鄂尔多斯盆地下寺湾地区延长组页岩气储层非均质性特征

The heterogeneity of shale gas reservoir in the Yanchang Formation,Xiasiwan area,Ordos Basin

鄂尔多斯盆地三叠系延长组长7、长9页岩是页岩油气勘探的重要层位,本文在岩心观测、薄片观察、脉冲渗透率测试、有机碳含量测试、气体组分分析、测井解释方法的基础上,对陆相页岩层内岩性、地化参数、微观孔隙结构、力学参数的非均质特征进行研究。研究认为陆相页岩储层砂质纹层发育密度和频率值较高,纹层中的大孔隙与页岩中的中孔和微孔构成复杂的孔隙体系,造成页岩储层层内非均质性极强,可有效改善页岩层系的物性,为游离气的富集和运移提供有利空间和有效通道,对游离气的渗流和富集具有积极意义。非均质程度较弱的页岩段,砂质纹层发育程度低,物性致密,排烃能力最弱,富集较多的吸附气。陆相页岩成储机制受控于其较强的非均质性,同时页岩强非均质性段,脆性矿物含量高,有利于页岩储层的压裂开采。

Chang 7and Chang 9shales are the main reservoir for shale gas enrichment in the Yanchang Formation of Ordos Basin.The heterogeneity of the macro framework,geochemical parameters,microscopic pore structure and mechanical parameters was analyzed on the basis of the core analytical data and logging interpretation results of lacustrine shale.The results show that the density and frequency of siliceous lamina are high and the heterogeneity is strong.The siliceous lamina can effectively improve the property of shale,and provide favorable space for free gas enrichment and migration.Shale section with stronger heterogeneity has better physical properties for the free gas seepage and enrichment.There are more siliceous lamina developed in the shale section with weak heterogeneity where the physical properties are poor.The stranded hydrocarbon content is high.There is no hydrocarbon migration and hydrocarbon expulsion is difficult,so adsorbed gas gets more and more,and it is easy to be enriched.Therefore,the lacustrine shale gas enrichment mechanism is controlled by its heterogeneity.Strong heterogeneity shows high content of brittleness mineral,which is advantageous to the shale reservoir fracturing.