The Huizhou sag is situated on the continental shelf of the northern continental margin of the South China Sea. In this paper we present a grid of reflection seismic and well data to characterize the basin structure a...The Huizhou sag is situated on the continental shelf of the northern continental margin of the South China Sea. In this paper we present a grid of reflection seismic and well data to characterize the basin structure and prominent unconformities. We employ EBM and 2DMOVE softwares to explore the subsidence history and stratigraphic development history of the basin. We found a rapid subsidence period since 15.5 Ma. Moreover, we calculated the stretching factors of the upper crust and the whole crust in the Huizhou sag. The results show the values are 1.10–1.13 and 1.08–1.31, respectively, indicating faulting in Huizhou sag is relatively small. It is noteworthy that the faults map reveals en echelon distribution at the north and south margins of the basin. We suggest en echelon faults here are caused by the subduction of Proto-South China Sea toward NW Borneo block and cease of the South China Sea. Considering the pronounced unconformities, subsidence rates, fault activities and sediment thickness, the Cenozoic tectonic evolution of the basin can be divided into rifting（49–32 Ma）, post-rifted（32–15.5 Ma） and rapid subsidence（15.5–0 Ma） stages. Our study will shed new light on the tectonics of SE Asia and petroleum exploration in the South China Sea.展开更多
The Ordos Basin(OB)in the western part of the North China Craton(NCC),was located at the jointed area of multi-plates and has recorded the Mesozoic tectonic characteristics.Its tectonic evolution in the Mesozoic is si...The Ordos Basin(OB)in the western part of the North China Craton(NCC),was located at the jointed area of multi-plates and has recorded the Mesozoic tectonic characteristics.Its tectonic evolution in the Mesozoic is significant to understand the tectonic transformation of the northern margin of the NCC.In this work,the detrital zircon and apatite(U-Th)/He chronological system were analyzed in the northern part of the OB,and have provided new evidence for the regional tectonic evolution.The(U-Th)/He chronological data states the weighted ages of 240‒235 Ma,141 Ma with the peak distribution of 244 Ma,219 Ma,173 Ma,147‒132 Ma.The thermal evolution,geochronological data,and regional unconformities have proved four stages of regional tectonic evolution for the OB and its surroundings in the Mesozoic:(1)The Late Permian-Early Triassic;(2)the Late Triassic-Early Jurassic;(3)the Late Jurassic-Early Cretaceous;(4)the Late Cretaceous-Early Paleogene.It is indicated that the multi-directional convergence from the surrounding tectonic units has controlled the Mesozoic tectonic evolution of the OB.Four-stage tectonic evolution reflected the activation or end of different plate movements and provided new time constraints for the regional tectonic evolution of the NCC in the Mesozoic.展开更多
Based on the coalbed methane(CBM)/coal-rock gas(CRG)geological,geophysical,and experimental testing data from the Daji block in the Ordos Basin,the coal-forming and hydrocarbon generation&accumulation characterist...Based on the coalbed methane(CBM)/coal-rock gas(CRG)geological,geophysical,and experimental testing data from the Daji block in the Ordos Basin,the coal-forming and hydrocarbon generation&accumulation characteristics across different zones were dissected,and the key factors controlling the differential CBM/CRG enrichment were identified.The No.8 coal seam of the Carboniferous Benxi Formation in the Daji block is 8-10 m thick,typically overlain by limestone.The primary hydrocarbon generation phase occurred during the Early Cretaceous.Based on the differences in tectonic evolution and CRG occurrence,and with the maximum vitrinite reflectance of 2.0%and burial depth of 1800 m as boundaries,the study area is divided into deeply buried and deeply preserved,deeply buried and shallowly preserved,and shallowly buried and shallowly preserved zones.The deeply buried and deeply preserved zone contains gas content of 22-35 m^(3)/t,adsorbed gas saturation of 95%-100%,and formation water with total dissolved solid(TDS)higher than 50000 mg/L.This zone features structural stability and strong sealing capacity,with high gas production rates.The deeply buried and shallowly preserved zone contains gas content of 16-20 m^(3)/t,adsorbed gas saturation of 80%-95%,and formation water with TDS of 5000-50000 mg/L.This zone exhibits localized structural modification and hydrodynamic sealing,with moderate gas production rate.The shallowly buried and shallowly preserved zone contains gas content of 8-16 m^(3)/t,adsorbed gas saturation of 50%-70%,and formation water with TDS lower than 5000 mg/L.This zone experienced intense uplift,resulting in poor sealing and secondary alteration of the primary gas reservoir,with partial adsorbed gas loss,and low gas production rate.A depositional unification and structural divergence model is proposed,that is,although coal seams across the basin experienced broadly similar depositional and tectonic histories,differences in tectonic intensity have led to spatial heterogeneity in the maximum burial depth(i.e.,thermal maturity of coal)and current burial depth and occurrence of CRG(i.e.,gas content and occurrence state).The research results provide valuable guidance for advancing the theoretical understanding of CBM/CRG enrichment and for improving exploration and development practices.展开更多
The northwestern margin of Junggar Basin is the region with the richest oil sand resources in China.For better understanding the enrichment rules and deployment of exploration and development of regional oil sand,it i...The northwestern margin of Junggar Basin is the region with the richest oil sand resources in China.For better understanding the enrichment rules and deployment of exploration and development of regional oil sand,it is of great scientific significance to study the accumulation conditions of oil sand in different strata and mining areas of the Junggar Basin.Through a large number of field investigations,drilling verification and sampling tests,it is found that the oil sand in the region covers an area of 2000 km^(2),with shallow and thick reservoir,and predicted resource of 180 million tons.The oil sand resources are mainly distributed in four geological strata,namely the Middle Triassic Karamay Formation,Early Jurassic Badaowan Formation,Late Jurassic Qigu Formation,and Early Cretaceous Qingshuihe Formation.The reservoir is mainly composed of sandstone with high porosity and permeability,and the reservoir space is mainly intergranular pores with a medium average oil content.The oil sand deposit in the region is a typical destructive oil reservoir.The crude oil in the oil sand layer is degraded and thickened from the deep to the shallow,the content of saturated hydrocarbon decreased,and the content of aromatic hydrocarbon,non-hydrocarbon and asphaltene increased.The oil source comes from the deep Permian hydrocarbon-generating depression.Unconformities,faults and marginal fan delta-braided river depositional systems constitute effective migration and storage systems.Caprocks of the Upper Triassic Baijiantan Formation,Lower Jurassic Sangonghe Formation and Lower Cretaceous Hutubihe Formation were formed by three large scale lake transgressions.The Indosinian,Yanshan and Late Yanshan movements are the main driving forces for the migration of deep oil and gas to the shallow edge to form oil sand deposits.It is considered that the oil sand in the northwestern margin of Junggar Basin is of a slope complex migration type.展开更多
The carbonate-rich shale of the Permian Wujiaping Formation in Sichuan Basin exhibits significant heterogeneity in its lithology and pore structure,which directly influence its potential for shale gas extraction.This ...The carbonate-rich shale of the Permian Wujiaping Formation in Sichuan Basin exhibits significant heterogeneity in its lithology and pore structure,which directly influence its potential for shale gas extraction.This study assesses the factors that govern pore heterogeneity by analyzing the mineral composition of the shale,as well as its pore types and their multifractal characteristics.Three primary shale facies-siliceous,mixed,and calcareous-are identified based on mineralogy,and their multifractal characteristics reveal strongly heterogeneous pore structures.The brittleness of siliceous shale,rich in quartz and pyrite,is favorable for hydraulic fracturing;while calcareous shale,with higher levels of calcite,exhibits reduced brittleness.Multifractal analysis,using nitrogen adsorption isotherms,reveals complex pore structures across different shale facies,with siliceous shale showing better pore connectivity and uniformity.The types of pores in shales include organic matter pores,interparticle pores,and intraparticle pores,among which organic matter pores are the most abundant.Pore size distribution and connectivity are notably higher in siliceous shale compared to calcareous shale,which exhibit a predominance of micropores and more isolated pore structures.Pore heterogeneity of the carbonate-rich shale in the Wujiaping Formation is primarily governed by its intrinsic mineral composition,carbonate diagenesis,mechanical compaction,and its subsequent thermal maturation with the micro-migration of organic matter.This study highlights the importance of mineral composition,especially the presence of dolomite and calcite,in shaping pore heterogeneity.These findings emphasize the critical role of shale lithofacies and pore structure in optimizing shale gas extraction methods.展开更多
