirs.To solve this problem,this paper discusses the classification standard of helium-rich gas reservoirs.Based on this,the origin,source and enrichment process of helium in typical helium-rich gas reservoirs are studied,highlighting the contribution of main helium sources to helium-rich gas reservoirs.In addition,helium enrichment models of helium-rich gas reservoir in petroliferous basins are established.And the following research results are obtained.First,6 helium enrichment models of two categories(crust-source helium enrichment and crust-mantle mixing helium enrichment)are established for different petroliferous basins in China.Second,helium-rich gas reservoirs are characterized by using the multiple helium supply and diverse helium enrichment model.And no matter what enrichment model it is,the contribution of the main helium source to gas reservoirs is indispensable.Third,the helium in the gas reservoirs of central and western basins is mainly crust-source helium,and its enrichment models include ancient formation water moving upward along the fault to dilute helium,helium enrichment in the process of natural gas migration along ancient reservoirs,and helium enrichment of shale gas.Fourth,the helium in the helium-rich gas reservoirs of eastern basins is of crust-mantle mixing origin and its enrichment models are mainly hydrocarbon gas based,carbon dioxide based and nitrogen based.In conclusion,the establishment of the helium enrichment models of helium-rich gas reservoirs in petroliferous basins provides reference and guidance for studying helium enrichment laws and main controlling factors and is of great significance to the evaluation of favorable helium exploration areas.展开更多
The relationship between fracture calcite veins and shale gas enrichment in the deep Ordovician Wufeng Formation-Silurian Longmaxi Formation (Wufeng-Longmaxi) shales in southern Sichuan Basin was investigated through ...The relationship between fracture calcite veins and shale gas enrichment in the deep Ordovician Wufeng Formation-Silurian Longmaxi Formation (Wufeng-Longmaxi) shales in southern Sichuan Basin was investigated through core and thin section observations, cathodoluminescence analysis, isotopic geochemistry analysis, fluid inclusion testing, and basin simulation. Tectonic fracture calcite veins mainly in the undulating part of the structure and non-tectonic fracture calcite veins are mainly formed in the gentle part of the structure. The latter, mainly induced by hydrocarbon generation, occurred at the stage of peak oil and gas generation, while the former turned up with the formation of Luzhou paleouplift during the Indosinian. Under the influence of hydrocarbon generation pressurization process, fractures were opened and closed frequently, and oil and gas episodic activities are recorded by veins. The formation pressure coefficient at the maximum paleodepth exceeds 2.0. The formation uplift stage after the Late Yanshanian is the key period for shale gas migration. Shale gas migrates along the bedding to the high part of the structure. The greater the structural fluctuation is, the more intense the shale gas migration activity is, and the loss is more. The gentler the formation is, the weaker the shale gas migration activity is, and the loss is less. The shale gas enrichment in the core of gentle anticlines and gentle synclines is relatively higher.展开更多
Stable isotopic compositions （δ18O and 6D） have been utilized as a useful indicator for evaluating the current and historical climatic and environmental changes. Therefore, it is vital to understand the relationshi...Stable isotopic compositions （δ18O and 6D） have been utilized as a useful indicator for evaluating the current and historical climatic and environmental changes. Therefore, it is vital to understand the relationship be- tween the stable isotopic contents in lake water and the variations of lake level, particularly in Lake Qinghai, China. In this study, we analyzed the variations of isotope compositions （δ18O, 6D and d-excess） in lake water and pre- cipitation by using the samples that were collected from Lake Qinghai region during the period from 2009 to 2012. The results showed that the average isotopic contents of δ18O and 6D in lake water were higher than those in pre- cipitation, which were contrary to the variations of d-excess. The linear regression correlations between δ18O and 6D in lake water and precipitation showed that the local evaporative line （LEL） in lake water （δD=5.88δ18O-2.41） deviated significantly from the local meteoric water line （LMWL）in precipitation （δD=8.26δ18O＋16.91）, indicating that evaporative enrichment had a significant impact on isotopic contents in lake water. Moreover, we also quanti- fied the Eli ratio （evaporation-to-input ratio） in Lake Qinghai based on the lake water isotopic enrichment model derived from the Rayleigh equation. The changes of E/I ratios （ranging from 0.29 to 0.36 between 2009 and 2012） clearly revealed the shifts of lake levels in Lake Qinghai in recent years. The average E/I ratio of 0.40 reflected that water budget in Lake Qinghai was positive, and consistent with the rising lake levels and the increasing lake areas in many lakes of the Tibetan Plateau. These findings provide some evidences for studying the hydrological balance or water budget by using δ18O values of lake sedimentary materials and contribute to the reconstruction of paleo- lake water level and paleoclimate from an isotopic enrichment model in Lake Qinghai.展开更多
Taking the tight oil of the Zhongnan sag in the Ordos Basin,Jimusar sag in the Junggar Basin and Qingxi sag in the Jiuquan Basin as study objects,based on field survey,dissection of tight oil reservoirs,sample test,mo...Taking the tight oil of the Zhongnan sag in the Ordos Basin,Jimusar sag in the Junggar Basin and Qingxi sag in the Jiuquan Basin as study objects,based on field survey,dissection of tight oil reservoirs,sample test,modeling experiment and comprehensive analysis,this study reveals that the tight oil accumulates at start-up pressure,advances under differential pressure,diffuses at alternating fast and low speeds,charges in stepped large area and migrates rapidly through fractures,and enriches in dominant fractures and pores.The root cause of ladder-like charge is the multiple scales of pores.The widespread source rock with high hydrocarbon generation intensity is the material basis for tight oil enrichment;the dominant source reservoir assemblage is the basic unit for tight oil enrichment;fractures and beddings are conducive to local rapid migration of tight oil;fractures and pores work together to control the enrichment of tight oil.Two typical accumulation models of tight oil are established,namely"source reservoir in coexistence,four optimal factors controlling enrichment around central area,and large-scale continuous distribution"for a large freshwater lake clastic rock basin and"source reservoir integration,four optimal factors controlling enrichment,central area distribution,small in size but high in enrichment degree"for a small saline lake diamictite depression.展开更多
Based on formation testing data of more than 40 wells with industrial oil flow, systematic observation of 1 010.26 m long cores taken from 4 wells and test data of over 10 000 core samples combining with drilling and ...Based on formation testing data of more than 40 wells with industrial oil flow, systematic observation of 1 010.26 m long cores taken from 4 wells and test data of over 10 000 core samples combining with drilling and pilot fracturing data of multiple wells, the geological characteristics of the upper submember of the Sha 4 Member to the lower submember of the Sha 3 Member of Paleogene(Es4s-Es3x) in the Jiyang Depression were investigated to find out factors controlling the enrichment of shale oil and the accumulation model of shale oil, and a comprehensive evaluation method for shale oil sweet spots was established. It is found through the study that the target shale layer is characterized by strong heterogeneity, weak diagenesis, low thermal evolution and high content of clay and carbonate minerals. Shale lithofacies, microcrack, thin interlayer and abnormal pressure are the main factors affecting enrichment and stable production of shale oil, the organic rich laminar shale has the best storage and oil-bearing capacity, microcrack network system improve the storage capacity and permeability of the shale, the thin interlayer is the main flow channel for stable shale oil production, and the abnormal high pressure layer is rich in free state shale oil and high in oil content. The shale oil layers in the target section were divided into three types: matrix, interlayer and fracture ones. According to the occurrence state and exploration practice of shale oil at home and abroad, it is concluded that the interlayer shale oil is the most profitable type at present. The selection parameters for the different types of shale oil were determined, and accordingly the favorable areas were pointed out by comprehensive evaluation of multiple factors. Vertical wells in the interlayer shale oil reservoir, such as Fan 159, Fan 143 and GX 26, were stimulated by volume fracturing and high conductivity channel fracturing jointly. After fracturing, they had a daily oil production of over 6 t, up to 44 t, and stable productivity. Shale oil is expected to become an important replacement energy resource in the Jiyang Depression.展开更多
