Laboratory study on screening and optimizing surfactant of water-based fracturing fluid for coalbed methane reservoir

Hydraulic fracturing can cause water blocking dasmage to coal reservoir, and adding surfactant to water-based fracturing fluid is an effective way to mitigate this damage. In this paper, 1.5% KCl solution was used as the base fluid, adding surfactant with different types and concentrations; 8 types of fracturing fluids were prepared, used for coal dust sedimentation experiment, contact angle measurement, surface tension measurement and centrifugal separation test with coking coal in Liulin zone of Hedong Coal Field and lean coal of Xishan Coal Field of Taiyuan, 0.05% AN combination solution was selected as the best surfactant system, which led to the composition of 1.5%KCl+0.05%AN active fracturing fluid. This fracturing fluid changed the wettability of coal reservoir, and the low surface tension of the fracturing fluid can decrease the capillary pressure, and the water blocking damage of coal reservoir will be controlled so as to decrease the start-up pressure gradient and increase the permeability. Regarding to the coalbed methane reservoir, the surfactant fracturing fluid (1.5%KCl+0.05%AN) has the stimulation effect, reduces the capillary pressure of fluid in coal pore, making the fracturing fluid easily access into the coalbed methane reservoir, thus significantly reducing the water blocking damage.