The effect of depositional facies and diagenesis on the reservoir potential of the Sakesar limestone has been assessed through core plug porosity and permeability data,scanning electron microscope(SEM),and petrographi...The effect of depositional facies and diagenesis on the reservoir potential of the Sakesar limestone has been assessed through core plug porosity and permeability data,scanning electron microscope(SEM),and petrographic study in three stratigraphic sections(Karuli,Badshah Pur,and Sardhai)of Central Salt Range.Field observations reveal three lithofacies:thin-bedded limestone with shale intercalation,thick-bedded nodular limestone,and highly fractured limestone.Based on a petrographic study,six microfacies have been identified:bioclastic mudstone facies(SKF-1),Lockhartia-nummulitic wackestone facies(SKF-2),Assilina-Alveolina packstone facies(SKF-3),Lockhartia-nummulitic packstone facies(SKF-4),Alveolina grainstone facies(SKF-5),and nummulitic grainstone facies(SKF-6).The Sakesar limestone shows various diagenetic changes such as compaction,dissolution,dolomitization,cementation,and fracturing,resulting in different types of pores.Two reservoir zones are identified in the Sakesar limestone:a mud-dominated reservoir in an outer ramp setting with interparticle and micropores and a bioclastic grain-dominated facies in an inner ramp setting with intraskeletal and fracture porosity.The porosity and permeability of grain-dominated facies(8%-30%and 0.8-8 mD)are higher than mud-dominated facies(4%-15%and 0.5-4 mD)due to intraskeletal/intraparticle pores and dolomitization.展开更多
Lower Paleozoic black shales are important source rocks worldwide.The Upper Ordovician-Lower Silurian Renheqiao Formation of the Baoshan Block is a low-maturity equivalent of the Wufeng-Longmaxi(WF-LMX)Shale of the Si...Lower Paleozoic black shales are important source rocks worldwide.The Upper Ordovician-Lower Silurian Renheqiao Formation of the Baoshan Block is a low-maturity equivalent of the Wufeng-Longmaxi(WF-LMX)Shale of the Sichuan Basin.However,organic matter(OM)characteristics in these low-maturity Lower Paleozoic shales are not well understood.In this study,50 Renheqiao Formation shale samples collected from seven outcrop sections and one drill core were investigated with organic petrology,organic geochemistry,R_(o)ck-Eval pyrolysis,N_(2) and CO_(2) adsorption,and scanning electron microscope(SEM)analyses to study the OM content,type,thermal maturity,and the development of OM-hosted pores in these Lower Paleozoic shales.The total organic carbon(TOC)content of the Renheqiao Formation shales varies,with the maximum content of 10.07 wt%.R_(o)ck-Eval pyrolysis results show that present OM in the Renheqiao Formation shales is Type IV kerogen,a result of advanced thermal maturation.Graptolite reflectance(GR_(o))ranges from 1.26%to 1.85%,and equivalent vitrinite reflectance(EqR_(o))converted from GR_(o) ranges from 1.08%to 1.51%,indicating that the studied Renheqiao Formation shales are dominantly within the late-mature stage.EqR_(o) based on R_(o)ck-Eval T_(max) shows large variations,which indicates that R_(o)ck-Eval T_(max) is not a reliable thermal maturity indicator for the Lower Paleozoic Renheqiao Formation shales.Caution should be applied when assessing the thermal maturity of high-maturity black shales based on T_(max) when the S2 values are too low.Organic petrographic observations show that OM in these shales is dominated by solid bitumen(>70 vol%of total OM),with minor contributions by graptolites and chitinozoans.The specific surface area and pore volume of shales are controlled by TOC content.Organic pores are hosted by solid bitumen and were not observed in graptolites when examined under the SEM.Although the Renheqiao Formation has a lower thermal maturity than the over-mature WF-LMX Shale,it is mature enough that primary oil-prone macerals have been thermally transformed and could not be identified under the microscope.展开更多
Fracture-cave reservoirs are widely developed in carbonate formations and account for over 55%of global petroleum reserves.The productivity,formation mechanisms,and in-situ stress states of these reservoirs,characteri...Fracture-cave reservoirs are widely developed in carbonate formations and account for over 55%of global petroleum reserves.The productivity,formation mechanisms,and in-situ stress states of these reservoirs,characterized by fault-fracture-cave systems,are inherently interconnected.However,solely relying on geometric characterizations of natural fractures and cavities fails to meet the demands of modern petroleum exploration and development,particularly due to their complex structures,significant spatial heterogeneity,and strong geomechanical anisotropy.A critical challenge remains:how to safely and efficiently drill high-yield wells through highly fractured and cavernous zones while mitigating drilling risks.Consequently,establishing geomechanical models for fracture-cave reservoirs and predicting 3D stress fields are imperative for well trajectory optimization and reservoir reconstruction.This study integrates seismic interpretations of strike-slip faults with multi-attribute inversions of fracture-cave reservoirs.Using ANSYS 21.0 software,a homogeneous geomechanical model was constructed based on finely characterized geometries of fracturecave systems.Rock mechanics parameters,interpreted from conventional logging data and seismic attributes,were inverted to generate 3D distributions.These parameters were subsequently incorporated into the homogeneous model to develop a heterogeneous geomechanical framework.In-situ stress orientations were calibrated using drilling-induced fracture data,enabling predictions of the contemporary stress field in complex fracture-cave reservoirs.The methodology was validated in the Yueman Block of the Tarim Basin’s deep carbonate reservoir.Results revealed stress distribution patterns and key controlling factors,which were applied to evaluate wellbore stability,fracture reactivation risks,and optimize well trajectories.This approach provides a technical foundation for safe and efficient exploration-development of fracture-cave reservoirs worldwide.展开更多
Accurate reservoir permeability determination is crucial in hydrocarbon exploration and production.Conventional methods relying on empirical correlations and assumptions often result in high costs,time consumption,ina...Accurate reservoir permeability determination is crucial in hydrocarbon exploration and production.Conventional methods relying on empirical correlations and assumptions often result in high costs,time consumption,inaccuracies,and uncertainties.This study introduces a novel hybrid machine learning approach to predict the permeability of the Wangkwar formation in the Gunya oilfield,Northwestern Uganda.The group method of data handling with differential evolution(GMDH-DE)algorithm was used to predict permeability due to its capability to manage complex,nonlinear relationships between variables,reduced computation time,and parameter optimization through evolutionary algorithms.Using 1953 samples from Gunya-1 and Gunya-2 wells for training and 1563 samples from Gunya-3 for testing,the GMDH-DE outperformed the group method of data handling(GMDH)and random forest(RF)in predicting permeability with higher accuracy and lower computation time.The GMDH-DE achieved an R^(2)of 0.9985,RMSE of 3.157,MAE of 2.366,and ME of 0.001 during training,and for testing,the ME,MAE,RMSE,and R^(2)were 1.3508,12.503,21.3898,and 0.9534,respectively.Additionally,the GMDH-DE demonstrated a 41%reduction in processing time compared to GMDH and RF.The model was also used to predict the permeability of the Mita Gamma well in the Mandawa basin,Tanzania,which lacks core data.Shapley additive explanations(SHAP)analysis identified thermal neutron porosity(TNPH),effective porosity(PHIE),and spectral gamma-ray(SGR)as the most critical parameters in permeability prediction.Therefore,the GMDH-DE model offers a novel,efficient,and accurate approach for fast permeability prediction,enhancing hydrocarbon exploration and production.展开更多
The origin of tight reservoirs in the Yanchang Formation of the Ordos Basin and their relationship with hydrocarbon charging remain unclear.Based on petrological observations,physical property analysis,fluid inclusion...The origin of tight reservoirs in the Yanchang Formation of the Ordos Basin and their relationship with hydrocarbon charging remain unclear.Based on petrological observations,physical property analysis,fluid inclusion system analysis and in situ U-Pb dating,the sequence of tight sandstone reservoir densification and oil charging was determined.Through petrological observations,fluid inclusion analysis and physical property analysis,it is concluded that compaction and cementation are the primary causes of reservoir densification.When the content of calcite cement is less than or equal to 7%,compaction dominates densification;otherwise,cementation becomes more significant.However,determining the exact timing of compaction densification proved challenging.Microscopic observations revealed that oil charging likely occurred either before or during the densification of the reservoir.According to in situ U-Pb dating and the porosity evolution curve,cementation densification occurred between 167.0±20.0 Ma and 151.8 Ma.Temperature measurements of the aqueous inclusions indicate that oil charging occurred between 125.0 and 96.0 Ma,suggesting that densification preceded oil charging.This study provides valuable insights for the future exploration of tight oil reservoirs in the Ordos Basin.展开更多
Shale oil resources are abundant on Earth,of which hybrid sedimentary shale(HSS)oil is an important component,including high and medium-low organic matter content(TOC).Oil content,especially the oiliness gradation,is ...Shale oil resources are abundant on Earth,of which hybrid sedimentary shale(HSS)oil is an important component,including high and medium-low organic matter content(TOC).Oil content,especially the oiliness gradation,is a key parameter for shale oil evaluation and numerous studies had been conducted.However,most studies concentrated on the HSS with high TOC,making oil content evaluation of the HSS with medium-low TOC challenging.The Paleocene Shahejie Formation(E2s)shale in Dongpu Depression is a typical HSS with low-moderate TOC,showing great shale oil resource potential.Integrated geochemical characterization of 270 core samples were conducted and results show that,the E2s shale has fairgood hydrocarbon generation potential,with TOC ranging from 0.06%to 3.6%(Avg.0.86%)andⅡ1-Ⅱ2 kerogen type in thermally mature.The hydrocarbon generation potential decreases with kerogen types changing from type I toⅢ,but S1C and the oil saturation index(OSI)(S1*100/TOC>100)increase from type I toⅡ1,and then decrease from typeⅡ2 toⅢ,indicating shale with typeⅡ2 kerogen have the greatest oil content.This is related to the diferences in hydrocarbon expulsion efciency caused by diferential hydrocarbon generation potential and pore-microfractures evolution among shales with diferent kerogen types.Signifcant oil micro-migration occurred in E2s shale,with micro-migration quantity(∆Q)ranging from-846 to 993 mg/g(Avg.-120 mg/g),and 90%and 10%shale exhibit hydrocarbon intra-micro-migration(∆Q<0)and extra-micro-migration(∆Q>0).The shale with typeⅡ2 kerogen has the greatest intra-micro-migration.Based on S1C,TOC and OSI values and their evolution pattern,shale oil resources were classifed into enriched,moderately enriched,less efcient and invalid resources,accounting for 11%,53%,16%and 21%respectively,with S1C thresholds of 3.5 and 0.5 mg/g,OSI threshold of 100 mg/g.Compared with previous grading criteria,the gradation criterion established in this study is relatively lower,which is mainly due to the lower TOC and clay mineral content in HSS.Enriched and moderately enriched resources are mainly shales with typeⅡ2 kerogen,followed by typeⅡ1 kerogen,and the E2s4 U and E2s3 L shale are the most favorable targets for further shale oil exploration.The established oiliness gradation criteria are applicable for the HSS with TOC in other parts of the world.展开更多
