Geochemical and Geological Characterization of Marine-Continental Transitional Shale: A Case Study in the Ordos Basin, NW China

The organic-rich shale of the Shanxi and Taiyuan Formation of the Lower Permian deposited in a marinecontinental transitional environment are well developed in the Ordos Basin,NW China,which is considered to contain a large amount of shale hydrocarbon resources.This study takes the Lower Permian Shanxi and Taiyuan shale collected from well SL~# in the Ordos Basin,NW China as an example to characterize the transitional shale reservoir.Based on organic geochemistry data,X-ray diffraction(XRD)analysis,field-emission scanning electron microscopy(FE-SEM)observations,the desorbed gas contents of this transitional shale were systematically studied and the shale gas potential was investigated.The results indicate that the Lower Permian Shanxi and Taiyuan shale has a relatively high total organic carbon(TOC)(average TOC of 4.9%)and contains type III kerogen with a high mature to over mature status.XRD analyses show that an important characteristic of the shale is that clay and brittle minerals of detrital origin comprise the major mineral composition of the marine-continental transitional shale samples,while the percentages of carbonate minerals,pyrite and siderite are relatively small.FE-SEM observations reveal that the mineral matrix pores are the most abundant in the Lower Permian shale samples,while organic matter(OM)pores are rarely developed.Experimental analysis suggests that the mineral compositions mainly govern the macropore development in the marine-continental transitional shale,and mineral matrix pores and microfractures are considered to provide space for gas storage and migration.In addition,the desorption experiments demonstrated that the marine-continental transitional shale in the Ordos Basin has a significantly potential for shale gas exploration,ranging from 0.53 to 2.86 m^3/t with an average value of 1.25m^3/t,which is in close proximity to those of terrestrial shale(1.29 m^3/t)and marine shale(1.28 m^3/t).In summary,these results demonstrated that the Lower Permian marine-continental transitional shale in the Ordos Basin has a significantly potential for shale gas exploration.

Lithofacies and pore features of marine-continental transitional shale and gas enrichment conditions of favorable lithofacies:A case study of Permian Longtan Formation in the Lintanchang area,southeast of Sichuan Basin,SW China

In this work,the Permian Longtan marine-continental transitional shale in the southeast of Sichuan Basin was taken as study object.Through petrology and geochemical analysis,lithofacies types of the marine-continental transitional shale were classified,key controlling factors of physical properties and gas content of the different shale lithofacies were analyzed.The research results show that the Longtan Formation marine-continental transitional shale in the study area has four types of lithofacies,namely,organic-lean calcareous shale,organic-lean mixed shale,organic-lean argillaceous shale,and organic-rich argillaceous shale,among which the organic-rich argillaceous shale is the most favorable lithofacies of the study area.The pore types of different lithofacies vary significantly and the clay mineral-related pore is the dominant type of the pore system in the study area.The main controlling factor of the physical properties is clay mineral content,and the most important factor affecting gas content is TOC content.Compared with marine shale,the marine-continental transitional shale has low average values,wide distribution range,and strong heterogeneity in TOC content,porosity,and pore structure parameters,but still contains some favorable layers with high physical properties and gas contents.The organic-rich clay shale deposited in tidal flat-lagoon system is most likely to form shale gas sweet spots,so it should be paid more attention in shale gas exploration.

Full-Sized Pore Structure and Fractal Characteristics of Marine-Continental Transitional Shale: A Case Study in Qinshui Basin, North China

