Pore structure characteristics,gas content,and micro-scale gas occurrence mechanisms were investigated in the Shan_(2)^(3)sub-member marine-continental transitional shale of the southeastern margin of the Ordos Basin ...Pore structure characteristics,gas content,and micro-scale gas occurrence mechanisms were investigated in the Shan_(2)^(3)sub-member marine-continental transitional shale of the southeastern margin of the Ordos Basin using scanning electron microscope images,lowtemperature N_(2)/CO_(2)adsorption and high-pressure mercury intrusion,methane isothermal adsorption experiments,and CH4-saturated nuclear magnetic resonance(NMR).Two distinct shale types were identified:organic pore-rich shale(Type OP)and microfracture-rich shale(Type M).The Type OP shale exhibited relatively well-developed organic matter pores,while the Type M shale was primarily characterized by a high degree of microfracture development.An experimental method combining methane isothermal adsorption on crushed samples and CH4-saturated NMR of plug samples was proposed to determine the adsorbed gas,free gas,and total gas content under high temperature and pressure conditions.There were four main research findings.(1)Marine-continental transitional shale exhibited substantial total gas content in situ,ranging from 2.58 to 5.73 cm^(3)/g,with an average of 4.35 cm^(3)/g.The adsorbed gas primarily resided in organic matter pores through micropore filling and multilayer adsorption,followed by multilayer adsorption in clay pores.(2)The changes in adsorbed and free pore volumes can be divided into four stages.Pores of<5 nm exclusively contain adsorbed gas,while those of 5-20 nm have a high proportion of adsorbed gas alongside free gas.Pores ranging from 20 to 100 nm have a high proportion of free gas and few adsorbed gas,while pores of>100 nm and microfractures are almost predominantly free gas.(3)The proportion of adsorbed gas in Type OP shale exceeds that in Type M,reaching 66%.(4)Methane adsorbed in Type OP shale demonstrates greater desorption capability,suggesting a potential for enhanced stable production,which finds support in existing production well data.However,it must be emphasized that high-gas-bearing intervals in both types present valuable opportunities for exploration and development.These data may support future model validations and enhance confidence in exploring and developing marine-continental transitional shale gas.展开更多
The basic geological characteristics of the Qiongzhusi Formation reservoirs and conditions for shale gas enrichment and high-yield were studied by using methods such as mineral scanning,organic and inorganic geochemis...The basic geological characteristics of the Qiongzhusi Formation reservoirs and conditions for shale gas enrichment and high-yield were studied by using methods such as mineral scanning,organic and inorganic geochemistry,breakthrough pressure,and triaxial mechanics testing based on the core,logging,seismic and production data.(1)Both types of silty shale,rich in organic matter in deep water and low in organic matter in shallow water,have good gas bearing properties.(2)The brittle mineral composition of shale is characterized by comparable feldspar and quartz content.(3)The pores are mainly inorganic pores with a small amount of organic pores.Pore development primarily hinges on a synergy between felsic minerals and total organic carbon content(TOC).(4)Dominated by Type I organic matters,the hydrocarbon generating organisms are algae and acritarch,with high maturity and high hydrocarbon generation potential.(5)Deep-and shallow-water shale gas exhibit in-situ and mixed gas generation characteristics,respectively.(6)The basic law of shale gas enrichment in the Qiongzhusi Formation was proposed as“TOC controlled accumulation and inorganic pore controlled enrichment”,which includes the in-situ enrichment model of“three highs and one over”(high TOC,high felsic mineral content,high inorganic pore content,overpressured formation)for organic rich shale represented by Well ZY2,and the in-situ+carrier-bed enrichment model of“two highs,one medium and one low”(high felsic content,high formation pressure,medium inorganic pore content,low TOC)for organic-poor shale gas represented by Well JS103.It is a new type of shale gas that is different from the Longmaxi Formation,enriching the formation mechanism of deep and ultra-deep shale gas.The deployment of multiple exploration wells has achieved significant breakthroughs in shale gas exploration.展开更多
By reviewing the research progress and exploration practices of shale gas geology in China,analyzing and summarizing the geological characteristics,enrichment laws,and resource potential of different types of shale ga...By reviewing the research progress and exploration practices of shale gas geology in China,analyzing and summarizing the geological characteristics,enrichment laws,and resource potential of different types of shale gas,the following understandings have been obtained:(1)Marine,transitional,and lacustrine shales in China are distributed from old to new in geological age,and the complexity of tectonic reworking and hydrocarbon generation evolution processes gradually decreases.(2)The sedimentary environment controls the type of source-reservoir configuration,which is the basis of“hydrocarbon generation and reservoir formation”.The types of source-reservoir configuration in marine and lacustrine shales are mainly source-reservoir integration,with occasional source-reservoir separation.The configuration types of transitional shale are mainly source-reservoir integration and source-reservoir symbiosis.(3)The resistance of rigid minerals to compression for pore preservation and the overpressure facilitate the enrichment of source-reservoir integrated shale gas.Good source reservoir coupling and preservation conditions are crucial for the shale gas enrichment of source-reservoir symbiosis and source-reservoir separation types.(4)Marine shale remains the main battlefield for increasing shale gas reserves and production in China,while transitional and lacustrine shales are expected to become important replacement areas.It is recommended to carry out the shale gas exploration at three levels:Accelerate the exploration of Silurian,Cambrian,and Permian marine shales in the Upper-Middle Yangtze region;make key exploration breakthroughs in ultra-deep marine shales of the Upper-Middle Yangtze region,the new Ordovician marine shale strata in the North China region,the transitional shales of the Carboniferous and Permian,as well as the Mesozoic lacustrine shale gas in basins such as Sichuan,Ordos and Songliao;explore and prepare for new shale gas exploration areas such as South China and Northwest China,providing technology and resource reserves for the sustainable development of shale gas in China.展开更多
Gas-bearing shales have become a major source of future natural gas production worldwide.It has become increasingly urgent to develop a reliable prediction model and corresponding workflow for identifying shale gas sw...Gas-bearing shales have become a major source of future natural gas production worldwide.It has become increasingly urgent to develop a reliable prediction model and corresponding workflow for identifying shale gas sweet spots.The formation of gas-bearing shales is closely linked to relative sealevel changes,providing an important approach to predicting sweet spots in the Wufeng-Longmaxi shale in the southern Sichuan Basin,China.Three types of marine shale gas sweet spots are identified in the shale based on their formation stages combined with relative sea-level changes:early,middle,and late transgression types.This study develops a prediction model and workflow for identifying shale gas sweet spots by analyzing relative sea-level changes and facies sequences.Predicting shale gas sweet spots in an explored block using this model and workflow can provide a valuable guide for well design and hydraulic fracturing,significantly enhancing the efficiency of shale gas exploration and development.Notably,the new prediction model and workflow can be utilized for the rapid evaluation of the potential for shale gas development in new shale gas blocks or those with low exploratory maturity.展开更多
