Natural gas characteristics and gas-source comparisons of the Lower Triassic Feixianguan Formation,Eastern Sichuan Basin,China

There is great controversy regarding the origin and source of natural gas in the Lower Triassic Feix-ianguan Formation in the Eastern Sichuan Basin.This seriously restricts the study of natural gas dy-namics in the Feixianguan Formation and thus hampers natural gas exploration in the region,so further study is urgently required.Using experimental tests of natural gas composition,stable isotopes,and noble gas isotopes with gas chromatography(GC)and mass spectrometry(MS)studies of source rock and reservoir asphalt saturated hydrocarbons,the natural gas geochemical characteristics,the genetic identification and a gas-source comparison of the Feixianguan Formation were studied.Then,con-strained by the thermal history,the histories of gas generation and expulsion were restored by basin simulation technology.Finally,a gas accumulation model was established for the Feixianguan Formation.The results showed that(1)the H_(2)S-rich and H2S-poor gas reservoirs of the Feixianguan Formation are distributed on the east and west sides of the Kaijiang-Liangping trough in the Eastern Sichuan Basin,respectively.The carbon and hydrogen isotope compositions of the natural gas in the gas reservoirs are generally heavy and have typical characteristics of high-maturity dry gas reservoirs.(2)The natural gas of the Feixianguan Formation is organic thermogenic gas,which is mainly oil-type gas generated by the secondary cracking of crude oil.The gas-generating parent material is mainly type II kerogen.(3)The natural gas of the Feixianguan Formation in the Eastern Sichuan Basin was mainly generated by argil-laceous source rocks of the Upper Permian Longtan Formation.(4)Natural gas accumulation occurred as follows:the paleo-structure heights were filled with crude oil in the Early Jurassic,and paleo-oil res-ervoirs were formed in the Feixianguan Formation;during the Middle-Late Jurassic,the paleo-oil res-ervoirs were cracked when the reservoir temperatures rose above 160 C,and paleo-gas reservoirs were formed.Since the end of the Late Jurassic,the paleo-gas reservoirs have been adjusted and reformed to form the present-day natural gas reservoirs.These results provide a basis for studying natural gas accumulation dynamics of the Feixianguan Formation in the Eastern Sichuan Basin.

Superimposed hydrocarbon accumulation through multi-source and multi-stage evolution in the Cambrian Xixiangchi Group of eastern Sichuan Basin:A case study of the Pingqiao gas-bearing anticline

The Xixiangchi Group in eastern Sichuan Basin has great potential for natural gas exploration.However,there is a lack of in-depth studies of the hydrocarbon sources and the formation and evolution of gas reservoirs in this Group.Systematic investigation about the gas reservoir in Pingqiao anticline was consequently carried out in terms of characteristics of reservoir bitumen,the geochemical characteristics of natural gas,diagenetic minerals,and fluid inclusions.Based on this,combined with the reconstruction of the burial history,thermal evolution history and uplifting history of strata,and analysis of the regional tectonic settings,the hydrocarbon sources were identified and the formation and evolutionary processes of the gas reservoirs in Xixiangchi Group was revealed in this study.It was shown that the gas reservoirs have mixed gas sources from the shale source rocks in the Lower Cambrian Qiongzhusi Formation and in the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation,and experienced several evolutionary stages,including the paleo-oil reservoir stage from the Late Siliurian to the Middle Permian,the paleo-gas reservoir stage from the Late Permian to the Early Cretaceous,and the superimposed accumulation and mixed-source gas reservoir stage since the Late Cretaceous.The mixed-source gas reservoir is formed by the adjustment of the Xixiangchi Group paleo-gas reservoirs and depressurization of the overpressure Wufeng-Longmaxi shale gas reservoirs and the charging of gas into the Xixiangchi Group reservoir of the Pingqiao anticline since the Late Cretaceous,which show obvious superimposed accumulation characteristics.There are different accumulation patterns in different geological periods.The accumulation pattern of the“old source-young reservoir”(i.e.hydrocarbons generated from older source rocks accumulating in younger reservoirs)dominates before the Late Cretaceous,and that of“juxtaposed young source-old reservoir”(i.e.hydrocarbons generated from younger source rocks accumulating in juxtaposed older reservoirs)dominates after the Early Cretaceous.Moreover,faults acted as critical vertical pathways for hydrocarbon migration during the evolution of the Xixiangchi Group gas reservoirs.This model provides new insights and theoretical basis for evaluation and mapping of the Xixiangchi Group play fairway in eastern Sichuan Basin.

