LI Xianwen¹, HOU Yuting², GU Yonghong¹, ZHANG Cunwang², MOU Chunguo¹, QI Ning³, PAN Lin³

1. Oil and Gas Technology Research Institute, Changqing Oilfield Company, PetroChina, Xi’an City 710018, Shaanxi Province, China;

2. Exploration Department, Changqing Oilfield Company, PetroChina, Xi’an City 710018, Shaanxi Province, China;

3. School of Petroleum Engineering, China University of Petroleum (East China), Qingdao City 266580, Shandong Province, China

Abstract: The conductivity of acid etched fractures is one of the key parameters to evaluate the acid fracturing effect. At present, the experimental research on acid etch of fractures in carbonate reservoirs focuses mainly on limestone reservoirs, and the related research on dolomite reservoirs is rarely reported. The acid–rock reaction characteristics of limestone and dolomite reservoirs are obviously different. In order to study the acid etch morphology and microscopic reaction mechanism of dolomite reservoir fractures, we carried out experimental study on the acid etch conductivity of fractures with the core of dolomite reservoir in a block as the object and comparatively analyzed the micro-morphology of acid etch of limestone and dolomite slates by 3D laser scanning. Through the short-term conductivity experiment, the trend in conductivity of acid etched fractures under the influence of physical properties of the reservoir and acid concentration was analyzed. Compared with limestone, dolomite has a lower surface reaction speed. Moreover, its acid–rock reaction speed is an order of magnitude less than that of limestone. The acid solution of dolomite leads to less etch and its dissolution is mainly along the joint surface. High acid concentration is conducive to the solutions’ deep permeation through the acid etched joint surface, so as to connect matrix and fracture. In addition, the acid solution of a high concentration can more fully etch the wall surfaces of acid fractures to improve the non-uniform etch degree and obtain fractures of greater conductivity. Through numerical simulation, it was found that alternating acid injection could effectively improve the non-uniform etch degree of dolomite slates, the conductivity of acid etched fractures, and the acid fracturing effect.