Prediction of production decline and evaluation of the adsorbed/free gas ratio are critical for determining the lifespan and production status of shale gas wells.Traditional production prediction methods have some sho...Prediction of production decline and evaluation of the adsorbed/free gas ratio are critical for determining the lifespan and production status of shale gas wells.Traditional production prediction methods have some shortcomings because of the low permeability and tightness of shale,complex gas flow behavior of multi-scale gas transport regions and multiple gas transport mechanism superpositions,and complex and variable production regimes of shale gas wells.Recent research has demonstrated the existence of a multi-stage isotope fractionation phenomenon during shale gas production,with the fractionation characteristics of each stage associated with the pore structure,gas in place(GIP),adsorption/desorption,and gas production process.This study presents a new approach for estimating shale gas well production and evaluating the adsorbed/free gas ratio throughout production using isotope fractionation techniques.A reservoir-scale carbon isotope fractionation(CIF)model applicable to the production process of shale gas wells was developed for the first time in this research.In contrast to the traditional model,this model improves production prediction accuracy by simultaneously fitting the gas production rate and δ^(13)C_(1) data and provides a new evaluation method of the adsorbed/free gas ratio during shale gas production.The results indicate that the diffusion and adsorption/desorption properties of rock,bottom-hole flowing pressure(BHP)of gas well,and multi-scale gas transport regions of the reservoir all affect isotope fractionation,with the diffusion and adsorption/desorption parameters of rock having the greatest effect on isotope fractionation being D∗/D,PL,VL,α,and others in that order.We effectively tested the universality of the four-stage isotope fractionation feature and revealed a unique isotope fractionation mechanism caused by the superimposed coupling of multi-scale gas transport regions during shale gas well production.Finally,we applied the established CIF model to a shale gas well in the Sichuan Basin,China,and calculated the estimated ultimate recovery(EUR)of the well to be 3.33×10^(8) m^(3);the adsorbed gas ratio during shale gas production was 1.65%,10.03%,and 23.44%in the first,fifth,and tenth years,respectively.The findings are significant for understanding the isotope fractionation mechanism during natural gas transport in complex systems and for formulating and optimizing unconventional natural gas development strategies.展开更多
The 128.6-m-thick,shale-dominated Klimoli,Wulalike and Lashizhong formations exposed at the Hatuke Creek Section in the Zhuozishan area of Inner Monglia,North China,have been investigated for conodonts.Detailed strati...The 128.6-m-thick,shale-dominated Klimoli,Wulalike and Lashizhong formations exposed at the Hatuke Creek Section in the Zhuozishan area of Inner Monglia,North China,have been investigated for conodonts.Detailed stratigraphical collections of conodonts preserved on bedding planes from graptolitic shales,supplemented by additional discrete conodonts acid-leached from limestones,enable a refinement of the conodont biostratigraphic scheme at this section.Four successive conodont biozones,ranging in age from mid Darriwilian to late Sandbian(Stage slices Dw2–Sa2),are identified:the Dzikodus tablepointensis Biozone,the Eoplacognathus suecicus Biozone,the Pygodus serra Biozone,and the Pygodus anserinus Biozone,in ascending order.New sub-biozones,based on morphotypes of the biozonal index species,are proposed for the Pygodus serra and Pygodus anserinus biozones,providing alternatives when the traditional sub-biozones are unrecognizable.The biozonation is clearly correlated with the coeval Baltoscandian,South American and South China reference standard successions.The diverse preservation states of conodont bedding plane assemblages suggest that the alteration of conodonts in graptolitic shales represents a diagenetic process,challenging the prevailing hypothesis of pre-diagenetic dissolution.This study highlights the crucial role of previously overlooked conodont bedding plane assemblages in correlating Ordovician slope/basin facies shales,which holds great potential for marine shale gas exploration.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
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
Shale gas wells often face challenges in maintaining continuous and stable production due to their coexistence with high-and low-pressure wells within the same development block,which leads to issues involving mixed-p...Shale gas wells often face challenges in maintaining continuous and stable production due to their coexistence with high-and low-pressure wells within the same development block,which leads to issues involving mixed-pressure flows.Traditional pipeline optimization methods used in conventional gas well blocks fail to address the unique needs of shale gas wells,such as the precise planning of airflow paths,pressure distribution,and compression.This study proposes a pressure-controlled production optimization strategy specifically designed for shale gas wells operating under mixed-pressure flow conditions.The strategy aims to improve production stability and optimize system efficiency.The decline in production and pressure for individual wells over time is forecasted using a predictive model that accounts for key factors of system optimization,such as reservoir depletion,wellbore conditions,and equipment performance.Additionally,the model predicts the timing and impact of liquid loading,which can significantly affect production.The optimization process involves analyzing the existing gathering pipeline network to determine the most efficient flow directions and compression strategies based on these predictions,while the strategy involves adjusting compressor settings,optimizing flow rates,and planning pressure distribution across the network to maximize productivity while maintaining system stability.By implementing these strategies,this study significantly improves gas well productivity and enhances the adaptability and efficiency of the gathering and transportation system.The proposed approach provides systematic technical solutions and practical guidance for the efficient development and stable production of shale gas fields,ensuring more robust and sustainable pipeline operations.展开更多
Shale gas in southern China is found to contain economically valuable helium(He),which is inconsistent with conventional perspective that hydrocarbon gases in shale would dilute He to sub-economic levels.The adsorptio...Shale gas in southern China is found to contain economically valuable helium(He),which is inconsistent with conventional perspective that hydrocarbon gases in shale would dilute He to sub-economic levels.The adsorption of gases in the nanopores of organic matter is considered a crucial factor influencing the shale gas composition.The adsorption behaviors of He,methane(CH_(4))and their mixtures in kerogen nanopores were performed by the Grand Canonical Monte Carlo simulation.The molecular simulations of pure He reveal that He can be adsorbed in shale and the adsorption capacity of He increases with the burial depth of shale.Before the hydrocarbon generation from kerogen,He has been continually generated in shale,the simulations further demonstrate that pure He can be partially preserved in shale as adsorbed gas phase.The simulations of competitive adsorption between CH_(4) and He show that the adsorption selectivity of CH_(4)/He is consistently higher than 1.0 under the simulated conditions.This indicates that the previously adsorbed He will be displaced by CH_(4) and subsequently concentrated in hydrocarbon gas as free gas phase during the process of hydrocarbon gas generation from kerogen.After the termination of hydrocarbon gas generation,He continues to be generated in shale and preferentially concentrated in free shale gas.Therefore,the concentration of He in shale gas will gradually increase with the generation time of He.In addition,our simulations indicate that high pressure and deep burial depth can enhance the adsorption of He in kerogen,suggesting that deeply buried organic-rich shale probably retains more adsorbed helium.Molecular simulations of He adsorption provide new insights into the accumulation process of He in shale gas and are of great significance for assessing helium resource potential in shale gas.展开更多
Over more than a decade of development,medium to deep shale gas reservoirs have faced rapid production declines,making sustained output challenging.To harness remaining reserves effectively,advanced fracturing techniq...Over more than a decade of development,medium to deep shale gas reservoirs have faced rapid production declines,making sustained output challenging.To harness remaining reserves effectively,advanced fracturing techniques such as infill drilling are essential.This study develops a complex fracture network model for dual horizontal wells and a four-dimensional in-situ stress evolution model,grounded in elastic porous media theory.These models simulate and analyze the evolution of formation pore pressure and in-situ stress during production.The investigation focuses on the influence of infill well fracturing timing on fracture propagation patterns,individual well productivity,and the overall productivity of well clusters.The findings reveal that,at infill well locations,the maximum horizontal principal stress undergoes the most significant reduction,while changes in the minimum horizontal principal stress and vertical stress remain minimal.The horizontal stress surrounding the infill well may reorient,potentially transitioning the stress regime from strike-slip to normal faulting.Delays in infill well fracturing increase lateral fracture deflection and diminish fracture propagation between wells.Considering the stable production phase and cumulative gas output of the well group,the study identifies an optimal timing for infill fracturing.Notably,larger well spacing shifts the optimal timing to a later stage.展开更多
