Based on the data of measured formation pressure, drilling fluid density of key exploration wells and calculated pressure by well logging, combined with the analysis of natural gas geological conditions, the character...Based on the data of measured formation pressure, drilling fluid density of key exploration wells and calculated pressure by well logging, combined with the analysis of natural gas geological conditions, the characteristics and formation mechanisms of formation fluid overpressure systems in different foreland basins and the relationship between overpressure systems and large-scale gas accumulation are discussed.(1) The formation mechanisms of formation overpressure in different foreland basins are different. The formation mechanism of overpressure in the Kuqa foreland basin is mainly the overpressure sealing of plastic salt gypsum layer and hydrocarbon generation pressurization in deep–ultra-deep layers, that in the southern Junggar foreland basin is mainly hydrocarbon generation pressurization and under-compaction sealing, and that in the western Sichuan foreland basin is mainly hydrocarbon generation pressurization and paleo-fluid overpressure residual.(2) There are three common characteristics in foreland basins, i.e. superimposed development of multi-type overpressure and multi-layer overpressure, strong–extremely strong overpressure developed in a closed foreland thrust belt, and strong–extremely strong overpressure developed in a deep foreland uplift area.(3) There are four regional overpressure sealing and storage mechanisms, which play an important role in controlling large gas fields, such as the overpressure of plastic salt gypsum layer, the overpressure formed by hydrocarbon generation pressurization, the residual overpressure after Himalayan uplift and denudation, and the under-compaction overpressure.(4) Regional overpressure is an important guarantee for forming large gas fields, the sufficient gas source, large-scale reservoir and trap development in overpressure system are the basic conditions for forming large gas fields, and the overpressure system is conducive to forming deep to ultra-deep large gas fields.展开更多
Based on the contemporary strategy of Petro China and the“Super Basin Thinking”initiative,we analyze the petroleum system,the remaining oil and gas resource distribution,and the Super Basin development scheme in the...Based on the contemporary strategy of Petro China and the“Super Basin Thinking”initiative,we analyze the petroleum system,the remaining oil and gas resource distribution,and the Super Basin development scheme in the Sichuan Basin with the aim of unlocking its full resource potential.We conclude that,(1)The three-stage evolution of the Sichuan Basin has resulted in the stereoscopic distribution of hydrocarbon systems dominated by natural gas.The prospecting Nanhua-rift stage gas system is potentially to be found in the ultra-deep part of the basin.The marine-cratonic stage gas system is distributed in the Sinian to Mid-Triassic formations,mainly conventional gas and shale gas resources.The foreland-basin stage tight sand gas and shale oil resources are found in the Upper Triassic-Jurassic formations.Such resource base provides the foundation for the implementation of Super Basin paradigm in the Sichuan Basin.(2)To ensure larger scale hydrocarbon exploration and production,technologies regarding deep to ultra-deep carbonate reservoirs,tight-sand gas,and shale oil are necessarily to be advanced.(3)In order to achieve the full hydrocarbon potential of the Sichuan Basin,pertinent exploration strategies are expected to be proposed with regard to each hydrocarbon system respectively,government and policy supports ought to be strengthened,and new cooperative pattern should be established.Introducing the“Super Basin Thinking”provides references and guidelines for further deployment of hydrocarbon exploration and production in the Sichuan Basin and other developed basins.展开更多
The Lower Cambrian Longwangmiao dolomite gas reservoirs in the Sichuan Basin are characterized by well-developed natural micro-fractures and dissolved pores and cavities.Due to the strong heterogeneity of reservoirs a...The Lower Cambrian Longwangmiao dolomite gas reservoirs in the Sichuan Basin are characterized by well-developed natural micro-fractures and dissolved pores and cavities.Due to the strong heterogeneity of reservoirs and the serious damage of drilling and completion fluids,acid placement is difficult,and especially the acidizing stimulation of long-interval highly deviated wells or horizontal wells is more difficult.In this paper,the diverting mechanism and rheological behavior of viscoelastic surfactant(VES)based diverting acid was firstly investigated,and the diverting acid with good diversion performance and low secondary damage was selected as the main acid.Then,based on the experimental results of its rheological behaviors,an empirical model of effective viscosity was fitted and a two-scale wormhole propagation model was coupled.And accordingly,a mathematical model for the acidizing of self-diverting acid was established to simulate the pH value,Ca^(2+)concentration,effective viscosity and wormhole shape under the effect of diverting acid in long-interval highly deviated wells that are non-uniformly damaged.Finally,gelled acid and 5%VES diverting acid were compared in terms of their etched wormhole shapes,flow rate dis-tribution and acid imbibition profiles.It is shown that the diverting acid can obviously improve the acid imbibition profile of strong-heterogeneity reservoirs to intensify low-permeability reservoir stimulation.In view of the strong heterogeneity of Longwangmiao dolomite reservoirs and the complexities of drilling and completion fluid damage in the Sichuan Basin,a placement technology was developed for variable VES concentration diverting acid in horizontal wells and long-interval highly deviated wells completed with slotted liners.This acid placement technology has been practically applied in 8 wells and their cumulative gas production rate tested at the wellhead is 1233.46×10^(4)m^(3)/d.The average production stimulation ratio per well is up to 1.95.It provides a support for the efficient development of the Longwangmiao giant gas reservoir.展开更多
In recent years,much attention has been paid to the development environment,biogenetic compositions and hydrocarbon generation characteristics of ancient source rocks in the deep strata of the Sichuan Basin because oi...In recent years,much attention has been paid to the development environment,biogenetic compositions and hydrocarbon generation characteristics of ancient source rocks in the deep strata of the Sichuan Basin because oil and gas exploration extends continuously to the deep and ultra-deep strata and a giant gas field with the explored reserves of more than 1×10^(12)m^(3)was discovered in the Middle and Upper ProterozoiceLower Paleozoic strata in the stable inherited paleo-uplift of the central Sichuan Basin.Based on the previous geological research results,outcrop section of the Datangpo Fm,Nanhua System,at the southeastern margin of the Sichuan Basin was observed and the samples taken from the source rocks were tested and analyzed in terms of their organic geochemistry and organic petrology.It is shown that high-quality black shale source rocks of the Datangpo Fm are developed in the tensional background at the southeastern margin of the Sichuan Basin between two glacial ages,i.e.,Gucheng and Nantuo ages in the Nanhua Period.Their thickness is 16e180 m and mineral compositions are mainly clay minerals and clastic quartz.Besides,shale in the Datangpo Fm is of high-quality sapropel type source rock with high abundance at an overmature stage,and it is characterized by low pristane/phytane ratios(0.32-0.83),low gammacerane abundance,high-abundance tricyclic terpane and higher-content C_(27)and C_(29)gonane,indicating that biogenetic compositions are mainly algae and microbes in a strong reducing environment with low salinity.It is concluded that the Datangpo Fm source rocks may be developed in the rift of Nanhua System in central Sichuan Basin.Paleo-uplifts and paleo-slopes before the Caledonian are the favorable locations for the accumulation of dispersed liquid hydrocarbons and paleo-reservoirs derived from the Datangpo Fm source rocks.In addition,scale accumulation zones of dispersed organic matter cracking gas and paleo-reservoirs originated from the Datangpo Fm source rocks may be discovered in the stable area inside the Sichuan Basin.展开更多
The largest Precambrian gas field (Anyue gas field) in China has been discovered in the central Sichuan Basin. However, the deep ancient Ediacaran (Sinian) dolomite presents a substantial challenge due to their tightn...The largest Precambrian gas field (Anyue gas field) in China has been discovered in the central Sichuan Basin. However, the deep ancient Ediacaran (Sinian) dolomite presents a substantial challenge due to their tightness and heterogeneity, rather than assumed large-area stratified reservoirs controlled by mound-shoal microfacies. This complicates the characterization of “sweet spot” reservoirs crucial for efficient gas exploitation. By analyzing compiled geological, geophysical and production data, this study investigates the impact of strike-slip fault on the development and distribution of high-quality “sweet spot” (fractured-vuggy) reservoirs in the Ediacaran dolomite of the Anyue gas field. The dolomite matrix reservoir exhibits low porosity (less than 4%) and low permeability (less than 0.5×10^(-3) μm^(2)). Contrarily, fractures and their dissolution processes along strike-slip fault zone significantly enhance matrix permeability by more than one order of magnitude and matrix porosity by more than one time. Widespread “sweet spot” fracture-vuggy reservoirs are found along the strike-slip fault zone, formed at the end of the Ediacaran. These fractured reservoirs are controlled by the coupling mechanisms of sedimentary microfacies, fracturing and karstification. Karstification prevails at the platform margin, while both fracturing and karstification control high-quality reservoirs in the intraplatform, resulting in reservoir diversity in terms of scale, assemblage and type. The architecture of the strike-slip fault zone governed the differential distribution of fracture zones and the fault-controlled “sweet spot” reservoirs, leading to wide fractured-vuggy reservoirs across the strike-slip fault zone. In conclusion, the intracratonic weak strike-slip fault can play a crucial role in improving tight carbonate reservoir, and the strike-slip fault-related “sweet spot” reservoir emerges as a unique and promising target for the efficient development of deep hydrocarbon resources. Tailored development strategies need to be implemented for these reservoirs, considering the diverse and differential impacts exerted by strike-slip faults on the reservoirs.展开更多
