Modeling study on supercritical CO2 fracturing applicability and capacity to stimulate reservoirs with different permeabilities

Abstract

Hydraulic fracturing (HF) using water-based fluids is an effective approach for reservoir stimulation in the exploitation of unconventional resources. Recently, supercritical carbon dioxide (S–CO2) has been proposed as a prospective fracturing fluid in reservoir stimulation because it exhibits higher fracturing capacity compared with water-based fracturing fluid. However, S–CO2 appears to have a distinct drawback of intensifying leak-off when used in reservoirs with relatively high rock matrix permeability (RMP). In this work, a modeling study on water fracturing and S–CO2 fracturing (SCF) was implemented in reservoirs with varied RMPs to assess their applicability. In the modeling, the natural fracture system in the reservoir was considered through the discrete fracture network method for simulating different reservoirs. The lower viscosity and density of S–CO2 compared with those of water enable the easier fracturing of reservoir rocks and allow the generation of more complex fracture networks. However, the intensifying leak-off of S–CO2 due to fracture propagation can hamper the build-up of hydraulic pressure and affect fracture propagation, especially in reservoirs with relatively high RMP. The inflection of fracture length development during HF can also reflect the impact of fluid leak-off. Permeability determines the final fracture network of SCF, and the injection rate increase can offset the leak-off to a certain extent; however, the improvement in fracturing results becomes limited. The modeling results clearly demonstrate the importance of RMP, which can directly determine the applicability and capacity of SCF.