Based on 10 shale samples collected from 4 wells in Qinshui Basin,we investigate the full-sized pore structure and fractal characteristics of Marine-Continental transitional shale by performing organic geochemistry,mineralogical composition,Nitrogen gas adsorption(N2 adsorption)and Nuclear Magnetic Resonance(NMR)measurements and fractal analysis.Results show that the TOC content of the shale samples is relatively high,with an average value of 2.44wt%,and the thermal evolution is during the mature-over mature stage.The NMR T2 spectrum can be used to characterize the fullsized pore structure characteristics of shale.By combining N2 adsorption pore structure parameters and NMR T2 spectrums,the surface relaxivity of samples are calculated to be between 1.7877 um/s and 5.2272 um/s.On this basis,the T2 spectrums are converted to full-sized pore volume and surface area distribution curves.The statistics show that the pore volume is mainly provided by mesopore,followed by micropore,and the average percentages are 65.04%and 30.83%respectively;the surface area is mainly provided by micropore,followed by mesopore,and the average percentages are 60.8004%and 39.137%respectively;macropore contributes little to pore volume and surface area.The pore structure characteristics of shale have no relationship with TOC,but strong relationships with clay minerals content.NMR fractal dimensions Dmicro and Dmeso have strong positive relationships with the N2 adsorption fractal dimensions D1 and D2 respectively,indicating that Dmicro can be used to characterize the fractal characteristics of pore surface,and Dmeso can be used to characterize the fractal characteristics of pore structure.The shale surface relaxivity is controlled by multiple factors.The increasing of clay mineral content,pore surface area,pore surface fractal dimension and the decreasing of average pore size,will all lead to the decreasing of shale surface relaxivity.

Geological conditions and reservoir characteristics of various shales in major shalehosted regions of China

China is home to shales of three facies:Marine shale,continental shale,and marine-continental transitional shale.Different types of shale gas are associated with significantly different formation conditions and major controlling factors.This study compared the geological characteristics of various shales and analyzed the influences of different parameters on the formation and accumulation of shale gas.In general,shales in China’s several regions exhibit high total organic carbon(TOC)contents,which lays a sound material basis for shale gas generation.Marine strata generally show high degrees of thermal evolution.In contrast,continental shales manifest low degrees of thermal evolution,necessitating focusing on areas with relatively high degrees of thermal evolution in the process of shale gas surveys for these shales.The shales of the Wufeng and Silurian formations constitute the most favorable shale gas reservoirs since they exhibit the highest porosity among the three types of shales.These shales are followed by those in the Niutitang and Longtan formations.In contrast,the shales of the Doushantuo,Yanchang,and Qingshankou formations manifest low porosities.Furthermore,the shales of the Wufeng and Longmaxi formations exhibit high brittle mineral contents.Despite a low siliceous mineral content,the shales of the Doushantuo Formation feature a high carbonate mineral content,which can increase the shales’brittleness to some extent.For marine-continental transitional shales,where thin interbeds of tight sandstone with unequal thicknesses are generally found,it is recommended that fracturing combined with drainage of multiple sets of lithologic strata should be employed to enhance their shale gas production.

Preliminary Estimation of Paleoproductivity via TOC and Habitat Types:Which Method Is More Reliable?—A Case Study on the Ordovician-Silurian Transitional Black Shales of the Upper Yangtze Platform, South China

New total organic carbon （TOC） data from the two Ordovician-Silurian transitional graptolite-bearing black shale intervals, the Wufeng （五峰） Formation and the Longmaxi （龙马溪） Formation in Central Guizhou （贵州） and West Hubei （湖北）, respectively, as well as previously reported TOC data from the same intervals in other places on the Yangtze platform of South China, have been used to produce an initial estimate of the primary paleoproductivity via a conventional inverse method （i.e., Rpp.inverse）. The values of the Rpp.inverse are estimated to be 32 （43-21） gC/（m^2·a）（Wufeng Formation） and 21 （27-16） gC/（m^2·a） （Longmaxi Formation）. Also, simultaneously, the habitat types （i.e., HT; cf., BA： benthic assemblage） and their temporal and spatial changes have been documented from the same succession, and an initial estimate of the primary paleoproductivity has been produced using a forward method （i.e., Rpp-forward） Beingbounded mainly by the peritidal to inner-shelf environment shelly-facies or mixed-facies successions with BA1 to BA3 faunas both at the top and the base, which indicates the habitat types from HT Ⅱ to HT Ⅲ2, the biohabitat type of the two graptolite-bearing black shale intervals can be limited to HT III to HT IV, corresponding to the inner shelf to the outer shelf, with depths from roughly 60 m to 200-300 m. Based on the current data from the South China Sea and the southern part of the East China Sea, values of Rpp-forward should be about 100 to 400 gC/（m^2·a）. The difference in the results via the two methods suggests that paleoproductivity estimates from the geological strata need to be made cautiously, with particular attention paid to the paleogeographic setting, oxic-anoxic conditions, as also the preservation factor of organic carbon.

