川西坳陷须五段页岩微观孔隙结构发育控制因素及其成藏意义

Controlling factors and accumulation significance of microscopic pore structure in the fifth member of Xujiahe Formation in the Western Sichuan Depression

以川西坳陷须五段页岩为例,首先运用氮气吸附法对页岩纳米孔隙进行测定,通过等温线和DFT模型分析,对页岩的微观孔隙结构进行表征;然后通过等温吸附实验研究了页岩的甲烷吸附性能,通过解吸法测定了页岩的含气量;最后探讨了页岩微观孔隙结构发育的主要控制因素及其对页岩气成藏的意义。结果表明:川西坳陷须五段页岩孔隙结构较复杂,主要由中孔组成,主体孔径位于2~50 nm,中孔提供了主要的孔隙体积;在85℃条件下页岩甲烷吸附的兰氏体积为0.79~4.99 m3/t,页岩的含气量为0.50~2.44 m3/t;有机碳含量、伊/蒙间层矿物含量、脆性矿物含量以及热演化程度是控制页岩微观孔隙结构发育的主要因素;微孔和中孔对页岩气的吸附能力极强,在其内部有大量页岩气以结构化方式存在,增加了页岩气的存储量。

This paper presents a study on the fifth member of Xujiahe Formation in the Western Sichuan Depression. The shale pore was measured using nitrogen adsorption method. The pore volume, pore specific surface area and pore size distribution were studied through the isotherms and DFT model analysis. Then the isothermal adsorption experiment was done to obtain the Langmuir volume, and the shale gas content were acquired using desorption method. Based on all of these, discussed the controlling factors of microscopic pore structure and its influence on shale gas accumulation. The results show that, the pore structure of the fifth member of Xujiahe Formation in the Western Sichuan Depression is relatively complex, which is composed of mesopores and the sizes of the mesopores are in a range of 2-50 nm, occupying most of the pore volume. The Langmuir volume of methane adsorption in shales range from 0.79 to 4.99 m3/t under the condition of 85 and the shale gas content are 0.50-2.44 m3/t. The main factors controlling the microscopic pore structure there are organic carbon content (TOC), the content of illite/smectite interstratified clay mineral, brittle minerals content and thermal evolution maturity. The micropores and mesopores have a strong ability to absorb shale gas, the interior of which is structured filled with the shale gas, thus increase shale gas storage capacity. © 2015, China Coal Society. All right reserved.