Pure shales in the first member of Qingshankou Formation(simplified as Qing 1 Member)in the southern Songliao Basin,i.e.,the semi-deep and deep lacustrine shales,are characterized by a high content of clay minerals an...Pure shales in the first member of Qingshankou Formation(simplified as Qing 1 Member)in the southern Songliao Basin,i.e.,the semi-deep and deep lacustrine shales,are characterized by a high content of clay minerals and poor hydrocarbon mobility,making the development of shale oil difficult.According to the drilling and testing results,the shale of Qing 1 Member can be classified into 3 lithofacies,i.e.,bedded argillaceous shale,laminated diamictite shale,and interbedded felsic shale.The TOC and brittle minerals control the enrichment of shale oil,of them,TOC controls the total oil content,in other words,the total oil content increases with the increase of TOC;while the laminae made up of brittle minerals contain a large number of bigger intergranular pores which are favorable enrichment space for movable shale oil.In consideration of the origins of the 3 lithofacies,two shale oil enrichment models are classified,i.e.,the deep lacustrine high-TOC bedded argillaceous shale(Model-I)and the semi-deep lacustrine moderate-high-TOC laminated diamictite shale(Model-II).In the Model-I,the shale is characterized by high hydrocarbon generation ability,high total oil content,abundant horizontal bedding fractures,and vertical and high angle fractures locally;the complex fracture network formed by horizontal bedding fractures and vertical fractures improve the storage capacity and permeability of the shale reservoir,increase the enrichment space for movable oil.In the Model-II,the shale is characterized by good hydrocarbon generation ability and fairly high total oil content,and as the brittle laminae contain large intergranular pores,the shale has a higher movable oil content.Based on the two models,shale oil sweet-spot areas of 2880 km2 in the southern Songliao Basin are favorable for further exploration.Aimed at the difficulties in reservoir fracturing of the lacustrine shale with a high content of clay minerals,the composite fracturing technology with supercritical carbon dioxide was used in the shale oil reservoir for the first time,realizing large-scale volume fracturing in shale with a high content of clay minerals and strong heterogeneity,marking a breakthrough of oil exploration in continental shale with a high content of clay minerals in China.展开更多
|Editorial Note| Since reform and opening up,China has embarked on a path of development featuring socialism with Chinese characteristics,scoring remarkable achievements that have drawn attention from all over the wor...|Editorial Note| Since reform and opening up,China has embarked on a path of development featuring socialism with Chinese characteristics,scoring remarkable achievements that have drawn attention from all over the world.What has reform and opening up achieved?What are its experiences?What are the intrinsic values of socialism with Chinese characteristics?How is China’s development path viewed in the international community? This paper gives an overview of these questions,shedding light on the problems that the country faces and optimism about its future.展开更多
The basic geological characteristics of the Qiongzhusi Formation reservoirs and conditions for shale gas enrichment and high-yield were studied by using methods such as mineral scanning,organic and inorganic geochemis...The basic geological characteristics of the Qiongzhusi Formation reservoirs and conditions for shale gas enrichment and high-yield were studied by using methods such as mineral scanning,organic and inorganic geochemistry,breakthrough pressure,and triaxial mechanics testing based on the core,logging,seismic and production data.(1)Both types of silty shale,rich in organic matter in deep water and low in organic matter in shallow water,have good gas bearing properties.(2)The brittle mineral composition of shale is characterized by comparable feldspar and quartz content.(3)The pores are mainly inorganic pores with a small amount of organic pores.Pore development primarily hinges on a synergy between felsic minerals and total organic carbon content(TOC).(4)Dominated by Type I organic matters,the hydrocarbon generating organisms are algae and acritarch,with high maturity and high hydrocarbon generation potential.(5)Deep-and shallow-water shale gas exhibit in-situ and mixed gas generation characteristics,respectively.(6)The basic law of shale gas enrichment in the Qiongzhusi Formation was proposed as“TOC controlled accumulation and inorganic pore controlled enrichment”,which includes the in-situ enrichment model of“three highs and one over”(high TOC,high felsic mineral content,high inorganic pore content,overpressured formation)for organic rich shale represented by Well ZY2,and the in-situ+carrier-bed enrichment model of“two highs,one medium and one low”(high felsic content,high formation pressure,medium inorganic pore content,low TOC)for organic-poor shale gas represented by Well JS103.It is a new type of shale gas that is different from the Longmaxi Formation,enriching the formation mechanism of deep and ultra-deep shale gas.The deployment of multiple exploration wells has achieved significant breakthroughs in shale gas exploration.展开更多
The high-quality laminated source rock organic matter(OM)originated from planktonic algae,and its sedimentation was affected by global climate change significantly in the upper Xiaganchaigou Formation of the western Q...The high-quality laminated source rock organic matter(OM)originated from planktonic algae,and its sedimentation was affected by global climate change significantly in the upper Xiaganchaigou Formation of the western Qaidam Basin.However,coupling research on the paleoenvironment change and OM enrichment during the sedimentation period of the source rock is still lacking.This study from the aspects of sedimentary petrology,geochemistry and paleontology palynology,the paleoenvironment of source rock is restored and the OM enrichment model is established in the study area.Firstly,kerogen maceral identification indicates that the kerogen maceral is mainly composed of Botryococcus,accompanied with amorphous organic matter and plant debris.Secondly,arid climate and relatively active tectonic were observed during the deposition of the source rock.The water column was received felsic source from the continental island arc tectonic background,and has the environmental characteristics of relatively saline,shallow depth,medium low productivity,fast sedimentation rate and anoxic reduction and so on.Lastly,the first-order controlling factors for the OM enrichment are anoxic water conditions and suitable sedimentation rate,and the secondary controlling factor is paleoproductivity.Through the coupling study of paleoclimate,paleoenvironment and OM enrichment,the paleoclimate high frequency alternating evolution was the root cause of sedimentary environment change and OM enrichment of the laminated shale in the Upper Xiaganchaigou Formation.The study on the OM enrichment mechanism of algae in Qaidam provides a good model for understanding the coupling relationship between the algae bloom in the saline lake basins and the environments,and provides important theoretical basis for predicting shale oil“sweet spot”and production well sites arrangement for the continental saline lacustrine basins.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.42072150)and we thank the sponsors of these projects.