Porosity model and pore evolution of transitional shales:an example from the Southern North China Basin

The evolution of shale reservoirs is mainly related to two functions:mechanical compaction controlled by ground stress and chemical compaction controlled by thermal effect.Thermal simulation experiments were conducted to simulate the chemical compaction of marine-continental transitional shale,and X-ray diffraction(XRD),CO2 adsorption,N2 adsorption and high-pressure mercury injection(MIP)were then used to characterize shale diagenesis and porosity.Moreover,simulations of mechanical compaction adhering to mathematical models were performed,and a shale compaction model was proposed considering clay content and kaolinite proportions.The advantage of this model is that the change in shale compressibility,which is caused by the transformation of clay minerals during thermal evolution,may be considered.The combination of the thermal simulation and compaction model may depict the interactions between chemical and mechanical compaction.Such interactions may then express the pore evolution of shale in actual conditions of formation.Accordingly,the obtained results demonstrated that shales having low kaolinite possess higher porosity at the same burial depth and clay mineral content,proving that other clay minerals such as illite-smectite mixed layers(I/S)and illite are conducive to the development of pores.Shales possessing a high clay mineral content have a higher porosity in shallow layers(<3500 m)and a lower porosity in deep layers(>3500 m).Both the amount and location of the increase in porosity differ at different geothermal gradients.High geothermal gradients favor the preservation of high porosity in shale at an appropriate Ro.The pore evolution of the marine-continental transitional shale is divided into five stages.Stage 2 possesses an Ro of 1.0%-1.6%and has high porosity along with a high specific surface area.Stage 3 has an Ro of 1.6%-2.0%and contains a higher porosity with a low specific surface area.Finally,Stage 4 has an Ro of 2.0%-2.9%with a low porosity and high specific surface area.

Favorable lithofacies types and genesis of marine- continental transitional black shale: A case study of Permian Shanxi Formation in the eastern margin of Ordos Basin, NW China

Based on core description,thin section identification,X-ray diffraction analysis,scanning electron microscopy,low-temperature gas adsorption and high-pressure mercury intrusion porosimetry,the shale lithofacies of Shan23 sub-member of Permian Shanxi Formation in the east margin of Ordos Basin was systematically analyzed in this study.The Shan23 sub-member has six lithofacies,namely,low TOC clay shale(C-L),low TOC siliceous shale(S-L),medium TOC siliceous shale(S-M),medium TOC hybrid shale(M-M),high TOC siliceous shale(S-H),and high TOC clay shale(C-H).Among them,S-H is the best lithofacies,S-M and M-M are the second best.The C-L and C-H lithofacies,mainly found in the upper part of Shan23 sub-member,generally developed in tide-dominated delta facies;the S-L,S-M,S-H and M-M shales occurring in the lower part of Shan23 sub-member developed in tide-dominated estuarine bay facies.The S-H,S-M and M-M shales have good pore struc-ture and largely organic matter pores and mineral interparticle pores,including interlayer pore in clay minerals,pyrite inter-crystalline pore,and mineral dissolution pore.C-L and S-L shales have mainly mineral interparticle pores and clay mineral in-terlayer pores,and a small amount of organic matter pores,showing poorer pore structure.The C-H shale has organic mi-cro-pores and a small number of interlayer fissures of clay minerals,showing good micro-pore structure,and poor meso-pore and macro-pore structure.The formation of favorable lithofacies is jointly controlled by depositional environment and diagen-esis.Shallow bay-lagoon depositional environment is conducive to the formation of type II2 kerogen which can produce a large number of organic cellular pores.Besides,the rich biogenic silica is conducive to the preservation of primary pores and en-hances the fracability of the shale reservoir.