The study area is rich in shale gas resources and has reached the stage of comprehensive development. Shale gas extraction poses risks such as induced seismicity and well closure, compounded by the limited availabilit...The study area is rich in shale gas resources and has reached the stage of comprehensive development. Shale gas extraction poses risks such as induced seismicity and well closure, compounded by the limited availability of fi xed seismic monitoring stations nearby. To address these challenges, a dense observation array was developed within the study area to monitor and analyze microseismic activity during hydraulic fracturing. Microseismic events generated by hydraulic fracturing typically exhibit low amplitude and signal-to-noise ratio, rendering traditional manual analysis methods impractical. To overcome these limitations, an innovative artifi cial intelligence method combining picking-association-location (PAL) and match-expand- shift-stack (MESS) techniques (PALM) has been utilized for automated seismic detection. Numerous factors influence the accuracy of microseismic detection and localization. To evaluate these factors, the effects of various velocity structure models, instrument types, and station distributions on seismic location were analyzed and compared. The results indicate that the PALM method significantly mitigates the influence of velocity structure models on seismic location accuracy. Additionally, the use of broadband seismic instruments and a uniform station distribution enhances the precision of seismic location results. Furthermore, by integrating data from diff erent types of observation instruments, a comprehensive seismic catalog for the study area was established. These fi ndings not only enhance seismic location accuracy but also provide valuable guidance for optimizing regional seismic monitoring network design and improving seismic risk assessment.展开更多
This study introduces a comprehensive and automated framework that leverages data-driven method-ologies to address various challenges in shale gas development and production.Specifically,it harnesses the power of Auto...This study introduces a comprehensive and automated framework that leverages data-driven method-ologies to address various challenges in shale gas development and production.Specifically,it harnesses the power of Automated Machine Learning(AutoML)to construct an ensemble model to predict the estimated ultimate recovery(EUR)of shale gas wells.To demystify the“black-box”nature of the ensemble model,KernelSHAP,a kernel-based approach to compute Shapley values,is utilized for elucidating the influential factors that affect shale gas production at both global and local scales.Furthermore,a bi-objective optimization algorithm named NSGA-Ⅱ is seamlessly incorporated to opti-mize hydraulic fracturing designs for production boost and cost control.This innovative framework addresses critical limitations often encountered in applying machine learning(ML)to shale gas pro-duction:the challenge of achieving sufficient model accuracy with limited samples,the multidisciplinary expertise required for developing robust ML models,and the need for interpretability in“black-box”models.Validation with field data from the Fuling shale gas field in the Sichuan Basin substantiates the framework's efficacy in enhancing the precision and applicability of data-driven techniques.The test accuracy of the ensemble ML model reached 83%compared to a maximum of 72%of single ML models.The contribution of each geological and engineering factor to the overall production was quantitatively evaluated.Fracturing design optimization raised EUR by 7%-34%under different production and cost tradeoff scenarios.The results empower domain experts to conduct more precise and objective data-driven analyses and optimizations for shale gas production with minimal expertise in data science.展开更多
Field development practices in many shale gas regions(e.g.,the Changning region)have revealed a persistent issue of suboptimal reserve utilization,particularly in areas where the effective drainage width of production...Field development practices in many shale gas regions(e.g.,the Changning region)have revealed a persistent issue of suboptimal reserve utilization,particularly in areas where the effective drainage width of production wells is less than half the inter-well spacing(typically 400-500 m).To address this,infill drilling has become a widely adopted and effective strategy for enhancing reservoir contact andmobilizing previously untapped reserves.However,this approach has introduced significant inter-well interference,complicating production dynamics and performance evaluation.The two primary challenges hindering efficient deployment of infill wells are:(1)the quantitative assessment of hydraulic and pressure connectivity between infill wells and their associated parent wells,and(2)the accurate estimation of platform-scale Estimated Ultimate Recovery(EUR)following infill implementation.This study presents a novel framework to quantify inter-well connectivity by deriving a material balance equation tailored for shale gas infill well groups,explicitly incorporating gas adsorption and desorption mechanisms.The model simultaneously evaluates formation pressure evolution and crossflow behavior between wells,offering a robust analytical basis for performance prediction.For infill wells intersecting the drainage boundaries of parent wells,EUR is estimated using an analytical model developed for multi-stage hydraulically fractured horizontal wells.Meanwhile,the EUR of the parent wells is obtained by summing their pre-infill EUR with the final inter-well crossflow contribution.展开更多
Milling bridge plugs in shale gas wells with severe casing deformation often leads to the accumulation of cuttings,increasing the risk of stuck drill bits.Friction in the wellbore further complicates tool deployment i...Milling bridge plugs in shale gas wells with severe casing deformation often leads to the accumulation of cuttings,increasing the risk of stuck drill bits.Friction in the wellbore further complicates tool deployment into the horizontal section,posing challenges to efficient plug drilling and achieving wellbore access to the target layer.This paper integrates the theory of positive displacement motors and models their actual working characteristics to study the milling of bridge plugs in severely deformed horizontal wells.It examines the effects of coiled tubing diameter and wall thickness on the bending load of horizontal sections and discusses key technical requirements,including the timing of plug drilling,extending the run in the horizontal section,parameter control,and real-time field analysis.Field practices have shown that after casing deformation occurs,priority should be given to drilling out the bridge plugs below the point of deformation.The primary factors contributing to stuck drills in deformed wells include smaller mill shoe sizes and larger cuttings sizes.Short well-washing cycles and targeted cuttings removal can effectively reduce sticking risks.If sticking occurs,high-tonnage pulling should be avoided.Instead,releasing the stick through up-anddown string motion,combined with high-volume nozzle spraying and annulus pumping,is recommended.The selection of coiled tubing should consider diameter,wall thickness,and steel grade to handle complex situations.Larger diameters,thicker walls,and low-frequency,multi-head hydraulic oscillators are more effective for unlocking horizontal sections.This approach can reduce the risk of drill sticking and solve the problem of horizontal section lock-ups,offering a reliable solution for smooth drilling and efficient production in wells with severe casing deformation.展开更多