文摘The relationship between marine transgression and the distribution of lacustrine organic matter has restricted shale oil and gas exploration for decades.In this study,the research objective is to analyze the sedimentary environment and evaluate its influence on organic matter in transgressive lacustrine shale.The study uses various analyses including total organic carbon(TOC),Rock-Eval pyrolysis,gas chromatography-mass spectrometry(GC-MS),trace element and isotope analysis.Finally,the study proposes an enrichment model for organic matter.The lacustrine shale of the second member of the Funing Formation(E_(1)f^(2))is divided into three sequences.The results indicate that the depositional environment of the organic matter during this period was an arid and humid,reduced,closed,rift lake basin.In the first sequence,high salinity resulted from increased evaporation,leading to low primary biological productivity.At this time,the lake basin belonged to a salinized closed lake basin.Intermittent transgressions began in the second sequence,with the deep lake area still being dominated by a reducing environment.The third sequence saw the environment evolve into a closed lake basin characterized by a warm and humid freshwater environment with high primary productivity.Marine transgressions introduce a substantial amount of marine plankton,nutrient elements,as well as more CO_(2) and CO_(3)^(2−)into the lake,leading to increased primary productivity.The sedimentary model for transgressive lacustrine source rocks proposed here serves as an example for similar transgressive lake basins.
基金Supported by National Natural Science Foundation of China(42572132,U24B6001,41872150,42230310,U2344209).
文摘The occurrence types and controlling factors of organic matter in the sepiolite-containing successions of the first member of Mid-Permian Maokou Formation(Mao-1 Member for short)in the Eastern Sichuan Basin,SW China,have been investigated through outcrop section measurement,core observation,thin section identification,argon ion polishing-field scanning electron microscopy,energy spectrum analysis,X-ray diffraction,total organic carbon content(TOC),major and trace element analysis.Finally,the symbiotic adsorption model of sepiolite for organic matter enrichment has been established.The results show that the sepiolite-containing successions of the Mao-1 Member are composed of the rhythmite of mudstone,argillaceous limestone and limestone,with five depositional intervals vertically and the organic matter mostly developed in the mudstone and argillaceous limestone layers within the lower three intervals.The organic matter occurrence types are mostly layered or nodular in macro to meso-scale,blocky-vein-like under a microscope,but scattered,interstitial or adsorbed at a mesoscopic scale.It underwent transition processes from lower to higher salinity,from oxygen-poor and anoxic reduction to oxygen-poor and localized oxygen enrichment on the palaeo-environment of the Mao-1 Member.The first two intervals of the early depositional phase of Mao-1 Member constitute the cyclothems of mudstone,argillaceous limestone and limestone and quantities of fibrous-feathered sepiolite settle down within the Tongjiang-Changshou sag with continuous patchy organic matter from adsorption of alginate by sepiolite in intercrystalline,bedding surfaces and interlayer pores.The third and fourth intervals in the mid-depositional phase are mostly composed of the mudstone and argillaceous limestone alternations with the continuous patchy or banded organic matter in the surface and inter-crystalline pores of fibrous,feathered and flaky sepiolite.And the fifth interval in the late depositional phase of the Mao-1 Member comprises the cyclothems of extremely thin layered argillaceous limestone and thick-layered limestone with the fibrous sepiolite depositing in the argillaceous limestone and irregular organic matter dispersing around the sepiolite.Therefore,the symbiotic adsorption between organic matter and sepiolite effectively enhances the preservation efficiency of organic matter and improves the source rock quality of the Mao-1 Member,which enhances our understanding on the enrichment model of the depositional organic matter.
基金supported by the Key Science and Technology Projects of Inner Mongolia Autonomous Region (No. 2019ZD001)the State Key Laboratory of North China Crop Improvement and Regulationthe DeutscheForschungsgemeinschaft (DFG, German Research Foundation)–328017493/GRK 2366 (Sino-German International Research Training Group AMAIZE-P)。
文摘Cadmium (Cd) pollution of agricultural soil is of public concern due to its high potential toxicity and mobility.This study aimed to reveal the risk of Cd accumulation in soil and wheat/maize systems,with a specific focus on the source-specific ecological risk,human health risk and Cd enrichment model.For this we investigated more than 6100 paired soil and grain samples with 216 datasets including soil Cd contents,soil pH and grain Cd contents of 85 sites from China.The results showed that mining activities,sewage irrigation,industrial activities and agricultural practices were the critical factors causing Cd accumulation in wheat and maize cultivated sites.Thereinto,mining activities contributed to a higher Cd accumulation risk in the southwest China and Middle Yellow River regions;sewage irrigation influenced the Cd accumulation in the North China Plain.In addition,the investigated sites were classified into different categories by comparing their soil and grain Cd contents with the Chinese soil screening values and food safety values,respectively.Cd enrichment models were developed to predict the Cd levels in wheat and maize grains.The results showed that the models exhibited a good performance for predicting the grain Cd contents among safe and warning sites of wheat (R2=0.61 and 0.72,respectively);while the well-fitted model for maize was prone to the overestimated sites (R2=0.77).This study will provide national viewpoints for the risk assessments and prediction of Cd accumulation in soil and wheat/maize systems.
