异常高压对四川盆地龙马溪组页岩气藏的影响

四川盆地下志留统龙马溪组黑色页岩主要为浅海—深水陆棚相沉积，分布面积广，厚度大。龙马溪组页岩气高产层段地层压力均为异常高压，研究认为，欠压实增压、矿物成岩作用、构造挤压和有机质热演化增压，是造成该层异常高压的主要因素。异常高压对页岩气藏的影响，一方面，能够全面抑制烃源岩热演化，使生气镜质体反射率下限上移；另一方面，能减缓压实等成岩作用，使储集层保存相对较高的孔隙度和渗透率，并通过诱导有机酸的溶蚀和岩石有效应力的减小，形成次生孔隙和微裂缝，提高了储集层的渗流能力，但对压裂改造提出了更高的要求。此外，随着地层压力的增高，吸附气的含量也会随之增加，使得页岩气藏含气性更佳。总体来说，异常高压有利于页岩气的富集。

Influences of Abnormal High Pressure on Longmaxi Shale Gas Reservoir in Sichuan Basin

The Longmaxi black shales of the Early Silurian in Sichuan basin is mainly deposited in shallow-deep water shelf sedimentary environment, with big thickness and wide distribution. High-output intervals of the shale gas wells in Longmaxi formation are all in abnormal high pressure. The study suggests that undercompaction pressurization, minerals digenesis, tectonic compression and thermal evolution of organic matter are considered to be the main factors causing the abnormal high pressure. The abnormal high pressure has many effects on the shale gas reservoirs. Firstly, it can restrain the thermal evolution of source rocks, and raise vitrinite reflectance lower limit for gas generation threshold. Secondly, it can slow down the digenesis of compaction for keeping higher porosity and permeability, and form secondary pores and micro-fractures by organic acids corrosion and rock effective stress decrease, hence improve the ability of reservoir seepage and put forward higher requirements for the fracturing modification. Thirdly, the content of absorption gas increases quickly with formation pressure raise, which makes the gas-bearing of the shale reservoir better. In short，comprehensive influences of abnormal high pressure are favorable for enrichment of shale gas