The lithologic Longwangmiao Fm gas reservoirs are situated in the Moxi Block of the Anyue Gas Field,central Sichuan Basin.Due to their great heterogeneity affected by the differential roles of lithologic facies and ka...The lithologic Longwangmiao Fm gas reservoirs are situated in the Moxi Block of the Anyue Gas Field,central Sichuan Basin.Due to their great heterogeneity affected by the differential roles of lithologic facies and karstification,huge differences exist in the single-well gas yield tests.To improve the development efficiency of gas reservoirs and achieve the goal of“high yield but with few wells to be drilled”,it is especially important to establish a high-yield gas well mode by use of cores,logging,seismic data,etc.,and through analysis of reservoir properties,high-yield controlling factors,and seismic response features of quality reservoirs and so on.The followingfindings were achieved.(1)The positive relationship between yield and the thickness of dissolved vug reservoirs is obvious.(2)The dissolved vug reservoirs are reflected as the type of honeycomb dark patches from the image logging and the conventional logging is featured generally by“Three Lows and Two Highs(i.e.,low GR,low RT and low DEN but high AC and high CNL)”.(3)From the seismic profile,the highlighted spots(strong peaks)correspond to the bottom boundary of the Longwangmiao Fm reservoirs.The trough waves in larger amplitude represents that there are more well-developed karsts in the reservoirs.On this basis,high-quality 3D seismic data was used for tracking andfine interpretation of those highlighted spots and trough waves on the strong peaks to describe the plane distribution of high-yield dissolved vug reservoirs in this study area.This study is of great significance to the good planning of development wells and well trajectory planning and adjustment.As a result,high-thickness dissolved vug reservoirs have been targeted in this study area with the tested gas yield of 28 wells reaching up to 100104 m3/d among the completed and tested 30 wells in total.展开更多
After nearly 60 years of development,many old gasfields in the Sichuan Basin have come to middleelate development stages with low pressure and low yield,and some are even on the verge of abandonment,but there are plen...After nearly 60 years of development,many old gasfields in the Sichuan Basin have come to middleelate development stages with low pressure and low yield,and some are even on the verge of abandonment,but there are plenty remaining gas resources still undeveloped.Analysis shows that gasfields which have the conditions for the secondary development are faced with many difficulties.For example,it is difficult to produce low permeable reserves and to unset the hydraulic seal which is formed by active formation water.In this paper,therefore,the technical route and selection conditions of old gasfields for the secondary development were comprehensively elaborated with its definition as the beginning.Firstly,geological model forward modeling and production performance inversion characteristic curve diagnosis are performed by using the pressure normalization curve and the identification and quantitative description method for multiple sets of storageeseepage body of complex karst fractureecavity systems is put forward,after the multiple storageeseepage body mode of fractureecavity systems is established.Combined with the new occurrence mode of gas and water in U-shape pipes,a new calculation technology for natural gas reserves of multiple fractureecavity systems with strong water invasion is developed.Secondly,a numerical model of poreecavityefracture triple media is built,and simulation and result evaluation technology for the production pattern of“drainage by horizontal wells+gas production by vertical wells”in bottom-water fracture and cavity gas reservoirs with strong water invasion is developed.Thirdly,the geological model of gas reservoirs is reconstructed with the support of the integration technologies which are formed based onfine gas reservoir description.Low permeable reserves of gas reservoirs are evaluated based on each classification.The effective producing ratio is increased further by using the technologies of well pattern optimization,horizontal-well geosteering and staged acid fracturing.And fourthly,overall simulation,optimization and prediction technology for regional pipeline net-works is developed by building a multi-node multi-link gas transmission pipeline network model.Application shows that this technology plays an important role in productivity construction,recovery factor improvement,production decline delay and production stabilization of old gasfields.展开更多
Horizontal shale gas well fracturing is mostly carried out by pumping bridge plugs.In the case of casing deformation,the bridge plug can not be pumped down to the designated position,so the hole sections below the def...Horizontal shale gas well fracturing is mostly carried out by pumping bridge plugs.In the case of casing deformation,the bridge plug can not be pumped down to the designated position,so the hole sections below the deformation could not be stimulated according to the design program.About 30%of horizontal shale gas wells in the Changning and Weiyuan Blocks,Sichuan Basin,suffer various casing deformation after fracturing.Previously,the hole sections which could not be stimulated due to casing deformation were generally abandoned.As a result,the resources controlled by shale gas wells weren't exploited effectively and the fracturing effect was impacted greatly.There are a lot of difficulties in investigating casing deformation,such as complex mechanisms,various influencing factors and unpredictable deformation time.Therefore,it is especially important to seek a staged fracturing technology suitable for the casing deformation sections.In this paper,the staged fracturing technology with sand plugs inside fractures and the staged fracturing technology with temporary plugging balls were tested in casing deformation wells.The staged fracturing technology with sand plugs inside fractures was carried out in the mode of single-stage perforation and single-stage fracturing.The staged fracturing technology with temporary plugging balls was conducted in the mode of single perforation,continuous fracturing and staged ball dropping.Then,two kinds of technologies were compared in terms of their advantages and disadvantages.Finally,they were tested on site.According to the pressure response,the pressure monitoring of the adjacent wells and the microseismic monitoring in the process of actual fracturing,both technologies are effective in the stimulation of the casing deformation sections,realizing well control reserves efficiently and guaranteeing fracturing effects.展开更多
Since 2014,great gas discoveries have been achieved in the Upper Paleozoic Shuangyushi zone in the piedmont zone of the Longmenshan mountains,northwestern Sichuan Basin,where multiple gas wells with industrial flows h...Since 2014,great gas discoveries have been achieved in the Upper Paleozoic Shuangyushi zone in the piedmont zone of the Longmenshan mountains,northwestern Sichuan Basin,where multiple gas wells with industrial flows have been drilled and completed successively in the Middle Permian Qixia Fm and Middle Devonian Guanwushan Fm,etc.Along with the steady progress of exploration there,to make a further in-depth study on the characteristics of the frontal–piedmont zones in the Longmenshan thrust–nappe structures will be of great significance to both a better understanding of Upper Paleozoic gas reservoirs in this study area and the expansion of oil and gas exploration field.In view of this,based on the newly deployed 3D seismic surveys,gravity–magnetic–electronic data,and practical drilling information from exploration wells like Well ST 9,the characteristics of the frontal–piedmont zones in the Longmenshan thrust–nappe structures are analyzed as well as the features of the buried structures,gas reservoir forming conditions and exploration prospect there.The following findings were obtained:(1)A huge buried structure belt is developed underlying the Longmenshan front fault belt No.1(LSFFB 1)and marine strata are thus formed below the Lower Triassic Jialingjiang Fm due to the roles of compressive folding,extrusion and deformation;(2)The detachment horizons from LSFFB 1 go from shallower in the south to deeper in the north,turning from Cambrian slipping in the south to basement-involved in the north.The Paleozoic and its overlying strata were overall uplifted with a higher degree northward and so did the strata between the up-thrown and down-thrown sides of the faults with a greater displacement distance and higher folding degree,resulting in that the Paleozoic strata in the north are 1500 higher uplifted than those in the south;(3)In the western Jiange and Guangyuan areas,the eastern LSFFB 1 presents a tectonic pattern of“three steps”as a whole.In conclusion,there are good gas reservoir forming conditions in LSFFB 1,the down-thrown sides of which cover an area of 1800 km2,where the Guanwushan Fm and Qixia Fm provide good accumulation and preservation conditions for gas reservoirs,which will become favorable gas exploration targets in the deep marine strata in NW Sichuan Basin.展开更多
Gas field water is generally characterized by complex contaminant components and high salinity.Its proper treatment has always been the great concern in the field of environmental protection of oil&gas fields.In t...Gas field water is generally characterized by complex contaminant components and high salinity.Its proper treatment has always been the great concern in the field of environmental protection of oil&gas fields.In this paper,the wastewater from a gas field in the Sichuan Basin with high salinity and more contaminants(e.g.sulfides)was treated as a case study for the standard-reaching discharge.Lab experiments were carried out to analyze the adaptability and effectiveness of coagulation-desulfurization composite treatment technology,chemical oxidation based ammonia nitrogen removal technology and cryogenic multi-efficacy distillation technology in the treatment of wastewater in this field.The results show that the removal rate of sulfides and oils is over 90%if polymeric ferric sulfate(PFS)is taken as the coagulant combined with TS-1 desulfurization agent.Besides,the removal rate of ammonia nitrogen is over 96%if CA-1 is taken as the oxidant.Finally,after the gas field water is treated by means of cryogenic three-efficacy distillation technology,chloride concentration of distilled water is below 150 mg/L and COD_(cr)concentration is less than 60 mg/L.It is concluded that after the whole process treatment,the main contaminant indicators of wastewater in this case study can satisfy the grade one standard specified in the IntegratedWastewater Discharge Standard(GB 8978-1996)and the chloride concentration can meet the requirement of the Standards for Irrigation Water Quality(GB 5084-2005).To sum up,the above mentioned composite technologies are efficient to the wastewater treatment in sour gas fields.展开更多
