鄂尔多斯盆地陆相页岩微观孔隙类型及对页岩气储渗的影响

摘要

为深入研究鄂尔多斯陆相页岩储层微观孔隙特征及成藏地质意义,特选取了延长矿区本溪组、山西组、延长组长7、长9段的页岩钻井岩心进行了氩离子抛光-扫描电镜实验、压汞实验、氦气吸脱附实验以及相关的地化等实验,实现了对孔隙特征从电镜下直观观察到吸脱附实验间接定性反映,以及对孔隙结构从宏孔到微孔的定量测试.研究结果表明,鄂尔多斯陆相页岩存在粒间孔、粒内孔、晶间孔、溶蚀孔、有机孔及微裂缝共6种微观孔隙类型.其中粒间孔、粒内孔普遍存在,且以黏土矿物聚合体粒间孔和层间粒内孔最为发育,粒间孔孔径多在微纳米级,粒内孔多在几十个纳米内；晶间孔和溶蚀孔仅少量存在于某些特定矿物中,孔径多为纳米级；有机孔相对不发育,以赋存于黏附-结合态有机质中且呈凹坑状、片麻状有机孔为特征,孔径多在20 nm以内；微裂缝少量存在,多为脆性矿物裂开缝或大型贯通式裂缝.另外,分析得出黏土矿物集合体粒间孔和层间粒内孔对研究区页岩气的赋存和运移贡献最大且是储层各向异性(渗透性)的主要控制因素,晶间孔及溶蚀孔次之；有机孔因相对不发育,可能贡献较小.同时微裂缝的影响不容忽视,是沟通宏孔与中孔的主要微通道.%For further research on microscopic pore characteristics and geological accumulation significance of Ordos continental shale reservoir,samples from drilling cores of Benxi,Shanxi and member 7 and 9 of Yanchang Formation were collected to perform a series of experiments,including the Focused Ion BeamScanning Electron Microscopy (FIB-SEM),Mercury Injection,Helium Sorption-Desorption (HSD) and related chemical and physical experiments.The FIB-SEM confirmed that there are six kinds of microscopic pore types in Ordos continental shale,including inter-particle,intra-particle,inter-crystal,dissolution,organic pores and micro-cracks,of which the inter-particle pore (micro-scale) and intra-particle pore (nanoscale) of the clay minerals are most prevalent,coinciding with pore characterization by HSD; the dissolution pore and inter-crystal pore only exist in certain minerals with pore size in nanoscale; organic pore are also not well developed,with pore size less than 20 nm,characterized by its inclined occurrence in adhesive-combination organic matter and its pitted or gneissic shape; micro-cracks are a few,which are mostly brittle mineral splits or large through-type cracks.Furthermore,the results show that the inter-particle pores of clay mineral aggregation and intra-particle pores between layers make the greatest contribution to the occurrence and transportation of shale oil and gas,which is also the mainly controlling factor of the anisotropic of the shale reservoir.Inter-crystal pore and dissolution pore are ranked the second; organic pores are relatively undeveloped,so its contribution to permeability is small,but it still plays an important role in the occurrence of shale oil and gas.Meanwhile,the impact of micro-cracks cannot be ignored,which are the main channel connecting macropores with mesopores.