Simulation and analysis of matrix stimulation by diverting acid system considering temperature field

摘要

In the acidizing process, the problem of an uneven distribution of acid owing to excessive heterogeneity of carbonate rocks is increasing. Diverting acid with intelligent diverting characteristics is a key technology used to distribute acid uniformly in heterogeneous carbonate reservoirs. The process of diverting an acid stimulation is accompanied by some complex processes, such as a reactive mass transfer, porous media heat transfer, reaction heat release, and changes in the chemical characteristics. The current evaluation model of diverting an acid stimulation in theory has not considered such factors. In addition, an experimental evaluation method is difficult to apply to simulate the formation conditions under high temperature and pressure. Therefore, in this paper, we first evaluate the rheological properties of a novel VES diverting acid, and then establish an equation of acid viscosity change under the influence of multiple factors. Finally, a multi-reservoir diverting acidizing model with comprehensive consideration of the heat transfer, mass transfer, and chemical properties was established, and the effects of diverting the acidizing under reservoir conditions was simulated and analyzed.An experimental evaluation of novel VES diverting acid shows that the growth of a secondary wormhole is longer and the dissolution morphology is more uniform than that of the main wormhole. During the process of diversion, there is an obvious protrusion in the pressure drop curve of the acid. The simulation and analysis results show the following: The simulation of acid entering into multiple layers shows that diverting the acid can effectively increase the amount of acid entering into the low permeability layer, which results in a better development of a wormhole in a low permeability layer. It also reduces the non-uniformity of the acid distribution between the layers. The effects of the bottomhole temperature on the diverting acid viscosity exceed the effect of the reaction rate and the diffusion coefficient, which results in a higher bottomhole temperature, and worse diversion effect. The injection displacement of acid has a slight effect on the diverting effect. The higher the displacement, the better the effect of diversion. The heterogeneity of a formation has a significant effect on the diverting effect, namely, the higher the heterogeneity, the weaker the effect.