The black shales of Wufeng and Longmaxi Formation(Late Ordovician-Early Silurian period)in Sichuan Basin are the main strata for marine shale gas exploration,which have a yearly shale gas production of 228×10^(8)...The black shales of Wufeng and Longmaxi Formation(Late Ordovician-Early Silurian period)in Sichuan Basin are the main strata for marine shale gas exploration,which have a yearly shale gas production of 228×10^(8)m^(3)and cumulative shale gas production of 919×10^(8)m^(3).According to the lithological and biological features,filling sequences,sedimentary structures and lab analysis,the authors divided the Wufeng/Guanyinqiao and Longmaxi Formations into shore,tidal flat,shoal,shallow water shelf and deep water shelf facies,and confirmed that a shallow water deposition between the two sets of shales.Although both Formations contain similar shales,their formation mechanisms differ.During the deposition of Wufeng shale,influenced by the Caledonian Movement,the Central Sichuan and Guizhou Uplifts led to the transformation of the Sichuan Basin into a back-bulge basin.Coinstantaneous volcanic activity provided significant nutrients,contributing to the deposition of Wufeng Formation black shales.In contrast,during the deposition of Longmaxi shale,collisions caused basement subsidence,melting glaciers raised sea levels,and renewed volcanic activity provided additional nutrients,leading to Longmaxi Formation black shale accumulation.Considering the basic sedimentary geology and shale gas characteristics,areas such as Suijiang-Leibo-Daguan,Luzhou-Zigong,Weirong-Yongchuan,and Nanchuan-Dingshan are identified as key prospects for future shale gas exploration in the Wufeng-Longmaxi Formations.展开更多
To address the issue of uneven temperature distribution in shale gas oil-based drill cuttings pyrolysis furnaces,a numerical model was developed using Fluent software.The effects of nitrogen flow rate,heating tube spa...To address the issue of uneven temperature distribution in shale gas oil-based drill cuttings pyrolysis furnaces,a numerical model was developed using Fluent software.The effects of nitrogen flow rate,heating tube spacing,and furnace dimensions on the internal temperature field were thoroughly analyzed from a mechanistic perspective.The results indicated that non-uniform radiation from the heating tubes and flow disturbances induced by the nitrogen stream were the primary causes of localized heat concentration.Under no-load conditions,the maximum deviation between simulated and on-site measured temperatures was 1.5%,validating the model’s accuracy.Further-more,this study investigated the trade-offs between temperature uniformity,energy consumption,and construction costs.The findings provide a crucial design basis and a reliable simulation platform for developing and optimizing pyrolysis equipment.展开更多
As shale gas technology has advanced,the horizontal well fracturing model has seen widespread use,leading to substantial improvements in industrial gas output from shale gas wells.Nevertheless,a swift decline in the p...As shale gas technology has advanced,the horizontal well fracturing model has seen widespread use,leading to substantial improvements in industrial gas output from shale gas wells.Nevertheless,a swift decline in the productivity of individual wells remains a challenge that must be addressed throughout the development process.In this study,gas wells with two different wellbore trajectory structures are considered,and the OLGA software is exploited to perform transient calculations on various tubing depth models.The results can be articulated as follows.In terms of flow patterns:for the deep well A1(upward-buckled),slug flow occurs in the Kick-off Point position and above;for the deep well B1(downward-inclined),slug flow only occurs in the horizontal section.Wells with downward-inclined horizontal sections are more prone to liquid accumulation issues.In terms of comparison to conventional wells,it is shown that deep shale gas wells have longer normal production durations and experience liquid accumulation later than conventional wells.With regard to optimal tubing placement:for well A1(upward-buckled),it is recommended to place tubing at the Kick-off Point position;for well B1(downward-inclined),it is recommended to place tubing at the lower heel of the horizontal section.Finally,in terms of production performance:well A1(upward-buckled)outperforms well B1(downward-inclined)in terms of production and fluid accumulation.In particular,the deep well A1 is 1.94 times more productive and 1.3 times longer to produce than conventional wells.Deep well B1 is 1.87 times more productive and 1.34 times longer than conventional wells.展开更多
The drilling gas production situation indicates a certain correlation between the shale gas reservoir in the Sichuan Basin and the high and low changes in formation resistivity.These variations are observed in the fir...The drilling gas production situation indicates a certain correlation between the shale gas reservoir in the Sichuan Basin and the high and low changes in formation resistivity.These variations are observed in the first member of the Longmaxi Formation to the Wufeng Formation at the bottom of the Longmaxi Formation.Given this correlation and based on the logging electrical data,this study employs the wide-field electromagnetic method(WFEM)to experimentally detect the electrical characteristics of the deep shale gas target layer in the Yibin area of southern Sichuan.The study also tests the regularity and effectiveness of the electrical parameters for evaluating favorable areas of shale gas reservoirs.In terms of specific operation,the structural pattern of the study area is implemented based on the wide-field electromagnetic results and geological data for comprehensive analysis,which identifies the main hidden faults and their influence range on low resistance.The detailed spatial distribution of the upper Ordovician Wufeng Formation and the lower Silurian Longmaxi Formation in the target layer with a buried depth of 2000-5000m is described.This layer exhibits the characteristics of a continuous and stable distribution of organic shale.After verifying the subsequent electrical logging data,the electrical logging curve is found to be essentially consistent with the shape and trend of the wide-field resistivity curve.This consistency demonstrates the effectiveness of WFEM in detecting shale gas layers.展开更多
Organic matter(OM)is the primary gas occurrence carrier in shale reservoirs due to their abundant nanopores.To reveal the OM pore structure,adsorption capacity and evolution during thermal maturation,this study collec...Organic matter(OM)is the primary gas occurrence carrier in shale reservoirs due to their abundant nanopores.To reveal the OM pore structure,adsorption capacity and evolution during thermal maturation,this study collected data from samples spanning the entire evolution stage,from immature to over-mature.Scanning Electron Microscope(SEM)observation and low temperature gases adsorption experiments were used to qualitatively-semi-quantitatively and quantitatively analyze OM pore structure evolution,and CH_(4) isothermal adsorption experiments were used to reveal the adsorption capacity evolution.Then,the influence and mechanism of matu rity and hydrocarbon generation on pore development and adsorption capacity were quantitatively reviewed based on the experimental data.The results show that OM pores are poorly developed in the immature stage due to weak hydrocarbon generation,although micro-fractures are occasionally found at the edges of OM particles.In the low maturity stage,OM pores are partially developed due to liquid hydrocarbon generation,with liquid hydrocarbons also filling some OM pores.The contribution of total organic carbon content(TOC)to adsorption extent is not significant in these two stages.From high to high-over maturity stages,massive gaseous hydrocarbons are generated,significantly improving the surface porosity of OM.Clear positive linear correlations are observed between TOC and adsorption amount.However,the development of OM pores significantly declines when thermal maturity(R_(o))exceeds 3.5%due to excessive aromatization.The accuracy of research on the evolution of pore structure and adsorption capacity is limited by several factors:(ⅰ)errors caused by sample specification,calculation processes,parameter settings,and kerogen models in isothermal adsorption experiments and molecular simulations;(ⅱ)difficulty in achieving control variables due to the strong heterogeneity of natural maturation shale samples;and(ⅲ)the need to enhance compatibility between thermal simulation experiments and natural thermal evolution.Therefore,isothermal adsorption experiments on bulk shale and molecular simulations of intact shale model are necessary,taking into account the dynamic temperature and pressure of in-situ reservoirs.Moreover,shale samples with varying maturity,influenced by their distance from the paleo-thermal source,may provide significant verification for thermal simulation experiments.展开更多
基金the Science and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance,China(No.2020CX030101)the National Natural Science Foundation of China(No.42222209)the Scientific Research and Technological Development Program of CNPC,China(No.2023ZZ0801).
