A Comparative Study of Acid Stimulation Techniques and Acid Recipes for a Low-Permeability and High-Temperature Dolomite Reservoir

Summary In this study, we present a comparative evaluation of acid stimulation techniques and acid formulations for a low-permeability, high-temperature dolomite gas reservoir in Austria. The objective is to determine the relative effectiveness of acid-wash vs. bullhead stimulation and to assess the performance of conventional strong acids against organic weak acids under simulated wellbore conditions. Laboratory experiments were conducted using micro- and millidarcy core plugs and a coreflooding rig to replicate field-scale stimulation scenarios. Screening criteria included pH profiling, visual and microscopic inspection, core plug weight loss, and gas permeability enhancement. For the cleaning chemical efficiency, two experiments with mudcake were also performed for acid stimulation treatment. The results indicate that the bullhead technique consistently outperformed acid wash in terms of acid penetration and core damage mitigation. Furthermore, strong acid formulations demonstrated superior performance over organic acids, with tests producing a continuous open channel from inlet to outlet. The study also evaluated the role of wellbore cleaning chemicals in removing filter cake formed by oil-based drilling mud. The cleaning fluid, containing an emulsion breaker, significantly improved stimulation outcomes, as confirmed by visual beaker tests and filter cake consistency analysis. The bullhead method combined with strong acid and effective cleaning agents is recommended for field-scale stimulation of fractured dolomite reservoir with millidarcy permeability. These findings underscore the importance of selecting appropriate stimulation strategies and pretreatment protocols to optimize reservoir productivity.