Testing method and controlling factors of specific surface area of shales

Shale has the characteristics of rich organic matter, complex mineral components and developed nanopores. Large surface area of shale has a strong adsorption capacity and large amount of adsorbed gas. The specific surface area of shale is an important factor for the adsorption of shale gas, while there are several factors which can affect the test results of specific surface area. Longmaxi shale in the south of Sichuan Basin was taken as an example. A method for the low pressure N2 adsorption to test the shale's specific surface area is established. Following this, the key factors affecting shale's specific surface area were discussed. The research indicates, the measured specific surface area of shale with different particle size (2-5 mm) is almost equal. Accordingly, the recommended particle size is about 3mm. After 200℃, the specific surface area of the sample reaches the maximum when the adsorbed water and part of the interlayer water of clay minerals is removed. Therefore, the recommended pretreatment optimum temperature is 200℃. TOC and specific surface area have positive linear relationship. The higher the organic maturity of the shale is, the more the organic pores were generated after the organic matter thermal cracking. So more organic pores are conducive to the adsorption and storage of natural gas. The specific surface area and quartz content show a good positive correlation. Because of a strong ability of anti-compaction, the quartz particle has a supporting function to the surrounding pores. The correlation between specific surface area and other factors is not strong. The specific surface area is of great significance for the resources potential evaluation of shale gas. © 2015, Science Press. All right reserved.