Surface permeability improvement and gas control extraction test of low permeability thin coal seam in Guizhou province——Taking the YP-7 well of Shanjiaoshu Mine as an example

Abstract

Multiple and thin coal seams develop in Guizhou province, and the thin coal seams below 1.5 m in the coal measures of Longtan Formation account for more than 50% of the total coal seams. As for the surface gas control technology of thin coal seam mining, there is no single successful surface gas control case of thin coal seam for reference. Based on this, taking YP-7 well in Shanchushu Mine, Guizhou Province as an example, numerical simulation software was used to analyze the influence of fracturing fluid and proppant parameter changes of a single thin coal seam on the reconstruction effect, providing guidance for the optimization of surface fracturing technology of low-permeability thin coal seam gas Wells, and improving the gas extraction and treatment effect. Simulation studies and engineering tests show that fracturing pump displacement and sand ratio have significant effects on reservoir reconstruction. In the fracturing process, the fracturing liquid system of active water +KCL is used to reduce coal seam damage, and the transformation effect of thin coal seam is improved by large liquid volume, medium and high discharge, high sand volume, medium and high sand ratio, slug plus sand, and the permeability of coal seam after fracturing is increased by 6 070 times. In terms of drainage system, combined with mining pressure relief in coal mine, the method of controlling powder production and rapid pressure reduction is implemented to improve the fracturing fluid return rate of low permeability thin coal seam and expand the desorption radius. Within the desorption range of coal seam tons of coal gas decreased by 4.49 m3/t within 6 months of opening and pumping, and it is expected that the coal seam gas content within the pressure fracture network range will be reduced to less than 8 m3/t after opening and pumping for 2 years. The recovery rate of coalbed methane in the corresponding range reached 51.53%. The results show that the pressure is relatively stable during the fracturing process of YP-7 well, and the slight accumulation of quartz sand causes the pressure to rise. However, the plugging can be quickly solved with medium and high displacement, the drainage and production process is continuous and stable, and no sand and powder are produced, and the daily gas volume reaches more than 900 m3. According to the research and practice of comprehensive gas control of surface fracturing and mining pressure relief in this well, it provides guidance for the comprehensive gas control engineering practice of thin coal seam in Guizhou Province.

Keywords

• thin coal seam
• coalbed methane
• hydraulic fracturing
• drainage system
• desorption radius
• surface fracturing