基金Supported by the PetroChina Science and Technology Major Project(2019E-2601,2018E-11)
文摘Compared with marine facies shale strata,lacustrine shale strata are more complicated in geological conditions,and thus more difficult to explore and develop.To realize economic exploration and development of lacustrine shale oil,the geological regularities of accumulation and high yield of retained movable petroleum in shale should be understood first.In this work,taking the shale strata of Kong 2 Member and Sha 3 Member in the Paleogene of Huanghua depression in the Bohai Bay Basin as examples,based on the previous joint analysis results of over ten thousand core samples and the latest oil testing,production test and geochemical data of more than 30 horizontal wells,accumulation conditions and models of retained movable petroleum in lacustrine shale were studied comprehensively.The study shows that at moderate organic matter abundance(with TOC from 2%to 4%),shale strata have the best match between oil content and brittleness,and thus are rich in oil and good in fracability.Moderate ancient lake basin size and moderate sediment supply intensity are the internal factors leading to best coupling of organic matter abundance and brittle mineral content in the shale formation.Moderate thermal evolution maturity of Ro of 0.7%–1.0%(at burial depth of 3200 to 4300 m)is the interval where oil generation from thermal evolution and oil adsorption by kerogen in shale layers match best,and retained movable petroleum is high in proportion.Moderate diagenetic evolution stage(3200 to 4300 m in the middle diagenetic stage A)is conducive to the formation of a large number of dissolved pores and organic matter pores,which provide storage space for shale oil enrichment.Moderate development degree of natural fractures(without damaging the shale oil roof and floor sealing conditions)is conducive to the storage,seepage and preservation of shale oil.The research results have overthrown the general understanding that high organic matter abundance,high maturity,and high development degree of natural fractures are conducive to shale oil enrichment,and have guided the comprehensive evaluation of shale oil and gas sweet spots and well deployment in the second member of the Kongdian Formation in the Cangdong sag and the Shahejie Formation in the Qikou sag.Industrial development of the shale oil in Kong 2 Member of the Cangdong sag has made major breakthrough,and important signs of shale oil have been found in Sha 3 Member of the Qikou sag,demonstrating huge exploration potential of lacustrine shale oil.
基金Supported by the PetroChina Science and Technology Major Project(2016E0201)。
文摘Based on the geochemical,seismic,logging and drilling data,the Fuyu reservoirs of the Lower Cretaceous Quantou Formation in northern Songliao Basin are systematically studied in terms of the geological characteristics,the tight oil enrichment model and its major controlling factors.First,the Quantou Formation is overlaid by high-quality source rocks of the Upper Cretaceous Qingshankou Formation,with the development of nose structure around sag and the broad and continuous distribution of sand bodies.The reservoirs are tight on the whole.Second,the configuration of multiple elements,such as high-quality source rocks,reservoir rocks,fault,overpressure and structure,controls the tight oil enrichment in the Fuyu reservoirs.The source-reservoir combination controls the tight oil distribution pattern.The pressure difference between source and reservoir drives the charging of tight oil.The fault-sandbody transport system determines the migration and accumulation of oil and gas.The positive structure is the favorable place for tight oil enrichment,and the fault-horst zone is the key part of syncline area for tight oil exploration.Third,based on the source-reservoir relationship,transport mode,accumulation dynamics and other elements,three tight oil enrichment models are recognized in the Fuyu reservoirs:(1)vertical or lateral migration of hydrocarbon from source rocks to adjacent reservoir rocks,that is,driven by overpressure,hydrocarbon generated is migrated vertically or laterally to and accumulates in the adjacent reservoir rocks;(2)transport of hydrocarbon through faults between separated source and reservoirs,that is,driven by overpressure,hydrocarbon migrates downward through faults to the sandbodies that are separated from the source rocks;and(3)migration of hydrocarbon through faults and sandbodies between separated source and reservoirs,that is,driven by overpressure,hydrocarbon migrates downwards through faults to the reservoir rocks that are separated from the source rocks,and then migrates laterally through sandbodies.Fourth,the differences in oil source conditions,charging drive,fault distribution,sandbody and reservoir physical properties cause the differential enrichment of tight oil in the Fuyu reservoirs.Comprehensive analysis suggests that the Fuyu reservoir in the Qijia-Gulong Sag has good conditions for tight oil enrichment and has been less explored,and it is an important new zone for tight oil exploration in the future.
基金Project supported by National Natural Science Foundation of China(No.41272167)S&T project of CNOOC Gas&Power Group(No.QDKY-2017-YFZX-12).
文摘The coal measure of Middle Jurassic Walloon Subgroup is the main reservoir of coalbed methane(CBM)reservoirs in the Surat Basin,Australia,and it is a set of typical low-rank,high-yield coal measure.To figure out the CBM accumulation conditions and enrichment models of this coal measure,its distribution characteristics,source rock characteristics,reservoir characteristics and preservation conditions were inves-tigated based on mud logging,experimental and testing data.Then,based on the analysis results of gas origin and gas bearing property of this coal measure,3 CBM development areas in northeastern Surat Basin were analyzed and compared in terms of its gas enrichment model,and favorable conditions for CBM accumulation and enrichment of Walloon coal measure(WCM)was summarized.It is indicated that tectonic movements,groundwater conditions and macerals provide favorable conditions for gas generation of Walloon coal.The roof,floor and interbed of this coal measure are lithologically tight,presenting a good sealing capacity.Besides,the Walloon CBM reservoir is a mixed origin gas reservoir with the secondary biogenic methane as the dominant component formed in a monocline structure jointly sealed by hydrodynamic force and lithology.CBM enrichment is controlled by 3 factors,i.e.,local structure,methane generating capacity of coal bed and underground hydrodynamic force,and it can be divided into 3 models,i.e.,anticline model,syncline model and slope model,among which,the CBM enrichment degree of the former two models is higher.Finally,different from other CBM reservoirs,the Walloon CBM reservoir satisfies four favorable conditions in CBM accumulation and enrichment,including dual-carbon source,efficient methane generation,moderate hydrodynamic force and double sealing.
