Study on the influence of mineral heterogeneity and temperature on acid–rock reaction behavior in mixed sedimentary reservoirs

Abstract

Mixed sedimentary rocks present considerable challenges for petroleum and geothermal resource development due to their strong heterogeneity. Acidizing is an effective stimulation technique to enhance the productivity of such reservoirs. To investigate the impact of rock heterogeneity on matrix acidizing performance, this study assumes the coexistence of carbonate and non-reactive minerals within each mesh and constructs three mineral distribution models: uniform, banded, and blocky. Based on a coupled thermo–hydro–chemical two-scale model, the effects of mineral composition, mineral distribution, temperature, and reaction heat on wormhole development in mixed sedimentary rocks are systematically analyzed. The results show that the content of non-reactive minerals significantly affects acidizing efficiency. A high content reduces efficiency, whereas a low content suppresses branching and lowers acid consumption. Mineral distribution patterns strongly influence wormhole morphology and acidizing efficiency. Uniform distributions promote branching and higher acid consumption, while banded patterns favor dominant channels, with the breakthrough pore volume (PV_bt) reduced by 46 % compared with the uniform distribution. In blocky distributions, acidizing efficiency is more sensitive to the injection rate. Initial wormhole formation near the wellbore is mainly controlled by the original permeability, while mineral distribution governs the selection and branching of dominant wormholes. Temperature exerts a limited effect on dissolution patterns. However, increasing temperature accelerates wormhole growth and branching, thereby reducing acidizing efficiency, while higher injection rates can mitigate this effect. The influence of reaction heat on PV_bt decreases with increasing temperature. In low-temperature reservoirs, reaction heat enhances local temperature and reaction rate, resulting in a 9.3 % reduction in PV_bt. Moreover, reaction heat significantly alters the reservoir thermal field, raising the overall temperature by approximately 10 °C and forming high-temperature zones around wormhole walls and tips. This study provides useful insights for optimizing acidizing treatments in mixed sedimentary reservoirs.