川东地区五峰—龙马溪组超深层页岩孔隙结构特征及主控因素

Pore structure characteristics and main controlling factors of the ultra-deep shales of the Wufeng-Longmaxi Formation in Eastern Sichuan Basin

利用低压CO 2和N 2吸附实验,研究川东地区五峰—龙马溪组超深层页岩的孔隙结构特征及主控因素,对比周缘地区五峰—龙马溪组中浅层和深层页岩样品,分析压实作用对页岩孔隙结构特征的影响。结果表明:川东地区五峰—龙马溪组超深层页岩孔隙类型以有机质孔为主,孔隙形态主要为墨水瓶孔(细颈和广体孔),介孔和微孔约占总孔体积的90%。其中,微孔孔径峰值分布于0.35、0.50和0.79 nm,非微孔孔径主要分布于2.00~10.00 nm。超深层页岩孔隙结构受控于总有机碳质量分数,石英对孔隙的形成与保存也有一定控制作用,黏土矿物的自身强延展性易受压实作用影响,不利于颗粒间孔隙的发育与保存。相较于中浅层和深层页岩,超深层页岩的介孔/微孔体积比明显较低,压实作用影响超深层页岩的孔隙结构特征,使介孔和较大微孔受较强压实作用影响而演化为孔径更小的微孔,导致超深层页岩孔径缩小。该结果为四川盆地超深层页岩气勘探与开发提供指导。

CO 2 and N 2 gas adsorption are used to study the pore structure characteristics of Wufeng-Longmaxi ultra-deep shales from Eastern Sichuan Basin.A group of Wufeng-Longmaxi mid-shallow shales and deep shales from peripheral area are selected as parallel samples in order to study the effect of burial depth on pore structure characteristics of shales.The results show that the pore types in the Wufeng-Longmaxi ultra-deep shales are mainly organic pores.The morphology of pores is mainly ink bottle pore(fine-neck and wide-body pore).Mesopores and micropores account for about 90%of the total pore volume.The pore diameter of micropores is distributed around 0.35,0.50 and 0.79 nm,and the pore diameter of non-microporous pores is mainly distributed in the range of 2.0010.00 nm.The pore structure of ultra-deep shales is mainly controlled by its TOC mass fraction,and quartz also plays a certain role in controlling the formation and preservation of pores.Clay minerals are easy to be influenced by compaction due to the nature of strong ductility,which is not conducive to the development and preservation of intergranular pores.The mesopore volume or micropore volume of ultra-deep shales is significantly lower than that of mid-shallow shales and deep shales,indicating that burial depth will also affect the pore structure characteristics of ultra-deep shales.Under ultra-deep burial conditions,mesopores and larger micropores are subjected to strong compaction and evolve into micropores with smaller pore diameter,resulting in the overall pore diameter reduction of ultra-deep shales.This result provides guidance for the exploration and development of ultra-deep shale gas in Sichuan Basin.