文摘Pore structure characteristics,gas content,and micro-scale gas occurrence mechanisms were investigated in the Shan_(2)^(3)sub-member marine-continental transitional shale of the southeastern margin of the Ordos Basin using scanning electron microscope images,lowtemperature N_(2)/CO_(2)adsorption and high-pressure mercury intrusion,methane isothermal adsorption experiments,and CH4-saturated nuclear magnetic resonance(NMR).Two distinct shale types were identified:organic pore-rich shale(Type OP)and microfracture-rich shale(Type M).The Type OP shale exhibited relatively well-developed organic matter pores,while the Type M shale was primarily characterized by a high degree of microfracture development.An experimental method combining methane isothermal adsorption on crushed samples and CH4-saturated NMR of plug samples was proposed to determine the adsorbed gas,free gas,and total gas content under high temperature and pressure conditions.There were four main research findings.(1)Marine-continental transitional shale exhibited substantial total gas content in situ,ranging from 2.58 to 5.73 cm^(3)/g,with an average of 4.35 cm^(3)/g.The adsorbed gas primarily resided in organic matter pores through micropore filling and multilayer adsorption,followed by multilayer adsorption in clay pores.(2)The changes in adsorbed and free pore volumes can be divided into four stages.Pores of<5 nm exclusively contain adsorbed gas,while those of 5-20 nm have a high proportion of adsorbed gas alongside free gas.Pores ranging from 20 to 100 nm have a high proportion of free gas and few adsorbed gas,while pores of>100 nm and microfractures are almost predominantly free gas.(3)The proportion of adsorbed gas in Type OP shale exceeds that in Type M,reaching 66%.(4)Methane adsorbed in Type OP shale demonstrates greater desorption capability,suggesting a potential for enhanced stable production,which finds support in existing production well data.However,it must be emphasized that high-gas-bearing intervals in both types present valuable opportunities for exploration and development.These data may support future model validations and enhance confidence in exploring and developing marine-continental transitional shale gas.
基金Supported by the Sinopec Major Science and Technology Project(P22081)National Natural Science Foundation of China(U24B60001).
文摘The basic geological characteristics of the Qiongzhusi Formation reservoirs and conditions for shale gas enrichment and high-yield were studied by using methods such as mineral scanning,organic and inorganic geochemistry,breakthrough pressure,and triaxial mechanics testing based on the core,logging,seismic and production data.(1)Both types of silty shale,rich in organic matter in deep water and low in organic matter in shallow water,have good gas bearing properties.(2)The brittle mineral composition of shale is characterized by comparable feldspar and quartz content.(3)The pores are mainly inorganic pores with a small amount of organic pores.Pore development primarily hinges on a synergy between felsic minerals and total organic carbon content(TOC).(4)Dominated by Type I organic matters,the hydrocarbon generating organisms are algae and acritarch,with high maturity and high hydrocarbon generation potential.(5)Deep-and shallow-water shale gas exhibit in-situ and mixed gas generation characteristics,respectively.(6)The basic law of shale gas enrichment in the Qiongzhusi Formation was proposed as“TOC controlled accumulation and inorganic pore controlled enrichment”,which includes the in-situ enrichment model of“three highs and one over”(high TOC,high felsic mineral content,high inorganic pore content,overpressured formation)for organic rich shale represented by Well ZY2,and the in-situ+carrier-bed enrichment model of“two highs,one medium and one low”(high felsic content,high formation pressure,medium inorganic pore content,low TOC)for organic-poor shale gas represented by Well JS103.It is a new type of shale gas that is different from the Longmaxi Formation,enriching the formation mechanism of deep and ultra-deep shale gas.The deployment of multiple exploration wells has achieved significant breakthroughs in shale gas exploration.
基金Supported by the National Natural Science Foundation of China(42172165,42272143)Project of SINOPEC Science and Technology Department(P24181,KLP24017).
文摘By reviewing the research progress and exploration practices of shale gas geology in China,analyzing and summarizing the geological characteristics,enrichment laws,and resource potential of different types of shale gas,the following understandings have been obtained:(1)Marine,transitional,and lacustrine shales in China are distributed from old to new in geological age,and the complexity of tectonic reworking and hydrocarbon generation evolution processes gradually decreases.(2)The sedimentary environment controls the type of source-reservoir configuration,which is the basis of“hydrocarbon generation and reservoir formation”.The types of source-reservoir configuration in marine and lacustrine shales are mainly source-reservoir integration,with occasional source-reservoir separation.The configuration types of transitional shale are mainly source-reservoir integration and source-reservoir symbiosis.(3)The resistance of rigid minerals to compression for pore preservation and the overpressure facilitate the enrichment of source-reservoir integrated shale gas.Good source reservoir coupling and preservation conditions are crucial for the shale gas enrichment of source-reservoir symbiosis and source-reservoir separation types.(4)Marine shale remains the main battlefield for increasing shale gas reserves and production in China,while transitional and lacustrine shales are expected to become important replacement areas.It is recommended to carry out the shale gas exploration at three levels:Accelerate the exploration of Silurian,Cambrian,and Permian marine shales in the Upper-Middle Yangtze region;make key exploration breakthroughs in ultra-deep marine shales of the Upper-Middle Yangtze region,the new Ordovician marine shale strata in the North China region,the transitional shales of the Carboniferous and Permian,as well as the Mesozoic lacustrine shale gas in basins such as Sichuan,Ordos and Songliao;explore and prepare for new shale gas exploration areas such as South China and Northwest China,providing technology and resource reserves for the sustainable development of shale gas in China.
文摘Gas-bearing shales have become a major source of future natural gas production worldwide.It has become increasingly urgent to develop a reliable prediction model and corresponding workflow for identifying shale gas sweet spots.The formation of gas-bearing shales is closely linked to relative sealevel changes,providing an important approach to predicting sweet spots in the Wufeng-Longmaxi shale in the southern Sichuan Basin,China.Three types of marine shale gas sweet spots are identified in the shale based on their formation stages combined with relative sea-level changes:early,middle,and late transgression types.This study develops a prediction model and workflow for identifying shale gas sweet spots by analyzing relative sea-level changes and facies sequences.Predicting shale gas sweet spots in an explored block using this model and workflow can provide a valuable guide for well design and hydraulic fracturing,significantly enhancing the efficiency of shale gas exploration and development.Notably,the new prediction model and workflow can be utilized for the rapid evaluation of the potential for shale gas development in new shale gas blocks or those with low exploratory maturity.
基金supported by the Natural Science Foundation of China(Grant No.42302170)National Postdoctoral Innovative Talent Support Program(Grant No.BX20220062)+3 种基金CNPC Innovation Found(Grant No.2022DQ02-0104)National Science Foundation of Heilongjiang Province of China(Grant No.YQ2023D001)Postdoctoral Science Foundation of Heilongjiang Province of China(Grant No.LBH-Z22091)the Natural Science Foundation of Shandong Province(Grant No.ZR2022YQ30).