The presence of inorganic constituents in coal is controlled by different geological factors,which,in turn,affect the technological,environmental,and health impacts of the coal.The main aim of this study is to objecti...The presence of inorganic constituents in coal is controlled by different geological factors,which,in turn,affect the technological,environmental,and health impacts of the coal.The main aim of this study is to objectively assess the mineralogical and geochemical characteristics of a thickest low-rank coal seam in the Lower Indus Basin southeastern Pakistan,and further investigate different controlling factors.The analytical results of major oxides,trace elements,and rare earth elements revealed that the weathering conditions were progressively variable and moderate.The sediment source,mainly of felsic and intermediate composition,was dominated by granitic rocks.The geochemical assessment reveals different depositional factors like marine environment influenced,while transitional and freshwater sediments influenced the center of the coal peat mire.Strontium,Zinc,and several hazardous trace elements,including Cu,Ni,Cr,and Co,have higher concentrations in these coals compared to world low-rank,U.S.,and Chinese coals.The relatively higher concentration of Sr in the thick coal seam in the Lower Indus Basin,compared to other coals seams in Pakistan and the enrichment of Sr was primarily controlled by the denudation of crystalline rocks and marine influx in the coal-basin.The REY distribution pattern showed that enrichment of medium and heavy rare earth elements is higher than light rare earth elements in the coal seam.The Gd distribution pattern in the coal seam demonstrated that strong positive anomalies had a good affinity with paleo-acidic water concentration in the study area.The higher concentration of Sr and other elements enables a better assessment understanding of the coal geochemical history.展开更多
Understanding the origin of natural gas in deep and ultra-deep reservoirs with multiple potential source rocks remains challenging due to the complex thermal evolution of hydrocarbons at high temperatures and multi-st...Understanding the origin of natural gas in deep and ultra-deep reservoirs with multiple potential source rocks remains challenging due to the complex thermal evolution of hydrocarbons at high temperatures and multi-stage accumulation processes.This study investigates the origin of natural gas in deep hydrothermal dolomite reservoirs of the Maokou Formation,eastern Sichuan Basin,using hydrocarbon inclusion analysis,radiometric U-Pb dating of calcite cements,maturity modeling of potential source rocks,and constraints on reactivation periods of the nearby No.15 Fault System.Results indicate an oil charging event at approximately 246.9 Ma,followed by two episodes of gas charging at 222.4 Ma and 175.2 Ma.Furthermore,the oil and gas charging events occurred synchronously with activities of the No.15 Fault System,suggesting that its reactivation induced episodic hydrocarbon migration.Maturity modeling indicates that during the oil charging period,source rocks in the Qiongzhusi,WufengLongmaxi,and first member of the Maokou formations reached the stages of dry gas generation,significant oil generation,and the threshold of oil generation,respectively.During the subsequent twoepisode gas charging periods,the Qiongzhusi and Wufeng-Longmaxi formations progressed to dry and wet gas generation stages,respectively,while the first member of the Maokou Formation attained the oil generation stage.The hydrocarbon charging time and maturity history of potential source rocks indicate that:1)oil in hydrothermal dolomite reservoirs predominantly originated from the Wufeng-Longmaxi Formation at approximately 246.9 Ma;2)during the subsequent gas charging episodes,the WufengLongmaxi Formation could contribute wet gas,while the Qiongzhusi Formation likely supplied cracking gas from kerogen and residual liquid hydrocarbon;3)all oil in the hydrothermal dolomite reservoirs underwent thermal cracking to gas at approximately 110 Ma.This study indicates that gas pools in(ultra-)deep carbonate reservoirs of the Sichuan Basin have mixed genetic origins,with contributions from multiple sources.The multidisciplinary approach,combining direct dating of hydrocarbon charge events and simulation of hydrocarbon generation,proves robust and effective in identifying the origin of natural gas in(ultra-)deep reservoirs.展开更多
Carbonaceous debris(CD)is widely distributed in the sandstone of the Daying Uranium Deposit,northern Ordos Basin,and coexists with uranium minerals,which provides a favorable case for studying their relationship.Vitri...Carbonaceous debris(CD)is widely distributed in the sandstone of the Daying Uranium Deposit,northern Ordos Basin,and coexists with uranium minerals,which provides a favorable case for studying their relationship.Vitrinite reflectance(VR),macerals,moisture,volatile matter,ash,total sulfur(S_t)and uranium concentration of CD within the sandstone were studied.The results show that VR ranges from 0.372%Ro to 0.510%Ro with an average value of 0.438%Ro,indicating that CD is in the stage of lignite.The contents of vitrinite(V),inertinite(I)and minerals range from 83.18%–99.48%,0–7.70%,and 0.34%–15.72%,respectively,with the corresponding average value of 95.51%,1.34%,and 3.15%,respectively which indicates that V is the major maceral.Moisture on air dried basis(M_(ad)),volatile matter yield on dry,ash-free basis(V_(daf)),ash yield on dried basis(A_d)and S_t mostly range from 7.95%–16.09%,44.70%–66.54%,4.84%–26.24% and 0.24%–1.12%,respectively,while their average values are 12.43%,53.41%,16.57% and 0.77%,respectively.It suggests that CD is of medium-high moisture,super-high volatile matter,low-medium ash and low sulfur.Uranium concentration ranges from 29 ppm to 92 ppm with an average value of 50 ppm,and uranium concentration increases with the decreased distance to CD.On the whole,M_(ad )and V_(daf) decrease with increasing burial depth,which indicates that CD experienced the burial metamorphism.However,M_(ad) and V_(daf) obviously decrease in uranium-rich areas whereas A_d and S_(t )noticeably increase.Comprehensive studies suggest that there is a certain relationship between uranium enrichment and CD.CD in the stage of lignite helps the adsorption of uranium.On one hand,radioactivity uranium enrichment makes organic matter maturation increase with a decrease in moisture and volatile matter.On the other hand,an increase in organic matter maturation,caused by radioactivity uranium enrichment,results in an increase in uranium minerals,which is instructive in the study of regional uranium mineralization and metallogenic regularity.展开更多
Organic matter(OM)nanopores developed in transitional facies shales,i.e.,the Upper Permian Longtan and Dalong Formations in the Yangtze Platform,China,were investigated to determine the corre-sponding influence of the...Organic matter(OM)nanopores developed in transitional facies shales,i.e.,the Upper Permian Longtan and Dalong Formations in the Yangtze Platform,China,were investigated to determine the corre-sponding influence of thermal maturity and OM types within the geological conditions.A suite of 16 core samples were taken from Type-Ⅲ Longtan shales and Type-Ⅱ Dalong shales from two wells covering a ma-turity(Ro,vitrinite reflectance)ranging from 1.22%to 1.43%and 2.62%to 2.97%,respectively.Integrated analysis of the shale samples was carried out,including field-emission scanning electron microscopy(FESEM),low-pressure N2 and CO2 adsorption,high-pressure CH4 adsorption,and mercury intrusion capillary pressure(MICP)analysis.The fluid inclusions of liquid and gas hydrocarbons trapped in calcite vein samples in Dalong shales of two wells were studied using laser Raman and fluorescence spectroscopy.FE-SEM images indicated that OM pores in different formations varied substantially in terms of shape,size,and distribution density.OM pores in Type-Ⅱ Dalong shales of Well XY1 were mainly micropore,sparsely distributed in the gas-prone kerogen with a spot-like and irregular shape,while bitumen rarely developed observable pores.In contrast,the morphology of OM pores in Type-Ⅲ Longtan shales were significantly different,which was due to differences in the OM type.The primary OM pores in some terrestrial woody debris in Longtan shales had a relatively larger pore diameter,ranging from hundreds of nanometers to a few micrometers and were al-most all rounded in shape,which might be one of the factors contributing to larger pore volume and gas adsorption capacity than Dalong shales of Well XY1.Comparing Dalong shales of Well XY1 with relatively lower thermal maturity,there were abundant spongy-like pores,densely developed in the pyrobitumen in Type-Ⅱ Dalong shales of Well EY1,with an irregular shape and diameter ranging from several to hundreds of nanometers.Many blue fluorescent oil inclusions and a small number of CH4 inclusions mixed with C2H6 could be observed within calcite veins in Dalong shales of Well XY1,whereas only CH4 inclusions could be identified within calcite veins in Dalong shales of Well EJ1.Therefore,thermal maturity not only controlled the type of hydrocarbons generated,but also makes a significant contribution to the formation of OM pores,resulting in larger pore volumes and adsorption capacity of Type-Ⅱ shale samples in the dry gas window.展开更多
