鄂尔多斯盆地西南部上古生界山西组一段古构造特征及其对油气的控制作用

Paleo-structure features in the 1st member of the Upper Paleozoic Shanxi Formation and its influences on gas accumulation in southwestern Ordos Basin

基于鄂尔多斯盆地西南部最新地震、地质资料和勘探成果,通过构造演化史分析和古构造恢复等手段,重点研究了鄂尔多斯盆地西南部上古生界山西组1段古构造特征,并分析了古构造对油气分布的控制作用。通过地层对比分析,明确了二叠系山1段的沉积-构造-沉降特征。构造演化史和成藏期次揭示,西南部上古生界构造-成藏关键变革期为侏罗纪末期和早白垩世末期。通过对不同构造演化阶段山1段古构造的恢复,认为三叠纪末期、侏罗纪末期和早白垩世末期上古生界山1段古构造具有继承性和迁移性。其中古隆起和古斜坡在侏罗纪末期发育广泛,西倾斜坡范围呈逐渐收窄趋势,天环坳陷形成于早白垩世末期。在构造变形与成藏期次分析的基础上,认为侏罗纪末期山1古构造可能是控制鄂尔多斯盆地西南部上古生界气藏分布的关键因素。研究区上古生界天然气缺乏长距离运移的条件,早白垩世末期的油气充注围绕着侏罗纪末期山1段的古构造进行,表现为近源或源内成藏。

Based on the latest seismic data,geological understanding and exploration results in the Southwestern Ordos Basin,paleo-deformation characteristics of the 1 st member of the Upper Paleozoic were studied using tectonic evolution analysis and paleo-structure restoration,and controlling effects of paleo-structure on hydrocarbon distribution were analyzed. According to the strata correlation,the sedimentary,deformation,and subsidence characteristics of the 1 st member of the Permian Shanxi Formation are identified. The tectonic evolution and hydrocarbon accumulation stages revealed that the key periods of the Upper Paleozoic tectono-hydrocarbon accumulation are the Late Jurassic and the end of the Early Cretaceous in the Southweste. Through the restoration of Shan 1 paleo-structure in different tectonic evolution stages,the ancient structure of the Upper Paleozoic Shan 1 in Late Triassic,Late Jurassic and end of Early Cretaceous share similarities but also demonstrate gradual evolution through time. The paleo-uplift and paleo-slope are widely developed in the late Jurassic,while the western slope gradually narrowed and the Tianhuan Depression is formed at the end of the Early Creta-ceous. Based on the analysis of tectonic deformation and hydrocarbon accumulation stages,it is believed that the Late Jurassic Shan 1 paleo-structure is the key factor controlling the distribution of the Upper Paleozoic gas reservoirs in the Southwest Ordos basin. Due to the lack of long-distance migration of the gas in the Upper Paleozoic reservoirs in the study area,the Early Cretaceous hydrocarbon charge is focused around the Late Jurassic ancient structure highs of Shan 1 member. Thus the hydrocarbon accumulation model is characterized by near-source or intra-source accumulation.