Determination of ball sealers used for the multi-layer hydraulic fracturing in coal seams

When the multi-layer hydraulic fracturing is operated in well-developed multiple coal seams with thin single layer and small space between layers, the reasonable number of ball sealers is the guarantee for smooth operation of the said fracturing and the best cumulative stimulation result. The difference in reservoir properties between coal seams and sandstone beds will lead to such problems as the accelerating pressure in operation, bad frac result in coal seams, etc. Therefore, the determination of actual ball sealers under different geological conditions will help solve those bottlenecking problems. Then, according to the basic principle of the multilayer hydraulic fracturing, this paper thoroughly analyzes the influencing factors. On this basis, the geological and mathematical models of the number of ball sealers are built for the multi-layer hydraulic fracturing in different hard coal seams or the interbedded hard and soft coal seams. With the above models, the number of ball sealers was designed for the multi-layer hydraulic fracturing in the 8 # and 9 # Luling Coal Mine of the Huaibei area. The application result shows that this study will provide theoretical basis for the determination of the number of ball sealers for the multi-layer hydraulic fracturing in different coal seam combinations.