A systematic analysis of southwestern Ordos Basin's sedimentary characteristics,internal architectural element association styles and depositional model was illustrated through core statistics,well logging data an...A systematic analysis of southwestern Ordos Basin's sedimentary characteristics,internal architectural element association styles and depositional model was illustrated through core statistics,well logging data and outcrop observations in Chang 8 oil-bearing group.This analysis indicates that shallow water delta sediments dominated by a fluvial system is the primary sedimentary system of the Chang 8 oil-bearing group of the Yanchang Formation in southwestern Ordos Basin.Four microfacies with fine grain sizes are identified: distributary channels,sheet sandstone,mouth bar and interdistributary fines.According to the sandbody's spatial distribution and internal architecture,two types of sandbody architectural element associations are identified: amalgamated distributary channels and thin-layer lobate sandstone.In this sedimentary system,net-like distributary channels at the delta with a narrow ribbon shape compose the skeleton of the sandbody that extends further into the delta front and shades into contiguous lobate distribution sheet sandstone in the distal delta front.The mouth bar is largely absent in this system.By analyzing the palaeogeomorphology,the palaeostructure background,sedimentary characteristics,sedimentary facies types and spatial distribution of sedimentary facies during the Chang 8 period,a distinctive depositional model of the Chang 8 shallow water fluvial-dominated delta was established,which primarily consists of straight multi-phase amalgamated distributary channels in the delta plain,net-like distributary channels frequently diverting and converging in the proximal delta front,sheet sandstones with dispersing contiguous lobate shapes in the distal delta front,and prodelta or shallow lake mudstones.展开更多
The gravity flow deposit were mainly developed in the lowstand systems tract（LST） of the first member of Upper Miocene Huangliu Formation（Ehl1） in Dongfang area, Yinggehai Basin, has become a valuable target for g...The gravity flow deposit were mainly developed in the lowstand systems tract（LST） of the first member of Upper Miocene Huangliu Formation（Ehl1） in Dongfang area, Yinggehai Basin, has become a valuable target for gas exploration and production. The gravity flow sedimentary characteristics of lithofacies associations, sedimentary texture, seismic facies and logging facies were described in detail on the basis of integrated analysis of cores, logging and seismic data. The sedimentary microfacies types composed of neritic sandbar, continental shelf mud, main channel, bifurcated or cross-cutting distributary channel, overspill, and natural levee are revealed under the constraint of high resolution sequence stratigraphic framework in the Ehl1. The gravity flow deposit system in the LST is divided into three evolution stages corresponding to periods of three parasequence sets. The gravity flow deposit was induced in the early LST, expanded rapidly in the middle LST and decreased slightly in the late LST. But its developing scale decreased sharply in the transgression systems tract（TST） and finally vanished in the highstand systems tract（HST）. This spatial evolution rule is constrained by the integrated function of sediments supply of the Vietnam Blue River in the LST, the development of local gradient change in sea floor（micro-topography, i.e., flexure slope break）, and the fall in relative sea level. On the basics of the deep study of the coupling relationship among the three main control factors, the sedimentary model is established as an optimal component of ＂source-channel-sink＂ for shallow marine turbidite submarine fan.展开更多
The Pearl River Mouth Basin （PRMB） covers an area of approximately 20× 104 km2.However,oil-gas fields detected in this area thus far are highly concentrated and controlled predominantly by second-order structur...The Pearl River Mouth Basin （PRMB） covers an area of approximately 20× 104 km2.However,oil-gas fields detected in this area thus far are highly concentrated and controlled predominantly by second-order structural belts,the seven largest of which aggregate proved oil reserves of 7.7× 108 m3,accounting for 86％ of the total discovered reserve in the basin.These second-order structures have one common phenomenon：oil is contained in all traps present in them.In other words,they are all belt-wide petroliferous reservoirs.Research has identified eight types of second-order structural belts under two categories in the eastern PRMB.Their petroliferous properties are subject to three typical constraints：petroliferous properties of subsags hosting these structural belts,locations of these belts in the petroleum system,and availability of traps prior to the hydrocarbon expulsion and migration.The formation and distribution of oil reservoirs in these belts are characterized by subsag-belt integration and ＂three-in-one＂.The former indicates that sags and the second-order structural belts within the supply range of the sags constitute the basic units of hydrocarbon accumulations and are therefore inseparable.The latter indicates that a belt-wide petroliferous second-order structural belt always contains three important elements：hydrocarbon richness,effective pathway and pre-existing traps.展开更多
Organic-rich lacustrine shales are widely distributed in China and have significant potential for unconventional shale gas and oil production although the primary factors controlling the deposition of lacustrine shale...Organic-rich lacustrine shales are widely distributed in China and have significant potential for unconventional shale gas and oil production although the primary factors controlling the deposition of lacustrine shale are disputed. This work clarifies the different characteristics of tectonic evolution and shale among sub-basins in the Bohai Bay Basin in eastern China as a case study by studying basal subsidence, tectonic subsidence rate, basin extensional proportions and shale chemical characteristics. The paper summarizes the correlation between structure and shale deposition, and concludes that tectonic activity is the primary controlling factor for shale development. Episodic tectonic activity controls not only the timing of shale deposition（with the greatest shale deposition occurring primarily during the peak period of basin tectonic activity） but also the spatial distribution of shale（located mainly in areas of maximum subsidence）, the migration pattern of shale（conforming to that of the basin subsidence center）, and shale strata thickness. Tectonic activity also affects the total organic carbon content and organic matter type in shale. When the tectonic activity was the most active and basal subsidence was the maximum, the total organic carbon content of the shale reached its highest value with organic matter type mainly Type I. As tectonic activity weakened, the total organic carbon content decreased, and the organic matter type changed from Type I to Type I-III.展开更多
The Nanpu（南堡） sag has previously been modeled as（1） a pull-apart basin,（2） a rift ba-sin,without significant strike-slip deformation,and（3） a transtensional basin.We present a new model for the Nanpu sag in ...The Nanpu（南堡） sag has previously been modeled as（1） a pull-apart basin,（2） a rift ba-sin,without significant strike-slip deformation,and（3） a transtensional basin.We present a new model for the Nanpu sag in which the basin is a transtensional fault-termination basin.Although transten-sional fault-termination basins is an important basin type,it is not as well studied as other classic basin types.On the base of 3D seismic data interpretation,the faults geometries and kinematics and their controls on depocenters are presented.The Nanpu sag is developed in the context of dextral transten-sion of the Bohai（渤海） Bay basin and attributed to a transtensional fault-termination basin.During deposition of the Es3-Es2 members,the basin border Xi＇nanzhuang（西南庄） fault and Baigezhuang（柏各庄） fault linked to a mixed normal and strike-slip fault system,or a linked fault system controlled the basin by dominant extension and weak strike-slip and created fan-shaped depocenters surrounded by the two faults.From Es1 Member to Dongying（东营） Formation,two major depocenters controlled by two mixed normal and sinistral strike-slip fault systems are located on the Linque（林雀） and Caofeidian（曹妃甸） subsags.During deposition of the Guantao（馆陶）-Minghuazhen（明化镇） Forma-tion,the Nanpu sag successively developed and significantly expanded.展开更多
基金supported by grants from the Natural Science Foundation of China (Nos. 41272121 , 91028009 , 41302082)the Program of Introducing Talents of Discipline to Universities (No. B14031)
文摘The Huizhou sag is situated on the continental shelf of the northern continental margin of the South China Sea. In this paper we present a grid of reflection seismic and well data to characterize the basin structure and prominent unconformities. We employ EBM and 2DMOVE softwares to explore the subsidence history and stratigraphic development history of the basin. We found a rapid subsidence period since 15.5 Ma. Moreover, we calculated the stretching factors of the upper crust and the whole crust in the Huizhou sag. The results show the values are 1.10–1.13 and 1.08–1.31, respectively, indicating faulting in Huizhou sag is relatively small. It is noteworthy that the faults map reveals en echelon distribution at the north and south margins of the basin. We suggest en echelon faults here are caused by the subduction of Proto-South China Sea toward NW Borneo block and cease of the South China Sea. Considering the pronounced unconformities, subsidence rates, fault activities and sediment thickness, the Cenozoic tectonic evolution of the basin can be divided into rifting（49–32 Ma）, post-rifted（32–15.5 Ma） and rapid subsidence（15.5–0 Ma） stages. Our study will shed new light on the tectonics of SE Asia and petroleum exploration in the South China Sea.
