基于孔隙结构的页岩渗透率研究

页岩渗透率对勘探开发至关重要，微观孔隙结构是影响页岩渗透率的主要因素。测定了龙马溪组与牛蹄塘组页岩的TOC含量与矿物组分，开展了高压压汞试验和低温液氮试验，测定了页岩的孔隙分布特征 及渗透率，研究了地质参数、孔隙结构对页岩渗透率的影响。研究结果表明：①页岩样品TOC含量越大，有机质孔隙的数量及孔隙度越高。黏土矿物含量的增加提高了页岩的渗透率，而脆性矿物中的孔隙发育较差，且 与渗透率和孔隙度呈负相关。②龙马溪组和牛蹄塘组页岩样品内分布着墨水瓶形孔隙结构，这类孔隙孔喉狭窄、孔隙之间连通性差。两组页岩孔径为4~40 nm，中孔在流体的赋存和运移方面承担着主要任务。③龙马溪 组岩样在孔径为4 nm左右呈单峰分布，牛蹄塘组岩样在孔径为4 nm和7 nm左右呈双峰分布。相对于孔隙表面积和孔隙体积，孔隙形态与连通程度对页岩渗透率有着更为重要的影响。

Study on Shale Permeability Based on Pore Structure

Shale permeability is very important for exploration and utilization,and the micro pore structure is the main factor affecting shale permeability.In this paper,the TOC content and mineral composition of the shale of Longmaxi Formation and Niutitang Formation were determined.High-pressure mercury injection experiment and low-temperature nitrogen adsorption experimentwere carried out.The pore distribution and permeability of shale were measured.The effect of geological parameters and pore structure on shale permeability was studied.The study results show that:(1) The number of organic pores increases with the increasing of TOC content in the shale sample,thus the porosity increases.The permeability of shale increases with the increase of clay mineral content.The pores in brittle minerals are poorly developed and negatively correlated with permeability and porosity.(2) Ink bottle-shaped pore structure are distributed in the shale samples of Longmaxi Formation and Niutitang Formation.The pore throat is narrow and the interpore connectivity is poor.The pore size of the two groups of shales is between 4 nm and 40 nm,and the mesopores is the main channel for fluid occurrence and migration.(3) The shale samples of Longmaxi Formation have a single peak distribution at a pore size of about 4 nm,and the shale samples of Niutitang Formation have a bimodal distribution at a pore size of about 4 nm and 7 nm.Relative to pore surface area and pore volume,pore morphology and connectivity have a more important effect on shale permeability.