Research on parameter optimization design of CO₂ foam fracturing for deep coal rock gas in Shenfu area

Abstract

Deep coal seams are the key successor area for large-scale development of coalbed methane in China. However, deep coal reservoirs are characterized by “three highs and two lows”, and conventional hydraulic fracturing and foam fracturing are prone to water-sensitivity damage and poor adaptability, restricting efficient explo. The coal seams in the Shenfu area extend over 2,000 meters in depth and contain substantial natural gas reserves. However, technical challenges arise from low natural gas production rates in these reservoirs and the inability to create effective complex fracture networks using conventional fracturing methods. These factors pose significant obstacles to conducting hydraulic fracturing operations in deep coal gas reservoirs. Currently, there is a lack of systematic theoretical frameworks for optimizing fracturing construction parameters based on the characteristics of deep coalbed methane reservoirs. To address this issue, this study establishes a three-dimensional geological model for horizontal wells and a numerical simulation model for fracture propagation.Base this model, we analyzed how key operational parameters—including pumping rate, fracturing fluid volume, and proppant concentration—influence the propagation behavior of CO2 foam fractures in deep coalbed methane reservoirs. By comparing the 2D fracture propagation patterns, we optimized key operational parameters such as pumping rate, fracturing fluid injection volume, and proppant concentration. The results show that increasing the pumping rate accelerates foam flow and shortens the heat exchange time, leading to lower temperature and higher net pressure inside the fracture. Raising the injection volume expands the coverage of low-temperature foam, achieving uniform cooling across the entire fracture and increasing net pressure. A higher proppant concentration increases the viscosity of the sand-carrying fluid, enhances heat transfer, and continuously elevates the net pressure within the fracture.