Influence of structural damage on evaluation of microscopic pore structure in marine continental transitional shale of the Southern North China Basin:A method based on the low-temperature N2 adsorption experiment

Structural damage from sample preparation processes such as cutting and polishing may change the pore structure of rocks.However,changes in pore structure caused by this structural damage from crushing and its effect on marine continental transitional shale have not been well documented.The changes of microscopic pore structure in marine continental transitional shale during the sample preparation have important research value for subsequent exploration and development of shale gas.In this study,the pore structures of transitional shale samples from the Shanxi-Taiyuan Formation of the Southern North China Basin under different degrees of damage were analyzed through low-temperature N;adsorption experiments,combined with X-ray diffraction,total organic carbon,vitrinite reflectance analysis,and scanning electron microscopy.The results showed that(1)With increasing structural damage,the specific surface area(SSA)changed within relatively tight bounds,while the pore volume(PV)varied significantly,and the growth rate(maximum)exhibited a certain critical value with the crushing mesh number increasing from 20 to 200.(2)The ratio of SSA to PV can be used as a potential proxy for evaluating the influence of changes in the pore structure.(3)Correlation analysis revealed that the microscopic pore structure of marine continental transitional shale from the Shanxi-Taiyuan Formations is mainly controlled by organic matter and clay minerals.Clay minerals play a leading role in the development of microscopic pores and changes in pore structure.

Discovery of Marine-terrestrial Transitional Facies Shale Gas in Taiyuan Formation of Zhenjia 1 Well,Northern Shaanxi,Ordos basin

Objective At present, there is controversy regarding the existence of marine-terrestrial transitional facies that can act as a source of shale gas. This detailed study of Carboniferous-Permian age geological data from the northern Shaanxi area （China） provides new insight for this type of shale gas. In addition, a new deposition and accumulation pattern for this type of shale gas is established.

Geological characteristics and development potential of transitional shale gas in the east margin of the Ordos Basin,NW China

The shales in the 2nd Member of Shanxi formation in the east margin of the Ordos Basin were deposited in a marine-nonmarine transitional environment during the Permian.Based on the recent breakthroughs in the shale gas exploration and theoretical understandings on the shale gas of the study area,with a comparison to marine shale gas in the Sichuan Basin and marine-nonmarine transitional shale gas in the U.S.,this study presents the geological characteristics and development potential of marine-nonmarine transitional gas in the study area.Four geological features are identified in the 2nd Member of the Shanxi Formation in the study area has:(1)stable sedimentary environment is conductive to deposition of widely distributed organic shale;(2)well-developed micro-and nanoscale pore and fracture systems,providing good storage capacity;(3)high content of brittle minerals such as quartz,leading to effectively reservoir fracturing;and(4)moderate reservoir pressure and relatively high gas content,allowing efficient development of shale gas.The 2nd Member of Shanxi Formation in the east margin of Ordos Basin is rich in shale gas resource.Three favorable zones,Yulin-Linxian,Shiloubei-Daning-Jixian,and Hancheng-Huangling are developed,with a total area of 1.28×104 km2 and resources between 1.8×1012 and 2.9×1012m3,indicating a huge exploration potential.Tests of the 2nd Member of Shanxi Formation in vertical wells show that the favorable intervals have stable gas production and high reserves controlled by single well,good recoverability and fracability.This shale interval has sufficient energy,stable production capacity,and good development prospects,as evidenced by systematic well testing.The east margin of the Ordos Basin has several shale intervals in the Shanxi and Taiyuan formations,and several coal seams interbedded,so collaborative production of different types of natural gas in different intervals can be considered.The study results can provide reference for shale gas exploration and development and promote the rapid exploitation of shale gas in China.

