Acid-etching fracture morphology and conductivity for alternate stages of self-generating acid and gelled acid during acid-fracturing

Abstract Initial fracture morphology and variation of acid-rock reaction temperature caused by alternate stages were ignored in the traditional alternate multistage acid-fracturing experiments, so a new design method of experiment simulation was proposed with these considerations in this paper. Alternate multistage acid-fracturing experiments were carried out based on this new method through using self-generating acid and gelled acid, while the influence of alternate stages on acid-etching fracture morphology and conductivity were also investigated. The study shows that acid smoothing the peaks are stronger than deepening the valleys on rough fracture during alternate acid-fracturing and the tortuosity of fracture surface also increased after acidizing. Injection time of self-generating acid at high temperature caused by alternate stages is the main influences on the acid-etching pattern, while that of gelled acid has little effect. Excessive dissolved-rock of one alternate stage is beneficial to creating high initial conductivity, but the retention rate of conductivity is the lowest under medium and high closure stress. Although rough initial fracture has a little contribution to generation high conductivity, two alternate stages with moderate acid-etching creates high conductivity and improves the retention rate of conductivity under medium and high closure stress. It is useful to select reasonable alternate stages for self-generating acid and gelled acid in multistage acid-fracturing treatment.