中国南方海相页岩气保存机理及模式

Preservation mechanism and model of marine shale gas in southern China

保存条件是控制页岩气富集和高产的关键因素,我国四川盆地五峰组—龙马溪组页岩气已实现了商业化开发,但受到保存条件的影响,页岩气富集差异性明显,对勘探开发目标优选提出了挑战。因此,深化中国南方海相页岩气保存机理及模式研究对扩大页岩气勘探开发成效、提高页岩气产量具有重要意义。本文以四川盆地及周缘地区五峰组—龙马溪组页岩为研究对象,应用盆地模拟、流体包裹体分析、覆压孔隙度和渗透率实验、页岩三轴岩石力学测试等技术方法,取得了3方面认识:(1)揭示了页岩气构造保存机理,构造演化控制了页岩微裂缝开启、游离气富集和地层超压发育,差异构造演化过程及强度控制了页岩气赋存状态及含气量,构造抬升开始晚、强度小对页岩气保存有利;(2)阐明了页岩气顶底板封闭机理为岩性和物性封闭,岩性致密、页岩厚度、微观孔隙结构是顶底板封闭的关键控制因素,页岩气自封闭机理为毛管力和分子间作用力封闭,受控于孔隙连通性和甲烷吸附作用;(3)基于埋深和构造变形强度,建立了海相页岩气正向构造高部位和负向构造低部位保存模式。正向构造页岩气保存受控于裂缝发育程度,埋深大于页岩破裂深度、背斜两翼夹角大于120°有利于页岩气保存,负向构造页岩气保存受控于平行页理方向的封闭性,埋深大于页岩覆压渗透率突变带、斜坡倾角小于10°有利于页岩气保存。本文对中国海相页岩气勘探开发具有重要意义。

Shale gas has been successfully developed in the Wufeng-Longmaxi Formation in the Sichuan basin,China.However,due to the influence of shale gas preservation,shale gas enrichment varies significantly,which has challenged the optimization of shale gas exploration and development targets.Therefore,it is of great significance to study the mechanism and mode of marine shale gas preservation and to increase the shale gas production.In this paper,the Wufeng-Longmaxi Formation marine shales in the Sichuan basin were used to conduct an integrated procedure including basin modeling,fluid inclusion analysis,overburden porosity and permeability,triaxial rock mechanics tests.Major findings include:①tectonic evolution controlled the micro-cracks,free gas enrichment and overpressure.Differing tectonic evolution processes and their intensity control the occurrence and shale gas contents.The late uplift and low tectonic intensity is favorable for shale gas preservation;②the mechanism of top and bottom sealing is lithological and physical sealing.Tight lithology,thickness and pore structure of shales control the top and bottom sealing.The mechanism of self-sealing shale gas are the capillary and intermolecular forces,which are controlled by pore connectivity and methane adsorption;③based on burial depth and deformation evolution,the preservation models of marine shale gas in the upper part of anticline structure and the lower part of syncline structure have been established.Burial depth greater than fracture depth,and an angle greater than 120°are conducive to the anticline preservation of shale gas.The buried depth of permeability decrease and an angle less than 10°are conducive to the preservation of shale gas.This paper is of great significance for further exploration and development of marine shale gas in China.