基金This study was jointly supported by the Science&Technology Fundamental Resources Investigation Program(2022FY101800)National Science Foundation(92162212)+1 种基金the project from the Key Laboratory of Tectonics and Petroleum Resources(China University of Geosciences,Wuhan)(TPR-2022-22)the International Geoscience Programme(IGCP-675)。
文摘The Ordos Basin(OB)in the western part of the North China Craton(NCC),was located at the jointed area of multi-plates and has recorded the Mesozoic tectonic characteristics.Its tectonic evolution in the Mesozoic is significant to understand the tectonic transformation of the northern margin of the NCC.In this work,the detrital zircon and apatite(U-Th)/He chronological system were analyzed in the northern part of the OB,and have provided new evidence for the regional tectonic evolution.The(U-Th)/He chronological data states the weighted ages of 240‒235 Ma,141 Ma with the peak distribution of 244 Ma,219 Ma,173 Ma,147‒132 Ma.The thermal evolution,geochronological data,and regional unconformities have proved four stages of regional tectonic evolution for the OB and its surroundings in the Mesozoic:(1)The Late Permian-Early Triassic;(2)the Late Triassic-Early Jurassic;(3)the Late Jurassic-Early Cretaceous;(4)the Late Cretaceous-Early Paleogene.It is indicated that the multi-directional convergence from the surrounding tectonic units has controlled the Mesozoic tectonic evolution of the OB.Four-stage tectonic evolution reflected the activation or end of different plate movements and provided new time constraints for the regional tectonic evolution of the NCC in the Mesozoic.
基金Supported by the China National Science and Technology Major Project(2025ZD1405700)CNPC Science and Technology Project(2023YQX20117).
文摘Based on the coalbed methane(CBM)/coal-rock gas(CRG)geological,geophysical,and experimental testing data from the Daji block in the Ordos Basin,the coal-forming and hydrocarbon generation&accumulation characteristics across different zones were dissected,and the key factors controlling the differential CBM/CRG enrichment were identified.The No.8 coal seam of the Carboniferous Benxi Formation in the Daji block is 8-10 m thick,typically overlain by limestone.The primary hydrocarbon generation phase occurred during the Early Cretaceous.Based on the differences in tectonic evolution and CRG occurrence,and with the maximum vitrinite reflectance of 2.0%and burial depth of 1800 m as boundaries,the study area is divided into deeply buried and deeply preserved,deeply buried and shallowly preserved,and shallowly buried and shallowly preserved zones.The deeply buried and deeply preserved zone contains gas content of 22-35 m^(3)/t,adsorbed gas saturation of 95%-100%,and formation water with total dissolved solid(TDS)higher than 50000 mg/L.This zone features structural stability and strong sealing capacity,with high gas production rates.The deeply buried and shallowly preserved zone contains gas content of 16-20 m^(3)/t,adsorbed gas saturation of 80%-95%,and formation water with TDS of 5000-50000 mg/L.This zone exhibits localized structural modification and hydrodynamic sealing,with moderate gas production rate.The shallowly buried and shallowly preserved zone contains gas content of 8-16 m^(3)/t,adsorbed gas saturation of 50%-70%,and formation water with TDS lower than 5000 mg/L.This zone experienced intense uplift,resulting in poor sealing and secondary alteration of the primary gas reservoir,with partial adsorbed gas loss,and low gas production rate.A depositional unification and structural divergence model is proposed,that is,although coal seams across the basin experienced broadly similar depositional and tectonic histories,differences in tectonic intensity have led to spatial heterogeneity in the maximum burial depth(i.e.,thermal maturity of coal)and current burial depth and occurrence of CRG(i.e.,gas content and occurrence state).The research results provide valuable guidance for advancing the theoretical understanding of CBM/CRG enrichment and for improving exploration and development practices.
基金granted by the Xinjiang Geological Exploration Fund。
文摘The northwestern margin of Junggar Basin is the region with the richest oil sand resources in China.For better understanding the enrichment rules and deployment of exploration and development of regional oil sand,it is of great scientific significance to study the accumulation conditions of oil sand in different strata and mining areas of the Junggar Basin.Through a large number of field investigations,drilling verification and sampling tests,it is found that the oil sand in the region covers an area of 2000 km^(2),with shallow and thick reservoir,and predicted resource of 180 million tons.The oil sand resources are mainly distributed in four geological strata,namely the Middle Triassic Karamay Formation,Early Jurassic Badaowan Formation,Late Jurassic Qigu Formation,and Early Cretaceous Qingshuihe Formation.The reservoir is mainly composed of sandstone with high porosity and permeability,and the reservoir space is mainly intergranular pores with a medium average oil content.The oil sand deposit in the region is a typical destructive oil reservoir.The crude oil in the oil sand layer is degraded and thickened from the deep to the shallow,the content of saturated hydrocarbon decreased,and the content of aromatic hydrocarbon,non-hydrocarbon and asphaltene increased.The oil source comes from the deep Permian hydrocarbon-generating depression.Unconformities,faults and marginal fan delta-braided river depositional systems constitute effective migration and storage systems.Caprocks of the Upper Triassic Baijiantan Formation,Lower Jurassic Sangonghe Formation and Lower Cretaceous Hutubihe Formation were formed by three large scale lake transgressions.The Indosinian,Yanshan and Late Yanshan movements are the main driving forces for the migration of deep oil and gas to the shallow edge to form oil sand deposits.It is considered that the oil sand in the northwestern margin of Junggar Basin is of a slope complex migration type.
基金supported by research projects P23057 and JKK4624004 of Jianghan Oilfield Company,SINOPEC.
文摘The carbonate-rich shale of the Permian Wujiaping Formation in Sichuan Basin exhibits significant heterogeneity in its lithology and pore structure,which directly influence its potential for shale gas extraction.This study assesses the factors that govern pore heterogeneity by analyzing the mineral composition of the shale,as well as its pore types and their multifractal characteristics.Three primary shale facies-siliceous,mixed,and calcareous-are identified based on mineralogy,and their multifractal characteristics reveal strongly heterogeneous pore structures.The brittleness of siliceous shale,rich in quartz and pyrite,is favorable for hydraulic fracturing;while calcareous shale,with higher levels of calcite,exhibits reduced brittleness.Multifractal analysis,using nitrogen adsorption isotherms,reveals complex pore structures across different shale facies,with siliceous shale showing better pore connectivity and uniformity.The types of pores in shales include organic matter pores,interparticle pores,and intraparticle pores,among which organic matter pores are the most abundant.Pore size distribution and connectivity are notably higher in siliceous shale compared to calcareous shale,which exhibit a predominance of micropores and more isolated pore structures.Pore heterogeneity of the carbonate-rich shale in the Wujiaping Formation is primarily governed by its intrinsic mineral composition,carbonate diagenesis,mechanical compaction,and its subsequent thermal maturation with the micro-migration of organic matter.This study highlights the importance of mineral composition,especially the presence of dolomite and calcite,in shaping pore heterogeneity.These findings emphasize the critical role of shale lithofacies and pore structure in optimizing shale gas extraction methods.
基金funded by the National Key Research and Development Program of China(Nos.2022YFF0801202,2022YFF0801200)。
文摘The effect of depositional facies and diagenesis on the reservoir potential of the Sakesar limestone has been assessed through core plug porosity and permeability data,scanning electron microscope(SEM),and petrographic study in three stratigraphic sections(Karuli,Badshah Pur,and Sardhai)of Central Salt Range.Field observations reveal three lithofacies:thin-bedded limestone with shale intercalation,thick-bedded nodular limestone,and highly fractured limestone.Based on a petrographic study,six microfacies have been identified:bioclastic mudstone facies(SKF-1),Lockhartia-nummulitic wackestone facies(SKF-2),Assilina-Alveolina packstone facies(SKF-3),Lockhartia-nummulitic packstone facies(SKF-4),Alveolina grainstone facies(SKF-5),and nummulitic grainstone facies(SKF-6).The Sakesar limestone shows various diagenetic changes such as compaction,dissolution,dolomitization,cementation,and fracturing,resulting in different types of pores.Two reservoir zones are identified in the Sakesar limestone:a mud-dominated reservoir in an outer ramp setting with interparticle and micropores and a bioclastic grain-dominated facies in an inner ramp setting with intraskeletal and fracture porosity.The porosity and permeability of grain-dominated facies(8%-30%and 0.8-8 mD)are higher than mud-dominated facies(4%-15%and 0.5-4 mD)due to intraskeletal/intraparticle pores and dolomitization.
