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.

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.

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.

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.

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。

四川盆地东缘寒武系盐下油气勘探领域探讨

地球物理资料显示四川盆地东缘齐岳山附近寒武系高台组膏盐岩层下深部存在逆冲构造,其形成过程以及油气地质意义未见深入研究。笔者等综合四川盆地东部石柱地区线束三维和建南地区二维地震反射资料,并结合钻井资料以及区域地质研究成果,从构造继承性的角度探讨四川盆地震旦系灯影组台缘带类型,并分析了川东地区寒武系盐下油气圈闭特征。研究获得如下认识:①川东齐岳山北段构造变形强烈,普遍发育基底卷入构造,构造样式受青白口纪—南华纪裂谷与转换带构造位置的控制。②依据构造继承关系将盆内灯影组台缘带划分为德阳—安岳地区原生型台缘带、万源—达州地区继承型台缘带以及石柱地区继承—改造型台缘带。③依据青白口纪—南华纪裂谷的分布和后期构造作用影响大小,认为沿齐岳山向南至南川一带存在与石柱地区相似的灯影组继承—改造型台缘带,忠县、南川以西存在灯影组继承型台缘带。④研究区新元古界—下寒武统烃源岩、灯影组—龙王庙组滩相白云岩储层与寒武系膏盐岩层系构成完整的生储盖组合。⑤寒武系盐下基底逆冲可形成成排、成带的构造,与灯影组继承—改造型台缘带、龙王庙组滩相白云岩储层配置,形成断层相关的构造—岩性圈闭带,成为川东地区油气规模聚集有利区。研究认为四川盆地东部石柱地区震旦纪—早寒武世早期继承了青白口纪—南华纪裂谷构造特征,燕山期构造反转,高台组盐下形成基底卷入逆冲构造,具备生储盖等基本石油地质条件,具有重要的油气勘探现实意义。

川东地区中寒武统高台组蒸发岩特征和沉积模式

为明确川东地区中寒武统高台组蒸发岩特征与发育模式,综合野外观察、岩心描述、薄片鉴定、测井及地震资料,在对高台组蒸发岩的岩性及成因类型进行分析的基础上,讨论其沉积模式以及与油气的关系。研究结果表明:1)蒸发岩主要为含膏白云岩类、石膏岩和膏盐岩,存在清水和浑水两种蒸发岩岩性组合序列,蒸发岩厚度具有由西向东逐渐增厚的特点,沉积中心分别位于建深1井区—巫溪一线和太和1井区—石柱一线,蒸发岩盖层以“宽广圆环状”覆盖川东大部分地区;2)蒸发岩在干旱炎热的古环境、障壁滩形成的封闭环境、海水的周期性波动以及物源补给的共同作用下形成清水潟湖和浑水潟湖,即源控多潟湖成因环境;3)高台组蒸发岩厚度与龙王庙组储层的分布存在一定的负相关关系,即厚层蒸发岩控低含气储层,薄层蒸发岩控高含气储层;4)蒸发岩为盖层的储盖组合包括浑水潟湖成因的岩下储层和清水潟湖成因的岩间储层,薄层蒸发岩岩下储层含气规模较大,岩间储层的非均质性较强,厚度较薄,总体上呈中—低孔低渗的特征,研究区发育3个天然气有利勘探区带,分别位于北部、中部以及南部地区,是川东地区潜在的后备勘探领域。

