Evaluation of Acid Fracture Conductivity of the Austin Chalk Formation

Abstract The Austin Chalk formation has been producing hydrocarbons since the 1980s using horizontal well technology. Although multistage proppant fracturing is the main development strategy for this unconventional reservoir, acid fracturing remains a strong alternative due to the high carbonate content of the formation. The viability of acid fracturing depends on how much etching can be achieved to create conductivity, whether live acid can effectively transport through the fracture, and whether the created conductivity can be sustained under closure stress. In this study, downhole cores from the Austin Chalk formation were used to evaluate the performance of acid fracturing under realistic reservoir conditions. The workflow included cutting API conductivity samples, scanning fracture surfaces before and after acid injection, and estimating etched volume. The acid injection experiment was conducted at 185°F using 15% HCl, followed by fracture conductivity measurements at increasing closure stresses. Conductivity results from the acid etched samples were compared to those obtained from a propped fracture test, which was conducted using 100-mesh sand at a concentration of 0.05 lbm/ft2. The results show that acid fracturing can generate sufficient conductivity in the Austin Chalk, comparable to or higher than that achieved with 100-mesh proppant at 0.05 lbm/ft2. This conductivity was sustained at elevated closure stresses up to 6,000 psi. The formation’s layered geologic structure strongly influenced results, and uneven etching patterns contributed more to conductivity than total etched volume alone. Supporting tests on Austin Chalk outcrop samples confirmed similar behavior. These findings reinforce the argument that acid fracturing is a strong alternative stimulation method to improve productivity in the Austin Chalk formation.