Fine-grained gravity flow sedimentation and its influence on development of shale oil sweet sections in lacustrine basins in China

The geological conditions and processes of fine-grained gravity flow sedimentation in continental lacustrine basins in China are analyzed to construct the model of fine-grained gravity flow sedimentation in lacustrine basin,reveal the development laws of fine-grained deposits and source-reservoir,and identify the sweet sections of shale oil.The results show that fine-grained gravity flow is one of the important sedimentary processes in deep lake environment,and it can transport fine-grained clasts and organic matter in shallow water to deep lake,forming sweet sections and high-quality source rocks of shale oil.Fine-grained gravity flow deposits in deep waters of lacustrine basins in China are mainly fine-grained high-density flow,fine-grained turbidity flow(including surge-like turbidity flow and fine-grained hyperpycnal flow),fine-grained viscous flow(including fine-grained debris flow and mud flow),and fine-grained transitional flow deposits.The distribution of fine-grained gravity flow deposits in the warm and humid unbalanced lacustrine basins are controlled by lake-level fluctuation,flooding events,and lakebed paleogeomorphology.During the lake-level rise,fine-grained hyperpycnal flow caused by flooding formed fine-grained channel–levee–lobe system in the flat area of the deep lake.During the lake-level fall,the sublacustrine fan system represented by unconfined channel was developed in the flexural slope breaks and sedimentary slopes of depressed lacustrine basins,and in the steep slopes of faulted lacustrine basins;the sublacustrine fan system with confined or unconfined channel was developed on the gentle slopes and in axial direction of faulted lacustrine basins,with fine-grained gravity flow deposits possibly existing in the lower fan.Within the fourth-order sequences,transgression might lead to organic-rich shale and fine-grained hyperpycnal flow deposits,while regression might cause fine-grained high-density flow,surge-like turbidity flow,fine-grained debris flow,mud flow,and fine-grained transitional flow deposits.Since the Permian,in the shale strata of lacustrine basins in China,multiple transgression-regression cycles of fourth-order sequences have formed multiple source-reservoir assemblages.Diverse fine-grained gravity flow sedimentation processes have created sweet sections of thin siltstone consisting of fine-grained high-density flow,fine-grained hyperpycnal flow and surge-like turbidity flow deposits,sweet sections with interbeds of mudstone and siltstone formed by fine-grained transitional flows,and sweet sections of shale containing silty and muddy clasts and with horizontal bedding formed by fine-grained debris flow and mud flow.The model of fine-grained gravity flow sedimentation in lacustrine basin is significant for the scientific evaluation of sweet shale oil reservoir and organic-rich source rock.

Geological characterization and exploration potential of shale gas in the Carboniferous Jiusi Formation,northern Guizhou and Yunnan provinces,SW China

Dark mudstones and shales of the Carboniferous Jiusi Formation are widely developed in northern Guizhou and Yunnan provinces, SW China. However, the distribution, reservoir characterization, and exploration potential of organic-rich shales in this area are yet to be quantified, thus limiting the prospect of shale gas in this area. This study investigates the basic geological conditions of Jiusi shale gas, using core data, well-logs, and some other test data, obtaining the following results. The organic-rich shales are mainly composed of deltaic-to-shallow-shelf deposits, with thickness ranging from 0 to 450 m, and above 350 m around the subsidence center. The organic matter is mainly type Ⅱ kerogen with TOC content of mostly 1%–2%, indicating a moderate maturity. The argillaceous shale reservoirs are indicative of strong heterogeneity, high clay minerals content, low porosity, low permeability, high specific surface area, and relatively developed secondary porosity. The gas-log anomaly intervals obtained from the survey wells have a cumulative thickness that is apparently greater than 200 m, and a few shale intervals showing high desorbed and adsorbed gas contents. Due to complex structures in the study area, conditions responsible for shale gas occurrence and trapping are generally moderate. However, areas having wide and gentle folds with moderate depth of burial reveals relatively favorable conditions of hydrocarbon traps. In contrast with typical marine-continental transitional shales, the Jiusi shale have better geological conditions for shale gas preservation. The analysis of the geological framework and hydrocarbon potential of Carboniferous Jiusi Formation provide more insight for the exploration of Carboniferous shale gas in southern China.

