Experimental Investigation of Wormhole Propagation During Alternative Acidizing in Carbonate Reservoirs

Matrix acidification is a crucial method for reservoir stimulation, creating wormholes that connect the formation to the wellbore across damaged zones. The use of traditional acids like hydrochloric acid presents challenges such as rapid reaction rates, restricted acid penetration depth, excessive acid leak-off, and casing corrosion, particularly in high-temperature environments. This study investigates an alternative acidizing approach by exploring the effectiveness of GLDA, an environmentally friendly chelating agent, combined with emulsified and cross-linked acids. High-pressure and high-temperature (HPHT) core-flood experiments were performed to evaluate the performance of these stimulation fluids on Indiana Limestone cores both individually and in combination. High-resolution CT scanning and 3D core reconstruction were employed to analyze the stimulation fluids’ impact on pore structure and wormhole formation. The experiments identified an optimal injection rate of 1 ml/min for all three working fluids. Alternating acidification using GLDA as a first-stage treatment followed by emulsified or cross-linked acid reduced acid consumption by 56.4–65.9% compared to single-phase acidizing treatments. During subsequent stages with emulsified acid and cross-linked acid, the initial pores created by GLDA were effectively expanded, resulting in reduced fluid pressure and more efficient acidification treatment. The GLDA pretreatment can create advantageous channels for wormhole propagation through chelation. This approach not only demonstrates a reduction in acid usage but also enhances reservoir stimulation efficiency. Integrating GLDA with cross-linked or emulsified acids offers a more sustainable and effective strategy for carbonate reservoir stimulation, presenting new opportunities for improved oil recovery and environmental benefits.