Mineralogy Impact on Acid Fracture Design in Naturally Fractured Carbonates

[Image: see text] The impacts of a natural fracture on the propagation of a hydraulic fracture has been extensively studied in the past decade. However, there were only minor attempts to understand the impact of natural fractures on acid distribution during acid fracturing. This study provides an understanding of the impact of natural fractures on acid fracturing designs in limestone and dolomite formations. A built-in-house model that solves fracture propagation, acid transport and dissolution, heat transfer, and reservoir productivity was utilized. A sensitivity analysis was conducted to investigate the impact of temperature, injection rate, and acid type. One of the significant differences between limestone and dolomite is the dissolution profile in the hydraulic fracture. The maximum dissolution happens close to the wellbore in limestone, but far from the wellbore in dolomite at low acid temperatures. Also, the hydraulic fracture in dolomite could have lower conductivity (i.e., permeability) compared to the intersecting natural fractures, which is not usually the case in limestone. Hence, the productivity enhancement by acid fracturing in limestone formation is higher than in dolomite. In general, natural fractures reduce productivity, and their negative impact is more significant in dolomite. The sensitivity study showed that the acid temperature significantly impacts fractured well productivity of dolomite, especially at high reservoir permeability where higher dissolution is desired. It is observed that the optimum injection rate that maximizes productivity is much higher in limestone than in dolomite. Also, acid retardation does not positively impact the productivity of dolomite compared to limestone; however, high viscosity might be needed to keep the hydraulic fracture open. This is the first study to reveal mineralogy’s impact on acid fracture performance in naturally fractured carbonates.