Structural Analysis of the Multi-layer Detachment Folding in Eastern Sichuan Province

A serial of＂comb-like and trough-like＂folds developed in eastern Sichuan,controlled by the multi-layer detachment folding,is different from the classical Jura-type structure in their development.The key factor resulting in the development of these structures is the occurrence of detachment layers in different parts of Neoprotozoic to Mesozoic stratigraphy of study area,which, from the bottom to the top,are the lower part of Banxi Group,Lower Cambrian（Niutitang Formation）,Lower Silurian（Longmaxi Formation and Luoreping Formation）,Upper Permian （Wujiaping Formation） and Lower Triassic（Daye Formation）.On the basis of field survey combined with sand-box modeling,this study argued that the detachment layer of the lower part of Banxi Group controlled the development of the＂comb-like＂folds,and the lower part of Cambrian detachment layer controlled the development of＂trough-like＂folds.Because of several detachment layers occurring in the study area,the development of duplex structures different scales is an important deformation mechanism,and the duplexes are the important structures distinguished from the typical detachment folding structures.Due to these duplexes,the surface structures and structural highs may not be the structural highs in the depth.Meanwhile,the detachment layers are good channels for oil/ gas migration benefiting the understanding of accumulation and migration of oil and gas.

Geochemical characteristics and diagenetic systems of dolomite reservoirs of the Changxing Formation in the eastern Sichuan Basin, China

In order to discuss the relationship between dolomite reservoirs and diagenetic systems of the Changxing Formation, we studied carbon, oxygen and strontium stable isotopes, iron, manganese and strontium trace elements and the Mg/Ca （mol%） ratio, dolomite order degree, and determined that burial dolomitization is the key to controlling the distribution of high quality dolomite reservoir in the Changxing Formation in the eastern Sichuan Basin. The dolomite of the Changxing Formation is divided into four diagenetic systems： （1） penecontemporaneous stage syngenetic brine diagenetic system, （2） early diagenetic stage strata seal brine diagenetic system, （3） middle-late diagenetic stage mixed hot brine diagenetic system and （4） tectonic uplift stage mixed hydrothermal fluid diagenetic system. New understanding of the controlling factors and distribution of dolomite reservoir development is discussed. Reef shoal facies belts controlled regional reservoir distribution and the scale of development. Burial dolomitization of a strata seal brine diagenetic system is the foundation of reservoir development, mainly developing pore reservoir. Burial dolomitization of mixed hot brine diagenetic system expanded the reservoir distribution and improved the reservoir quality, mainly developing pore-vug reservoir. Fracturing and dissolution of a mixed hydrothermal fluid diagenetic system is the key to improving the reservoir quality, mainly developing pore-vug-crack complex reservoirs.

Depositional System of the Carboniferous Huanglong Formation,Eastern Sichuan Basin:Constraints from Sedimentology and Geochemistry