文摘Prediction of production decline and evaluation of the adsorbed/free gas ratio are critical for determining the lifespan and production status of shale gas wells.Traditional production prediction methods have some shortcomings because of the low permeability and tightness of shale,complex gas flow behavior of multi-scale gas transport regions and multiple gas transport mechanism superpositions,and complex and variable production regimes of shale gas wells.Recent research has demonstrated the existence of a multi-stage isotope fractionation phenomenon during shale gas production,with the fractionation characteristics of each stage associated with the pore structure,gas in place(GIP),adsorption/desorption,and gas production process.This study presents a new approach for estimating shale gas well production and evaluating the adsorbed/free gas ratio throughout production using isotope fractionation techniques.A reservoir-scale carbon isotope fractionation(CIF)model applicable to the production process of shale gas wells was developed for the first time in this research.In contrast to the traditional model,this model improves production prediction accuracy by simultaneously fitting the gas production rate and δ^(13)C_(1) data and provides a new evaluation method of the adsorbed/free gas ratio during shale gas production.The results indicate that the diffusion and adsorption/desorption properties of rock,bottom-hole flowing pressure(BHP)of gas well,and multi-scale gas transport regions of the reservoir all affect isotope fractionation,with the diffusion and adsorption/desorption parameters of rock having the greatest effect on isotope fractionation being D∗/D,PL,VL,α,and others in that order.We effectively tested the universality of the four-stage isotope fractionation feature and revealed a unique isotope fractionation mechanism caused by the superimposed coupling of multi-scale gas transport regions during shale gas well production.Finally,we applied the established CIF model to a shale gas well in the Sichuan Basin,China,and calculated the estimated ultimate recovery(EUR)of the well to be 3.33×10^(8) m^(3);the adsorbed gas ratio during shale gas production was 1.65%,10.03%,and 23.44%in the first,fifth,and tenth years,respectively.The findings are significant for understanding the isotope fractionation mechanism during natural gas transport in complex systems and for formulating and optimizing unconventional natural gas development strategies.
基金supported by the National Natural Science Foundation of China (Nos. 42572017, 42172037)the State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, CAS (Nos. 213107, 173122)the International Geoscience Programme (IGCP) project 735 “Rocks and the Rise of Ordovician Life: Filling knowledge gaps in the Early Palaeozoic biodiversification”
文摘The 128.6-m-thick,shale-dominated Klimoli,Wulalike and Lashizhong formations exposed at the Hatuke Creek Section in the Zhuozishan area of Inner Monglia,North China,have been investigated for conodonts.Detailed stratigraphical collections of conodonts preserved on bedding planes from graptolitic shales,supplemented by additional discrete conodonts acid-leached from limestones,enable a refinement of the conodont biostratigraphic scheme at this section.Four successive conodont biozones,ranging in age from mid Darriwilian to late Sandbian(Stage slices Dw2–Sa2),are identified:the Dzikodus tablepointensis Biozone,the Eoplacognathus suecicus Biozone,the Pygodus serra Biozone,and the Pygodus anserinus Biozone,in ascending order.New sub-biozones,based on morphotypes of the biozonal index species,are proposed for the Pygodus serra and Pygodus anserinus biozones,providing alternatives when the traditional sub-biozones are unrecognizable.The biozonation is clearly correlated with the coeval Baltoscandian,South American and South China reference standard successions.The diverse preservation states of conodont bedding plane assemblages suggest that the alteration of conodonts in graptolitic shales represents a diagenetic process,challenging the prevailing hypothesis of pre-diagenetic dissolution.This study highlights the crucial role of previously overlooked conodont bedding plane assemblages in correlating Ordovician slope/basin facies shales,which holds great potential for marine shale gas exploration.
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 Foundation of China under Grant 52325402,52274057 and 52074340the National Key R&D Program of China under Grant 2023YFB4104200+1 种基金the Major Scientific and Technological Projects of CNOOC under Grant CCL2022RCPS0397RSN111 Project under Grant B08028.
文摘Shale gas wells often face challenges in maintaining continuous and stable production due to their coexistence with high-and low-pressure wells within the same development block,which leads to issues involving mixed-pressure flows.Traditional pipeline optimization methods used in conventional gas well blocks fail to address the unique needs of shale gas wells,such as the precise planning of airflow paths,pressure distribution,and compression.This study proposes a pressure-controlled production optimization strategy specifically designed for shale gas wells operating under mixed-pressure flow conditions.The strategy aims to improve production stability and optimize system efficiency.The decline in production and pressure for individual wells over time is forecasted using a predictive model that accounts for key factors of system optimization,such as reservoir depletion,wellbore conditions,and equipment performance.Additionally,the model predicts the timing and impact of liquid loading,which can significantly affect production.The optimization process involves analyzing the existing gathering pipeline network to determine the most efficient flow directions and compression strategies based on these predictions,while the strategy involves adjusting compressor settings,optimizing flow rates,and planning pressure distribution across the network to maximize productivity while maintaining system stability.By implementing these strategies,this study significantly improves gas well productivity and enhances the adaptability and efficiency of the gathering and transportation system.The proposed approach provides systematic technical solutions and practical guidance for the efficient development and stable production of shale gas fields,ensuring more robust and sustainable pipeline operations.
基金supported by the National Key Research and Development Program of China(Grant No.2021YFA0719000)the Science Foundation of China University of Petroleum,Beijing(No.2462025XKBH007)the Research Foundation of China University of Petroleum-Beijing at Karamay(No.XQZX20240019)。
文摘Shale gas in southern China is found to contain economically valuable helium(He),which is inconsistent with conventional perspective that hydrocarbon gases in shale would dilute He to sub-economic levels.The adsorption of gases in the nanopores of organic matter is considered a crucial factor influencing the shale gas composition.The adsorption behaviors of He,methane(CH_(4))and their mixtures in kerogen nanopores were performed by the Grand Canonical Monte Carlo simulation.The molecular simulations of pure He reveal that He can be adsorbed in shale and the adsorption capacity of He increases with the burial depth of shale.Before the hydrocarbon generation from kerogen,He has been continually generated in shale,the simulations further demonstrate that pure He can be partially preserved in shale as adsorbed gas phase.The simulations of competitive adsorption between CH_(4) and He show that the adsorption selectivity of CH_(4)/He is consistently higher than 1.0 under the simulated conditions.This indicates that the previously adsorbed He will be displaced by CH_(4) and subsequently concentrated in hydrocarbon gas as free gas phase during the process of hydrocarbon gas generation from kerogen.After the termination of hydrocarbon gas generation,He continues to be generated in shale and preferentially concentrated in free shale gas.Therefore,the concentration of He in shale gas will gradually increase with the generation time of He.In addition,our simulations indicate that high pressure and deep burial depth can enhance the adsorption of He in kerogen,suggesting that deeply buried organic-rich shale probably retains more adsorbed helium.Molecular simulations of He adsorption provide new insights into the accumulation process of He in shale gas and are of great significance for assessing helium resource potential in shale gas.
