Simulation-based optimization of matrix acidizing in heterogeneous, high-temperature carbonate reservoirs: a multi-well case study

Carbonate reservoirs present significant production challenges due to rock heterogeneity, tight formations, and formation damage. Matrix acidizing, a stimulation technique that dissolves formation minerals at sub-fracturing pressure, is commonly employed to mitigate formation damage and enhance permeability. While the effectiveness of viscoelastic diverting acid (VDA) and emulsified acid (SXE) is well established, optimizing their interactions under varying concentrations and volumes remains a key gap. This study addresses this gap through a structured, simulation-based sensitivity analysis of matrix acidizing in a high-temperature, dense, and heterogeneous carbonate reservoir in a Middle Eastern oilfield. Simulations were conducted by incorporating data from eight wells with a history of acid stimulation. A two-stage validation against actual pre-treatment and post-treatment flow rates yielded a maximum relative error of 5.5%, demonstrating that the simulation model closely matched the historical well flow rates. This provides confidence that the simulation-based approach can be reliably applied at the field scale. Sensitivity analysis was performed across four parameters: acid type, acid concentration, diverter concentration, and diverter volume. The novel contribution of this work lies in the direct, scenario-based comparison of hydrochloric acid (HCl) and SXE across these parameters, resulting in well-specific optimization guidelines rather than generalized recommendations. The analysis revealed that switching from HCl to SXE consistently reduced the skin factor and increased production, while higher acid concentrations (28% versus 15%) improved outcomes for both acid systems. Increasing VDA concentration and volume improved production using HCl. In contrast, these changes had minimal impact when using SXE, indicating that SXE requires less diversion. Notably, for HCl systems, effective diversion was found to compensate for lower acid strength. In many of the studied wells, HCl 15% with increased diverter volume performed comparably to or better than HCl 28% with reduced diverter volume. The optimal SXE scenario (SXE 28% with VDA 15% at one-third of the main acid volume) achieved a post-treatment flow rate 2.77 times higher than the pre-treatment rate, while the optimal HCl scenario (HCl 28% with VDA 28% at a volume equal to the main acid) achieved a 2.21-fold improvement. Although the HCl-based scenario produced greater fluid penetration, the SXE-based scenario yielded wormhole regimes closer to the dominant wormhole regime, correlating with superior productivity. The simulation framework and scenario-specific recommendations developed in this study provide a structured roadmap for designing more efficient acid treatments in reservoirs with similar high-temperature, heterogeneous carbonate formations.