Favorable lithofacies and pore characteristics of the Permian Longtan Formation shale in the southern Sichuan Basin

The marine–continental transitional shale (MCTS) reservoirs of the Longtan Formation (LTF) are widely distributed in the Sichuan Basin. However, the LTF shale exhibits considerable variations in mineral composition and pore characteristics, which makes identifying the 'sweet spot'a challenging task. To address this issue, 10 samples from four typical shale gas wells in the LTF in the southern Sichuan Basin were selected and analyzed for total organic carbon (TOC) content, whole-rock composition using X-ray diffraction (XRD), low-pressure gas adsorption, and high-pressure mercury intrusion. The lithofacies distribution and pore structure of the MCTS were studied to determine the pore structural characteristics and the primary factors influencing pore formation in different types of shale lithofacies in the LTF. The lithofacies of the LTF shale in the study area can be classified into three categories: siliceous clay shale, clay shale and mixed shale. Mineral content has a significant impact on the pore characteristics, while TOC content has a minor effect on the pore volume and specific surface area of micropores and mesopores. It can be inferred that the mesopores in the MCTS are mainly related to clay mineral pores, and mineral dissolution and TOC content are not the primary factors contributing to pore formation.

碳中和目标下中国天然气工业进展、挑战及对策

天然气在21世纪中叶将迈入“鼎盛期”,“天然气时代”正在到来。回顾全球天然气工业历程,梳理美国页岩革命启示,总结中国天然气发展历史与成果进展,分析天然气在能源绿色低碳转型中的地位与挑战,提出当前和未来中国天然气工业的发展对策。中国天然气工业经历了起步、增长、跨越3个发展阶段,已成为世界第4大天然气生产国与第3大消费国;天然气勘探开发理论技术取得重大成就,为储量产量规模增长提供了重要支撑。碳中和目标下,推动绿色可持续发展,天然气工业发展挑战与机遇并存。天然气低碳优势显著,“气电调峰”助力新能源发展;同时,开采难度与成本加大等问题更突出。为保障国家能源安全,实现经济社会与生态环境和谐共生,碳中和进程中,立足“统筹布局、科技创新;多能互补、多元融合;灵活高效、优化升级”,完善产供储销体系建设,加速推动天然气工业发展:①加大天然气勘探开发力度,规划部署重点勘探开发领域,突破关键理论,强化技术攻关,持续支撑增储上产;②推进天然气绿色创新发展,突破新技术,拓展新领域,融合新能源;③优化天然气供需转型升级,加大管道气、液化天然气布局和地下储气库建设,建立储备体系,提升应急调节能力和天然气一次能源消费比例,助力能源消费结构转型,实现资源利用低碳化、能源消费清洁化。