基金supported by the National Natural Science Foundation of China(Grant No.52374043)the Southwest Oil&Gas Field Branch in PetroChina(Grant No.JS2023-115)。
文摘Over more than a decade of development,medium to deep shale gas reservoirs have faced rapid production declines,making sustained output challenging.To harness remaining reserves effectively,advanced fracturing techniques such as infill drilling are essential.This study develops a complex fracture network model for dual horizontal wells and a four-dimensional in-situ stress evolution model,grounded in elastic porous media theory.These models simulate and analyze the evolution of formation pore pressure and in-situ stress during production.The investigation focuses on the influence of infill well fracturing timing on fracture propagation patterns,individual well productivity,and the overall productivity of well clusters.The findings reveal that,at infill well locations,the maximum horizontal principal stress undergoes the most significant reduction,while changes in the minimum horizontal principal stress and vertical stress remain minimal.The horizontal stress surrounding the infill well may reorient,potentially transitioning the stress regime from strike-slip to normal faulting.Delays in infill well fracturing increase lateral fracture deflection and diminish fracture propagation between wells.Considering the stable production phase and cumulative gas output of the well group,the study identifies an optimal timing for infill fracturing.Notably,larger well spacing shifts the optimal timing to a later stage.
基金the support of the China Three Gorges Corporation Science and Technology Fund, with the numbers 0799275the support of the National Natural Science Foundation of China, with the numbers 42174177 and 62106239。
文摘The study area is rich in shale gas resources and has reached the stage of comprehensive development. Shale gas extraction poses risks such as induced seismicity and well closure, compounded by the limited availability of fi xed seismic monitoring stations nearby. To address these challenges, a dense observation array was developed within the study area to monitor and analyze microseismic activity during hydraulic fracturing. Microseismic events generated by hydraulic fracturing typically exhibit low amplitude and signal-to-noise ratio, rendering traditional manual analysis methods impractical. To overcome these limitations, an innovative artifi cial intelligence method combining picking-association-location (PAL) and match-expand- shift-stack (MESS) techniques (PALM) has been utilized for automated seismic detection. Numerous factors influence the accuracy of microseismic detection and localization. To evaluate these factors, the effects of various velocity structure models, instrument types, and station distributions on seismic location were analyzed and compared. The results indicate that the PALM method significantly mitigates the influence of velocity structure models on seismic location accuracy. Additionally, the use of broadband seismic instruments and a uniform station distribution enhances the precision of seismic location results. Furthermore, by integrating data from diff erent types of observation instruments, a comprehensive seismic catalog for the study area was established. These fi ndings not only enhance seismic location accuracy but also provide valuable guidance for optimizing regional seismic monitoring network design and improving seismic risk assessment.
基金funded by the National Natural Science Foundation of China(42050104).
文摘This study introduces a comprehensive and automated framework that leverages data-driven method-ologies to address various challenges in shale gas development and production.Specifically,it harnesses the power of Automated Machine Learning(AutoML)to construct an ensemble model to predict the estimated ultimate recovery(EUR)of shale gas wells.To demystify the“black-box”nature of the ensemble model,KernelSHAP,a kernel-based approach to compute Shapley values,is utilized for elucidating the influential factors that affect shale gas production at both global and local scales.Furthermore,a bi-objective optimization algorithm named NSGA-Ⅱ is seamlessly incorporated to opti-mize hydraulic fracturing designs for production boost and cost control.This innovative framework addresses critical limitations often encountered in applying machine learning(ML)to shale gas pro-duction:the challenge of achieving sufficient model accuracy with limited samples,the multidisciplinary expertise required for developing robust ML models,and the need for interpretability in“black-box”models.Validation with field data from the Fuling shale gas field in the Sichuan Basin substantiates the framework's efficacy in enhancing the precision and applicability of data-driven techniques.The test accuracy of the ensemble ML model reached 83%compared to a maximum of 72%of single ML models.The contribution of each geological and engineering factor to the overall production was quantitatively evaluated.Fracturing design optimization raised EUR by 7%-34%under different production and cost tradeoff scenarios.The results empower domain experts to conduct more precise and objective data-driven analyses and optimizations for shale gas production with minimal expertise in data science.
文摘Field development practices in many shale gas regions(e.g.,the Changning region)have revealed a persistent issue of suboptimal reserve utilization,particularly in areas where the effective drainage width of production wells is less than half the inter-well spacing(typically 400-500 m).To address this,infill drilling has become a widely adopted and effective strategy for enhancing reservoir contact andmobilizing previously untapped reserves.However,this approach has introduced significant inter-well interference,complicating production dynamics and performance evaluation.The two primary challenges hindering efficient deployment of infill wells are:(1)the quantitative assessment of hydraulic and pressure connectivity between infill wells and their associated parent wells,and(2)the accurate estimation of platform-scale Estimated Ultimate Recovery(EUR)following infill implementation.This study presents a novel framework to quantify inter-well connectivity by deriving a material balance equation tailored for shale gas infill well groups,explicitly incorporating gas adsorption and desorption mechanisms.The model simultaneously evaluates formation pressure evolution and crossflow behavior between wells,offering a robust analytical basis for performance prediction.For infill wells intersecting the drainage boundaries of parent wells,EUR is estimated using an analytical model developed for multi-stage hydraulically fractured horizontal wells.Meanwhile,the EUR of the parent wells is obtained by summing their pre-infill EUR with the final inter-well crossflow contribution.
基金supported by Major Technology Promotion Project of CNPC,China(No.2022ZT01)Major Field Test Project of CNPC,China(No.2019F-31-04)CNPC Chuanqing Drilling Engineering Company Science and Technology Special Project,China(No.CQ2024B-11-Z2-4).
文摘Milling bridge plugs in shale gas wells with severe casing deformation often leads to the accumulation of cuttings,increasing the risk of stuck drill bits.Friction in the wellbore further complicates tool deployment into the horizontal section,posing challenges to efficient plug drilling and achieving wellbore access to the target layer.This paper integrates the theory of positive displacement motors and models their actual working characteristics to study the milling of bridge plugs in severely deformed horizontal wells.It examines the effects of coiled tubing diameter and wall thickness on the bending load of horizontal sections and discusses key technical requirements,including the timing of plug drilling,extending the run in the horizontal section,parameter control,and real-time field analysis.Field practices have shown that after casing deformation occurs,priority should be given to drilling out the bridge plugs below the point of deformation.The primary factors contributing to stuck drills in deformed wells include smaller mill shoe sizes and larger cuttings sizes.Short well-washing cycles and targeted cuttings removal can effectively reduce sticking risks.If sticking occurs,high-tonnage pulling should be avoided.Instead,releasing the stick through up-anddown string motion,combined with high-volume nozzle spraying and annulus pumping,is recommended.The selection of coiled tubing should consider diameter,wall thickness,and steel grade to handle complex situations.Larger diameters,thicker walls,and low-frequency,multi-head hydraulic oscillators are more effective for unlocking horizontal sections.This approach can reduce the risk of drill sticking and solve the problem of horizontal section lock-ups,offering a reliable solution for smooth drilling and efficient production in wells with severe casing deformation.
基金supported by the project of the China Geological Survey(DD20221661).