The Ojarly gas field,the major supplier of the Project PhaseⅡof the Right Bank of the Amu Darya River,is just small but valuable like a golden bean,although it has good reservoir properties and a high gas production ...The Ojarly gas field,the major supplier of the Project PhaseⅡof the Right Bank of the Amu Darya River,is just small but valuable like a golden bean,although it has good reservoir properties and a high gas production capacity,the occurrence of continuous sharp decline of pressure in the well production shows a great difference from the previous well test program.In view of this,an integrated analysis method was established for the whole gas well production process to discover the three main reasons causing the abnormal well pressure.First,the formation energy and pressure dropped so fast that the wellhead pressure also fell over the period.Second,there was abnormal fluids pressure drop in the wellbore tube and throttling effect might occur in the production tube,so the pressure drop became abnormally increased.Third,due to the abnormally-increasing gas-yield pressure drop and unusually-decreasing gas productivity,the wellhead oil pressure dropped significantly.Also,through dynamic monitoring and in-depth analysis,it is also considered that due to the high density of drilling fluids and well-developed pores and caverns in the reservoirs,more and more barites separated from the fluids would be settled down covering the pay zones,so both the gas-generating capacity and production pressure significantly decreased.On this basis,some technical countermeasures were taken such as re-stimulation of reservoirs,removal of gas-producing channels,increase of seepage capacity,etc.In addition,by use of sand-flushing and acidizing,both the comprehensive skin factor and the production pressure drop were reduced to improve the well gas production capacity and maintain high productivity effectively.This study provides a technical support for long-term sustainable development and production of this gas field.展开更多
Based on the basic data of drilling,logging,testing and geological experiments,the geological characteristics of the Permian Dalong Formation marine shales in the northern Sichuan Basin and the factors controlling sha...Based on the basic data of drilling,logging,testing and geological experiments,the geological characteristics of the Permian Dalong Formation marine shales in the northern Sichuan Basin and the factors controlling shale gas enrichment and high yield are studied.The results are obtained in four aspects.First,the high-quality shale of the Dalong Formation was formed after the deposition of the Permian Wujiaping Formation,and it is developed in the Kaijiang-Liangping trough in the northern part of Sichuan Basin,where deep-water continental shelf facies and deep-water reduction environment with thriving siliceous organisms have formed the black siliceous shale rich in organic matter.Second,the Dalong Formation shale contains both organic and inorganic pores,with stratification of alternated brittle and plastic minerals.In addition to organic pores,a large number of inorganic pores are developed even in ultra-deep(deeper than 4500 m)layers,contributing a total porosity of more than 5%,which significantly expands the storage space for shale gas.Third,the limestone at the roof and floor of the Dalong Formation acted as seal rock in the early burial and hydrocarbon generation stage,providing favorable conditions for the continuous hydrocarbon generation and rich gas preservation in shale interval.In the later reservoir stimulation process,it was beneficial to the lateral extension of the fractures,so as to achieve the optimal stimulation performance and increase the well-controlled resources.Combining the geological,engineering and economic conditions,the favorable area with depth less than 5500 m is determined to be 1800 km2,with resources of 5400×10^(8) m^(3).Fourth,the shale reservoirs of the Dalong Formation are thin but rich in shale gas.The syncline zone far away from the main faults in the high and steep tectonic zone,eastern Sichuan Basin,with depth less than 5500 m,is the most favorable target for producing the Permian shale gas under the current engineering and technical conditions.It mainly includes the Nanya syncline,Tanmuchang syncline and Liangping syncline.展开更多
Previous studies on post-fracturing flowback fluids focus primarily on their cleaning and discharge,high salinity sources,and damage to gas reservoirs.An analysis of the geochemical characteristics of these fluids hel...Previous studies on post-fracturing flowback fluids focus primarily on their cleaning and discharge,high salinity sources,and damage to gas reservoirs.An analysis of the geochemical characteristics of these fluids helps develop an improved understanding of the preservation condition and fracturing performance of shale gas reservoirs.This study analyzed the ion,total dissolved solids(TDS)concentration,and stable isotope characteristics of post-fracturing flowback fluids from five horizontal shale gas wells in the Luzhou area.Among these wells,two were subjected to hydraulic fracturing using fresh water,and three using reused flowback fluids.The results indicate that with increasing flowback time,the post-fracturing flowback fluids from wells subjected to hydraulic fracturing using fresh water showed increased TDS concentration,heavier stable isotopes,and the presence of new ion components.These results indicate the mixing of a large volume of formation water into the fluids.In contrast,postfracturing flowback fluids from wells subjected to hydraulic fracturing using reused flowback fluids exhibited a slow increase in the TDS concentration and stable isotopes.As the flowback time increased,the trends in TDS concentration and stable isotope ratios of post-fracturing flowback fluids from shale gas wells subjected to fracturing using fresh water evolved toward those of post-fracturing flowback fluids from shale gas wells undergoing fracturing using reused flowback fluids.Measurements show that post-fracturing flowback fluids from both well types exhibited roughly the same properties after one year of shale gas production.This result suggests that post-fracturing flowback fluids from wells using reused flowback fluids progressively took on the formation water properties.In particular,postfracturing flowback fluids from well Lu 211—a well subjected to hydraulic fracturing using fresh water—showed a low sodium-chloride coefficient,a low coefficient of variation,high TDS concentration,heavy stable isotopes,and a high nitrate ion concentration.This indicates a formation water source of the fluids and the poor sealing of the formation water,which hinders shale gas enrichment.The quantification of the fracturing fluid and formation water contents in the post-fracturing flowback fluids reveals that higher TDS concentration and heavier stable isotopes in the fluids appear to correspond to higher formation water content and lower fracturing fluid content,as well as higher fracturing performance.A systematic analysis of the geochemical characteristics and flowback pattern of fracturing fluids indirectly provides insights into the flow path of formation water,water body mixing,rock-water interactions,and fluid sources.Besides,the analysis offers a new perspective for understanding the preservation conditions and fracturing performance of shale gas reservoirs.展开更多
This study takes shale samples from the Jiaoshiba block in the Fuling shale gas field of the Sichuan Basin,and uses the true triaxial testing system to conduct a series of mechanical experiments under deep shale reser...This study takes shale samples from the Jiaoshiba block in the Fuling shale gas field of the Sichuan Basin,and uses the true triaxial testing system to conduct a series of mechanical experiments under deep shale reservoir conditions after shale hydration.Stress-strain data and mechanical parameters of shale after hydration under high temperature and high pressure were obtained to investigate the effects of reservoir temperature,hydration time and horizontal stress difference on the mechanical strength of shale after hydration.By using nonlinear regression and interpolation methods,a prediction model for the mechanical strength of shale after hydration was constructed,and the mechanical strength chart of deep shale under high stress difference was plotted.First,higher hydration temperature,longer hydration reaction time,and greater horizontal stress difference cause shale to enter the yield stage earlier during the compression process after hydration and to exhibit more prominent plastic characteristics,lower peak strength,peak strain,residual strength and elastic modulus,and higher Poisson's ratio.Second,the longer the hydration time,the smaller the impact of hydration temperature on the mechanical strength of deep shale is.As the horizontal stress difference increases,the peak strength and residual strength weaken intensely,and the peak strain,elastic modulus and Poisson's ratio deteriorate slowly.Third,the mechanical strength of shale decreases significantly in the first 5 days of hydration,but gradually stabilizes as the hydration time increases.Fourth,the visual mechanical strength chart helps to understand the post-fracturing dynamics in deep shale gas reservoir fracturing site and adjust the drainage and production plan in time.展开更多
Taking the natural gas reservoirs of the Sinian Dengying Formation on the east and west sides(Gaoshiti-Moxi area and north slope of central Sichuan paleo-uplift on the east;Weiyuan and Well Datan-1 block on the west)o...Taking the natural gas reservoirs of the Sinian Dengying Formation on the east and west sides(Gaoshiti-Moxi area and north slope of central Sichuan paleo-uplift on the east;Weiyuan and Well Datan-1 block on the west)of the Deyang-Anyue rift trough in the Sichuan Basin,China,as the research object,the geochemical parameters(component,isotopic composition)of natural gas from the Dengying Formation in different areas are compared,and then the differences in geochemical characteristics of Dengying natural gas on the east and west sides of the Deyang-Anyue rift trough and their genesis are clarified.First,the Dengying gas reservoirs on both sides of the rift trough are predominantly composed of oil-cracking gas with high maturity,which is typical dry gas.Second,severely modified by thermochemical sulfate reduction(TSR)reaction,the Dengying gas reservoirs on the east side exhibit high H2S and CO_(2) contents,with an elevated δ^(13)C_(2) value(average value higher than-29‰).The Dengying gas reservoirs in the Weiyuan area are less affected by TSR modification,though the δ^(13)C_(1) values are slightly greater than that of the reservoirs on the east side with partial reversal of carbon isotope composition,likely due to the water-soluble gas precipitation and accumulation mechanism.The Dengying gas reservoir of Well Datan-1 shows no influence from TSR.Third,the Dengying gas reservoirs reflect high helium contents(significantly higher than that on the east side)in the Weiyuan and Datan-1 areas on the west side,which is supposed to attribute to the widespread granites in basement and efficient vertical transport along faults.Fourth,controlled by the paleo-salinity of water medium in the depositional period of the source rock,the δ^(2)HCH_(4) values of the Dengying gas reservoirs on the west side are slightly lighter than those on the east side.Fifth,the Dengying natural gas in the Datan-1 area is contributed by the source rocks of the Sinian Doushantuo Formation and the third member of the Dengying Formation,in addition to the Cambrian Qiongzhusi Formation.展开更多