基金supported by the National Major Science and Technology Project“Test and application of reconnaissance and evaluation technologies for shale gas”(No.:2016ZX05034004)the Project of China Geological Survey“Basic geologic survey of Lower Paleozoic marine shale gas in Sichuan Basin”(No.:DD20160176)+1 种基金“Survey on strategic zone of shale gas in Longmaxi Formation,Sichuan Basin”(No.:DD20160193)“Survey on shale gas enrichment conditions in Sichuan Basin”(No.:12120114071401).
文摘Marine shale gas in the southern Sichuan Basin is the most successful area of shale gas exploration and development in China.In order to open up new shale gas fields and search for new shale gas reserves and production replacement blocks,it is necessary to continuously establish and complete the standards on shale gas reservoir evaluation and area selection under different structural settings.The early exploration practice shows that shale in the mountainous complex structural area along the southwestern margin of the Sichuan Basin varies greatly in the gas bearing property,so systematical analysis and study on the shale gas enrichment mechanisms in this area is of great significance to searching for new shale gas exploration areas.Based on drilling data of 5 wells in the mountainous complex structural area along the southwestern margin of the Sichuan Basin,the main factors controlling the shale gas bearing property and the shale gas enrichment model were discussed based on the systematical experiments and analysis of the outcrops,cores and cuttings of Longmaxi Formation shale from the aspects of organic geochemistry,physical property,gas content,hydrocarbon generation history and pore evolution history,so as to lay a solid geological basis for the birth of a new shale gas area.And the following research results were obtained.First,the shale of the first submember of first Member of Longmaxi Formation(S1l11)in the mountainous complex structural area along the southwestern margin of the Sichuan Basin has an average TOC of 3.02%–4.97%and Ro of 2.38%–3.37%,and the average total gas content in local enrichment zones is up to 4.62 m^(3)/t,so it is classified as quality shale.Second,the detailed studies on hydrocarbon generation history indicate that the shale has the characteristics of“low thermal evolution rate and low maturity”.It is characterized by late hydrocarbon generation,low thermal evolution rate,low current maturity and short late diffusion time,which are favorable for shale gas enrichment.Third,the pore evolution history reveals that shale pore evolution can be divided into six stages,i.e.,sharp pore reduction,pore reduction,organic pore formation,pore preservation,organic pore dissipation and karstification,and organic pore and TOC are the most direct control factors of shale gas content.Fourth,favorable shelf facies belt is conducive to the formation of large-scale reservoir space and effective pores,and diversities of preservation conditions under different structural styles and at different structural positions control different pore evolution stages.The shale gas in the mountainous complex structural area is characterized by horizontal zoning and differential enrichment.“Low thermal evolution rate and low maturity”and“slow structural uplifting”are beneficial to the long-term enrichment and preservation of shale gas.In conclusion,the mountainous complex structural area along the southwestern margin of the Sichuan Basin has a shale gas enrichment model of“sedimentation controlling source rocks,diagenesis controlling reservoirs and structure controlling preservation”.This research result provides idea and reference for searching for new shale gas areas and fields.
基金Supported by the National Major Science and Technology Project(No.2016ZX05061)the Project of Sinopec Science&Technology Department.
文摘To understand the shale gas reservoirs in the first member of the Permian Maokou Formation(Mao 1 Member)in Nanchuan area of the Sichuan Basin,we used outcrops,cores,mineralogical and geochemical datas,thin-section analysis,and argon-ion-polishing scanning electron microscopy results with logging and seismic attribute prediction techniques to study the sedimentary facies,source rocks,reservoir properties and types.The geological characteristics and enrichment model of shale gas reservoirs of the Mao 1 Member were revealed and are summarized as follows:(1)the Maokou Formation can be divided into four members from bottom to top.The Mao 1 Member is located in the relatively deep-water gentle slope of a carbonate platform,comprising well-developed dark-gray/grayish-black carbonaceous mudstone,calcareous mudstone,argillaceous limestone,and bioclastic limestone.Carbonaceous and calcareous mudstones,with a relatively high total organic carbon content(TOC0.5-5.1%)and moderate thermal maturity(Ro:2.0-2.3%),are potentially good hydrocarbon source rocks with possibly new type of atypical shale gas reservoir;(2)organic pores,dissolution pores,grain margin fractures,and shrinkage fractures are developed in the Mao 1 Member and may form a reservoir of a complex“poreefractureenetwork,”which is beneficial to gas storage and migration;(3)the shale gas in the Mao 1 Member has the accumulation and enrichment model of“integrated source and reservoir,continuous distribution,and structurefracture dual reservoir control”with a continuous distribution area exceeding 500 km^(2)and a geological resource volume exceeding 70 billion cubic meters;therefore,it has great exploration potential for shale gas.The research results are crucial in improving the understanding of new type of shale gas geology and guide shale gas exploration in southeastern Sichuan.
基金Supported by the National Natural Science Foundation of China (41872128)the CNPC Major Science and Technology Project (2021DJ0101)。
文摘Based on the analysis of Upper Paleozoic source rocks, source-reservoir-caprock assemblage, and gas accumulation characteristics in the Ordos Basin, the gas accumulation geological model of total petroleum system is determined. Then, taking the Carboniferous Benxi Formation and the Permian Taiyuan Formation and Shanxi Formation as examples, the main controlling factors of gas accumulation and enrichment are discussed, and the gas enrichment models of total petroleum system are established. The results show that the source rocks, faults and tight reservoirs and their mutual coupling relations control the distribution and enrichment of gas. Specifically, the distribution and hydrocarbon generation capacity of source rocks control the enrichment degree and distribution range of retained shale gas and tight gas in the source. The coupling between the hydrocarbon generation capacity of source rocks and the physical properties of tight reservoirs controls the distribution and sweet spot development of near-source tight gas in the basin center. The far-source tight gas in the basin margin is mainly controlled by the distribution of faults, and the distribution of inner-source, near-source and far-source gas is adjusted and reformed by faults. Generally, the Upper Paleozoic gas in the Ordos Basin is recognized in four enrichment models: inner-source coalbed gas and shale gas, inner-source tight sandstone gas, near-source tight gas, and far-source fault-transported gas. In the Ordos Basin, inner-source tight gas and near-source tight gas are the current focuses of exploration, and inner-source coalbed gas and shale gas and far-source gas will be important potential targets in the future.
