Matrix acidizing is a stimulation treatment during which acid is injected below formation fracture pressure. The purpose of acidizing is to enlarge pore space or create channels through dissolution of plugging particles and formation minerals near the wellbore. Simulation of acidizing process is computationally expensive, especially for geochemical simulation which considers full-species transport and complex reactions. In this paper, geochemical modeling of acidizing process is implemented through coupling two simulation models. One is UTCOMP (a 3D reservoir simulator) which is responsible for calculations of fluid flow and solute transport. The other is IPhreeqc (a geochemical package) which is responsible for calculations of kinetic and equilibrium reactions among minerals and aqueous species. Acidizing simulation through the coupled model UTCOMP-IPhreeqc is computationally expensive, and geochemical calculations through IPhreeqc are the computational bottleneck. To improve the computational efficiency, geochemical calculations which take up the majority of the computational time are parallelized. And speedup techniques are implemented to reduce the number of IPhreeqc calls through monitoring the amount change of geochemical components. We have validated the coupled model UTCOMP-IPhreeqc through comparison with the analytical solution in previous work. Parallel performance is measured by comparing total CPU time, CPU time spent on geochemical calculations, and speedup ratios among simulation runs using different processor numbers. For heterogeneous matrix, different dissolution patterns are generated under different injection rates, and the computational time varies depending on the total injection time and the average time step size. For different dissolution patterns, the overall speedup ratio is up to 6.69 when using 16 processors, reducing 85% of CPU time compared with the case using a single processor. The speedup ratio for geochemical calculations is up to 14.21 when using 16 processors, saving 93% of CPU time compared with the case using a single processor. Besides parallel computing, the speedup techniques also improve the computational efficiency, and obtain optimal performance for wormhole dissolution patterns in which most of the geochemical reactions occur in a localized volume. The computational time is reduced to 49% maintaining 96% accuracy compared with the case without using speedup techniques. The coupled model UTCOMP-IPhreeqc has the modeling ability of full-species transport and complex reactions. On this basis, the presented model significantly improves the computational efficiency of UTCOMP-IPhreeqc through parallel computing and speedup techniques reducing the computational time of geochemical calculations.

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