Using analyses of the lithology,sequences,paleoenvironment,and tectonic setting,the depositional system of the Carboniferous Huanglong Formation in the eastern Sichuan Basin was identified.The lithological characteristics of the Lower Member,Middle Member,and Upper Member were analyzed and classified.Before the use of carbon,oxygen,and strontium isotopes in the analysis,all of the geochemical data were tested for validity.On the basis of the Z values obtained from carbon and oxygen isotopes,the paleoenvironments of the three members were elucidated.Lower Member was dominantly an enclosed marine environment with intense evaporation and little freshwater input into the sea.Middle Member developed in a semi-enclosed to normal marine environment with many rivers.Upper Member was formed in a normal marine environment.The east Sichuan Basin was enclosed by paleouplifts before the deposition of the Huanglong Formation,forming a relatively enclosed depositional setting.Paleogullies developed in the Silurian strata that underlie the Carboniferous rocks;these paleogullies can be identified.On the basis of a comprehensive analysis,we propose that the Huanglong Formation developed in a platform system.Four microfacies were identified：supratidal flat,dolostone flat,grain shoal,and shelf microfacies.The high-permeability and high-porosity characteristics of the grain shoal microfacies are favorable for hydrocarbon accumulation,while the supratidal flat and shelf microfacies developed very few high-quality reservoirs.The paleogullies,in which increased amounts of grain shoal microfacies developed,controlled the distribution of high-quality reservoirs.

Nanoscale Pore Characteristics of the Upper Permian Mudrocks from a Transitional Environment in and around Eastern Sichuan Basin, China

Nanoscale pore characteristics of the Upper Permian Longtan transitional mudrocks and their equivalent strata Wujiaping Formation marine mudrocks in and around the eastern Sichuan Basin was investigated using field emission scanning electron microscopy(FE-SEM)and low-pressure N2 adsorption experiments.The results indicate that the Upper Permian mudrock is at a mature stage with total organic carbon(TOC)values ranging between 0.47%and 12.3%.The Longtan mudrocks mainly contain vitrinite,and their mineral composition is primarily clay.In contrast,the Wujiaping mudrocks are dominated by sapropelinite and solid bitumen,and their mineral compositions are mainly quartz and a notably high amount of pyrite.The FE-SEM reveals that clay mineral pores and microcracks are the common pore types in the Longtan mudrocks.The specific surface area and pore volume depend on the clay content but are negatively correlated with the TOC.The generation of nanometer pores in the Longtan mudrocks is caused by high clay mineral contents.Meanwhile,the Wujiaping mudrock mainly contains OM pores,and the pore parameters are positively correlated with the TOC.The OM pore development exhibits remarkable differences in the Longtan and Wujiaping mudrocks,which might be related to their sedimentary facies and maceral fractions.Vitrinite and inertinite appear as discrete particles in these mudrocks and cannot generate pores during thermal maturation.Sapropelinite often contains many secondary pores,and solid bitumen with large particles,usually with several pores,is not the major contributor to the pore system of the investigated mudrock.

Study on the Quality Characteristics of Gas Field Water in Eastern Sichuan

Gas field water is the formation water produced together with natural gas in the process of natural gas exploitation.The gas field water treated is difficult to reach the standard due to its wide sources,numerous types and complex composition.In addition,it can pollute soil,surface water and groundwater.In this study,the quality and pollution characteristics of gas field water in eastern Sichuan were studied by conventional water quality determination and GC-MS.The results show that the main components of gas field water in eastern Sichuan were chloride,COD Cr,SS,anionic surfactant,sulfide and other substances.The gas field water could be divided into two types according to the characteristics of water quality,of which one had high mineralization and high organic compounds,and the other had high sulfur and high organic compounds.There were 17 kinds of organic pollutants in the gas field water,mainly including alkanes,alcohols,esters and a small amount of acids.

The Origin of Paleokarst in the Huanglong Formation of the Eastern Sichuan Basin:Evidence from δ^(13)C, δ^(18)O and ^(87)Sr/^(86)Sr