文摘Based on the combination of core observation,experimental analysis and testingand geological analysis,the main controlling factors of shale oil enrichment in the Lower Permian Fengcheng Formation in the Mahu Sag of the Junggar Basin are clarified,and a shale oil enrichment model is established.The results show that the enrichment of shale oil in the Fengcheng Formation in the Mahu Sag is controlled by the organic abundance,organic type,reservoir capacity and the amount of migration hydrocarbon in shale.The abundance of organic matter provides the material basis for shale oil enrichment,and the shales containing typesⅠandⅡorganic matters have good oil content.The reservoir capacity controls shale oil enrichment.Macropores are the main space for shale oil enrichment in the Fengcheng Formation,and pore size and fracture scale directly control the degree of shale oil enrichment.The migration of hydrocarbons in shale affects shale oil enrichment.The shale that has expelled hydrocarbons has poor oil content,while the shale that has received hydrocarbons migrated from other strata has good oil content.Lithofacies reflect the hydrocarbon generation and storage capacity comprehensively.The laminated felsic shale,laminated lime-dolomitic shale and thick-layered felsic shale have good oil content,and they are favorable lithofacies for shale oil enrichment.Under the control of these factors,relative migration of hydrocarbons occurred within the Fengcheng shale,which leads to the the difference in the enrichment process of shale oil.Accordingly,the enrichment mode of shale oil in Fengcheng Formation is established as"in-situ enrichment"and"migration enrichment".By superimposing favorable lithofacies and main controlling factors of enrichment,the sweet spot of shale oil in the Fengcheng Formation can be selected which has great significance for the exploration and development of shale oil.
基金supported by the China Geological Survey Project(DD20160204-3)the Discipline Innovation Team of Liaoning Technical University(LNTU20TD-05,LNTU20TD-14,LNTU20TD-30)+1 种基金the Guiding Program of Liaoning Natural Science Founds(2019-ZD-0046)the Scientific Research Funding Project of Liaoning Education Department(LJ2019JL004).
文摘The Middle Jurassic Xishanyao Formation in the central section of the southern Junggar Basin has substantial amounts of low-ranked coalbed methane(CBM)recourses and is typically characterized by multi superimposed coal seams.To establish the CBM enrichment model,a series of experimental and testing methods were adopted,including coal maceral observation,proximate analysis,low temperature nitrogen adsorption(LTNA),methane carbon isotope determination,porosity/permeability simulation caused by overburden,and gas content testing.The controlling effect of sedimentary environment,geological tectonic,and hydrogeological condition on gas content was analyzed in detail.The results demonstrate that the areas with higher gas content(an average of 8.57 m3/t)are mainly located in the Urumqi River-Santun River(eastern study area),whereas gas content(an average of 3.92 m3/t)in the Manasi River-Taxi River(western study area)is relatively low.Because of the combined effects of strata temperature and pressure,the gas content in coal seam first increases and then decreases with increasing buried depth,and the critical depth of the inflection point ranges from 600 m to 850 m.Affected by the changes in topography and water head height,the direction of groundwater migration is predicted from south to north and from west to east.Based on the gas content variation,the lower and middle parts of the Xishanyao Formation can be divided into three independent coalbearing gas systems.Within a single gas-bearing system,there is a positive correlation between gas content and strata pressure,and the key mudstone layers separating each gas-bearing system are usually developed at the end of each highstand system tract.The new CBM accumulation model of the multi-coals mixed genetic gas shows that both biological and thermal origins are found in a buried depth interval between 600 m and 850 m,suggesting that the coals with those depths are the CBM enrichment horizons and favorable exploration regions in the middle section of the southern Junggar Basin.An in-depth discussion of the low-rank CBM enrichment model with multi-coal seams in the study region can provide a basis for the optimization of CBM well locations and favorable exploration horizons.
基金supported by the National Natural Science Foundation of China“Water-soluble gas accumulation and its quantitative research method based on rare gas tracking”(No.41872162)the National Natural Science Foundation of China“Enrichment mechanism and resource potential of helium in superimposed basins in central-western China”(No.42141022).
文摘Owing to the characteristics of chemical inertness,low molecular weight,low boiling point,strong permeability and high heat conductivity,helium is extensively used in the fields of aerospace,low-temperature superconductivity,medicine and high tech,and it is a kind of irreplaceable strategic rare resource.So far,however,less research has been conducted on the enrichment of helium in natural gas reservoirs.To solve this problem,this paper discusses the classification standard of helium-rich gas reservoirs.Based on this,the origin,source and enrichment process of helium in typical helium-rich gas reservoirs are studied,highlighting the contribution of main helium sources to helium-rich gas reservoirs.In addition,helium enrichment models of helium-rich gas reservoir in petroliferous basins are established.And the following research results are obtained.First,6 helium enrichment models of two categories(crust-source helium enrichment and crust-mantle mixing helium enrichment)are established for different petroliferous basins in China.Second,helium-rich gas reservoirs are characterized by using the multiple helium supply and diverse helium enrichment model.And no matter what enrichment model it is,the contribution of the main helium source to gas reservoirs is indispensable.Third,the helium in the gas reservoirs of central and western basins is mainly crust-source helium,and its enrichment models include ancient formation water moving upward along the fault to dilute helium,helium enrichment in the process of natural gas migration along ancient reservoirs,and helium enrichment of shale gas.Fourth,the helium in the helium-rich gas reservoirs of eastern basins is of crust-mantle mixing origin and its enrichment models are mainly hydrocarbon gas based,carbon dioxide based and nitrogen based.In conclusion,the establishment of the helium enrichment models of helium-rich gas reservoirs in petroliferous basins provides reference and guidance for studying helium enrichment laws and main controlling factors and is of great significance to the evaluation of favorable helium exploration areas.
