首页|四川盆地川中—川西过渡带中侏罗统沙溪庙组致密砂岩相对优质储层成因机制

四川盆地川中—川西过渡带中侏罗统沙溪庙组致密砂岩相对优质储层成因机制

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川中—川西过渡带沙溪庙组天然气勘探潜力巨大,是四川盆地近几年勘探的热点.目前,制约沙溪庙组致密砂岩天然气勘探开发的问题较多,其中,"相对优质储层"的形成机理和综合预测是亟需解决的关键问题之一.针对这一科学问题,本次研究通过系统的物性分析、铸体薄片鉴定、扫描电镜分析以及储层地球化学分析等,开展了研究区沙溪庙组相对优质储层成因机制研究.研究结果表明:沙溪庙组致密砂岩以岩屑长石砂岩和长石岩屑砂岩为主.沙二段砂岩石英平均体积分数为35.27%,长石平均体积分数为35.37%,岩屑平均体积分数为29.36%,沙一段砂岩石英平均体积分数为37.79%,长石平均体积分数为24.01%,岩屑平均体积分数为38.20%,沙一段长石体积分数较高,沙二段岩屑体积分数较高.沙二段以变质岩岩屑为主(占岩屑体积分数的55%),沙一段则以岩浆岩岩屑为主(占岩屑体积分数的43%).储层孔隙类型以原生孔为主,长石溶蚀孔为辅,沙一段具有相对更高比例的原生孔和裂隙孔.沙二段砂岩中38.00%的样品孔隙度大于12%,25.25%的样品渗透率大于1 ×10-3μm2,沙一段砂岩仅3.09%的样品孔隙度大于12%,但41.22%的样品渗透率大于1 ×10-3μm2.总体表现为致密背景下发育一定的相对优质储层.其中沙二段储层孔隙度发育较好,而沙一段储层渗透性更佳,说明沙一段储层孔隙结构相对较好.沙溪庙组致密砂岩储层发育受控于岩矿组合-烃源体系-成岩系统.岩矿组合为成岩作用的演化提供物质基础,烃源体系决定溶蚀作用发育的强度,并为砂岩中主要自生矿物的沉淀提供必要的离子来源;成岩系统的开放程度则决定了体系内外离子的带进带出,进而影响了溶蚀作用和相应成岩产物的沉淀.沙二和沙一段砂岩岩矿组合的差异、沉积环境的不同、烃源体系以及成岩系统的开放程度是导致其成岩作用差异的主要原因.综上认为,高能沉积环境、早期保持性成岩作用(孔隙衬垫绿泥石)、多期次和多种类型的溶蚀作用以及局部微裂缝的发育改造,是研究区沙溪庙组相对优质储层发育的主要机制.
Genetic Mechanism of Relatively High-Quality Reservoirs of Middle Jurassic Shaximiao Formation Tight Sandstone in Transition Zone Between Central and Western Sichuan Basin
The Shaximiao Formation in the transition zone between the central and western Sichuan basin has great potential for natural gas exploration,which has become a hot spot of exploration in Sichuan basin in recent years.At present,there are many aspects restricting the exploration and development of tight sandstone natural gas in the Shaximiao Formation.The formation mechanism and synthesized prediction of"relatively high-quality reservoirs"are one of the key issues that need to be resolved urgently.In this paper,a series of analysis methods were performed,including systematic physical property analysis,blue-dye thin section identification,scanning electron microscopy analysis,and reservoir geochemical analysis,to determine the genetic mechanism of relatively high-quality reservoirs in the Shaximiao Formation.The results indicate that the tight Shaximiao sandstones are dominated by lithic feldspar sandstone and feldspar lithic sandstone.The average volume fraction of quartz,feldspar,and rock debris in the Second Member of the Shaximiao Formation(SMSF)are 35.27%,35.37%,and 29.36%respectively.The average volume fraction of quartz,feldspar,and rock debris in the First Member of the Shaximiao Formation(FMSM)are 37.79%,24.01%,and 38.20%respectively.The volume fraction of feldspar is relatively high compared to the FMSM,and the volume fraction of rock debris is relatively high compared to the SMSF.In terms of type and content of lithic fragments,sandstones in the SMSF are dominated by metamorphic fragments,accounting for 55%of the whole lithic fragments.By contrast,those in the FMSF are dominated by magmatic fragments,making up to 43%of the whole lithic fragments.In addition,the reservoir pore system is predominately composed of primary pores followed by feldspar dissolution pores,in which the FMSF is characterized by a higher content of those pores than the SMSF.In the SMSF,samples with porosity above 12%account for 38.00%,but with permeability above 1×10-3μm2 account for 25.25%.Those values in the FMSF are 3.09%and 41.22%,respectively.It is generally reflected that some relatively high-quality reservoirs tend to be developed under a tight background.The fact,that the SMSF reservoir is characterized by better porosity and the FMSF has better permeability,demonstrates that the pore structure of the FMSF reservoir is relatively better.Besides,The tight sandstone reservoir in Shaximiao Formation is controlled by litho-mineral association,hydrocarbon source system and diagenetic system.The litho-mineral association provided a material basis for the diagenetic evolution.The hydrocarbon source system controlled the dissolution intensity,and provided ions for main authigenic minerals precipitation in sandstone.The opening degree of the diagenetic system had an effect on the ions'in-and-out,and affected the dissolution and precipitation of the diagenetic products.The difference of litho-mineral association,variation of sedimentary environment,hydrocarbon source system and opening degree of diagenetic system in SMSF and FMSF are the main reasons for the differential diagenesis.

transition zone between the central and western Sichuan basinShaximiao Formationtight sandstonerelatively high-quality reservoirsgenetic mechanismSichuan basin

宋林珂、刘四兵、曾青高、周栋、唐大海、王锦西

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中国石油西南油气田公司致密油气勘探开发项目部,成都 610059

油气藏地质及开发工程国家重点实验室(成都理工大学),成都 610059

川中—川西过渡带 沙溪庙组 致密砂岩 相对优质储层 成因机制 四川盆地

国家自然科学基金

41972158

2024

吉林大学学报(地球科学版)
吉林大学

吉林大学学报(地球科学版)

CSTPCD北大核心
影响因子:1.062
ISSN:1671-5888
年,卷(期):2024.54(2)
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