渝东南复杂构造区常压页岩气地球物理勘探实践及攻关方向

中国南方常压页岩气资源潜力大,主要分布于四川盆地周缘构造复杂区及盆外褶皱带,具有地表、地下双复杂地质条件,地震采集品质差、成像精度低、甜点参数变化规律不清。本文系统总结了渝东南地区常压页岩气地震采集、成像处理、储层预测等方面的研究成果与技术进展:①形成了变密度三维观测系统设计技术、灰岩地表复杂山地地震激发接收技术,确保复杂地下构造反射波场充分采样,提升采集资料品质,提高施工效率。②完善了复杂山地地震叠前预处理技术、盆缘过渡带复杂构造成像技术、盆外褶皱带向斜构造成像技术,成果剖面信噪比高,有效频带宽,构造成像精度高。③基于岩石物理特征研究,实现优质页岩厚度、地层压力系数、脆性的定量预测;基于统计岩石物理,实现页岩有机碳含量、含气量、孔隙度的定量预测;利用有限元应力场模拟技术,揭示古应力场演化,实现多期构造改造叠加作用形成裂缝的定量预测;采用组合弹簧模型今应力场预测技术,明确今地应力场分布规律。通过攻关研究,有效指导了常压页岩气甜点预测与勘探开发,为南川常压页岩气田的发现提供了依据。下步应重点攻关基于5G无线节点接收的更加科学合理的地震采集技术、复杂山地高陡构造高精度自动化成像处理技术,以及“地质—工程—经济”一体化的甜点地震评价方法。

海陆过渡相页岩孔隙结构表征及页岩气渗流规律模拟

鄂尔多斯盆地大宁-吉县区块海陆过渡相页岩储层非均质性强,碳质页岩和纯页岩的孔隙结构特征及页岩气渗流规律具有明显的差异,然而目前针对不同岩性孔隙结构下的页岩气渗流规律研究较为缺乏。文中以这2种岩性页岩为研究对象,基于CT扫描、扫描电镜物理实验技术,测定了二者的基质孔隙和层理缝特征参数,对比了二者的孔隙结构差异,构建了考虑吸附效应和滑脱效应的格子玻尔兹曼数值模拟方法,分析了二者孔隙结构对页岩气渗流规律的影响。研究结果表明:1)碳质页岩裂缝呈空间网状结构,纯页岩裂缝为平行层理方向裂缝。与纯页岩相比,碳质页岩孔隙尺度较大,但孔隙数量较少,孔隙度更低。2)页岩孔隙中存在明显的滑脱效应。滑脱效应提高了气相流动速度,页岩气从孔隙壁面解吸减缓了孔隙压力降低速率,延长了生产时间。建议在开发纯页岩层段时,适当降低生产压差,增强小孔隙中的滑脱效应;在开发碳质页岩层段时,适当增加生产压差,通过解吸作用提高页岩气产量。

海陆过渡相页岩储层合层开采数值模拟研究

由于沉积环境的不同,海陆过渡相页岩与海相页岩存在较大差异。基于鄂尔多斯盆地东缘海陆过渡相页岩储层的特点,建立了纵向多岩性叠置储层水平井产能数值模型,分析了不同岩性组合模式下的气井单段生产动态特征,研究了煤层渗透率、储层叠置关系等关键参数以及生产制度对生产特征的影响。研究结果表明:①富煤型页岩储层合层开采初期气水同产,采出气主要来自砂岩和页岩储层的游离气,采出水主要来自压裂液及煤层水。煤层的渗透率越高,合层开采的累计产气量越大,累计产水量也随之提升。②含煤叠置组合类型进行合层开采最理想的空间叠置顺序为页—砂—煤,在该叠置顺序下,煤层产水对合层开采干扰最小。③煤层产气量受应力敏感的影响最大。

A Well Productivity Model for Multi-Layered Marine and Continental Transitional Reservoirs with Complex Fracture Networks

Using the typical characteristics of multi-layered marine and continental transitional gas reservoirs as a basis,a model is developed to predict the related well production rate.This model relies on the fractal theory of tortuous capillary bundles and can take into account multiple gas flow mechanisms at the micrometer and nanometer scales,as well as the flow characteristics in different types of thin layers(tight sandstone gas,shale gas,and coalbed gas).Moreover,a source-sink function concept and a pressure drop superposition principle are utilized to introduce a coupled flow model in the reservoir.A semi-analytical solution for the production rate is obtained using a matrix iteration method.A specific well is selected for fitting dynamic production data,and the calculation results show that the tight sandstone has the highest gas production per unit thickness compared with the other types of reservoirs.Moreover,desorption and diffusion of coalbed gas and shale gas can significantly contribute to gas production,and the daily production of these two gases decreases rapidly with decreasing reservoir pressure.Interestingly,the gas production from fractures exhibits an approximately U-shaped distribution,indicating the need to optimize the spacing between clusters during hydraulic fracturing to reduce the area of overlapping fracture control.The coal matrix water saturation significantly affects the coalbed gas production,with higher water saturation leading to lower production.