基金Supported by the PetroChina Science and Technology Project(2022KT1205).
文摘The relationship between fracture calcite veins and shale gas enrichment in the deep Ordovician Wufeng Formation-Silurian Longmaxi Formation (Wufeng-Longmaxi) shales in southern Sichuan Basin was investigated through core and thin section observations, cathodoluminescence analysis, isotopic geochemistry analysis, fluid inclusion testing, and basin simulation. Tectonic fracture calcite veins mainly in the undulating part of the structure and non-tectonic fracture calcite veins are mainly formed in the gentle part of the structure. The latter, mainly induced by hydrocarbon generation, occurred at the stage of peak oil and gas generation, while the former turned up with the formation of Luzhou paleouplift during the Indosinian. Under the influence of hydrocarbon generation pressurization process, fractures were opened and closed frequently, and oil and gas episodic activities are recorded by veins. The formation pressure coefficient at the maximum paleodepth exceeds 2.0. The formation uplift stage after the Late Yanshanian is the key period for shale gas migration. Shale gas migrates along the bedding to the high part of the structure. The greater the structural fluctuation is, the more intense the shale gas migration activity is, and the loss is more. The gentler the formation is, the weaker the shale gas migration activity is, and the loss is less. The shale gas enrichment in the core of gentle anticlines and gentle synclines is relatively higher.
基金financially supported by the National Natural Science Foundation of China (41130640, 91425301, 41321001, 41401057)the projects from the State Key Laboratory of Earth Surface Processes and Resource Ecology, Beijing Normal University
文摘Stable isotopic compositions （δ18O and 6D） have been utilized as a useful indicator for evaluating the current and historical climatic and environmental changes. Therefore, it is vital to understand the relationship be- tween the stable isotopic contents in lake water and the variations of lake level, particularly in Lake Qinghai, China. In this study, we analyzed the variations of isotope compositions （δ18O, 6D and d-excess） in lake water and pre- cipitation by using the samples that were collected from Lake Qinghai region during the period from 2009 to 2012. The results showed that the average isotopic contents of δ18O and 6D in lake water were higher than those in pre- cipitation, which were contrary to the variations of d-excess. The linear regression correlations between δ18O and 6D in lake water and precipitation showed that the local evaporative line （LEL） in lake water （δD=5.88δ18O-2.41） deviated significantly from the local meteoric water line （LMWL）in precipitation （δD=8.26δ18O＋16.91）, indicating that evaporative enrichment had a significant impact on isotopic contents in lake water. Moreover, we also quanti- fied the Eli ratio （evaporation-to-input ratio） in Lake Qinghai based on the lake water isotopic enrichment model derived from the Rayleigh equation. The changes of E/I ratios （ranging from 0.29 to 0.36 between 2009 and 2012） clearly revealed the shifts of lake levels in Lake Qinghai in recent years. The average E/I ratio of 0.40 reflected that water budget in Lake Qinghai was positive, and consistent with the rising lake levels and the increasing lake areas in many lakes of the Tibetan Plateau. These findings provide some evidences for studying the hydrological balance or water budget by using δ18O values of lake sedimentary materials and contribute to the reconstruction of paleo- lake water level and paleoclimate from an isotopic enrichment model in Lake Qinghai.
基金Supported by the National Natural Science Foundation of China(41672118)Strategic Cooperation Science and Technology Project Between China University of Petroleum and Petro China(ZLZX2020-01-06)。
文摘Taking the tight oil of the Zhongnan sag in the Ordos Basin,Jimusar sag in the Junggar Basin and Qingxi sag in the Jiuquan Basin as study objects,based on field survey,dissection of tight oil reservoirs,sample test,modeling experiment and comprehensive analysis,this study reveals that the tight oil accumulates at start-up pressure,advances under differential pressure,diffuses at alternating fast and low speeds,charges in stepped large area and migrates rapidly through fractures,and enriches in dominant fractures and pores.The root cause of ladder-like charge is the multiple scales of pores.The widespread source rock with high hydrocarbon generation intensity is the material basis for tight oil enrichment;the dominant source reservoir assemblage is the basic unit for tight oil enrichment;fractures and beddings are conducive to local rapid migration of tight oil;fractures and pores work together to control the enrichment of tight oil.Two typical accumulation models of tight oil are established,namely"source reservoir in coexistence,four optimal factors controlling enrichment around central area,and large-scale continuous distribution"for a large freshwater lake clastic rock basin and"source reservoir integration,four optimal factors controlling enrichment,central area distribution,small in size but high in enrichment degree"for a small saline lake diamictite depression.
基金Supported by the National Key Basic Research and Development Program(973 Program)China(2014CB239100)China National Science and Technology Major Project(2017ZX05049)
文摘Based on formation testing data of more than 40 wells with industrial oil flow, systematic observation of 1 010.26 m long cores taken from 4 wells and test data of over 10 000 core samples combining with drilling and pilot fracturing data of multiple wells, the geological characteristics of the upper submember of the Sha 4 Member to the lower submember of the Sha 3 Member of Paleogene(Es4s-Es3x) in the Jiyang Depression were investigated to find out factors controlling the enrichment of shale oil and the accumulation model of shale oil, and a comprehensive evaluation method for shale oil sweet spots was established. It is found through the study that the target shale layer is characterized by strong heterogeneity, weak diagenesis, low thermal evolution and high content of clay and carbonate minerals. Shale lithofacies, microcrack, thin interlayer and abnormal pressure are the main factors affecting enrichment and stable production of shale oil, the organic rich laminar shale has the best storage and oil-bearing capacity, microcrack network system improve the storage capacity and permeability of the shale, the thin interlayer is the main flow channel for stable shale oil production, and the abnormal high pressure layer is rich in free state shale oil and high in oil content. The shale oil layers in the target section were divided into three types: matrix, interlayer and fracture ones. According to the occurrence state and exploration practice of shale oil at home and abroad, it is concluded that the interlayer shale oil is the most profitable type at present. The selection parameters for the different types of shale oil were determined, and accordingly the favorable areas were pointed out by comprehensive evaluation of multiple factors. Vertical wells in the interlayer shale oil reservoir, such as Fan 159, Fan 143 and GX 26, were stimulated by volume fracturing and high conductivity channel fracturing jointly. After fracturing, they had a daily oil production of over 6 t, up to 44 t, and stable productivity. Shale oil is expected to become an important replacement energy resource in the Jiyang Depression.