文摘The black shales of Wufeng and Longmaxi Formation(Late Ordovician-Early Silurian period)in Sichuan Basin are the main strata for marine shale gas exploration,which have a yearly shale gas production of 228×10^(8)m^(3)and cumulative shale gas production of 919×10^(8)m^(3).According to the lithological and biological features,filling sequences,sedimentary structures and lab analysis,the authors divided the Wufeng/Guanyinqiao and Longmaxi Formations into shore,tidal flat,shoal,shallow water shelf and deep water shelf facies,and confirmed that a shallow water deposition between the two sets of shales.Although both Formations contain similar shales,their formation mechanisms differ.During the deposition of Wufeng shale,influenced by the Caledonian Movement,the Central Sichuan and Guizhou Uplifts led to the transformation of the Sichuan Basin into a back-bulge basin.Coinstantaneous volcanic activity provided significant nutrients,contributing to the deposition of Wufeng Formation black shales.In contrast,during the deposition of Longmaxi shale,collisions caused basement subsidence,melting glaciers raised sea levels,and renewed volcanic activity provided additional nutrients,leading to Longmaxi Formation black shale accumulation.Considering the basic sedimentary geology and shale gas characteristics,areas such as Suijiang-Leibo-Daguan,Luzhou-Zigong,Weirong-Yongchuan,and Nanchuan-Dingshan are identified as key prospects for future shale gas exploration in the Wufeng-Longmaxi Formations.
基金funded by the key research on industrialization technologies of low-cost highenergy-density cathode materials(project number:2023GY008)the Sichuan Provincial Science and Technology Program(project number:2024NSFSC1406).
文摘To address the issue of uneven temperature distribution in shale gas oil-based drill cuttings pyrolysis furnaces,a numerical model was developed using Fluent software.The effects of nitrogen flow rate,heating tube spacing,and furnace dimensions on the internal temperature field were thoroughly analyzed from a mechanistic perspective.The results indicated that non-uniform radiation from the heating tubes and flow disturbances induced by the nitrogen stream were the primary causes of localized heat concentration.Under no-load conditions,the maximum deviation between simulated and on-site measured temperatures was 1.5%,validating the model’s accuracy.Further-more,this study investigated the trade-offs between temperature uniformity,energy consumption,and construction costs.The findings provide a crucial design basis and a reliable simulation platform for developing and optimizing pyrolysis equipment.
文摘As shale gas technology has advanced,the horizontal well fracturing model has seen widespread use,leading to substantial improvements in industrial gas output from shale gas wells.Nevertheless,a swift decline in the productivity of individual wells remains a challenge that must be addressed throughout the development process.In this study,gas wells with two different wellbore trajectory structures are considered,and the OLGA software is exploited to perform transient calculations on various tubing depth models.The results can be articulated as follows.In terms of flow patterns:for the deep well A1(upward-buckled),slug flow occurs in the Kick-off Point position and above;for the deep well B1(downward-inclined),slug flow only occurs in the horizontal section.Wells with downward-inclined horizontal sections are more prone to liquid accumulation issues.In terms of comparison to conventional wells,it is shown that deep shale gas wells have longer normal production durations and experience liquid accumulation later than conventional wells.With regard to optimal tubing placement:for well A1(upward-buckled),it is recommended to place tubing at the Kick-off Point position;for well B1(downward-inclined),it is recommended to place tubing at the lower heel of the horizontal section.Finally,in terms of production performance:well A1(upward-buckled)outperforms well B1(downward-inclined)in terms of production and fluid accumulation.In particular,the deep well A1 is 1.94 times more productive and 1.3 times longer to produce than conventional wells.Deep well B1 is 1.87 times more productive and 1.34 times longer than conventional wells.
基金Supported by the Sichuan Natural Resources Investment Group Technology Innovation Project"Application Research of Wide Area Electromagnetic Method in Shale Gas Electrical Detection in Southern Sichuan"。
文摘The drilling gas production situation indicates a certain correlation between the shale gas reservoir in the Sichuan Basin and the high and low changes in formation resistivity.These variations are observed in the first member of the Longmaxi Formation to the Wufeng Formation at the bottom of the Longmaxi Formation.Given this correlation and based on the logging electrical data,this study employs the wide-field electromagnetic method(WFEM)to experimentally detect the electrical characteristics of the deep shale gas target layer in the Yibin area of southern Sichuan.The study also tests the regularity and effectiveness of the electrical parameters for evaluating favorable areas of shale gas reservoirs.In terms of specific operation,the structural pattern of the study area is implemented based on the wide-field electromagnetic results and geological data for comprehensive analysis,which identifies the main hidden faults and their influence range on low resistance.The detailed spatial distribution of the upper Ordovician Wufeng Formation and the lower Silurian Longmaxi Formation in the target layer with a buried depth of 2000-5000m is described.This layer exhibits the characteristics of a continuous and stable distribution of organic shale.After verifying the subsequent electrical logging data,the electrical logging curve is found to be essentially consistent with the shape and trend of the wide-field resistivity curve.This consistency demonstrates the effectiveness of WFEM in detecting shale gas layers.
基金the supports of the Na-tional Natural Science Foundation of China(No.U19B2007,42072202)the China Postdoctoral Science Foundation(No.2025MD774057)。
文摘Organic matter(OM)is the primary gas occurrence carrier in shale reservoirs due to their abundant nanopores.To reveal the OM pore structure,adsorption capacity and evolution during thermal maturation,this study collected data from samples spanning the entire evolution stage,from immature to over-mature.Scanning Electron Microscope(SEM)observation and low temperature gases adsorption experiments were used to qualitatively-semi-quantitatively and quantitatively analyze OM pore structure evolution,and CH_(4) isothermal adsorption experiments were used to reveal the adsorption capacity evolution.Then,the influence and mechanism of matu rity and hydrocarbon generation on pore development and adsorption capacity were quantitatively reviewed based on the experimental data.The results show that OM pores are poorly developed in the immature stage due to weak hydrocarbon generation,although micro-fractures are occasionally found at the edges of OM particles.In the low maturity stage,OM pores are partially developed due to liquid hydrocarbon generation,with liquid hydrocarbons also filling some OM pores.The contribution of total organic carbon content(TOC)to adsorption extent is not significant in these two stages.From high to high-over maturity stages,massive gaseous hydrocarbons are generated,significantly improving the surface porosity of OM.Clear positive linear correlations are observed between TOC and adsorption amount.However,the development of OM pores significantly declines when thermal maturity(R_(o))exceeds 3.5%due to excessive aromatization.The accuracy of research on the evolution of pore structure and adsorption capacity is limited by several factors:(ⅰ)errors caused by sample specification,calculation processes,parameter settings,and kerogen models in isothermal adsorption experiments and molecular simulations;(ⅱ)difficulty in achieving control variables due to the strong heterogeneity of natural maturation shale samples;and(ⅲ)the need to enhance compatibility between thermal simulation experiments and natural thermal evolution.Therefore,isothermal adsorption experiments on bulk shale and molecular simulations of intact shale model are necessary,taking into account the dynamic temperature and pressure of in-situ reservoirs.Moreover,shale samples with varying maturity,influenced by their distance from the paleo-thermal source,may provide significant verification for thermal simulation experiments.
