Acid fracturing is one of the stimulation methods used in carbonate formations and has been proved effective and economical. Because of the stochastic nature of acidizing in carbonate formation, designing and optimizing acid fracture treatment today still remain challenging. In the past, a simple acid fracture conductivity correlation was usually sufficient to estimate the overall average fracture conductivity in the formation, leading to the computation of the productivity index for fractured well performance. However, the statistical nature of heterogeneity could not be included in the modeling. Understanding the important role of heterogeneity to stimulation performance becomes a crucial step in design and optimization. In order to study the effect of this stochastic nature on acid fracturing, a fully 3D acid reaction model was developed based on the geostatistical parameters of the formation. This made it possible to describe local conductivity distribution related to acid transport and reaction process. In this study, we have developed a new interactive workflow allowing the model of the fracture propagation process, the acid etching process and the well production interactively. This paper presents the novel approach in integrating fracture propagation, acid fracturing, fracture conductivity, and reservoir simulation models in a seamless fashion for acid fracturing design.
In this new approach, the fracture geometry data for a hydraulic fracture is first obtained from commercial models of hydraulic fracture propagation, and then the 3D acid fracture model simulates acid etching and transport on the same gridding system from the fracture propagation model using the width distribution as the initial condition. We then calculate the fracture conductivity distribution along the created fracture considering the geostatistical parameters such as permeability correlation length and standard deviation in permeability of the formation. The final step of the approach is to predict well performance after stimulation with a reservoir flow simulator. The significant improvements of the new approach are capturing the geostatistical effect of the formation and modeling the acid etching and transport more accurately. The paper explains the methodology and illustrates the application of the approach with examples. The results from this study show that the new model can successfully design and optimize acid fracturing treatments.