Karst rocks from the Huanglong Formation exposed at the margin of the Eastern Sichuan Basin can be divided into four types：slightly corroded, moderately corroded porous, intensely corroded brecciated and intensely corroded and replaced secondary calcic karstic rocks. The carbon, oxygen and strontium isotope compositions of the various karst rocks are analyzed systematically and compared to rocks without karst corrosion. The results indicate that（1） the Huanglong Formation in the eastern Sichuan Basin was a restricted bay supplied and controlled by freshwater in which mudmicrite and mud-dolomicrite exhibit low δ13C and δ18O values and high 87Sr/86 Sr ratios;（2） all types of karstic rocks in the paleokarst reservoirs of the Huanglong Formation in the research area are affected by atmospheric freshwater with the δ13C and δ18O values and 87Sr/86 Sr ratios in the original formation approaching those of atmospheric freshwater, which reflects ancient hydrological conditions, fluid properties, isotopic source and the fractionation effect;（3） the intensely corroded and replaced secondary limestone is affected by a variety of diagenetic fluids, often reflected by δ13C and δ18O values, while the 87Sr/86 Sr ratios exhibit the strong degree of the corrosion;（4） after comparing the 87Sr/86 Sr ratios of each type of karst rock, the diagenetic fluids are determined to be mainly atmospheric freshwater, and depending on the strength of corrosion, and the low 87Sr/86 Sr ratio fluids in the layer will participate in the karst process. The carbon, oxygen, and strontium isotopes of different karstic reservoirs can provide meaningful geochemical information for forecasting and evaluating the development and distribution rules of the Huanglong Formation at the margin of the eastern Sichuan Basin in time and space.

Four Citiesin Eastern Sichuan

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Carbon isotopic composition of Early Triassic marine carbonates, Eastern Sichuan Basin, China

As the interval following the biggest Phanerozoic mass extinction at the end of Permian, the Early Triassic is characterized by an immature, poorly functioned ecosystem.The effects of these extreme environmental conditions can be mirrored by the changes in the δ13C record of marine carbonates.However, the details about the carbon isotopic composition and evolution of the Early Triassic seawater remain poorly understood.A dataset of new δ13C and δ18O values as well as selected major and trace element data (including concentrations of CaO, MgO, Mn, and Sr) was obtained from 113 marine carbonate samples collected in Eastern Sichuan Basin.The isotopic and elemental data are used to evaluate effects of thermochemical sulfate reduction on δ13C.The δ13C values of a few samples affected by thermochemical sulfate reduction were corrected.By combining carbonate δ13C results in our investigated sections, we constructed a composite curve of the Lower Triassic.The results reveal a δ13C anomaly of carbonate rocks throughout the Early Triassic, accompanied by some rapid jumps and falls, such as those from approximately -2‰ to the extremely high value of 8‰ within a period of about 5 Ma.The Early Triassic δ13C profile derived from Eastern Sichuan Basin shows a close correspondence with Guandao section in Guizhou Province, whereas it yields an excursion pattern differing from Chaohu section in Anhui Province of the Lower Yangtze region (with the δ13C value from the minimum around -6‰ to the maximum near 4‰).The higher δ13C values and the positive carbon isotope excursions in the Lower Triassic from Eastern Sichuan Basin were most likely a consequence of the principal environmental change that may include: (1) the barren land surface due to the absence of vegetation, (2) the loss of diverse marine invertebrate groups and marine carbonates, (3) the thriving of bacteria, algae and methanogenus in ocean ecosystems, and (4) the local effect of the repositories of isotopically light carbon occurred in the form of methane hydrates.This process ended at the Early-Middle Triassic boundary, which indicates that the biotic recovery started at the end of the Lower Triassic.The terrestrial vegetation and marine invertebrates, as the regulators for carbon cycle, are irreplaceable and demand strong protections.

Evolution and global correlation for strontium isotopic composition of marine Triassic from Huaying Mountains,eastern Sichuan,China

Strontium isotope stratigraphy (SIS) has progressively become an efficient chemostratigraphic tool in the research and correlation of global geological events, such as global sea level fluctuations, orogeny, and paleoclimatic and paleoenvironmental changes. In this paper, 87Sr/86Sr ratios of the Triassic marine carbonate rock samples from Huaying Mountains, eastern Sichuan are measured, and the corre-sponding Sr-isotopic curve is constructed, based on the fundamental principle of strontium isotope stratigraphy, analysis of rock fabric, luminescent intensity, chemical composition and representative evaluation for the coeval seawater information. The 87Sr/86Sr ratios show a rapid rise from 0.70721 near the Permian-Triassic transition to 0.70830 at the end of Early Triassic, and then they decline rapidly to 0.70787 in the early Middle Triassic. These data are generally coincident with 87Sr/86Sr ratios of coeval seawater from previous papers, and the curve is also similar to other previous curves. This indicates that the global geological events are the most important controlling factors to the strontium isotope evolution of the global seawater in the Early and Middle Triassic.

