西湖凹陷西斜坡W构造异常高压特征及对油气成藏的影响

Overpressure Features and Its Influences on Hydrocarbon Accumulation in the W Structure of West Slope of Xihu Sag

李斌 杨鹏程 蒋彦 陈现 李倩 李喆

LI Bin YANG Pengcheng JIANG Yan CHEN Xian LI Qian LI Zhe

中石化海洋石油工程有限公司上海物探分公司，上海　201208 中国石油化工股份有限公司上海海洋油气分公司勘探开发研究院，上海　200120

Shanghai Geophysical Branch, SINOPEC Offshore Oilfield Services Corporation Ltd., Shanghai 201208, China Institute of Exploration and Development, SINOPEC Shanghai Offshore Oil & Gas Company, Shanghai 200120, China

根据钻井、测井及分析化验资料对西湖凹陷西斜坡W构造的超压特征进行了分析，明确了超压封存箱的分布以及超压的成因，并通过超压封存箱内烃源岩热演化、储层成岩特征以及油气运聚特征的研究，总结了超压对油气成藏的影响。研究表明W构造超压封存箱主要分布在平下段，厚度为200～550 m，泥岩超压在全区广泛分布，储层超压仅分布在中块和南块，压力系数最高1.5。通过测井曲线综合分析、声波速度-密度交会图两种方法，结合地质背景确定W构造泥岩异常高压的成因主要为欠压实，也有生烃增压的贡献。储层超压主要是传递增压，有来自三潭深凹的远源超压传递。超压对油气成藏的影响主要表现为：超压抑制烃源岩干酪根热降解，拓宽生油窗；超压抑制储层压实，促进胶结作用及溶蚀作用；超压提供运移动力，超压封存箱内可以形成大型岩性油气藏。

Overpressure feature was analyzed based on drilling data, logging data and analysis assay data in the W structure of west slope of Xihu Sag, distribution of overpressure compartment and origin of overpressure were clarified, the influences on hydrocarbon accumulation were summarized by studying the thermal evolution of hydrocarbon source rock in overpressure compartment, characteristics of reservoir diagenesis, and features of hydrocarbon migration and accumulation. The results show that the overpressure compartment was mainly distributed in lower member of Pinghu Formation with the thickness of 200～550 m. The mudstone overpressure system was widely distributed in W structure while the reservoir overpressure system was only distributed in the central and south parts of study area with a maximum pressure coefficient of 1.5. Origin of mudstone overpressure was mainly determined as disequilibrium compaction and hydrocarbon-generating pressurization by log data analyses, acoustic velocity-density plots, and geological background analysis. Origin of reservoir overpressure was mainly determined as pressure transmission, which could be from Santan Sub-sag. The influences of overpressure on hydrocarbon accumulation are mainly manifested as: overpressure inhibits kerogen thermal degradation in source rocks and widens oil generation window; overpressure inhibits reservoir compaction, promoted reservoir cementation and reservoir dissolution; overpressure provides migration forces of oil and gas and large lithologic reservoirs can be formed in overpressure compartment.

https://doi.org/10.3969/j.issn.1008-2336.2021.02.011