Horizontal wells play a crucial role in enhancing shale gas reservoir production.This study employs transient multiphase simulation to investigate the impact of well trajectory on production optimization throughout a ...Horizontal wells play a crucial role in enhancing shale gas reservoir production.This study employs transient multiphase simulation to investigate the impact of well trajectory on production optimization throughout a well’s life cycle.The research uses OLGATM as a simulator to examine six well trajectories:toe-up,toe-down,smooth horizontal,undulated toe-up,undulated toe-down,and undulated horizontal.Initial findings indicate comparable production rates across different trajectories during the early production phase,with toe-up wells showing slightly better performances due to minimal slugging.However,as the reservoir pressure decreases,the well trajectory significantly influences production.Horizontal wells achieve the highest accumulated gas production rates due to minimal liquid holdup and back pressure.Toe-up wells experience early liquid accumulation and severe slugging,leading to increased back pressure and smaller production.The study highlights the positive effects of lateral undulations on toe-up and toe-down wells in terms of liquid unloading,however some emphasis is also put on their adverse influence on horizontal wells.展开更多
Helium is a valuable natural resource used widely in high-tech industries because of its unique physical and chemical properties.The study of helium in shale gas is still in its infancy,and the content,genesis,and enr...Helium is a valuable natural resource used widely in high-tech industries because of its unique physical and chemical properties.The study of helium in shale gas is still in its infancy,and the content,genesis,and enrichment patterns of helium in shale gas are not yet clear.In this paper,the concentrations and isotopic characteristics of helium were investigated in the Wufeng-Longmaxi shale gas in the Sichuan Basin and the periphery areas.The analytical results show that the concentrations of helium in the southern Sichuan shale gas fall in the range of 0.018-0.051 vol%with an average of 0.029 vol%.The helium abundance in Weiyuan shale gas are relatively low compared to those in conventional natural gas pools from the same area(generally greater than 0.20 vol%),reflecting the significance of long distance migration to the enrichment of helium in gas pools.The relatively low ratios of 3He and 4He in shale gas indicate that most of the helium are crustal derived helium.Further quantitative estimate based on helium,neon,and argon isotopic ratios suggest almost 100%crustal helium source.The helium residing in shale reservoirs can be deconvoluted into the indigenous helium generated in-situ by shale and exogenous helium generated from external helium source rocks and charged through faults and/or fractures networks.According to preliminary calculations,external helium source is required to meet the threshold of an economic helium-rich field of helium concentration of 0.1 vol%except for particular areas with extraordinarily high uranium and thorium concentration.Based on detailed study on typical helium-rich shale gas reservoirs,major advantageous features for helium's enrichment in shale gas include:(1)high-quality helium source rocks,(2)effective migration paths,and(3)diminished dilution effects of shale gas.Shale gas plays with underlying ancient cratonic basement,well developed source-connecting faults,and moderate pressure coefficient are potential targets for helium exploration.展开更多
Fracability evaluation is critical for efficiently extracting deep shale gas using hydraulic fracturing to avoid blind drilling and fracking.However,existing fracability indices often fail to systematically consider t...Fracability evaluation is critical for efficiently extracting deep shale gas using hydraulic fracturing to avoid blind drilling and fracking.However,existing fracability indices often fail to systematically consider the mechanical behavior of rocks at high temperatures and high pressures(HTHP),coupled with geostress distributions and heterogeneous reservoir characteristics.This critical omission limits their effectiveness in accurately identifying the optimal fracability sweet spots within deep reservoirs.In this work,a fracability evaluation model was proposed based on the combined weighting method,integrating the improved brittleness index,rock strength,geostresses and natural weakness characteristics.A fracability grading evaluation was carried out to determine the potential fracture characteristics corresponding to shales with different fracability levels.Additionally,the fracability index was used for field validation and applications.Results show that rock brittleness and fracability are not equivalent for deep reservoirs.The fracability index is closely related to the pay zones and actual gas production,with a correlation as high as 84%,implying that the proposed method has practical significance in both experimental and field applications.The above findings can provide theoretical guidance for the selection of fracturing candidates and the optimal design of fracturing in deep resource development.展开更多
Deep shale gas reservoirs in the southern Sichuan Basin are typically characterized by significant horizontal stress anisotropy(expressed as stress difference),variable brittleness-ductility in rock mechanics,and stro...Deep shale gas reservoirs in the southern Sichuan Basin are typically characterized by significant horizontal stress anisotropy(expressed as stress difference),variable brittleness-ductility in rock mechanics,and strong heterogeneity.These complex geomechanical conditions lead to pronounced differences in hydraulic fracturing outcomes among wells and sections.To investigate hydraulic fracture propagation and fracturing fluid injection behavior under varying geomechanical settings,true triaxial physical simulation tests were performed on 400×400×400 mm artificial rock samples.The samples were designed with different media properties based on similarity criteria.A sensitivity analysis was conducted to assess the effects of brittleness-ductility characteristics,natural fractures,and in-situ stress conditions.The results reveal that:(i)brittle samples with lower stress difference are favorable for forming complex,perforable fracture networks;(ii)brittle samples with higher stress difference tend to develop simple,planar hydraulic fractures,with natural fractures only slightly activated during very short injection periods;(iii)ductile behavior enhances the activation of natural fractures but reduces fracture complexity compared with brittle samples,even under lower stress difference;and(iv)for typical deep shale formations,larger fluid injection volumes combined with high-density,multi-cluster fracturing techniques are recommended.展开更多
The fluid evolution and reservoir formation model of the ultra-deep gas reservoirs in the Permian Qixia Formation of the northwestern Sichuan Basin are investigated by using thin section,cathodoluminescence,inclusion ...The fluid evolution and reservoir formation model of the ultra-deep gas reservoirs in the Permian Qixia Formation of the northwestern Sichuan Basin are investigated by using thin section,cathodoluminescence,inclusion temperature and U-Pb isotopic dating,combined with gas source identification plates and reservoir formation evolution profiles established based on burial history,thermal history,reservoir formation history and diagenetic evolution sequence.The fluid evolution of the marine ultra-deep gas reservoirs in the Qixia Formation has undergone two stages of dolomitization and one phase of hydrothermal action,two stages of oil and gas charging and two stages of associated burial dissolution.The diagenetic fluids include ancient seawater,atmospheric freshwater,deep hydrothermal fluid and hydrocarbon fluids.The two stages of hydrocarbon charging happened in the Late Triassic and Late Jurassic–Early Cretaceous respectively,and the Middle to Late Cretaceous is the period when the crude oil cracked massively into gas.The gas reservoirs in deep marine Permian strata of northwest Sichuan feature multiple source rocks,composite transportation,differential accumulation and late finalization.The natural gas in the Permian is mainly cracked gas from Permian marine mixed hydrocarbon source rocks,with cracked gas from crude oil in the deeper Sinian strata in local parts.The scale development of paleo-hydrocarbon reservoirs and the stable and good preservation conditions are the keys to the forming large-scale gas reservoirs.展开更多
基金Supported by the Petrochina Science and Technology Major Project(2016B-05)。
文摘Based on the data of measured formation pressure, drilling fluid density of key exploration wells and calculated pressure by well logging, combined with the analysis of natural gas geological conditions, the characteristics and formation mechanisms of formation fluid overpressure systems in different foreland basins and the relationship between overpressure systems and large-scale gas accumulation are discussed.(1) The formation mechanisms of formation overpressure in different foreland basins are different. The formation mechanism of overpressure in the Kuqa foreland basin is mainly the overpressure sealing of plastic salt gypsum layer and hydrocarbon generation pressurization in deep–ultra-deep layers, that in the southern Junggar foreland basin is mainly hydrocarbon generation pressurization and under-compaction sealing, and that in the western Sichuan foreland basin is mainly hydrocarbon generation pressurization and paleo-fluid overpressure residual.(2) There are three common characteristics in foreland basins, i.e. superimposed development of multi-type overpressure and multi-layer overpressure, strong–extremely strong overpressure developed in a closed foreland thrust belt, and strong–extremely strong overpressure developed in a deep foreland uplift area.(3) There are four regional overpressure sealing and storage mechanisms, which play an important role in controlling large gas fields, such as the overpressure of plastic salt gypsum layer, the overpressure formed by hydrocarbon generation pressurization, the residual overpressure after Himalayan uplift and denudation, and the under-compaction overpressure.(4) Regional overpressure is an important guarantee for forming large gas fields, the sufficient gas source, large-scale reservoir and trap development in overpressure system are the basic conditions for forming large gas fields, and the overpressure system is conducive to forming deep to ultra-deep large gas fields.
