鄂尔多斯盆地东西部长6与长8致密砂岩埋藏成岩-烃类充注与成藏-储集性能时空演化过程研究

Diagenetic events and hydrocarbon filling characteristics, distribution and inter-relationship of their products in sandstones, origin, medium condition and physi-chemical environment of major cements will be investigated, and diagenetic-hydrocarbon filling evolution sequence will be builled up, based upon identification and quantitative statistics in sandstone thin sections under microscope, measurements of cathodeluminescence and fluorescence, scanning electron microscope, electron probe, analysis of carbon, oxygen and strontium isotope, temperature and chemical components of liqiud inclusions in cements, and measurement of porosity and permeability, capillary pressure, image pore throat and snadstone grain size. Spatial-temporal dynamic evolution history of burial diagenetic-hydrocarbon accumulation-pore evolution, and time-sequence of densification and hydrocarbon accumulation of Chang 6 and Chang 8 tight sandstones in the eastern and western Ordos basin is reconstructed, on the basis of recovery of parameters such as strata erosion thickness, paleotemperature and paleopressure, depth of paleo water, by means of temperature, pressure and component measurement of hydrocarbon-bearing liqiud inclusions in cements, via acoustic time lag, depositional velosity, vitrinite reflectance, ancient geothermal gradient method. Impact of depositional-tectonic setting, provanence and parent rocks on sandstone types, maturity of mineral components and textures of sandstones and on diagenetic route, and its return resulted in different types of cements and medium condition and physi-chemical environment, thus pores, pore throat and reservoir quality differentiation of tight sandstones in the eastern and western Ordos basin will be discussed. Research resut is of great significance theoretically and realistically in understanding tectonic setting evolution and orogenic mountain- basin coupling process occurred in periphery of Ordos basin, diagenetic evolution process and hydrocarbon accumulation effect occurred in dynamic setting of tectonic evolution, deposition- -burial thermal -hydrocarbon migration and emplacement history, relationship between sandstone densification and hydrocarbon accumulation occurred in inner basin, and in promoting exploration and development in unconventional oil and gas resources both in Ordos basin and in other basins in China.

利用镜下鉴定、阴极发光与荧光、扫描电镜、电子探针、碳、氧、锶同位素及包体温压及成分等分析测试手段，查明鄂尔多斯盆地东西部长6、长8砂岩成岩事件与烃类充注及其产物的分布特征及相互关系，主要胶结物的成因及物理化学条件，建立砂岩的成岩-烃类充注演化序列。通过含烃包裹体温压与成分、声波时差、沉积速率等方法，恢复长6与长8地层剥蚀厚度、古温压等参数，结合埋藏－热史、烃类充注史模拟，重塑东西部长6砂岩、长8砂岩的埋藏成岩-成藏－孔隙时空动力学演化历史，以及砂岩致密化过程与成藏时序。探讨东西部延长组沉积构造背景、源区母岩性质对砂岩类型及成岩路径，以及储层沉积-埋藏成岩-烃类充注与成藏过程对孔隙演化与储集性能影响之差异。该研究对鄂尔多斯盆缘构造演化与山-盆耦合过程，和以盆地沉积构造-埋藏热演化-烃类充注史等动力学背景下的成岩演化过程与成藏效应的深入理解，推动非常规油气资源的勘探开发具有重要的理论与现实意义

碎屑锆石U-Pb定年等物源示踪与盆-山耦合过程的沉积响应研究结果显示，盆地西南部源区位置、构造转换发生在长8与长7沉积之间。长8期物源主要来自西部阿拉善地块和祁连造山带单一物源；长7期除来自与长8相同的西部物源外，南部秦岭造山带以火成岩为主的物质开始向盆内输入；长6沉积期秦岭造山带较年轻母岩成分的物质逐渐增加，此外盆地东部与东北部物源也开始向盆内提供充填物质。其沉积响应特征直接反映在长8、长7、长6沉积体系、相序组合、砂岩类型等的规律性时空分布特征方面。.长6、长7、长8储层主体均经历了早、晚2期明显的油气充注。早期油气充注（180～140Ma）对应于早成岩阶段B期，半成熟-低成熟烃类充注,范围广但充注强度较小。晚期油气充注（130～100Ma）对应于中成岩阶段A期，大量成熟烃类充注，规模和强度较大，是长6、长7、长8储层油气主成藏期。.受矿物成分的制约，各砂岩经历了差异性成岩作用与成岩-烃类充注演化过程，其成岩演化路径、油气侵位效果、致密化进程与成岩演化序列存在差异。高塑性岩屑砂岩经过早成岩阶段的强烈压实作用（约115~110Ma）后，大部分孔隙已丧失或丧失殆尽，成为低孔低渗储层、部分变为致密储层，含油性差，多数只经历了第1期油气充注，压实作用是导致其低渗与致密的主要原因。因此，第1期油气充注与高塑性岩屑砂岩致密化过程是边充注边致密。钙质胶结砂岩经历早成岩~中成岩早期（约135~130Ma）碳酸盐胶结作用之后孔隙基本丧失殆尽，成为致密储层。但后期发育次生溶孔者可见少量油气侵入，为先致密后成藏。含油砂岩经历了2期油气充注，早成岩B期~中成岩A期的压实作用（约170~100Ma）、浊沸石（约160~100Ma）与/或亮晶方解石胶结作用（约160~130Ma）是导致其低渗和致密的主要原因，与第1期油气的关系是先充注后致密，与第2期油气的关系是先致密后充注。

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