鄂西地区陡山沱组页岩储层孔隙特征及影响因素

Shale reservoirs in the Doushantuo Formation in western Hubei:Porosity and its controlling factors

关键词:  陡山沱组  页岩气  储层特征  影响因素  黄陵隆起

Key words:  Doushantuo Formation  shale gas  reservoir  controlling factor  Huangling uplift

摘要:

页岩储层孔隙结构是评价页岩气资源潜力的基础。本文基于有机碳含量、沥青反射率、X射线衍射、场发射扫描电镜（FE-SEM）及低温氮气吸附等方法，探讨鄂西地区震旦系陡山沱组页岩沉积组成、孔隙结构及其控制因素。结果表明：（1）陡山沱组为硅质和钙质页岩，TOC介于3.29%~6%，主要为I型干酪根，处于高-过成熟阶段；（2）陡山沱组页岩有机孔发育程度较低，无机孔提供主要储集空间，包括脆性矿物和黏土矿物的粒间孔、层间孔和部分溶蚀孔，以及少量微裂缝；（3）孔径分布范围为1.1~284nm，总孔体积平均为0.034ml/g，微孔、介孔和大孔体积分别为0.005ml/g、0.023ml/g和0.006ml/g，以介孔为主；（4）陡山沱组页岩TOC与孔体积无明显相关性，表明有机孔对孔体积贡献较小。硅质矿物和黏土矿物含量与页岩孔体积正相关性较好，表明矿物组成是陡山陀组页岩孔隙发育的主要控制因素。鄂西地区陡山沱组页岩具有良好的物质条件、生烃条件和页岩气储集空间，是潜在的页岩气勘探开发层系。

Abstract:

The pore structures of shale reservoirs are considered as the basis for the evaluation of shale gas resources. In the light of organic carbon content, asphalt reflectance, X-ray diffraction analysis, field emission scanning electron microscopy (FE-SEM) analysis and low temperatures nitrogen absorption method, the present paper gives a detailed discussion of the compositions, pore structures and controlling factors of the shale reservoirs in the Doushantuo Formation in western Hubei. The Doushantuo Formation is mainly made up of siliceous and calcareous shales. The total organic carbon contents vary from 3.29% to 6%, indicating the I-type kerogen and high maturation-overmaturation stages of the source rocks. The organic pores in the shales from the Doushantuo Formation are less developed, and the inorganic pores have provided the main storage spaces, including intergranular pores, interlayer pores and partial solution openings within the brittle minerals and clay minerals, as well as a small amount of microfractures. On the whole, the pore diameters range between 1.1 nm and 284 nm, and micropores, mesopores and macropores have the volumes of 0.005, 0.023 and 0.006 ml/g, respectively, with an average of 0.034 ml/g. There is no significant correlation between the total organic carbon contents and pore volumes in the shales from the Doushantuo Formation, indicating that the organic pores contribute little to the pore volumes. On the contrary, the contents of siliceous and clay minerals are positively correlated with the pore volumes, indicating that the mineral compositions are the main controlling factors of pore development in the Doushantuo Formation. The shales in the Doushantuo Formation in western Hubei may be considered potentially prospective for shale gas because of good hydrocarbon generation conditions and shale gas storage spaces.