This work presents the development of a methodology to numerically represent the acid treatment in a test plug, as well as to reproduce the different existing dissolution patterns and to obtain the corresponding values of pore volumes to breakthrough (PVBT). The numerical simulation is performed in a commercial CFD package that uses finite volume method. The modeling includes the effect of heterogeneous porosity/permeability and the presence of different types of minerals that impact the PVBT value, since they have different reaction rates at usual operation temperatures. Through these considerations, the formation of preferential channels, which are characteristics of the various patterns of wormhole, is captured by the numerical simulation.
The goal of this development is the extraction of the characteristic PVBT curves for any pair formation/acid by numerical simulation. It is possible through the use of measured data during drilling, such as average porosity and range of variation, rock mineralogy, etc., and through the knowledge of reaction rates for each pair formation/acid. Using these data, the simulation is able to extract PVBT curves for different numerical test plugs, making it possible to prepare a statistical analysis that has greater significance than just a few experimental tests.
The results show that PVBT curves obtained numerically are in good agreement with the physical behavior expected when compared to experiments. The variation range of the heterogeneous porosity and the presence of different minerals, which have distinct reactivity with acid, significantly change the behavior of the process for the same operating condition.
Better understanding of acid treatment in carbonates (both limestone and dolomite) is important since the new Brazilian petroleum reservoirs are located below pre-salt layer. These rock formations are commonly subjected to acid stimulation in order to increase reservoir productivity. Therefore, the numerical PVBT curves obtained from this work could be used in simpler models to simulate the acid treatment in a reservoir scale. The use of more accurate curves can help the engineers to improve the design of operation conditions and, thus, increase the production capacity and distribute uniformly the treatment.