海相与陆相页岩微观特征差异及其对可压性的影响

doi:10.7657/XJPG20220104

摘要/Abstract

摘要：

为确定海相与陆相页岩微观结构差异及其对可压性的影响,利用扫描电镜、核磁共振、CT扫描、岩石力学测试及水力压裂实验,结合分形几何与岩石力学理论,对四川盆地龙马溪组和鄂尔多斯盆地延长组页岩进行对比。陆相页岩黏土矿物含量高,约占45.3%,海相页岩以石英和长石等脆性矿物为主,约占67.9%。海相页岩孔隙度约为陆相页岩的2倍,海相页岩宏孔比例更高,孔径分布范围更广;陆相页岩中孔和小孔占比更高,天然裂缝及层理较发育。陆相页岩平均起裂压力较海相页岩低22.52%,高黏土矿物含量导致的低力学强度是其重要原因,而孔隙压力对陆相页岩起裂压力的影响较小。海相页岩水力压裂主裂缝为基本沿井筒对称的贯穿裂缝;陆相页岩发育的天然裂缝和层理容易捕获水力压裂裂缝,形成垂直于主裂缝的剪切裂缝,裂缝的开启和连通,有利于形成更复杂的裂缝网络。陆相页岩3个脆性指标均低于海相页岩,但陆相页岩起裂压力更低,缝网结构更好,具备良好的压裂潜力,采用单一脆性指标评价其可压性不准确。陆相页岩低孔隙度、低渗透率及高水敏性不利于水力压裂改造储集层。

关键词: 海相页岩, 陆相页岩, 微观结构, 可压性, 分形维数, 水力压裂, 裂缝

Abstract:

Taking the shales of the Longmaxi formation in the Sichuan basin and the Yanchang formation in the Ordos basin as examples, scanning electron microscopy, nuclear magnetic resonance, CT scanning, rock mechanics test and hydraulic fracturing experiments were carried out to investigate the differences in the shale microstructures between marine and continental facies, and then the influence of the differences on shale fracbility was analyzed, and the two kinds of shale were compared by considering fractal geometry and the theory of rock mechanics. According to the research results, the following findings are obtained: a.The continental shale (Yanchang formation) has a high content of clay minerals, accounting for about 45.3%, while the marine shale (Longmaxi formation) is dominated by brittle minerals such as quartz and feldspar, accounting for about 67.9%. b.The porosity of the marine shale is about twice that of the continental shale. c. The proportion of macropores in the marine shale is higher and the pore size distribution is wider, while mesopores and small pores in the continental shale occupy larger space, and natural fractures and beddings are developed. d.The average initial pressure of the continental shale is about 22.52% lower than that of the marine shale, mainly due to low mechanical strength caused by the high clay mineral content in the continental shale, but less effect from pore pressure. e.The major hydraulic fractures induced in the marine shale are transverse cracks that are basically symmetrical along the wellbore, while the natural fractures and beddings in the continental shale can easily capture hydraulic fractures, resulting in shear fractures perpendicular to the major fractures, and the open and connected beddings and weak surfaces are conducive to form a more complex fracture network in the continental shale. f.The three brittleness indicators of the continental shale are all lower than those of the marine shale, but the continental shale has advantages of lower initial pressure, better fracture network and better fracturing potential, so it is inaccurate to evaluate the compressibility of the continental shale by using a brittleness indicator. g.The low porosity, low permeability and high water sensitivity are not conducive to hydraulic fracturing stimulation to the continental shale reservoir.

Key words: marine shale, continental shale, microstructure, fracbility, fractal dimension, hydraulic fracturing, fracture

中图分类号:

TE122.2

王迎港, 申峰, 吴金桥, 孙晓, 穆景福, 汤积仁. 海相与陆相页岩微观特征差异及其对可压性的影响[J]. 新疆石油地质, 2022, 43(1): 26-33.

WANG Yinggang, SHEN Feng, WU Jinqiao, SUN Xiao, MU Jingfu, TANG Jiren. Differences in Microstructures Between Marine and Continental Shales and Its Influences on Shale Reservoir Fracbility[J]. Xinjiang Petroleum Geology, 2022, 43(1): 26-33.

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