The Mechanisms of Selective Mineral Dissolution for Permeability Enhancement in a Deep Tight Sandstone Gas Reservoir

The permeability of a deep tight sandstone gas reservoir could be greatly improved by selective mineral dissolution based on the chemical differences of mineral components. In this article, the responses of rock mechanical properties, the acid imbibition and flowback efficiency, and the self-supporting effect of fractures to the selective mineral dissolution are measured. The results show that (1) there is a certain degree of reduction in the elasticity modulus and Poisson’s ratio after selective mineral dissolution by acid. The uniaxial compressive strength reduction extent is 4–8%. The reduction of mechanical strength after the treatment of hydrochloric acid is greater than that of acetic acid; (2) the average flowback efficiency is 71.51% for hydrochloric acid and 58.95% for acetic acid; (3) the self-supporting fractures are formed by the selective mineral dissolution, which is conducive to the enhanced and maintained fracture conductivity; and (4) the selective mineral dissolution by acid can effectively widen and connect the matrix pores and generate new pores to improve the seepage capacity. Finally, the field application of selective mineral dissolution by acid is prospected in conjunction with fracturing technology in a deep tight sandstone gas reservoir. This study sheds light on the acid stimulation mechanisms by selective dissolution of minerals, which is helpful for enhancing the estimated ultimate recovery of deep tight sandstone gas.