Simulation and analysis of wormhole formation in carbonate rocks considering heat transmission process

Matrix acidizing is a widely-used technology to extract hydrocarbon energy by pumping acid fluid to erosion reservoir rock. In matrix acidizing, eroded pores called wormholes grow in rock and become high-conductivity channels of hydrocarbon. Most previous numerical studies focus on the chemical reaction and mass transport processes in wormhole propagation, but neglecting the potential influence of temperature variation. Thus, in order to better understand the process of wormhole propagation, a radial heat transfer model capturing heat transfer and reaction heat is introduced and coupled into two scale continuum model. The results of the simulations performed with the coupled model can easily be applied to cases under formation conditions. Compared with the existing two-scale continuum model, the numerical simulation results obtained with the coupled model show that both the dissolution patterns and the pore volume required to break through are affected by the temperature. The influence of the acid temperature around the wellbore on the matrix acidizing efficiency and on the optimal acid injection rate is more significant than that of the initial formation temperature. Furthermore, both the pore volume required for breakthrough and the optimal acid injection rate increase with the acid temperature, which is consistent with previous experimental results. The temperature around the wormhole is slightly higher when reaction heat is considered, and its effects on stimulation efficiency are not significant. The effects of the formation properties are analyzed by the coupled model, demonstrating that a larger volume of acid is required to break through a more homogeneous formation with higher porosity. (C) 2017 Elsevier B.V. All rights reserved.