Origin and source of CO_2 in natural gas from the eastern Sichuan Basin

The CO2 contents of natural gas from the eastern Sichuan Basin were mainly less than 2%,and they were generally large when the H2S contents were over 5%.The natural gas in the eastern Sichuan Basin showed high δ13C1 values uncorrelated with H2S contents,and the oil-associated gas generally displayed carbon isotopic reversal between methane and ethane,whereas the coal-derived gas samples displayed positive series.The δ13C values of CO2 in the natural gas could be divided into two types,one with low values(-24‰--12‰)and the other with high values(-8‰-4‰).The natural gas had low R/Ra values and broad CO2/3He values distinct from the mantle-derived gas,and the CO2 was typical of crustal origin.Natural gas with high δ13CCO2 values is distributed in the north region of the eastern Sichuan Basin,and CO2 in H2S-poor and H2S-free reservoirs was mainly derived from the thermal decomposition of carbonate rocks under Permian magmatism and high heat flow,whereas CO2 in the gas reservoirs with high TSR extent was derived mainly from the dedolomitization of carbonate reservoirs under acidic formation water,and the CO2 of TSR origin generally entered into the secondary calcite.The CO2 in natural gas in the south-central region of the eastern Sichuan Basin,which had been rarely affected by the Emeishan mantle plume,displayed low δ13C values and was of organic origin.Though the natural gas in Wolonghe gas field had experienced TSR,the low reaction extent and weak acidity of formation water could hardly have resulted in the dedolomitization,and therefore CO2 in the natural gas was mainly of TSR origin with low δ13C values.

Paleoecological associations of middle Llandovery (Silurian) corals from Huaying Mountain, eastern Sichuan Province

Corals are comparatively abundant in the upper member of the Baiyun'an Formation (upper Aeronian to lowerest Telychian, Llandovery, Silurian) of Huaying, eastern Sichuan Province, Southwest China. Three coral associations have been recognized, i.e., in ascending order, the Mesofavosites Association, the Dentilasma Association, and the Paraceriaster Association. The Mesofavosites Association occurs at horizons indicating a shallow and high-energy environment. It is dominated by large favositids accompanied by a few broken pieces of halysitids and small solitary rugose corals. The Dentilasma Association has a pretty high coral diversity, dominated by the solitary rugose coral Dentilasma meitanense, together with some subordinative heliolitids and favositids. The sedimentary evidence shows that this association might live in a quiet and nutritive shallow water environment. The Paraceriaster Association yields in the grayish green calcareous mudstone indicating a comparatively deep water environment. Systematically it contains abundant fasciculate Paraceriaster micropora and a few favositids. The distinction among these three coral associations shows that corals could adopt different adaptive strategies under different environments, which provide some new data for the investigation on the ecology of Silurian corals and further study on the "Lower Red Beds".

Precise Location of Earthquakes at the Eastern Boundaries of the Sichuan-Yunnan Rhombic Block

Based on the seismic station data sets from Sichuan and Yunnan provinces,we employed a multi-step seismic location method( Hypo2000 + Velest + HypoDD) to precisely locate the 7,787 earthquakes that occurred during 2010-2015 along the eastern boundaries of the Sichuan-Yunnan rhombic block,namely from southern Dawu to the Qiaojia segment.The final results show that location precision is greatly advanced and epicenter distribution exhibits good consistency with the linear distribution of the seismic faults. Earthquake distribution is quite intensive at the intersection region in the southern segment of the Xianshuihe fault,the Anninghe fault zone,the Xiaojinhe fault zone and the Daliangshan fault zone to the east. The depth profile of seismicity shows a clear stepwise activity along the active seismic fault zones. The profile crossing the faults of the Xianshuihe,Anninghe,and Daliangshan presents a complex interaction among faults near the multiple faults intersection region,Shimian,where the earthquakes are obviously divided into two groups in depth. Earthquakes are very rare at the depth of 15km-20 km,which is consistent with the region of the plastic rheology between 14km-19 km calculated by Zhu Ailan et al.,( 2005).

