Deflagration fracturing modification of nanoporous structure in the shale reservoirs of the Longmaxi Formation, Southern Sichuan, China

Abstract

Methane in-situ deflagration fracturing in shale is a revolutionary anhydrous technology. This paper selects shale samples from the Longmaxi Formation in Southern Sichuan to conduct deflagration fracturing tests with pressures ranging from 25 MPa to 91 MPa. Pore structure changes were experimentally measured to explore the modification differences of nanoscale pore characteristics under varying deflagration pressures. The results show that within the deflagration pressure range examined in this study, (1) Deflagration fracturing can alter the pore volume and specific surface area but does not affect the distribution characteristics of the pore size's peak position. The maximum increments of total pore volume occur at a pressure of 45 MPa. (2) When the deflagration pressure is less than 45 MPa, porosity gradually increases with rising deflagration pressure. When it is greater than 45 MPa, the porosity does not change significantly. With increasing deflagration pressure, it gradually increases: from nanopores, such as mesopores and macropores, to large pores and microcracks. (3) At the low deflagration pressure stage, under the influence of high temperature, slippage pores gradually increase, which is conducive to gas desorption and diffusion migration. As pressure increases, the impact of the explosion shock wave gradually increases, the volume of seepage pores increases significantly, and seepage dominates the migration mode.