伊-陕斜坡山2段包裹体古流体势恢复及天然气聚集条件

Using Fluid Inclusion Thermodynamic Modeling to Study Paleo-Fluid Potential and Natural Gas Migration and Accumulation of the No.2 Member of Shanxi Formation of the Upper Paleozoic in Yi-Shaan Slope,Ordos Basin

恢复自烃类生成以来的各个地史时期的古流体势,有助于正确认识油气藏的分布规律.通过对鄂尔多斯盆地伊-陕斜坡太原组—山西组砂岩储层流体包裹体样品的系统分析,将其油气充注划分为6个期次;结合埋藏史分析,确定出6期油气充注发生的时间.在此基础上,运用流体包裹体pVT热动力学模拟的方法,获得了6期油气充注的古压力数据,并计算出伊-陕斜坡山2段6期次天然气充注的古气势,分析了古气势分布及时空演化规律,认为区域构造和热史演化是其主要控制因素.结合区域地质资料,探讨了天然气运移与聚集规律:晚三叠世中期至中侏罗世末期,山2段储层气势西南高而北部、东北部低,天然气主要从西南向北、东北向运移;中侏罗世末期至早白垩世末期,气势西高东低,天然气主要由西向东就近运移,再向北和东北向运移;早白垩世末至现今,天然气藏进入聚集与散失的动平衡状态,形成现今分布特征.榆林及其南部地区是天然气聚集的最有利地带,其次为神木-米脂地区.

Reconstruction of paleo-fluid potential during each geological period after hydrocarbon generation may be helpful to clearly recognize the hydrocarbon reservoir distribution. In this research, the samples including reservoir fluid from Taiyuan and Shanxi formations of the Upper Paleozoic in Yi-Shaan slope, Ordos basin were obtained, and the systematic analysis of the sample was used to measure the homogenization temperature for all orders of fluid inclusions mainly in trails, salinity for aqueous inclusions and the fluorescence colors for hydrocarbon inclusions. The result indicates that there are six period times of hydrocarbon charging in the sandstone reservoirs, and the gas charging is statistically dominating. By integrating the average homogenization temperatures with burial historical curves, the six charging times are determined. By employing the fluid inclusion pVT thermodynamic modeling, the paleo-formation pressure of these six times of hydrocarbon charging is ob tained, and the six periods of paleo-gas potential of No. 2 member of Shanxi Formation of the Upper Paleozoic in Yi-Shaan slope are calculated, and the paleo-gas potential distribution and evolution are depicted, and the evolution of regional tectonics and geothermal history are found out to be the main controlling factors. According to the regional geological conditions, the law of the nature gas migration and accumulation of No. 2 member of Shanxi Formation of the Upper Paleozoic in YiShaan slope is discussed. From the middle Late Triassic to the late Middle Jurassic, the natural gas mainly migrated from southwest to north, northeast, because the paleo-gas potential in the southwest zone was higher than that in the north and northeast zones from the late Middle Jurassic to the late Early Cretaceous, the paleo-gas potential in the west zone was higher than that in the east zone and the natural gas migrated eastward and then northeastward; after that, the natural gas accumulation is in equilibrium with dissipation, which results in today＇s distribution features. The Yulin zone and the southern zone of Yulin have the most important significance to the exploration of the No. 2 member of Shanxi Formation of the Upper Paleozoic in Yi-Shaan slope, and secondly to the Shenmu Mizhi zone.