基金supported by the project of“Shale Gas Resources Investigation and Evaluation in the Baoshan Block”from Sinopec Exploration Company and the National Natural Science Foundation of China(41925014 and 42172192)。
文摘Lower Paleozoic black shales are important source rocks worldwide.The Upper Ordovician-Lower Silurian Renheqiao Formation of the Baoshan Block is a low-maturity equivalent of the Wufeng-Longmaxi(WF-LMX)Shale of the Sichuan Basin.However,organic matter(OM)characteristics in these low-maturity Lower Paleozoic shales are not well understood.In this study,50 Renheqiao Formation shale samples collected from seven outcrop sections and one drill core were investigated with organic petrology,organic geochemistry,R_(o)ck-Eval pyrolysis,N_(2) and CO_(2) adsorption,and scanning electron microscope(SEM)analyses to study the OM content,type,thermal maturity,and the development of OM-hosted pores in these Lower Paleozoic shales.The total organic carbon(TOC)content of the Renheqiao Formation shales varies,with the maximum content of 10.07 wt%.R_(o)ck-Eval pyrolysis results show that present OM in the Renheqiao Formation shales is Type IV kerogen,a result of advanced thermal maturation.Graptolite reflectance(GR_(o))ranges from 1.26%to 1.85%,and equivalent vitrinite reflectance(EqR_(o))converted from GR_(o) ranges from 1.08%to 1.51%,indicating that the studied Renheqiao Formation shales are dominantly within the late-mature stage.EqR_(o) based on R_(o)ck-Eval T_(max) shows large variations,which indicates that R_(o)ck-Eval T_(max) is not a reliable thermal maturity indicator for the Lower Paleozoic Renheqiao Formation shales.Caution should be applied when assessing the thermal maturity of high-maturity black shales based on T_(max) when the S2 values are too low.Organic petrographic observations show that OM in these shales is dominated by solid bitumen(>70 vol%of total OM),with minor contributions by graptolites and chitinozoans.The specific surface area and pore volume of shales are controlled by TOC content.Organic pores are hosted by solid bitumen and were not observed in graptolites when examined under the SEM.Although the Renheqiao Formation has a lower thermal maturity than the over-mature WF-LMX Shale,it is mature enough that primary oil-prone macerals have been thermally transformed and could not be identified under the microscope.
基金supported by the National Science and Technology Major Project of China(No.2025ZD1401403)the National Natural Science Foundation of China(No.42102156)+1 种基金the Tarim Oilfield Company R&D Center Project“Research and Application of Exploration Geomechanics Technology”(No.YF202505)the“CUG Scholar”Scientific Research Funds at China University of Geosciences(Wuhan)(No.2022046).
文摘Fracture-cave reservoirs are widely developed in carbonate formations and account for over 55%of global petroleum reserves.The productivity,formation mechanisms,and in-situ stress states of these reservoirs,characterized by fault-fracture-cave systems,are inherently interconnected.However,solely relying on geometric characterizations of natural fractures and cavities fails to meet the demands of modern petroleum exploration and development,particularly due to their complex structures,significant spatial heterogeneity,and strong geomechanical anisotropy.A critical challenge remains:how to safely and efficiently drill high-yield wells through highly fractured and cavernous zones while mitigating drilling risks.Consequently,establishing geomechanical models for fracture-cave reservoirs and predicting 3D stress fields are imperative for well trajectory optimization and reservoir reconstruction.This study integrates seismic interpretations of strike-slip faults with multi-attribute inversions of fracture-cave reservoirs.Using ANSYS 21.0 software,a homogeneous geomechanical model was constructed based on finely characterized geometries of fracturecave systems.Rock mechanics parameters,interpreted from conventional logging data and seismic attributes,were inverted to generate 3D distributions.These parameters were subsequently incorporated into the homogeneous model to develop a heterogeneous geomechanical framework.In-situ stress orientations were calibrated using drilling-induced fracture data,enabling predictions of the contemporary stress field in complex fracture-cave reservoirs.The methodology was validated in the Yueman Block of the Tarim Basin’s deep carbonate reservoir.Results revealed stress distribution patterns and key controlling factors,which were applied to evaluate wellbore stability,fracture reactivation risks,and optimize well trajectories.This approach provides a technical foundation for safe and efficient exploration-development of fracture-cave reservoirs worldwide.
基金supported by the Major National Science and Technology Programs in the“Thirteenth Five-Year”Plan period(Grant No.2017ZX05032-002-004)the Innovation Team Funding of Natural Science Foundation of Hubei Province,China(Grant No.2021CFA031)the Chinese Scholarship Council(CSC)and Silk Road Institute for their support in terms of stipend.
文摘Accurate reservoir permeability determination is crucial in hydrocarbon exploration and production.Conventional methods relying on empirical correlations and assumptions often result in high costs,time consumption,inaccuracies,and uncertainties.This study introduces a novel hybrid machine learning approach to predict the permeability of the Wangkwar formation in the Gunya oilfield,Northwestern Uganda.The group method of data handling with differential evolution(GMDH-DE)algorithm was used to predict permeability due to its capability to manage complex,nonlinear relationships between variables,reduced computation time,and parameter optimization through evolutionary algorithms.Using 1953 samples from Gunya-1 and Gunya-2 wells for training and 1563 samples from Gunya-3 for testing,the GMDH-DE outperformed the group method of data handling(GMDH)and random forest(RF)in predicting permeability with higher accuracy and lower computation time.The GMDH-DE achieved an R^(2)of 0.9985,RMSE of 3.157,MAE of 2.366,and ME of 0.001 during training,and for testing,the ME,MAE,RMSE,and R^(2)were 1.3508,12.503,21.3898,and 0.9534,respectively.Additionally,the GMDH-DE demonstrated a 41%reduction in processing time compared to GMDH and RF.The model was also used to predict the permeability of the Mita Gamma well in the Mandawa basin,Tanzania,which lacks core data.Shapley additive explanations(SHAP)analysis identified thermal neutron porosity(TNPH),effective porosity(PHIE),and spectral gamma-ray(SGR)as the most critical parameters in permeability prediction.Therefore,the GMDH-DE model offers a novel,efficient,and accurate approach for fast permeability prediction,enhancing hydrocarbon exploration and production.
基金supported by the project of the Exploration Department of the Huabei Oilfield Company of Sinopec(No.34550008-20-ZC0609-0031).
文摘The origin of tight reservoirs in the Yanchang Formation of the Ordos Basin and their relationship with hydrocarbon charging remain unclear.Based on petrological observations,physical property analysis,fluid inclusion system analysis and in situ U-Pb dating,the sequence of tight sandstone reservoir densification and oil charging was determined.Through petrological observations,fluid inclusion analysis and physical property analysis,it is concluded that compaction and cementation are the primary causes of reservoir densification.When the content of calcite cement is less than or equal to 7%,compaction dominates densification;otherwise,cementation becomes more significant.However,determining the exact timing of compaction densification proved challenging.Microscopic observations revealed that oil charging likely occurred either before or during the densification of the reservoir.According to in situ U-Pb dating and the porosity evolution curve,cementation densification occurred between 167.0±20.0 Ma and 151.8 Ma.Temperature measurements of the aqueous inclusions indicate that oil charging occurred between 125.0 and 96.0 Ma,suggesting that densification preceded oil charging.This study provides valuable insights for the future exploration of tight oil reservoirs in the Ordos Basin.
基金supported by the National Natural Science Foundation of China(U24B6002,42202133,U22B6004)CNPC Innovation Fund(2022DQ02-0106)+5 种基金Key Laboratory of Tectonics and Petroleum Resources of the Ministry of Education(TPR-2023-05)major science and technology projects of CNPC during the"14th five-year plan"(2021DJ0101)National Natural Science Foundation of China(41872148,42072174,42130803)Strategic Cooperation Technology Projects of the CNPC and CUPB(ZLZX2020-01-05)Sinopec Zhongyuan Oilfeld and CUPB Cooperation Project(31300027-23-ZC0613-0013)AAPG Foundation Grantsin-Aid Program(22272306).