川东地区侏罗系大安寨段页岩储层特征及发育控制因素

为探究陆相页岩储层特征及页岩储集空间发育的控制因素,文中以四川盆地东部大安寨段页岩为例,基于页岩岩心的分析化验资料,对页岩储层孔隙发育控制因素进行了研究,明确了优势岩相及甜点储层特征。研究结果表明:1)川东地区大安寨段页岩岩相类型包括硅质页岩、混合质页岩以及黏土质页岩,其中黏土质页岩总有机碳质量分数最高,其次为混合质页岩。2)页岩孔隙类型以片状黏土矿物晶间孔与有机质孔为主,裂缝以页理缝为主。3)页岩储集空间的发育主要受矿物组分、成岩作用以及构造因素的共同控制。4)基于页岩生烃潜力与储集能力,认为混合质页岩为大安寨段的优势页岩岩相。大安寨段页岩甜点储层段主要分布于大二亚段a小层,主要为混合质页岩与介壳灰岩的薄夹层。

川东地区龙潭组页岩岩性序列及勘探意义

川东地区龙潭组具有较大的页岩气勘探前景,该地层沉积于海陆过渡环境,沉积相变化快,岩性复杂,存在难以通过常规的矿物成分方法划分岩相以及当前岩相划分尚不精确的问题,制约了该地区龙潭组页岩有利岩相带识别及勘探。本文基于岩心观察、野外剖面实测和薄片鉴定,结合钻井的泥地比、单层岩性厚度,建立了川东地区龙潭组7种特征岩性组合模式(泥页岩型、富泥含砂型、富泥含灰型、灰泥互层型、富灰含泥型、致密灰岩型和火成岩型);综合TOC、孔隙度、含气性、脆性指数等页岩储层特征参数,明确了不同岩性组合在龙潭组各段的平面分布规律。研究表明,纵向上优势岩性组合主要为龙潭一段富泥含灰型和泥页岩型,龙潭二段主要为泥页岩型、灰泥互层型和富泥含灰型。平面上龙潭一段优势岩性组合富泥含灰型主要分布在开州—云阳一带,泥页岩型主要分布在重庆—綦江一带;龙潭二段优势岩性组合泥页岩型分布在巴南—綦江一带,灰泥互层型分布在达州一带,富泥含灰型分布在万州—梁平—石柱一带。该项研究成果为川东地区龙潭组页岩气勘探提供了重要依据。

川东红星地区二叠系茅口组页岩气勘探突破及富集主控因素

四川盆地二叠系页岩气具有良好的成藏条件和勘探潜力,继二叠系吴家坪组获得勘探突破后,将低勘探程度层系——茅口组“高灰”页岩气作为重要的勘探接替方向。利用HYM-1等井的岩心、测录井和分析化验资料,系统开展茅口组页岩气藏条件与富集特征的研究,认为茅口组四段一亚段页岩具有高碳、高灰、高孔隙度、高含气性、高杨氏模量、薄储层、多夹层的“五高一薄一多”的典型地质特征;与五峰组—龙马溪组等页岩相比,茅四段页岩碳酸盐矿物含量更高、黏土矿物含量更低,储集空间类型以有机质孔为主,无机孔较少,孔隙度平均4.27%,整体表现为高孔隙度;茅四段一亚段平均含气量为4.96m^(3)/t,具备较高的含气量。综合分析认为,富藻高碳页岩的发育、良好的储集能力和保存条件,以及页岩储层的可压裂性,是茅四段页岩气富集高产的主控因素。

