压力演化对页岩气储层的控制作用——以四川盆地五峰组—龙马溪组为例

中国南方海相页岩气勘探开发的实践表明，地层压力对于页岩气的保存及勘探开发具有重要的影响。为了进一步明确压力演化对页岩气储层演化的影响，以四川盆地及其周缘上奥陶统五峰组—下志留统龙马溪组页岩为例，依据岩相、物性、孔隙结构、包裹体分析与页岩微观特征等资料，研究了压力演化对页岩气储层的控制作用。研究结果表明：①页岩气储层物性与孔隙结构受岩相、埋深与压力演化的共同控制，孔隙压力超压对埋藏压实具有抑制作用，总体上有利于页岩有机孔的保持和物性向好；②泄压期次与泄压强度影响了五峰组—龙马溪组不同岩相页岩的差异演化对高应力敏感性黏土质页岩的影响尤为显著，而对硅质页岩的影响则较低；③区域抬升与泄压时期晚、泄压时期短和泄压强度低最有利于有机孔的保持和页岩气储层物性向好；④盆内深层页岩气泄压程度低，保存条件优越，储层物性普遍优于盆缘常压—超压区，富有机质硅质页岩与黏土质页岩均具有较好的储集性能；⑤盆缘常压区泄压程度较高，富黏土质页岩储集性能降低，封盖性增强，并逐渐演化为直接盖层。

Controlling effect of pressure evolution on shale gas reservoirs: A case study of the Wufeng–Longmaxi Formation in the Sichuan Basin

The exploration and development practice of marine shale gas in southern China shows that formation pressure has an important influence on the preservation, exploration and development of shale gas. In order to further clarify the influence of pressure evolution on the evolution of shale gas reservoirs, this paper took the shale of Upper Ordovician Wufeng Formation–Lower Silurian Longmaxi Formation in the Sichuan Basin and its periphery as the research object to study the controlling effect of pressure evolution on shale gas reservoirs based on lithofacies, physical property, pore structure, inclusion analysis, microscopic characteristics and other data. And the following research results were obtained. First, the physical properties and pore structures of a shale gas reservoir are under the joint control of lithofacies, burial depth and pressure evolution. And the pore overpressure inhibits the burial compaction, which is generally beneficial to the maintenance of organic pores and the improvement of physical properties. Second, the period and the intensity of pressure relief influence the differential evolution of different lithofacies in the Wufeng–Longmaxi Formation shale, and their influence on high stress-sensitive argillaceous shale is particularly obvious, but less on siliceous shale. Third, regional uplift and late pressure relief, and short pressure relief duration and low pressure relief intensity are the most beneficial to the maintenance of organic pores and the improvement of reservoir physical properties. Fourth, the deep shale gas reservoirs in the Sichuan Basin have low pressure relief degree and superior preservation conditions, and their physical properties are generally better than those in the normal pressure–overpressure area along the basin margin. And organic-rich siliceous shale and argillaceous shale both have better reservoir properties. Fifth, in the normal-pressure area along the basin margin, the pressure relief degree is higher, and the argillaceous-rich shale gradually evolves into direct cap rocks as its sealing capacity increases and the reservoir capacity decreases.