文摘Shale oil resources are abundant on Earth,of which hybrid sedimentary shale(HSS)oil is an important component,including high and medium-low organic matter content(TOC).Oil content,especially the oiliness gradation,is a key parameter for shale oil evaluation and numerous studies had been conducted.However,most studies concentrated on the HSS with high TOC,making oil content evaluation of the HSS with medium-low TOC challenging.The Paleocene Shahejie Formation(E2s)shale in Dongpu Depression is a typical HSS with low-moderate TOC,showing great shale oil resource potential.Integrated geochemical characterization of 270 core samples were conducted and results show that,the E2s shale has fairgood hydrocarbon generation potential,with TOC ranging from 0.06%to 3.6%(Avg.0.86%)andⅡ1-Ⅱ2 kerogen type in thermally mature.The hydrocarbon generation potential decreases with kerogen types changing from type I toⅢ,but S1C and the oil saturation index(OSI)(S1*100/TOC>100)increase from type I toⅡ1,and then decrease from typeⅡ2 toⅢ,indicating shale with typeⅡ2 kerogen have the greatest oil content.This is related to the diferences in hydrocarbon expulsion efciency caused by diferential hydrocarbon generation potential and pore-microfractures evolution among shales with diferent kerogen types.Signifcant oil micro-migration occurred in E2s shale,with micro-migration quantity(∆Q)ranging from-846 to 993 mg/g(Avg.-120 mg/g),and 90%and 10%shale exhibit hydrocarbon intra-micro-migration(∆Q<0)and extra-micro-migration(∆Q>0).The shale with typeⅡ2 kerogen has the greatest intra-micro-migration.Based on S1C,TOC and OSI values and their evolution pattern,shale oil resources were classifed into enriched,moderately enriched,less efcient and invalid resources,accounting for 11%,53%,16%and 21%respectively,with S1C thresholds of 3.5 and 0.5 mg/g,OSI threshold of 100 mg/g.Compared with previous grading criteria,the gradation criterion established in this study is relatively lower,which is mainly due to the lower TOC and clay mineral content in HSS.Enriched and moderately enriched resources are mainly shales with typeⅡ2 kerogen,followed by typeⅡ1 kerogen,and the E2s4 U and E2s3 L shale are the most favorable targets for further shale oil exploration.The established oiliness gradation criteria are applicable for the HSS with TOC in other parts of the world.
基金supported by the National Natural Science Foundation of China,funding numbers 41690131,41572327,51874280 and 5264015.
文摘The presence of inorganic constituents in coal is controlled by different geological factors,which,in turn,affect the technological,environmental,and health impacts of the coal.The main aim of this study is to objectively assess the mineralogical and geochemical characteristics of a thickest low-rank coal seam in the Lower Indus Basin southeastern Pakistan,and further investigate different controlling factors.The analytical results of major oxides,trace elements,and rare earth elements revealed that the weathering conditions were progressively variable and moderate.The sediment source,mainly of felsic and intermediate composition,was dominated by granitic rocks.The geochemical assessment reveals different depositional factors like marine environment influenced,while transitional and freshwater sediments influenced the center of the coal peat mire.Strontium,Zinc,and several hazardous trace elements,including Cu,Ni,Cr,and Co,have higher concentrations in these coals compared to world low-rank,U.S.,and Chinese coals.The relatively higher concentration of Sr in the thick coal seam in the Lower Indus Basin,compared to other coals seams in Pakistan and the enrichment of Sr was primarily controlled by the denudation of crystalline rocks and marine influx in the coal-basin.The REY distribution pattern showed that enrichment of medium and heavy rare earth elements is higher than light rare earth elements in the coal seam.The Gd distribution pattern in the coal seam demonstrated that strong positive anomalies had a good affinity with paleo-acidic water concentration in the study area.The higher concentration of Sr and other elements enables a better assessment understanding of the coal geochemical history.
基金financially supported by National Natural Science Foundation of China(No.92255302)the Joint Funds of the National Natural Science Foundation of China(No.U20B6001)。
文摘Understanding the origin of natural gas in deep and ultra-deep reservoirs with multiple potential source rocks remains challenging due to the complex thermal evolution of hydrocarbons at high temperatures and multi-stage accumulation processes.This study investigates the origin of natural gas in deep hydrothermal dolomite reservoirs of the Maokou Formation,eastern Sichuan Basin,using hydrocarbon inclusion analysis,radiometric U-Pb dating of calcite cements,maturity modeling of potential source rocks,and constraints on reactivation periods of the nearby No.15 Fault System.Results indicate an oil charging event at approximately 246.9 Ma,followed by two episodes of gas charging at 222.4 Ma and 175.2 Ma.Furthermore,the oil and gas charging events occurred synchronously with activities of the No.15 Fault System,suggesting that its reactivation induced episodic hydrocarbon migration.Maturity modeling indicates that during the oil charging period,source rocks in the Qiongzhusi,WufengLongmaxi,and first member of the Maokou formations reached the stages of dry gas generation,significant oil generation,and the threshold of oil generation,respectively.During the subsequent twoepisode gas charging periods,the Qiongzhusi and Wufeng-Longmaxi formations progressed to dry and wet gas generation stages,respectively,while the first member of the Maokou Formation attained the oil generation stage.The hydrocarbon charging time and maturity history of potential source rocks indicate that:1)oil in hydrothermal dolomite reservoirs predominantly originated from the Wufeng-Longmaxi Formation at approximately 246.9 Ma;2)during the subsequent gas charging episodes,the WufengLongmaxi Formation could contribute wet gas,while the Qiongzhusi Formation likely supplied cracking gas from kerogen and residual liquid hydrocarbon;3)all oil in the hydrothermal dolomite reservoirs underwent thermal cracking to gas at approximately 110 Ma.This study indicates that gas pools in(ultra-)deep carbonate reservoirs of the Sichuan Basin have mixed genetic origins,with contributions from multiple sources.The multidisciplinary approach,combining direct dating of hydrocarbon charge events and simulation of hydrocarbon generation,proves robust and effective in identifying the origin of natural gas in(ultra-)deep reservoirs.
基金supported by the 973 Project (No. 2015CB453003)Open Fund of Key Laboratory of Tectonics and Petroleum Resources (China University of Geosciences), Ministry of Education (No. TPR-2015-09)+2 种基金Geological Survey Foundation of Ministry of Finance of the People’s Republic of China (No. 12120115013701)Natural Science Foundation of China (No. 41502105)Fundamental Research Funds for the Central Universities, China University of Geosciences(Wuhan) (No. G1323511660)
文摘Carbonaceous debris(CD)is widely distributed in the sandstone of the Daying Uranium Deposit,northern Ordos Basin,and coexists with uranium minerals,which provides a favorable case for studying their relationship.Vitrinite reflectance(VR),macerals,moisture,volatile matter,ash,total sulfur(S_t)and uranium concentration of CD within the sandstone were studied.The results show that VR ranges from 0.372%Ro to 0.510%Ro with an average value of 0.438%Ro,indicating that CD is in the stage of lignite.The contents of vitrinite(V),inertinite(I)and minerals range from 83.18%–99.48%,0–7.70%,and 0.34%–15.72%,respectively,with the corresponding average value of 95.51%,1.34%,and 3.15%,respectively which indicates that V is the major maceral.Moisture on air dried basis(M_(ad)),volatile matter yield on dry,ash-free basis(V_(daf)),ash yield on dried basis(A_d)and S_t mostly range from 7.95%–16.09%,44.70%–66.54%,4.84%–26.24% and 0.24%–1.12%,respectively,while their average values are 12.43%,53.41%,16.57% and 0.77%,respectively.It suggests that CD is of medium-high moisture,super-high volatile matter,low-medium ash and low sulfur.Uranium concentration ranges from 29 ppm to 92 ppm with an average value of 50 ppm,and uranium concentration increases with the decreased distance to CD.On the whole,M_(ad )and V_(daf) decrease with increasing burial depth,which indicates that CD experienced the burial metamorphism.However,M_(ad) and V_(daf) obviously decrease in uranium-rich areas whereas A_d and S_(t )noticeably increase.Comprehensive studies suggest that there is a certain relationship between uranium enrichment and CD.CD in the stage of lignite helps the adsorption of uranium.On one hand,radioactivity uranium enrichment makes organic matter maturation increase with a decrease in moisture and volatile matter.On the other hand,an increase in organic matter maturation,caused by radioactivity uranium enrichment,results in an increase in uranium minerals,which is instructive in the study of regional uranium mineralization and metallogenic regularity.
基金We would like to thank the National Key R&D program of China(No.2017YFE0103600)the National Natural Science Foundation of China(Nos.41830431,41672139)the China National Science and Technology Major Projects(No.2016ZX05034002-003)for financial assistance to this research.