基金Supported by the China Geological Survey Project(DD20190115)
文摘Pure shales in the first member of Qingshankou Formation(simplified as Qing 1 Member)in the southern Songliao Basin,i.e.,the semi-deep and deep lacustrine shales,are characterized by a high content of clay minerals and poor hydrocarbon mobility,making the development of shale oil difficult.According to the drilling and testing results,the shale of Qing 1 Member can be classified into 3 lithofacies,i.e.,bedded argillaceous shale,laminated diamictite shale,and interbedded felsic shale.The TOC and brittle minerals control the enrichment of shale oil,of them,TOC controls the total oil content,in other words,the total oil content increases with the increase of TOC;while the laminae made up of brittle minerals contain a large number of bigger intergranular pores which are favorable enrichment space for movable shale oil.In consideration of the origins of the 3 lithofacies,two shale oil enrichment models are classified,i.e.,the deep lacustrine high-TOC bedded argillaceous shale(Model-I)and the semi-deep lacustrine moderate-high-TOC laminated diamictite shale(Model-II).In the Model-I,the shale is characterized by high hydrocarbon generation ability,high total oil content,abundant horizontal bedding fractures,and vertical and high angle fractures locally;the complex fracture network formed by horizontal bedding fractures and vertical fractures improve the storage capacity and permeability of the shale reservoir,increase the enrichment space for movable oil.In the Model-II,the shale is characterized by good hydrocarbon generation ability and fairly high total oil content,and as the brittle laminae contain large intergranular pores,the shale has a higher movable oil content.Based on the two models,shale oil sweet-spot areas of 2880 km2 in the southern Songliao Basin are favorable for further exploration.Aimed at the difficulties in reservoir fracturing of the lacustrine shale with a high content of clay minerals,the composite fracturing technology with supercritical carbon dioxide was used in the shale oil reservoir for the first time,realizing large-scale volume fracturing in shale with a high content of clay minerals and strong heterogeneity,marking a breakthrough of oil exploration in continental shale with a high content of clay minerals in China.
文摘|Editorial Note| Since reform and opening up,China has embarked on a path of development featuring socialism with Chinese characteristics,scoring remarkable achievements that have drawn attention from all over the world.What has reform and opening up achieved?What are its experiences?What are the intrinsic values of socialism with Chinese characteristics?How is China’s development path viewed in the international community? This paper gives an overview of these questions,shedding light on the problems that the country faces and optimism about its future.
基金Supported by the Sinopec Major Science and Technology Project(P22081)National Natural Science Foundation of China(U24B60001).
文摘The basic geological characteristics of the Qiongzhusi Formation reservoirs and conditions for shale gas enrichment and high-yield were studied by using methods such as mineral scanning,organic and inorganic geochemistry,breakthrough pressure,and triaxial mechanics testing based on the core,logging,seismic and production data.(1)Both types of silty shale,rich in organic matter in deep water and low in organic matter in shallow water,have good gas bearing properties.(2)The brittle mineral composition of shale is characterized by comparable feldspar and quartz content.(3)The pores are mainly inorganic pores with a small amount of organic pores.Pore development primarily hinges on a synergy between felsic minerals and total organic carbon content(TOC).(4)Dominated by Type I organic matters,the hydrocarbon generating organisms are algae and acritarch,with high maturity and high hydrocarbon generation potential.(5)Deep-and shallow-water shale gas exhibit in-situ and mixed gas generation characteristics,respectively.(6)The basic law of shale gas enrichment in the Qiongzhusi Formation was proposed as“TOC controlled accumulation and inorganic pore controlled enrichment”,which includes the in-situ enrichment model of“three highs and one over”(high TOC,high felsic mineral content,high inorganic pore content,overpressured formation)for organic rich shale represented by Well ZY2,and the in-situ+carrier-bed enrichment model of“two highs,one medium and one low”(high felsic content,high formation pressure,medium inorganic pore content,low TOC)for organic-poor shale gas represented by Well JS103.It is a new type of shale gas that is different from the Longmaxi Formation,enriching the formation mechanism of deep and ultra-deep shale gas.The deployment of multiple exploration wells has achieved significant breakthroughs in shale gas exploration.
基金supported by the Joint Funds of the National Natural Science Foundation of China(No.2024DJ8702)the Science and Technology Research Project of the China National Petroleum Corporation(No.2024DJ87)+1 种基金the National Natural Science Foundation of China(No.42272029)the“Light of West China”Program of the Chinese Academy of Sciences(No.xbzglzb2022025)。
文摘The high-quality laminated source rock organic matter(OM)originated from planktonic algae,and its sedimentation was affected by global climate change significantly in the upper Xiaganchaigou Formation of the western Qaidam Basin.However,coupling research on the paleoenvironment change and OM enrichment during the sedimentation period of the source rock is still lacking.This study from the aspects of sedimentary petrology,geochemistry and paleontology palynology,the paleoenvironment of source rock is restored and the OM enrichment model is established in the study area.Firstly,kerogen maceral identification indicates that the kerogen maceral is mainly composed of Botryococcus,accompanied with amorphous organic matter and plant debris.Secondly,arid climate and relatively active tectonic were observed during the deposition of the source rock.The water column was received felsic source from the continental island arc tectonic background,and has the environmental characteristics of relatively saline,shallow depth,medium low productivity,fast sedimentation rate and anoxic reduction and so on.Lastly,the first-order controlling factors for the OM enrichment are anoxic water conditions and suitable sedimentation rate,and the secondary controlling factor is paleoproductivity.Through the coupling study of paleoclimate,paleoenvironment and OM enrichment,the paleoclimate high frequency alternating evolution was the root cause of sedimentary environment change and OM enrichment of the laminated shale in the Upper Xiaganchaigou Formation.The study on the OM enrichment mechanism of algae in Qaidam provides a good model for understanding the coupling relationship between the algae bloom in the saline lake basins and the environments,and provides important theoretical basis for predicting shale oil“sweet spot”and production well sites arrangement for the continental saline lacustrine basins.