四川盆地东部下寒武统有效烃源岩与有利油气聚集区预测

为了评价四川盆地东部震旦系—下寒武统天然气勘探前景,在区域沉积--构造背景分析基础上,利用实测烃源岩总有机碳含量(TOC)、测井和二维地震数据,预测了下寒武统有效烃源岩;综合分析中三叠世末震旦系顶面古构造和下寒武统生烃中心分布,预测了有利油气聚集区。研究结果表明:晚震旦世至早寒武世强烈的沉积--构造分异导致在中上扬子地区形成台内断陷/裂陷槽、台内凹陷和台内凸起;四川盆地东部主要位于台内凸起,有效烃源岩厚度为50~150 m;习水—南川—石柱一带厚度小于30 m,有效烃源岩发育较差;平面上围绕四川盆地东部发育4个由裂陷槽和台内凹陷控制的烃源岩厚度中心及其对应的生烃中心,能够为震旦系—下寒武统提供充足的油气;四川盆地东部天然气勘探前景较好,川中古隆起及其围斜区是有利油气聚集区。

川东地区茅口组储层特征及主控因素

为阐明川东地区茅口组储层特征,厘清储层发育的主控因素,基于野外露头、钻井岩心以及大量测井资料,开展了川东地区茅口组储层特征研究。结果表明:1)亮晶颗粒灰岩、颗粒云岩与细—中晶白云岩为川东地区茅口组主要储集岩;2)溶洞与裂缝在石灰岩和白云岩中均有发育,孔隙主要分布于细—中晶白云岩中;3)茅口组储层主要分布于茅二a,b亚段,平面上受到颗粒滩及断裂带的控制;4)颗粒岩为茅口组储层提供了物质基础,是形成储层的最重要因素,断裂系统决定了储层的最终分布,表生期岩溶以及白云石化作用形成了大量储集空间,是改善储层质量的关键。研究认为,邻水—丰都一带沿15#基底断裂分布的茅二a,b亚段地层中的颗粒滩可以作为重点勘探开发目标。

川东地区中二叠统茅口组沉积微相与环境演变——以重庆市武隆区羊角剖面为例

近年来,川东地区中二叠统茅口组持续发现工业气流,研究该区域茅口组的沉积微相与环境演化对油气勘探具有重要意义。以重庆市武隆区羊角剖面为研究对象,在野外沉积特征观察的基础上,通过岩石薄片鉴定及地球化学分析,研究了沉积微相及该地区茅口组的沉积环境演化特征。研究表明羊角剖面茅口组主要发育5种沉积微相。茅口组下部主要为含生物碎屑泥晶灰岩和泥晶灰岩沉积微相,是水体能量低的较深水环境下的沉积产物。茅口组中部以亮晶生物碎屑灰岩、泥晶生物碎屑灰岩、生物碎屑泥晶灰岩和生物碎屑泥晶灰岩为主,亮晶生物碎屑灰岩的出现表明高能的沉积环境,水体较浅。茅口组上部以泥晶生物碎屑灰岩、生物碎屑泥晶灰岩和含生物碎屑微晶灰岩为主,此时水体再次变深。茅口组下部δ^(13)C_(carb)值较低,平均3.00‰,中-上部δ^(13)C_(carb)值主要在4.00‰以上。显示茅口组一段为缺氧环境,随后氧化性增强转换成贫氧环境,茅口组沉积晚期再次回到缺氧环境。川东地区茅口组沉积微相特征及海平面变化受冰期影响,全球海平面下降是沉积环境转变的主控因素,浅水沉积环境是高能颗粒滩发育的有利地质条件,高能滩发育是川东地区茅口组中-上部优质储层形成的主要原因。

