Analysis on fracture propagation law and fracturing parameter sensitivity of CO₂ foam fracturing in deep coalbed methane reservoirs of Shenfu block

Abstract

In the Shenfu block, deep methane reservoirs from coal seams at depths of 2000-3000 m face challenges such as high water consumption during conventional hydrofracturing, elevated treatment costs for the resulting fluids, and limited effectiveness in modifying the fracture network. CO2 foam fracturing, as a transformation technology focused on water conservation and carbon emission reduction, is well-suited to the sustainable development of deep coal deposits; however, the mechanisms governing fracture propagation vary depending on the construction parameters employed. Based on the actually measured geological parameters of the deep coal seams in the study area, a three-dimensional geological model was constructed using the Petrel software; the mass percentage of polyurethane foam was set at 50%; and 18 simulation scenarios were developed employing the one-dimensional variable method. Separate analyses are performed on the control laws of pumping displacement, single-stage injection volume and total proppant dosage upon 2D fracture morphology. Range analysis is further adopted to quantify the sensitivity of the three construction parameters to four evaluation indices, namely average fracture length, stimulated reservoir volume (SRV), average fracture width and fracture conductivity.. Results show that increasing the injection rate can elevate bottom-hole net pressure, stimulate the development of secondary branch fractures and improve the uniformity of proppant placement, which is the dominant factor controlling the extension length of the main fracture. Increasing the volume of liquid in each section allows for extending the duration of pure pressure effects and expanding the coverage area of the grid; The total volume of sand has little impact on the extent of crack propagation or the complexity of the crack network; however, it can significantly increase the degree of sand saturation within cracks, the constant width of cracks, and their long-term conductivity. Analysis of the data indicates that the injection rate exhibits maximum sensitivity to the average fracture length, whereas the total proppant volume is the dominant parameter determining the stimulated reservoir volume, fracture width, and conductivity. The study identified mechanisms for the differentiated regulation of various construction parameters, providing a theoretical foundation for optimizing the parameters of the bubble hydraulic fracturing process for deep coalbed methane using CO2.