THMCD modeling of carbonate acdizing with HCl acid

Abstract

Developing a Thermal–Hydrologic–Mechanical–Chemical–Damage (THMCD) coupling model for carbonate rock based on TOUGHREACT–FLAC3D simulator is innovatively put forward in this paper. In present study, a carbonate acidzing model with HCl acid, which considers thermal, fluid flow, mechanics, chemical reaction and mineral dissolution, and damage evolution, is carried out to explore the essence of acid fracturing. To consider the heterogeneity of rock materials, Weibull distribution function is adopted to consider the heterogeneity property of the carbonate in FLAC3D. The investigation results show that, initially the damage zone spreads uniformly within 5 m around the injection hole, then none-uniform propagation of the damage zone occurs due to the heterogeneity of the carbonate. The severely damaged areas are mainly concentrated around the injection hole, and the damaged area may extend about 10 m during carbonate acidizing with HCl acid. Based on the damage propagation principle, PH variation, ions concentration, temperature variation and permeability change are basically consistent with the damage distribution of the carbonate. The PH value within 5 m around the injection hole is relatively high due to the consume of the injected acid, and the minimum PH value is obtained at the periphery of the far damage zone during carbonate acidizing with HCl acid. The concentrations of the generated H + , Cl − , Ca 2 + and HCO 3 − are high in the vicinity of the fracturing hole, basically identical with the damage distribution of the carbonate. The magnitude of carbonate permeability in the damaged carbonate has increased dramatically compared with the initial permeability value. The new THMCD simulator leads to an enhanced elaboration of carbonate acidzing with HCl acid in oil engineering. • THMCD is carried out to explore the aessence of acid fracturing. • PH variation and permeability change are basically consistent with the damage distribution. • Permeability in the damaged carbonate has increased dramatically during acid fracturing.