Carbonate Matrix Stimulation with In-Situ Diverting Acid (ISDA) Systems: Field Scale Sensitivity Study

Abstract Uniform acid placement in carbonate formations is challenging, especially for long horizontal wells and/or highly heterogeneous strata. In many cases, operators and service companies overcome those challenges using 1) advanced completions, 2) coiled tubing, and/or 3) chemical diverters. This paper provides a road map to optimize carbonate acidizing with In-Situ Diverting Acid (ISDA), considering completion type and placement method. A field-proven carbonate acidizing model and a mechanistic model for the pressure response of ISDA are utilized. Those models accurately predict the flow of regular, organic, delayed, and ISDA systems in limestone and dolomite formations. Actual petrophysical data from the Middle East and Brazil were used to build the simulation cases for horizontal and vertical wells. An advanced acid placement simulator was used to study the effect of open hole, cased and perforated, slotted liner, and ICD completions and placement methods on the volume and number of stages of ISDA. Finally, specialized plots were generated considering petrophysical information, completion type, and placement method. The simulations from this study agree with many field observations and have shown that for bullheaded extended-reach open hole horizontal wells, the volume of ISDA required is proportional to the average permeability. A 10,000+ ft. lateral with an average. permeability < 3 md can be stimulated by bull-heading successfully with more than 95% acid coverage without chemical divergence. On the other hand, cased and perforated vertical wells with orders of magnitude permeability differences would require high volumes and multiple stages of diversion to distribute the acid properly. The completion type and placement method have a prominent effect on diversion design in acid treatments. Horizontal wells with limited entry liners and ICD completions can be successfully stimulated using a single-stage large volume diverter by bull-heading. Open hole laterals with an average permeability >100 md can be well-stimulated without diverters by CT. The specialized plots would provide engineers with a quick tool to design optimized acid treatments with or without chemical diverters, considering acid type, well geometry, placement method, completions, and petrophysical information. This study introduces the first physics-based plots for designing carbonate acid stimulation with chemical diverters. Simulation results agree with many field treatments. The generated plots provide a quick tool that saves time and effort without compromising the design quality of acid stimulation in carbonate reservoirs. This study paves the way for using physics-based AI to design acid stimulation.