四川盆地东部上石炭统黄龙组规模储层形成主控因素与发育模式

石炭系黄龙组是四川盆地东部地区(以下简称川东地区)重要的天然气产层之一,石炭系储层是控制气藏发育的关键因素。为了深入评价川东地区黄龙组储层,拓展勘探新领域,寻找接替区,在前人研究的基础上,应用大量钻井、岩心、露头和分析化验等资料,系统研究了黄龙组储层发育的主控因素和发育模式,并预测规模储层的展布。研究结果表明:(1)黄龙组储集岩主要为颗粒白云岩、角砾白云岩和晶粒白云岩,储集空间主要为晶间孔/晶间溶孔、粒间溶孔/粒内溶孔、溶洞和裂缝,颗粒滩为有利储集体,裂缝-溶蚀孔洞型储层质量好;(2)储层发育主要受乐山—龙女寺古隆起和开江古隆起、沉积作用及成岩作用的共同控制,古隆起控制颗粒滩分布和准同生期成岩作用,是规模成储的基础,准同生期白云石化作用、层间岩溶和风化壳岩溶作用的叠加是形成规模储层的关键,喜马拉雅构造运动产生大量构造裂缝,提高了储层的渗滤性和规模性;(3)一定厚度和较大面积的Ⅰ—Ⅲ类储层可形成规模储层区,对5个规模储层发育区进行了评价,已发现气藏主要分布在这5个区域的背斜构造部位。结论认为,川东地区石炭系仍有较大的天然气勘探开发潜力,向斜区发育大面积的规模储层,是下一步天然气增储上产的重要方向。

川东地区高陡构造带寒武系洗象池群天然气成藏条件

利用岩心、测井与地震资料,采用地震解释、平衡剖面以及包裹体检测等技术,恢复了川东地区高陡构造带的构造演化史,并对平桥、建南、梓里场构造的天然气来源、运聚与保存条件进行了分析。研究结果表明:(1)川东地区平桥断背斜圈闭东翼的单条逆断层使得下盘的龙马溪组烃源岩与上盘的洗象池群储层发生了侧向对接,天然气可穿过断裂带向上盘储层运移,具备较好的输导条件,且圈闭盖层未受到断裂作用破坏,保存条件良好,有利于天然气的聚集成藏。(2)建南断背斜圈闭翼部的多条平行的逆断层虽然实现了部分源-储对接,但是多条断层组合降低了其侧向输导能力,天然气未能大规模聚集。(3)梓里场断背斜圈闭的源-储配置与输导条件优良,但盖层的封盖能力较差,大多被断层破坏,钻探显示储层为水层。(4)川东地区高陡构造带寒武系洗象池群天然气聚集成藏的主控因素包括:断层或断层组合控制下的源-储配置、侧向输导条件以及盖层的封盖能力。

四川盆地东部地区早侏罗世湖泊古水深恢复

[目的]川东地区下侏罗统湖泊—三角洲沉积具有较大的勘探潜力,但基础地质研究的滞后制约了勘探进程,古水深恢复对川东地区下侏罗统岩相古地理恢复及页岩油气勘探具有重要指导意义。[方法]根据岩石类型、沉积构造和古生物化石分布特征,结合Fe/Mn比值、(Al+Fe)(/Ca+Mg)比值及干酪根类型对川东地区自流井组和凉高山组古水深变化趋势进行分析,并采用La-Co法、TOC法及Th/U比值法对早侏罗世古水深进行定量恢复。[结果与结论]沉积构造及古生物分布特征表明早侏罗世川东地区中部长期处于湖盆低洼位置,Fe/Mn比值和(Al+Fe)(/Ca+Mg)比值的变化趋势反映研究区东北部和南部为近岸浅水区。La-Co法、TOC法及Th/U比值法古水深恢复结果存在一定差异,La-Co法恢复的古水深与沉积相存在较大矛盾,Th/U比值法对浅湖沉积区古水深恢复较为可靠、但在滨湖及半深湖沉积区可靠度较低,而基于TOC法的古水深恢复结果最为可靠、与沉积相吻合度最高。早侏罗世川东地区湖泊浪基面约15 m,TOC法古水深恢复结果表明川东地区下侏罗统半深湖广泛发育,早侏罗世湖泊最大水深约60 m,广安—万州一带广泛发育半深湖—深湖沉积,有利于有机质的富集和保存,是页岩油气勘探的有利位置。