Optimization of Combustion Accelerant Jet Delivery Parameters for In situ Methane Combustion Explosion Fracturing in Formation Perforation

Abstract

Abstract. Methane in situ combustion and explosion fracturing in shale reservoirs uses methane desorbed from the reservoir as a fracturing agent for ignition and explosion. In a short period of time, mesh artificial fractures are generated around the gas reservoir, which is expected to greatly increase the discharge area and connectivity of the reservoir. In order to explore the feasibility of injecting and regulating the combustion accelerant in the formation perforation by jetting, a three-dimensional physical model of horizontal well-formation perforation was established by using RNG k–ε turbulence model and the component transport model. The influence of different nozzle combinations on the mixing degree of methane-combustion accelerant in the perforation under the condition of moving jet was simulated and studied. By comprehensively comparing the mixing degree of gas in the perforation, the distribution uniformity of methane, and the dilution degree of methane in the wellbore, the nozzle combination scheme with the best effect was selected. On this basis, the flow field parameter characteristics and methane mixing effect under the action of the moving jet of a porous nozzle were analyzed. The results show that the methane concentration in the wellbore is lower than the explosion limit, the wellbore will not be directly exploded, and the methane concentration in the wellbore is below the flammability limit (4%) and evenly distributed by using the combined scheme of one axially forward nozzle with a nozzle diameter of 2 mm, four radially lateral nozzles, two obliquely forward nozzles and two obliquely rear nozzles. In addition, the methane concentration in the perforation decreases with the increase of bottom hole temperature and nozzle pressure drop, and decreases with the bottom hole pressure and nozzle.