下扬子地区幕府山组陆缘海-台地黑色细粒沉积岩系沉积学和孔隙结构特征

黑色细粒沉积岩系沉积学和孔隙结构研究对于沉积环境恢复、页岩气储层评价和有利储层预测具有重要意义.利用下扬子地区最新完钻的XYZ-1钻井资料,综合钻井岩心、岩石薄片、XRD分析、氩离子-场扫描电镜等手段,开展幕府山组细粒沉积岩系的沉积学和孔隙结构研究.结果表明,幕府山组岩性组成以块状、纹层状深色(碳质)泥岩、浅灰色纹层状...

Sedimentology and Porosity Structures of the Epicontinental Sea-Platform Fine-Grained Deposits of Mufushan Formation in Lower Yangtze Area

The study of sedimentology and pore structure of black fine-grained sedimentary rock series is of great significance for environment, shale gas reservoir evaluation and favorable reservoir prediction.Using the newly drilled XYZ-1 well data in the Lower Yangtze area, based on systematic coring identification of Lower Cambrian Mufushan Formation, rock thin section, XRD (X-Ray Diffraction) analysis, and argon ion-field emission-scanning electron microscopy (Ar-FE-SEM), the sedimentology and pore structures of the fine-grained deposits series arestudied in this study.The results show that the lithologic composition of the Mufushan Formation is dominated by dark (carbonaceous) mudstone, light gray argillaceous limestone and cryptite, interbeded with marl, dolomitic limestone, terrigenouslimestone and dolomite, Andesite, breccia, etc., mainly composed of siliceous clay-mixed shale facies and siliceous clay-like shale facies. It is belong to the continental shelfshallow-sea carbonate platform-deep-water bay-tidal flat environment of the lower Yangtze ocean basin.The black argillutite (mud shale) of the Mufushan Formation has various pore types, the organic pores are 2-200 nm, the surface porosity ratio is 2.86%-15.90%, the pore distribution is relatively uniform, but the overall connectivity is poor, and some organic pores are inhomogeneity symbiotic with the brittle mineral or clay mineral. The inorganic pores are mainly intragranular, intergranular pores and dissolution pores, and some are intercrystalline pores and intermetallic pores. Except for the intercrystalline pores of pyrite, most of the inorganic pores are larger than 2 μm and the maximum is 50 μm.The micro-cracks in the shale are widely developed, and the micro-cracks of tectonic origin are complex in shape, and the slit width is generally 20-500 μm, generally filled with calcite and quartz. The length of diagenetic micro-cracks is generally greater than 10μm and the slit width is 50 to 200 nm. The black mud shale in the upper deep-water bay facies and lower parts of the mud flat and evaporate plat form of the Mufushan Formation has favorable conditions for the development of high quality shale gas reservoirs, due to a high TOC content from 2.65%-21.27%, average 6.30%, organic-inorganic pore system, and fracture system development, high clay minerals and brittle minerals content.