Numerical Investigation of Acid Stimulation Process in Carbonate Rocks with Heterogeneous Mineral Distributions

Abstract

Abstract Acid stimulation is a common well stimulation technique for the effective development of carbonate reservoirs, in which the acid solution is utilized under the formation fracture pressure to increase formation permeability while bypassing damaged domains around the wellbore. This study is motivated to evaluate the effect of mineral heterogeneity on acidizing efficiency in carbonate rocks. The two-scale continuum model is employed to describe the mass, momentum, and energy change during the acid stimulation process. In particular, the solid phase mass conservation equation is extended to consider mineral compositions, including reactive minerals of calcite and dolomite and non-reactive minerals of clay and quartz.Results indicate that mineral heterogeneity can affect both the acid consumption efficiency to achieve a breakthrough and the optimum acid injection rate corresponding to the minimum pore volume to breakthrough. The acid stimulation curve is more sensitive to the content of reactive components. More acid solution is needed to stimulate the core sample with a less reactive component of dolomite. The optimum acid injection rate increases as calcite content increases. When the reactive mineral distribution is not continuous, such as vertical or layered distribution, the acid stimulation curve is complicated by the competing reactions between reactive minerals.