鄂尔多斯盆地海陆过渡相页岩岩性组合特征及页岩气勘探潜力

中国海陆过渡相页岩气资源潜力大,是页岩气增储上产的重要接替领域,但海陆过渡相页岩沉积环境变化频繁,页岩、煤、砂岩以及石灰岩等岩性频繁互层,目前海陆过渡相页岩气勘探地质评价还处在初期阶段,有利页岩岩性组合及储层特征有待深入研究。为此,以鄂尔多斯盆地东南缘大吉区块下二叠统山西组二段三亚段(以下简称山23亚段)海陆过渡相页岩为研究对象,通过钻井岩心和野外露头观察,结合测井响应特征,划分了岩性组合类型,并基于扫描电镜、聚焦离子束扫描、气体吸附、高压压汞等实验技术手段,厘清了不同岩性组合页岩储层特征,明确了有利岩性组合类型和页岩气勘探意义。研究结果表明:①研究区山23亚段可划分为纯页岩型(S型)、富粉砂页岩型(SS型)、富砂页岩型(SSS型)以及富煤页岩型(CSS型)4种岩性组合类型;②S型组合页岩储层物性最优,总有机碳含量为6.87%,腐泥组含量可达50%,有机质类型兼具Ⅱ2型和Ⅲ型,含气性高,富含石英等脆性矿物,表现出“甜而脆”的特征;③S型组合页岩储集空间为有机孔+微裂缝,有机孔孔径介于10~300 nm,呈圆形或椭圆形;④山23亚段其余岩性组合页岩有机质类型为Ⅲ型,富含黏土矿物,有机孔发育程度低,微裂缝贡献对总孔隙体积最高为32%;⑤S型组合受海湾环境控制,海源与陆源的“双源”有机质以及非陆源石英等脆性矿物富集显著改善储层品质。结论认为,S型组合页岩具备连续型有效配置的烃源岩、储集层和聚集、保存的基础地质条件,且勘探开发实践已证实S型组合页岩是页岩气勘探开发的“黄金靶体”,并为下一步该区海陆过渡相页岩气的勘探指明了方向。

扬子地区奥陶纪—志留纪转折期多事件耦合关系及有机质富集

从地质事件的影响角度出发,讨论扬子地区奥陶纪—志留纪转折期多地质事件的耦合关系、地质事件的环境响应以及对富有机质页岩发育的影响。结果表明:构造运动增强的大陆硅酸盐风化作用以及火山事件增加的碳埋藏都导致大气CO_(2)浓度的下降,当达到阈值以下便引发赫南特冰期事件;火山喷发出的硫会在平流层形成硫酸盐气溶胶,增加反射率,促进冰期的发展;冰期增大纬度温度梯度,促进上升流的形成;冰期降温的突发性、水体硫化缺氧环境的扩张以及火山事件所输入的汞和砷等有毒重金属是导致晚奥陶世生物大灭绝事件(LOME)的主要机制;火山事件输入的火山灰和上升流给海洋表层带来大量营养元素,以及冰期海平面迅速下降期间导致溶解性无机磷酸盐(DIP)浓度的增加,增强海洋初级生产力,促进有机质的生产;大量有机质在沉降过程中消耗氧气导致深层形成最小含氧带(OMZ),火山灰快速吸收溶解氧以及冰期结束海平面快速上升都会导致水体缺氧条件的扩张,从而有利于有机质的保存;主要的沉积作用是悬浮沉积,但局部也因构造运动、水体变浅以及陆源输入增强等因素发育部分重力滑塌、浊流、碎屑流、风暴流沉积。