Experimental study on methane deflagration fracturing technology

The efficient development of shale gas resources is crucial for the economic development and bears the important mission in achieving the “dual carbon” goals in China. Given the large water consumption of hydraulic fracturing and the irreversible pollution of strata caused by fracturing fluids, the search for a more scientific and environment friendly fracturing technology has become a hot topic in recent years. A new approach for developing shale gas using methane in-situ deflagration fracturing technology has been proposed in this study. This technology uses spark ignition to ignite methane in the reservoir and the pumped-in combustion aid to create a detonation, relying on the instant high-pressure shock generated in the reservoir rock for fracturing, enabling the reservoir to generate a complex fracture network of a certain scale without control by geostress. Its advantages lie in preventing strata pollution and reducing surface transportation costs. It is expected to become an efficient and environment friendly low-cost waterless fracturing technology. Using a methane deflagration fracturing experimental system, including independently designed fracturing devices, gas charging, ignition control, and data acquisition systems, a large-scale ground fracturing physical modeling (ϕ2.0 m×1.5 m) experiment was carried out. The pressure-time curve of the cavity pressure in the fracturing tube and the wellbore pressure were recorded and compared with the wellbore pressure and fissure characteristics of explosion fracturing and hydraulic fracturing. The results show that the peak pressure in the wellbore during the deflagration process was 495.18 MPa, 82.5 times the injection pressure. The sample had low fragmentation and a small crush area, with 7 to 9 main fractures, and the fracture width was on the centimeter scale. Methane deflagration fracturing provides ample fracturing energy, a wide impact range, and the extent of damage to the wellbore can be controlled by injection pressure. Compared to explosion fracturing and hydraulic fracturing, the technology has a longer high-pressure action time, which is more conducive to the initiation and expansion of fractures. It produces more fractures than hydraulic fracturing and longer fractures than explosion fracturing, resulting in the best fracturing effects. Experimental studies have recorded the peak pressure and pressure rise rate achieved when methane-oxygen mixtures undergo detonation at high initial pressures. This validates the feasibility of using the methane in-situ deflagration fracturing technology for shale gas development and provides data reference and technical guidance for the future practical application of the technology.