Zhang Fengqi, Chen Zhixiong, Zhao Zhenyu, Gao Jianrong, Fu Ling, Li Chengshan, Zhang Lanxin
College of Earth Sciences and Engineering, Xi'an Shiyou University, Xi'an 710065, China.
Shaanxi Key Laboratory of Petroleum Accumulation Geology, Xi'an Shiyou University, Xi'an 710065, China.
ACS Omega. 2023 May 31;8(23):20536-20549. doi: 10.1021/acsomega.3c00877. eCollection 2023 Jun 13.
The upper Paleozoic strata in the western part of the Ordos Basin have rich oil and gas resources but low exploration levels. These strata were subjected to multiple tectonic events, such as the Caledonian, Hercynian, Indosinian, and Himalayan movements, which led to a relatively complex process of hydrocarbon accumulation in the study area. These strata also have obvious structural segmentation in the north-south direction. However, the accumulation periods of the upper Paleozoic strata in different structural sections of the western Ordos Basin and their differences are poorly understood. A total of 65 sandstone samples from the upper Paleozoic reservoirs in 16 representative wells were selected for fluid inclusion analyses. The results of fluid inclusion analyses, combined with the burial-thermal histories of representative wells, were used to determine the hydrocarbon accumulation periods of the main layers and summarize their patterns in different structural regions and layers. The results show that the formation of fluid inclusions in the main upper Paleozoic strata can be divided into two stages. The first-stage inclusions mainly occur in secondary quartz edges, and the second-stage inclusions mainly occur in healed microcracks. The inclusion types are dominantly hydrocarbon-bearing, brine, and minor nonhydrocarbon gas inclusions. The hydrocarbon components are mostly CH and minor asphaltene, and the nonhydrocarbon gases are dominantly CO and minor SO. The homogenization temperatures of the brine inclusions associated with hydrocarbon inclusions in major layers in the study area have a wide distribution and multiple peaks; the main peaks in the central part of a given tectonic area are slightly lower than those in the eastern part, and the main peaks in a given location tend to increase with decreasing burial depth. Hydrocarbon accumulation in the upper Paleozoic strata in the study area mainly occurred in the Early and Middle Jurassic and Early Cretaceous. The Early and Middle Jurassic were the mature oil and gas accumulation periods, and the Early Cretaceous was the high-maturity natural gas accumulation period and the most critical accumulation period. The accumulation period in the central part of a given structural region occurred earlier than that in the eastern part, and the accumulation period in different layers in a given location gradually shifted at a later time from deep to shallow.
鄂尔多斯盆地西部上古生界地层油气资源丰富，但勘探程度较低。这些地层经历了加里东、海西、印支和喜马拉雅运动等多次构造事件，导致研究区油气成藏过程相对复杂。这些地层在南北方向上也具有明显的构造分段性。然而，鄂尔多斯盆地西部不同构造区上古生界地层的成藏期及其差异尚不清楚。从16口代表性井的上古生界储层中选取了65个砂岩样品进行流体包裹体分析。流体包裹体分析结果结合代表性井的埋藏热史，确定了主要层位的油气成藏期，并总结了其在不同构造区和层位的模式。结果表明，上古生界主要地层流体包裹体的形成可分为两个阶段。第一阶段包裹体主要出现在次生石英边缘，第二阶段包裹体主要出现在愈合微裂缝中。包裹体类型以含烃、盐水和少量非烃气包裹体为主。烃类组分以CH为主，少量沥青质，非烃气以CO为主，少量SO。研究区主要层位与烃类包裹体伴生的盐水包裹体均一温度分布较宽且有多个峰值；特定构造区中部的主峰略低于东部，特定位置的主峰随埋藏深度减小而趋于升高。研究区上古生界地层油气成藏主要发生在早、中侏罗世和早白垩世。早、中侏罗世是成熟油气成藏期，早白垩世是高成熟天然气成藏期且是最关键的成藏期。特定构造区中部的成藏期早于东部，特定位置不同层位的成藏期在后期逐渐由深到浅推移。