基金National Science and Technology Major Project(2016ZX05004-001)China National Petroleum Corporation Science and Technology Project(2021DJ02)。
文摘Based on the contemporary strategy of Petro China and the“Super Basin Thinking”initiative,we analyze the petroleum system,the remaining oil and gas resource distribution,and the Super Basin development scheme in the Sichuan Basin with the aim of unlocking its full resource potential.We conclude that,(1)The three-stage evolution of the Sichuan Basin has resulted in the stereoscopic distribution of hydrocarbon systems dominated by natural gas.The prospecting Nanhua-rift stage gas system is potentially to be found in the ultra-deep part of the basin.The marine-cratonic stage gas system is distributed in the Sinian to Mid-Triassic formations,mainly conventional gas and shale gas resources.The foreland-basin stage tight sand gas and shale oil resources are found in the Upper Triassic-Jurassic formations.Such resource base provides the foundation for the implementation of Super Basin paradigm in the Sichuan Basin.(2)To ensure larger scale hydrocarbon exploration and production,technologies regarding deep to ultra-deep carbonate reservoirs,tight-sand gas,and shale oil are necessarily to be advanced.(3)In order to achieve the full hydrocarbon potential of the Sichuan Basin,pertinent exploration strategies are expected to be proposed with regard to each hydrocarbon system respectively,government and policy supports ought to be strengthened,and new cooperative pattern should be established.Introducing the“Super Basin Thinking”provides references and guidelines for further deployment of hydrocarbon exploration and production in the Sichuan Basin and other developed basins.
基金Project supported by the National Science and Technology Major Project“Large-scale Oil and Gas Fields and CBM Development:Demonstration Project of Large-scale Carbonate Gas Fields in Sichuan Basin”(Code:2016ZX05052)CNPC Major Science and Technology Project“Research and Application of Deep-Temperature and High-Pressure Sulfur Gas Reservoir Reformation Technology in Sichuan Basin”(Code:2016E-0609).
文摘The Lower Cambrian Longwangmiao dolomite gas reservoirs in the Sichuan Basin are characterized by well-developed natural micro-fractures and dissolved pores and cavities.Due to the strong heterogeneity of reservoirs and the serious damage of drilling and completion fluids,acid placement is difficult,and especially the acidizing stimulation of long-interval highly deviated wells or horizontal wells is more difficult.In this paper,the diverting mechanism and rheological behavior of viscoelastic surfactant(VES)based diverting acid was firstly investigated,and the diverting acid with good diversion performance and low secondary damage was selected as the main acid.Then,based on the experimental results of its rheological behaviors,an empirical model of effective viscosity was fitted and a two-scale wormhole propagation model was coupled.And accordingly,a mathematical model for the acidizing of self-diverting acid was established to simulate the pH value,Ca^(2+)concentration,effective viscosity and wormhole shape under the effect of diverting acid in long-interval highly deviated wells that are non-uniformly damaged.Finally,gelled acid and 5%VES diverting acid were compared in terms of their etched wormhole shapes,flow rate dis-tribution and acid imbibition profiles.It is shown that the diverting acid can obviously improve the acid imbibition profile of strong-heterogeneity reservoirs to intensify low-permeability reservoir stimulation.In view of the strong heterogeneity of Longwangmiao dolomite reservoirs and the complexities of drilling and completion fluid damage in the Sichuan Basin,a placement technology was developed for variable VES concentration diverting acid in horizontal wells and long-interval highly deviated wells completed with slotted liners.This acid placement technology has been practically applied in 8 wells and their cumulative gas production rate tested at the wellhead is 1233.46×10^(4)m^(3)/d.The average production stimulation ratio per well is up to 1.95.It provides a support for the efficient development of the Longwangmiao giant gas reservoir.
文摘In recent years,much attention has been paid to the development environment,biogenetic compositions and hydrocarbon generation characteristics of ancient source rocks in the deep strata of the Sichuan Basin because oil and gas exploration extends continuously to the deep and ultra-deep strata and a giant gas field with the explored reserves of more than 1×10^(12)m^(3)was discovered in the Middle and Upper ProterozoiceLower Paleozoic strata in the stable inherited paleo-uplift of the central Sichuan Basin.Based on the previous geological research results,outcrop section of the Datangpo Fm,Nanhua System,at the southeastern margin of the Sichuan Basin was observed and the samples taken from the source rocks were tested and analyzed in terms of their organic geochemistry and organic petrology.It is shown that high-quality black shale source rocks of the Datangpo Fm are developed in the tensional background at the southeastern margin of the Sichuan Basin between two glacial ages,i.e.,Gucheng and Nantuo ages in the Nanhua Period.Their thickness is 16e180 m and mineral compositions are mainly clay minerals and clastic quartz.Besides,shale in the Datangpo Fm is of high-quality sapropel type source rock with high abundance at an overmature stage,and it is characterized by low pristane/phytane ratios(0.32-0.83),low gammacerane abundance,high-abundance tricyclic terpane and higher-content C_(27)and C_(29)gonane,indicating that biogenetic compositions are mainly algae and microbes in a strong reducing environment with low salinity.It is concluded that the Datangpo Fm source rocks may be developed in the rift of Nanhua System in central Sichuan Basin.Paleo-uplifts and paleo-slopes before the Caledonian are the favorable locations for the accumulation of dispersed liquid hydrocarbons and paleo-reservoirs derived from the Datangpo Fm source rocks.In addition,scale accumulation zones of dispersed organic matter cracking gas and paleo-reservoirs originated from the Datangpo Fm source rocks may be discovered in the stable area inside the Sichuan Basin.
基金Supported by the PetroChina and Southwest Petroleum University Cooperation Project(2020CX010101)the National Natural ScienceFoundation of China(91955204).
文摘The largest Precambrian gas field (Anyue gas field) in China has been discovered in the central Sichuan Basin. However, the deep ancient Ediacaran (Sinian) dolomite presents a substantial challenge due to their tightness and heterogeneity, rather than assumed large-area stratified reservoirs controlled by mound-shoal microfacies. This complicates the characterization of “sweet spot” reservoirs crucial for efficient gas exploitation. By analyzing compiled geological, geophysical and production data, this study investigates the impact of strike-slip fault on the development and distribution of high-quality “sweet spot” (fractured-vuggy) reservoirs in the Ediacaran dolomite of the Anyue gas field. The dolomite matrix reservoir exhibits low porosity (less than 4%) and low permeability (less than 0.5×10^(-3) μm^(2)). Contrarily, fractures and their dissolution processes along strike-slip fault zone significantly enhance matrix permeability by more than one order of magnitude and matrix porosity by more than one time. Widespread “sweet spot” fracture-vuggy reservoirs are found along the strike-slip fault zone, formed at the end of the Ediacaran. These fractured reservoirs are controlled by the coupling mechanisms of sedimentary microfacies, fracturing and karstification. Karstification prevails at the platform margin, while both fracturing and karstification control high-quality reservoirs in the intraplatform, resulting in reservoir diversity in terms of scale, assemblage and type. The architecture of the strike-slip fault zone governed the differential distribution of fracture zones and the fault-controlled “sweet spot” reservoirs, leading to wide fractured-vuggy reservoirs across the strike-slip fault zone. In conclusion, the intracratonic weak strike-slip fault can play a crucial role in improving tight carbonate reservoir, and the strike-slip fault-related “sweet spot” reservoir emerges as a unique and promising target for the efficient development of deep hydrocarbon resources. Tailored development strategies need to be implemented for these reservoirs, considering the diverse and differential impacts exerted by strike-slip faults on the reservoirs.