川东—川北地区二叠系茅口组沉积演化及其油气地质意义

近年来,四川盆地二叠系茅口组的勘探思路和布井原则由原来的“占高点、沿长轴”转变为以寻找滩相孔隙型规模储层为目标,并取得了新突破,使其成为了勘探热点层系,这就需要详细的沉积演化研究来支撑。川东—川北地区是茅口组构造—沉积分异最为明显,也是勘探潜力较大的区域。对茅口组386口钻井的测井资料进行系统梳理,并利用野外剖面和钻井取心进行沉积相分析,结合测井曲线与沉积相,分析研究区茅口组的沉积演化。研究认为,川东—川北地区茅口组一段到茅口组二下亚段总体为碳酸盐缓坡,地层厚度和沉积相总体受川中古隆起的影响,局部发育低能滩;茅二上亚段到茅三段转变为具有镶边性质的碳酸盐台地,地层厚度和沉积相带展布转变为北西—南东向,自西向东依次发育台地相、台缘带、斜坡和陆棚相,台缘带发育高能滩相。研究区茅口组沉积期相对海平面总体经历了两次升降过程,对应地层分别为茅一段到茅二下亚段和茅二上亚段到茅三段。受区域海平面升降、区域构造活动以及碳酸盐台地类型的控制,茅一段到茅二下亚段缓坡发育具有岩溶和云化的滩相储层;茅二上亚段到茅三段海槽内发育潜在烃源岩,是非常规油气勘探潜在有利区,而海槽西侧则发育具重要勘探价值的规模性台缘带高能滩。

下川东震旦系气井复杂处理技术实践与认识——以YT1井为例

为了安全有效开发四川盆地下川东地区震旦系气藏,保障川渝地区天然气能源的有效接替,需对震旦系气井的开发难点进行研究,解决易发生的故障复杂。以中国石油西南油气田公司重点探井YT1井为研究对象,分析了该井面临的地层多压力系统、压力系统窗口大、井漏严重、井壁易缩径等地质难点,从井身结构、堵漏技术、防溢流技术、防塌技术等方面开展复杂处理技术研究。研究结果表明:①优化井身结构为五开非标结构,能有效封隔必封点;②大井眼段下侏罗统自流井组—上二叠统龙潭组综合应用随钻堵漏、复合堵漏、水泥堵漏技术,可有效提升堵漏成功率,降低复杂时率;③241.3 mm井眼奥陶系十字铺组—上寒武统洗象池组优化钻具组合,综合治理溢、漏、塌等复杂,可有效提升作业效率。结论认为:①沙溪庙—凉高山地层采用空气/雾化钻进未发生故障复杂,防漏、提速效果显著;②龙潭组—下寒武统筇竹寺组地层优选“水力振荡器+复合钻头+MWD定向”技术,23趟钻完成3150.94 m长段膏盐层井段定向作业;③190 mm井眼开展185 mm双向微扩眼器试验,解决了长段膏盐层缩径问题,三次扩眼后下套管顺利到位;④通过复杂防控技术集成应用,YT1井复杂时率降低至17.47%,避免了恶性卡钻;⑤推广应用下川东地区震旦系气藏复杂防控技术对川渝地区后续震旦系气藏深井技术研究具有指导意义。

川东地区三叠系嘉陵江组邻水-丰都台凹的发现及油气勘探意义

地质历史时期的构造-沉积分异作用对大型含油气盆地内碳酸盐岩层系的沉积充填过程及成藏地质条件具有重要影响。通过覆盖全区的二维地震及钻测井资料,对川东地区三叠系嘉陵江组沉积时期隆凹格局及古地理演化进行了精细刻画。研究结果表明:(1)从地震剖面、地层及岩性组合等特征上识别出邻水-丰都台凹,其两侧坡度为1°~2°,且左侧坡度大于右侧坡度;(2)邻水-丰都台凹与其他古地质单元共同控制了嘉二段沉积时期川东地区的古地理格局及构造-沉积分异特征,嘉二段沉积早—中期,颗粒滩沿邻水-丰都台凹周缘发育,晚期台凹内则大面积发育膏质潟湖沉积;(3)邻水-丰都台凹及周缘微古地貌控制沉积早期颗粒滩分布,台凹周缘地貌高部位更易形成优质白云岩储层,持续干旱、蒸发环境致使沉积晚期台凹内形成区域盖层沉积;(4)总体来看,嘉二段具备良好的成藏地质条件,有望成为寻找滩相整装气藏的战略勘探层系,建议将邻水-丰都台凹周缘台内滩相发育带作为川东地区嘉陵江组下步勘探重点区之一。