Fracture conductivity and rock appearance in volcanic reservoirs treated by various stimulation techniques

Abstract

Volcanic reservoirs have complex mineral compositions and highly heterogeneous physical and mechanical properties, making their stimulation quite problematic. This study aimed at clarifying acid-rock reaction and stimulation mechanisms in volcanic reservoirs using 3D scanners and conductivity testing devices. Tests on rock sample conductivity and appearance under such mainstream stimulation technologies as hydraulic fracturing, acid fracturing, and proppant-carrying acid fracturing (PCAF) were performed. The effects of proppant particle size, proppant concentration, acid volume and type, proppant-carrying acid type, and proppant-carrying acid concentration on conductivity and rock sample appearance were analyzed. The appearance of rock samples included dot-, pit-, and strip-like embeddings, as well as acid-etching pits and channels. Larger particle sizes and higher proppant concentrations produced wider propped fractures and higher flow conductivity. Due to complex mineral distribution, acid fracturing failed to produce long etched channels, and the obtained conductivity was low, with a maximum of 8 D·cm at a 5 MPa closure stress. Hydraulic fracturing and PCAF reached a maximum flow conductivity of 155 D·cm at a 5 MPa closure stress, indicating their applicability to volcanic reservoir stimulation. This work helps reveal the acid-rock reaction and stimulation mechanisms of volcanic reservoirs and provides a theoretical basis for their development.