基金supported by PetroChina Major Science and Technology Project"Key Technologies for Deep Oil and Gas Exploration and Development"(No.2014E-3208(GF)).
文摘The lithologic Longwangmiao Fm gas reservoirs are situated in the Moxi Block of the Anyue Gas Field,central Sichuan Basin.Due to their great heterogeneity affected by the differential roles of lithologic facies and karstification,huge differences exist in the single-well gas yield tests.To improve the development efficiency of gas reservoirs and achieve the goal of“high yield but with few wells to be drilled”,it is especially important to establish a high-yield gas well mode by use of cores,logging,seismic data,etc.,and through analysis of reservoir properties,high-yield controlling factors,and seismic response features of quality reservoirs and so on.The followingfindings were achieved.(1)The positive relationship between yield and the thickness of dissolved vug reservoirs is obvious.(2)The dissolved vug reservoirs are reflected as the type of honeycomb dark patches from the image logging and the conventional logging is featured generally by“Three Lows and Two Highs(i.e.,low GR,low RT and low DEN but high AC and high CNL)”.(3)From the seismic profile,the highlighted spots(strong peaks)correspond to the bottom boundary of the Longwangmiao Fm reservoirs.The trough waves in larger amplitude represents that there are more well-developed karsts in the reservoirs.On this basis,high-quality 3D seismic data was used for tracking andfine interpretation of those highlighted spots and trough waves on the strong peaks to describe the plane distribution of high-yield dissolved vug reservoirs in this study area.This study is of great significance to the good planning of development wells and well trajectory planning and adjustment.As a result,high-thickness dissolved vug reservoirs have been targeted in this study area with the tested gas yield of 28 wells reaching up to 100104 m3/d among the completed and tested 30 wells in total.
基金supported by the Scientific Rescarch Project of PetroChina Explonation&Production Company“Overall Plan of PetroChina Southwest Oil&Gas Field Company for Secondary Development of Gas Fields”(No.20100305-04).
文摘After nearly 60 years of development,many old gasfields in the Sichuan Basin have come to middleelate development stages with low pressure and low yield,and some are even on the verge of abandonment,but there are plenty remaining gas resources still undeveloped.Analysis shows that gasfields which have the conditions for the secondary development are faced with many difficulties.For example,it is difficult to produce low permeable reserves and to unset the hydraulic seal which is formed by active formation water.In this paper,therefore,the technical route and selection conditions of old gasfields for the secondary development were comprehensively elaborated with its definition as the beginning.Firstly,geological model forward modeling and production performance inversion characteristic curve diagnosis are performed by using the pressure normalization curve and the identification and quantitative description method for multiple sets of storageeseepage body of complex karst fractureecavity systems is put forward,after the multiple storageeseepage body mode of fractureecavity systems is established.Combined with the new occurrence mode of gas and water in U-shape pipes,a new calculation technology for natural gas reserves of multiple fractureecavity systems with strong water invasion is developed.Secondly,a numerical model of poreecavityefracture triple media is built,and simulation and result evaluation technology for the production pattern of“drainage by horizontal wells+gas production by vertical wells”in bottom-water fracture and cavity gas reservoirs with strong water invasion is developed.Thirdly,the geological model of gas reservoirs is reconstructed with the support of the integration technologies which are formed based onfine gas reservoir description.Low permeable reserves of gas reservoirs are evaluated based on each classification.The effective producing ratio is increased further by using the technologies of well pattern optimization,horizontal-well geosteering and staged acid fracturing.And fourthly,overall simulation,optimization and prediction technology for regional pipeline net-works is developed by building a multi-node multi-link gas transmission pipeline network model.Application shows that this technology plays an important role in productivity construction,recovery factor improvement,production decline delay and production stabilization of old gasfields.
基金Project supported by the National Key Basic Research and Development Program(973 Program)“Theory and Technology Adaptability of Shale Gas Development in Typical Marine Blocks in South China”(No.2013CB228006).
文摘Horizontal shale gas well fracturing is mostly carried out by pumping bridge plugs.In the case of casing deformation,the bridge plug can not be pumped down to the designated position,so the hole sections below the deformation could not be stimulated according to the design program.About 30%of horizontal shale gas wells in the Changning and Weiyuan Blocks,Sichuan Basin,suffer various casing deformation after fracturing.Previously,the hole sections which could not be stimulated due to casing deformation were generally abandoned.As a result,the resources controlled by shale gas wells weren't exploited effectively and the fracturing effect was impacted greatly.There are a lot of difficulties in investigating casing deformation,such as complex mechanisms,various influencing factors and unpredictable deformation time.Therefore,it is especially important to seek a staged fracturing technology suitable for the casing deformation sections.In this paper,the staged fracturing technology with sand plugs inside fractures and the staged fracturing technology with temporary plugging balls were tested in casing deformation wells.The staged fracturing technology with sand plugs inside fractures was carried out in the mode of single-stage perforation and single-stage fracturing.The staged fracturing technology with temporary plugging balls was conducted in the mode of single perforation,continuous fracturing and staged ball dropping.Then,two kinds of technologies were compared in terms of their advantages and disadvantages.Finally,they were tested on site.According to the pressure response,the pressure monitoring of the adjacent wells and the microseismic monitoring in the process of actual fracturing,both technologies are effective in the stimulation of the casing deformation sections,realizing well control reserves efficiently and guaranteeing fracturing effects.
基金supported by the National Major Science and Technology Project“Enrichment law and target evaluation of large gas fields in Permian-Middle Triassic in Sichuan Basin”(No.:2016ZX05007004)the CNPC Major Science and Technology Project“Study and application of key techniques for 30 billion m^(3)gas production in PetroChina Southwest Oil&Gas Field Company”(No.:2016E-06).
文摘Since 2014,great gas discoveries have been achieved in the Upper Paleozoic Shuangyushi zone in the piedmont zone of the Longmenshan mountains,northwestern Sichuan Basin,where multiple gas wells with industrial flows have been drilled and completed successively in the Middle Permian Qixia Fm and Middle Devonian Guanwushan Fm,etc.Along with the steady progress of exploration there,to make a further in-depth study on the characteristics of the frontal–piedmont zones in the Longmenshan thrust–nappe structures will be of great significance to both a better understanding of Upper Paleozoic gas reservoirs in this study area and the expansion of oil and gas exploration field.In view of this,based on the newly deployed 3D seismic surveys,gravity–magnetic–electronic data,and practical drilling information from exploration wells like Well ST 9,the characteristics of the frontal–piedmont zones in the Longmenshan thrust–nappe structures are analyzed as well as the features of the buried structures,gas reservoir forming conditions and exploration prospect there.The following findings were obtained:(1)A huge buried structure belt is developed underlying the Longmenshan front fault belt No.1(LSFFB 1)and marine strata are thus formed below the Lower Triassic Jialingjiang Fm due to the roles of compressive folding,extrusion and deformation;(2)The detachment horizons from LSFFB 1 go from shallower in the south to deeper in the north,turning from Cambrian slipping in the south to basement-involved in the north.The Paleozoic and its overlying strata were overall uplifted with a higher degree northward and so did the strata between the up-thrown and down-thrown sides of the faults with a greater displacement distance and higher folding degree,resulting in that the Paleozoic strata in the north are 1500 higher uplifted than those in the south;(3)In the western Jiange and Guangyuan areas,the eastern LSFFB 1 presents a tectonic pattern of“three steps”as a whole.In conclusion,there are good gas reservoir forming conditions in LSFFB 1,the down-thrown sides of which cover an area of 1800 km2,where the Guanwushan Fm and Qixia Fm provide good accumulation and preservation conditions for gas reservoirs,which will become favorable gas exploration targets in the deep marine strata in NW Sichuan Basin.
基金Project supported by National Demonstration Project“large-scale carbonate gas field development in the Sichuan Basin”(No.:2016ZX05052).