文摘Organic matter(OM)nanopores developed in transitional facies shales,i.e.,the Upper Permian Longtan and Dalong Formations in the Yangtze Platform,China,were investigated to determine the corre-sponding influence of thermal maturity and OM types within the geological conditions.A suite of 16 core samples were taken from Type-Ⅲ Longtan shales and Type-Ⅱ Dalong shales from two wells covering a ma-turity(Ro,vitrinite reflectance)ranging from 1.22%to 1.43%and 2.62%to 2.97%,respectively.Integrated analysis of the shale samples was carried out,including field-emission scanning electron microscopy(FESEM),low-pressure N2 and CO2 adsorption,high-pressure CH4 adsorption,and mercury intrusion capillary pressure(MICP)analysis.The fluid inclusions of liquid and gas hydrocarbons trapped in calcite vein samples in Dalong shales of two wells were studied using laser Raman and fluorescence spectroscopy.FE-SEM images indicated that OM pores in different formations varied substantially in terms of shape,size,and distribution density.OM pores in Type-Ⅱ Dalong shales of Well XY1 were mainly micropore,sparsely distributed in the gas-prone kerogen with a spot-like and irregular shape,while bitumen rarely developed observable pores.In contrast,the morphology of OM pores in Type-Ⅲ Longtan shales were significantly different,which was due to differences in the OM type.The primary OM pores in some terrestrial woody debris in Longtan shales had a relatively larger pore diameter,ranging from hundreds of nanometers to a few micrometers and were al-most all rounded in shape,which might be one of the factors contributing to larger pore volume and gas adsorption capacity than Dalong shales of Well XY1.Comparing Dalong shales of Well XY1 with relatively lower thermal maturity,there were abundant spongy-like pores,densely developed in the pyrobitumen in Type-Ⅱ Dalong shales of Well EY1,with an irregular shape and diameter ranging from several to hundreds of nanometers.Many blue fluorescent oil inclusions and a small number of CH4 inclusions mixed with C2H6 could be observed within calcite veins in Dalong shales of Well XY1,whereas only CH4 inclusions could be identified within calcite veins in Dalong shales of Well EJ1.Therefore,thermal maturity not only controlled the type of hydrocarbons generated,but also makes a significant contribution to the formation of OM pores,resulting in larger pore volumes and adsorption capacity of Type-Ⅱ shale samples in the dry gas window.
基金Project(SQ2013CB021013)supported by the National Key Basic Research Program of ChinaProject(41002045)supported by the National Natural Science Foundation of China
文摘A systematic analysis of southwestern Ordos Basin's sedimentary characteristics,internal architectural element association styles and depositional model was illustrated through core statistics,well logging data and outcrop observations in Chang 8 oil-bearing group.This analysis indicates that shallow water delta sediments dominated by a fluvial system is the primary sedimentary system of the Chang 8 oil-bearing group of the Yanchang Formation in southwestern Ordos Basin.Four microfacies with fine grain sizes are identified: distributary channels,sheet sandstone,mouth bar and interdistributary fines.According to the sandbody's spatial distribution and internal architecture,two types of sandbody architectural element associations are identified: amalgamated distributary channels and thin-layer lobate sandstone.In this sedimentary system,net-like distributary channels at the delta with a narrow ribbon shape compose the skeleton of the sandbody that extends further into the delta front and shades into contiguous lobate distribution sheet sandstone in the distal delta front.The mouth bar is largely absent in this system.By analyzing the palaeogeomorphology,the palaeostructure background,sedimentary characteristics,sedimentary facies types and spatial distribution of sedimentary facies during the Chang 8 period,a distinctive depositional model of the Chang 8 shallow water fluvial-dominated delta was established,which primarily consists of straight multi-phase amalgamated distributary channels in the delta plain,net-like distributary channels frequently diverting and converging in the proximal delta front,sheet sandstones with dispersing contiguous lobate shapes in the distal delta front,and prodelta or shallow lake mudstones.
基金supported by the National Natural Science Foundation of China (NSFC) (Nos. 41272122, 41202074, 41172123 and 40702023)the National Twelfth Five-Year Major Projects of Oil and Gas (No. 2011ZX05025-002-02-02)+1 种基金the Key Laboratory of Tectonics and Petroleum Resources (CUG)of Ministry of Education open issue (No. TPR-2013-08)the China University of Geosciences (Wuhan) Teaching Labor atory open funded projects
文摘The gravity flow deposit were mainly developed in the lowstand systems tract（LST） of the first member of Upper Miocene Huangliu Formation（Ehl1） in Dongfang area, Yinggehai Basin, has become a valuable target for gas exploration and production. The gravity flow sedimentary characteristics of lithofacies associations, sedimentary texture, seismic facies and logging facies were described in detail on the basis of integrated analysis of cores, logging and seismic data. The sedimentary microfacies types composed of neritic sandbar, continental shelf mud, main channel, bifurcated or cross-cutting distributary channel, overspill, and natural levee are revealed under the constraint of high resolution sequence stratigraphic framework in the Ehl1. The gravity flow deposit system in the LST is divided into three evolution stages corresponding to periods of three parasequence sets. The gravity flow deposit was induced in the early LST, expanded rapidly in the middle LST and decreased slightly in the late LST. But its developing scale decreased sharply in the transgression systems tract（TST） and finally vanished in the highstand systems tract（HST）. This spatial evolution rule is constrained by the integrated function of sediments supply of the Vietnam Blue River in the LST, the development of local gradient change in sea floor（micro-topography, i.e., flexure slope break）, and the fall in relative sea level. On the basics of the deep study of the coupling relationship among the three main control factors, the sedimentary model is established as an optimal component of ＂source-channel-sink＂ for shallow marine turbidite submarine fan.
文摘The Pearl River Mouth Basin （PRMB） covers an area of approximately 20× 104 km2.However,oil-gas fields detected in this area thus far are highly concentrated and controlled predominantly by second-order structural belts,the seven largest of which aggregate proved oil reserves of 7.7× 108 m3,accounting for 86％ of the total discovered reserve in the basin.These second-order structures have one common phenomenon：oil is contained in all traps present in them.In other words,they are all belt-wide petroliferous reservoirs.Research has identified eight types of second-order structural belts under two categories in the eastern PRMB.Their petroliferous properties are subject to three typical constraints：petroliferous properties of subsags hosting these structural belts,locations of these belts in the petroleum system,and availability of traps prior to the hydrocarbon expulsion and migration.The formation and distribution of oil reservoirs in these belts are characterized by subsag-belt integration and ＂three-in-one＂.The former indicates that sags and the second-order structural belts within the supply range of the sags constitute the basic units of hydrocarbon accumulations and are therefore inseparable.The latter indicates that a belt-wide petroliferous second-order structural belt always contains three important elements：hydrocarbon richness,effective pathway and pre-existing traps.
基金supported by China Postdoctoral Science Foundation (No. 2013M530680)the foundation of the Key Laboratory of Tectonics and Petroleum Resources (China University of Geosciences, Wuhan) of the Ministry of Education (No.TPR-2010-12)
文摘Organic-rich lacustrine shales are widely distributed in China and have significant potential for unconventional shale gas and oil production although the primary factors controlling the deposition of lacustrine shale are disputed. This work clarifies the different characteristics of tectonic evolution and shale among sub-basins in the Bohai Bay Basin in eastern China as a case study by studying basal subsidence, tectonic subsidence rate, basin extensional proportions and shale chemical characteristics. The paper summarizes the correlation between structure and shale deposition, and concludes that tectonic activity is the primary controlling factor for shale development. Episodic tectonic activity controls not only the timing of shale deposition（with the greatest shale deposition occurring primarily during the peak period of basin tectonic activity） but also the spatial distribution of shale（located mainly in areas of maximum subsidence）, the migration pattern of shale（conforming to that of the basin subsidence center）, and shale strata thickness. Tectonic activity also affects the total organic carbon content and organic matter type in shale. When the tectonic activity was the most active and basal subsidence was the maximum, the total organic carbon content of the shale reached its highest value with organic matter type mainly Type I. As tectonic activity weakened, the total organic carbon content decreased, and the organic matter type changed from Type I to Type I-III.
基金supported by the National Natural Science Foundation of China (No. 40402014)
文摘The Nanpu（南堡） sag has previously been modeled as（1） a pull-apart basin,（2） a rift ba-sin,without significant strike-slip deformation,and（3） a transtensional basin.We present a new model for the Nanpu sag in which the basin is a transtensional fault-termination basin.Although transten-sional fault-termination basins is an important basin type,it is not as well studied as other classic basin types.On the base of 3D seismic data interpretation,the faults geometries and kinematics and their controls on depocenters are presented.The Nanpu sag is developed in the context of dextral transten-sion of the Bohai（渤海） Bay basin and attributed to a transtensional fault-termination basin.During deposition of the Es3-Es2 members,the basin border Xi＇nanzhuang（西南庄） fault and Baigezhuang（柏各庄） fault linked to a mixed normal and strike-slip fault system,or a linked fault system controlled the basin by dominant extension and weak strike-slip and created fan-shaped depocenters surrounded by the two faults.From Es1 Member to Dongying（东营） Formation,two major depocenters controlled by two mixed normal and sinistral strike-slip fault systems are located on the Linque（林雀） and Caofeidian（曹妃甸） subsags.During deposition of the Guantao（馆陶）-Minghuazhen（明化镇） Forma-tion,the Nanpu sag successively developed and significantly expanded.
