苏里格气田下二叠统盒8段异常低压成因及其分布特征

苏里格气田下二叠统下石盒子组8段（盒8段）异常低压明显，但对其成因未达成共识。为此，统计分析了该区盒8段53口井的实测地层压力，发现产水层、产气层以及气水同产层的地层压力系数在垂向上均无明显变化规律，而在平面上呈南北向的条带状分布，形成多个异常低压系统。应用Fick气体扩散定律和盆地模拟技术，结合区域沉积、构造演化和天然气组成特征分析认为，盒8段河道砂体分布的局限性为异常地层压力的形成提供了必要封闭条件，天然气扩散作用虽然存在，但是扩散损失影响相对较小。盒8段异常低压的形成主要与晚白垩世以来的构造抬升、地层剥蚀以及构造热事件的消失有关。

Causes and distribution of abnormal low pressure in the 8th member of the Lower Permian Shihezi Formation in the Sulige Gas Field

The 8th member of the Lower Permian Shihezi Formation in the Sulige Gas Field is unusually low in formation pressure. However, the causes of low pressure are not clear. Therefore, the measured formation pressures of this interval in 53 wells are analyzed. The findings indicate that vertically, formation pressure coefficients of water producing layers, gas producing layers and water gas co producing layers show no obvious changing patterns, but laterally, they are in banded distribution, forming several abnormal low pressure systems. Based on an analysis of regional sedimentation, structural evolution and gas components, the Fick gas diffusion law and basin modeling techniques are used to study the causes of abnormal low pressure. It is believed that the limited distribution of channel sands in this interval provides necessary sealing conditions for the abnormal low pressure, and the influences of diffusion loss are relatively small though gas diffusion does exist. The abnormal low pressure in the studied interval is mainly caused by the post Cretaceous structural uplifting, erosion and tectonic thermal events.