文摘Gas field water is generally characterized by complex contaminant components and high salinity.Its proper treatment has always been the great concern in the field of environmental protection of oil&gas fields.In this paper,the wastewater from a gas field in the Sichuan Basin with high salinity and more contaminants(e.g.sulfides)was treated as a case study for the standard-reaching discharge.Lab experiments were carried out to analyze the adaptability and effectiveness of coagulation-desulfurization composite treatment technology,chemical oxidation based ammonia nitrogen removal technology and cryogenic multi-efficacy distillation technology in the treatment of wastewater in this field.The results show that the removal rate of sulfides and oils is over 90%if polymeric ferric sulfate(PFS)is taken as the coagulant combined with TS-1 desulfurization agent.Besides,the removal rate of ammonia nitrogen is over 96%if CA-1 is taken as the oxidant.Finally,after the gas field water is treated by means of cryogenic three-efficacy distillation technology,chloride concentration of distilled water is below 150 mg/L and COD_(cr)concentration is less than 60 mg/L.It is concluded that after the whole process treatment,the main contaminant indicators of wastewater in this case study can satisfy the grade one standard specified in the IntegratedWastewater Discharge Standard(GB 8978-1996)and the chloride concentration can meet the requirement of the Standards for Irrigation Water Quality(GB 5084-2005).To sum up,the above mentioned composite technologies are efficient to the wastewater treatment in sour gas fields.
基金CNPC Scientific Research and Technology DevelopmentProject “Key technology research and application for natural gas developmentof 16.5 m^(3) in the Right Bank of the Amu-Darya River, Turkmenistan” (No.:2011E-2505)National Science and Technology Major Project “Demonstra-tion Project of Natural Gas Development in Middle Zone of the Right Bank ofthe Amu-Darya River” (No.: 2011ZX05059).
文摘The Ojarly gas field,the major supplier of the Project PhaseⅡof the Right Bank of the Amu Darya River,is just small but valuable like a golden bean,although it has good reservoir properties and a high gas production capacity,the occurrence of continuous sharp decline of pressure in the well production shows a great difference from the previous well test program.In view of this,an integrated analysis method was established for the whole gas well production process to discover the three main reasons causing the abnormal well pressure.First,the formation energy and pressure dropped so fast that the wellhead pressure also fell over the period.Second,there was abnormal fluids pressure drop in the wellbore tube and throttling effect might occur in the production tube,so the pressure drop became abnormally increased.Third,due to the abnormally-increasing gas-yield pressure drop and unusually-decreasing gas productivity,the wellhead oil pressure dropped significantly.Also,through dynamic monitoring and in-depth analysis,it is also considered that due to the high density of drilling fluids and well-developed pores and caverns in the reservoirs,more and more barites separated from the fluids would be settled down covering the pay zones,so both the gas-generating capacity and production pressure significantly decreased.On this basis,some technical countermeasures were taken such as re-stimulation of reservoirs,removal of gas-producing channels,increase of seepage capacity,etc.In addition,by use of sand-flushing and acidizing,both the comprehensive skin factor and the production pressure drop were reduced to improve the well gas production capacity and maintain high productivity effectively.This study provides a technical support for long-term sustainable development and production of this gas field.
基金Supported by the PetroChina Science&Technology Special Project(2023ZZ21YJ04)PetroChina Gas Reservoir Evaluation Project(20230304-08)。
文摘Based on the basic data of drilling,logging,testing and geological experiments,the geological characteristics of the Permian Dalong Formation marine shales in the northern Sichuan Basin and the factors controlling shale gas enrichment and high yield are studied.The results are obtained in four aspects.First,the high-quality shale of the Dalong Formation was formed after the deposition of the Permian Wujiaping Formation,and it is developed in the Kaijiang-Liangping trough in the northern part of Sichuan Basin,where deep-water continental shelf facies and deep-water reduction environment with thriving siliceous organisms have formed the black siliceous shale rich in organic matter.Second,the Dalong Formation shale contains both organic and inorganic pores,with stratification of alternated brittle and plastic minerals.In addition to organic pores,a large number of inorganic pores are developed even in ultra-deep(deeper than 4500 m)layers,contributing a total porosity of more than 5%,which significantly expands the storage space for shale gas.Third,the limestone at the roof and floor of the Dalong Formation acted as seal rock in the early burial and hydrocarbon generation stage,providing favorable conditions for the continuous hydrocarbon generation and rich gas preservation in shale interval.In the later reservoir stimulation process,it was beneficial to the lateral extension of the fractures,so as to achieve the optimal stimulation performance and increase the well-controlled resources.Combining the geological,engineering and economic conditions,the favorable area with depth less than 5500 m is determined to be 1800 km2,with resources of 5400×10^(8) m^(3).Fourth,the shale reservoirs of the Dalong Formation are thin but rich in shale gas.The syncline zone far away from the main faults in the high and steep tectonic zone,eastern Sichuan Basin,with depth less than 5500 m,is the most favorable target for producing the Permian shale gas under the current engineering and technical conditions.It mainly includes the Nanya syncline,Tanmuchang syncline and Liangping syncline.
基金supported by China National Petroleum Corporation(NO:2023ZZ21)。
文摘Previous studies on post-fracturing flowback fluids focus primarily on their cleaning and discharge,high salinity sources,and damage to gas reservoirs.An analysis of the geochemical characteristics of these fluids helps develop an improved understanding of the preservation condition and fracturing performance of shale gas reservoirs.This study analyzed the ion,total dissolved solids(TDS)concentration,and stable isotope characteristics of post-fracturing flowback fluids from five horizontal shale gas wells in the Luzhou area.Among these wells,two were subjected to hydraulic fracturing using fresh water,and three using reused flowback fluids.The results indicate that with increasing flowback time,the post-fracturing flowback fluids from wells subjected to hydraulic fracturing using fresh water showed increased TDS concentration,heavier stable isotopes,and the presence of new ion components.These results indicate the mixing of a large volume of formation water into the fluids.In contrast,postfracturing flowback fluids from wells subjected to hydraulic fracturing using reused flowback fluids exhibited a slow increase in the TDS concentration and stable isotopes.As the flowback time increased,the trends in TDS concentration and stable isotope ratios of post-fracturing flowback fluids from shale gas wells subjected to fracturing using fresh water evolved toward those of post-fracturing flowback fluids from shale gas wells undergoing fracturing using reused flowback fluids.Measurements show that post-fracturing flowback fluids from both well types exhibited roughly the same properties after one year of shale gas production.This result suggests that post-fracturing flowback fluids from wells using reused flowback fluids progressively took on the formation water properties.In particular,postfracturing flowback fluids from well Lu 211—a well subjected to hydraulic fracturing using fresh water—showed a low sodium-chloride coefficient,a low coefficient of variation,high TDS concentration,heavy stable isotopes,and a high nitrate ion concentration.This indicates a formation water source of the fluids and the poor sealing of the formation water,which hinders shale gas enrichment.The quantification of the fracturing fluid and formation water contents in the post-fracturing flowback fluids reveals that higher TDS concentration and heavier stable isotopes in the fluids appear to correspond to higher formation water content and lower fracturing fluid content,as well as higher fracturing performance.A systematic analysis of the geochemical characteristics and flowback pattern of fracturing fluids indirectly provides insights into the flow path of formation water,water body mixing,rock-water interactions,and fluid sources.Besides,the analysis offers a new perspective for understanding the preservation conditions and fracturing performance of shale gas reservoirs.
基金Supported by the National Natural Science Foundation of China(U24A2084,U21B2071)Science and Technology Cooperation Project of CNPC-Southwest Petroleum University Innovation Consortium(2020CX030201)。
文摘This study takes shale samples from the Jiaoshiba block in the Fuling shale gas field of the Sichuan Basin,and uses the true triaxial testing system to conduct a series of mechanical experiments under deep shale reservoir conditions after shale hydration.Stress-strain data and mechanical parameters of shale after hydration under high temperature and high pressure were obtained to investigate the effects of reservoir temperature,hydration time and horizontal stress difference on the mechanical strength of shale after hydration.By using nonlinear regression and interpolation methods,a prediction model for the mechanical strength of shale after hydration was constructed,and the mechanical strength chart of deep shale under high stress difference was plotted.First,higher hydration temperature,longer hydration reaction time,and greater horizontal stress difference cause shale to enter the yield stage earlier during the compression process after hydration and to exhibit more prominent plastic characteristics,lower peak strength,peak strain,residual strength and elastic modulus,and higher Poisson's ratio.Second,the longer the hydration time,the smaller the impact of hydration temperature on the mechanical strength of deep shale is.As the horizontal stress difference increases,the peak strength and residual strength weaken intensely,and the peak strain,elastic modulus and Poisson's ratio deteriorate slowly.Third,the mechanical strength of shale decreases significantly in the first 5 days of hydration,but gradually stabilizes as the hydration time increases.Fourth,the visual mechanical strength chart helps to understand the post-fracturing dynamics in deep shale gas reservoir fracturing site and adjust the drainage and production plan in time.
基金Supported by the National Natural Science Foundation of China(42272161)PetroChina Science and Technology Major Project(2023ZZ16)Research Institute of Exploration and Development,PetroChina Southwest Oil&Gasfield Company(2024D101-01-06)。
文摘Taking the natural gas reservoirs of the Sinian Dengying Formation on the east and west sides(Gaoshiti-Moxi area and north slope of central Sichuan paleo-uplift on the east;Weiyuan and Well Datan-1 block on the west)of the Deyang-Anyue rift trough in the Sichuan Basin,China,as the research object,the geochemical parameters(component,isotopic composition)of natural gas from the Dengying Formation in different areas are compared,and then the differences in geochemical characteristics of Dengying natural gas on the east and west sides of the Deyang-Anyue rift trough and their genesis are clarified.First,the Dengying gas reservoirs on both sides of the rift trough are predominantly composed of oil-cracking gas with high maturity,which is typical dry gas.Second,severely modified by thermochemical sulfate reduction(TSR)reaction,the Dengying gas reservoirs on the east side exhibit high H2S and CO_(2) contents,with an elevated δ^(13)C_(2) value(average value higher than-29‰).The Dengying gas reservoirs in the Weiyuan area are less affected by TSR modification,though the δ^(13)C_(1) values are slightly greater than that of the reservoirs on the east side with partial reversal of carbon isotope composition,likely due to the water-soluble gas precipitation and accumulation mechanism.The Dengying gas reservoir of Well Datan-1 shows no influence from TSR.Third,the Dengying gas reservoirs reflect high helium contents(significantly higher than that on the east side)in the Weiyuan and Datan-1 areas on the west side,which is supposed to attribute to the widespread granites in basement and efficient vertical transport along faults.Fourth,controlled by the paleo-salinity of water medium in the depositional period of the source rock,the δ^(2)HCH_(4) values of the Dengying gas reservoirs on the west side are slightly lighter than those on the east side.Fifth,the Dengying natural gas in the Datan-1 area is contributed by the source rocks of the Sinian Doushantuo Formation and the third member of the Dengying Formation,in addition to the Cambrian Qiongzhusi Formation.
基金supported by a postdoctoral project from PetroChina Southwest Oil and Gas Field Company,titled“Research on Flow Behavior of Horizontal Shale Gas Wellbore Based on Reservoir-Wellbore Coupling”(Project Number:2024D103-02-08).
文摘Horizontal wells play a crucial role in enhancing shale gas reservoir production.This study employs transient multiphase simulation to investigate the impact of well trajectory on production optimization throughout a well’s life cycle.The research uses OLGATM as a simulator to examine six well trajectories:toe-up,toe-down,smooth horizontal,undulated toe-up,undulated toe-down,and undulated horizontal.Initial findings indicate comparable production rates across different trajectories during the early production phase,with toe-up wells showing slightly better performances due to minimal slugging.However,as the reservoir pressure decreases,the well trajectory significantly influences production.Horizontal wells achieve the highest accumulated gas production rates due to minimal liquid holdup and back pressure.Toe-up wells experience early liquid accumulation and severe slugging,leading to increased back pressure and smaller production.The study highlights the positive effects of lateral undulations on toe-up and toe-down wells in terms of liquid unloading,however some emphasis is also put on their adverse influence on horizontal wells.
基金support from CNPC Key and Core Technology Research Project(Grant No.2021ZG13).
文摘Helium is a valuable natural resource used widely in high-tech industries because of its unique physical and chemical properties.The study of helium in shale gas is still in its infancy,and the content,genesis,and enrichment patterns of helium in shale gas are not yet clear.In this paper,the concentrations and isotopic characteristics of helium were investigated in the Wufeng-Longmaxi shale gas in the Sichuan Basin and the periphery areas.The analytical results show that the concentrations of helium in the southern Sichuan shale gas fall in the range of 0.018-0.051 vol%with an average of 0.029 vol%.The helium abundance in Weiyuan shale gas are relatively low compared to those in conventional natural gas pools from the same area(generally greater than 0.20 vol%),reflecting the significance of long distance migration to the enrichment of helium in gas pools.The relatively low ratios of 3He and 4He in shale gas indicate that most of the helium are crustal derived helium.Further quantitative estimate based on helium,neon,and argon isotopic ratios suggest almost 100%crustal helium source.The helium residing in shale reservoirs can be deconvoluted into the indigenous helium generated in-situ by shale and exogenous helium generated from external helium source rocks and charged through faults and/or fractures networks.According to preliminary calculations,external helium source is required to meet the threshold of an economic helium-rich field of helium concentration of 0.1 vol%except for particular areas with extraordinarily high uranium and thorium concentration.Based on detailed study on typical helium-rich shale gas reservoirs,major advantageous features for helium's enrichment in shale gas include:(1)high-quality helium source rocks,(2)effective migration paths,and(3)diminished dilution effects of shale gas.Shale gas plays with underlying ancient cratonic basement,well developed source-connecting faults,and moderate pressure coefficient are potential targets for helium exploration.
基金supported by the National Natural Science Foun-dation of China(Nos.U24B2035 and U22A20166)the Postdoctoral Fellowship Program and China Postdoctoral Science Foundation(Nos.BX20250034 and 2024M763503)the Natural Science Foundation of Hubei Province of China(No.2024AFD374).
文摘Fracability evaluation is critical for efficiently extracting deep shale gas using hydraulic fracturing to avoid blind drilling and fracking.However,existing fracability indices often fail to systematically consider the mechanical behavior of rocks at high temperatures and high pressures(HTHP),coupled with geostress distributions and heterogeneous reservoir characteristics.This critical omission limits their effectiveness in accurately identifying the optimal fracability sweet spots within deep reservoirs.In this work,a fracability evaluation model was proposed based on the combined weighting method,integrating the improved brittleness index,rock strength,geostresses and natural weakness characteristics.A fracability grading evaluation was carried out to determine the potential fracture characteristics corresponding to shales with different fracability levels.Additionally,the fracability index was used for field validation and applications.Results show that rock brittleness and fracability are not equivalent for deep reservoirs.The fracability index is closely related to the pay zones and actual gas production,with a correlation as high as 84%,implying that the proposed method has practical significance in both experimental and field applications.The above findings can provide theoretical guidance for the selection of fracturing candidates and the optimal design of fracturing in deep resource development.
基金the National Natural Science Foundation of China(Nos.52204005,52192622,U20A20265)the Sichuan Science Fund for Young Scholars(23NSFSC4652).
文摘Deep shale gas reservoirs in the southern Sichuan Basin are typically characterized by significant horizontal stress anisotropy(expressed as stress difference),variable brittleness-ductility in rock mechanics,and strong heterogeneity.These complex geomechanical conditions lead to pronounced differences in hydraulic fracturing outcomes among wells and sections.To investigate hydraulic fracture propagation and fracturing fluid injection behavior under varying geomechanical settings,true triaxial physical simulation tests were performed on 400×400×400 mm artificial rock samples.The samples were designed with different media properties based on similarity criteria.A sensitivity analysis was conducted to assess the effects of brittleness-ductility characteristics,natural fractures,and in-situ stress conditions.The results reveal that:(i)brittle samples with lower stress difference are favorable for forming complex,perforable fracture networks;(ii)brittle samples with higher stress difference tend to develop simple,planar hydraulic fractures,with natural fractures only slightly activated during very short injection periods;(iii)ductile behavior enhances the activation of natural fractures but reduces fracture complexity compared with brittle samples,even under lower stress difference;and(iv)for typical deep shale formations,larger fluid injection volumes combined with high-density,multi-cluster fracturing techniques are recommended.
基金Supported by the Special Project of National Key R&D Plan(2017YFC0603106).
文摘The fluid evolution and reservoir formation model of the ultra-deep gas reservoirs in the Permian Qixia Formation of the northwestern Sichuan Basin are investigated by using thin section,cathodoluminescence,inclusion temperature and U-Pb isotopic dating,combined with gas source identification plates and reservoir formation evolution profiles established based on burial history,thermal history,reservoir formation history and diagenetic evolution sequence.The fluid evolution of the marine ultra-deep gas reservoirs in the Qixia Formation has undergone two stages of dolomitization and one phase of hydrothermal action,two stages of oil and gas charging and two stages of associated burial dissolution.The diagenetic fluids include ancient seawater,atmospheric freshwater,deep hydrothermal fluid and hydrocarbon fluids.The two stages of hydrocarbon charging happened in the Late Triassic and Late Jurassic–Early Cretaceous respectively,and the Middle to Late Cretaceous is the period when the crude oil cracked massively into gas.The gas reservoirs in deep marine Permian strata of northwest Sichuan feature multiple source rocks,composite transportation,differential accumulation and late finalization.The natural gas in the Permian is mainly cracked gas from Permian marine mixed hydrocarbon source rocks,with cracked gas from crude oil in the deeper Sinian strata in local parts.The scale development of paleo-hydrocarbon reservoirs and the stable and good preservation conditions are the keys to the forming large-scale gas reservoirs.
