Acid Fracturing Carbonate-Rich Shale: A Feasibility Investigation of Eagle Ford Formation
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AbstractDue to the high calcite content of the Eagle Ford Shale (<70%), the formation is a possible candidate for acid fracturing. Similar to hydraulic fracturing, acid fracturing injects pad fluids at a pressure greater than the fracture pressure to initialize fracture, and then inject acids to further propagate fractures and to etch the created fracture face with chemical reactions. In this study, twelve Eagle Ford Shale outcrop samples, four from each zone B, C and D, are used to determine the effect of surface etching pattern, acid concentration, calcite content, and Brinell Hardness on created acid fracture conductivity. The resultant surface etching volume is determined by a pre- and post-surface profilometer scan to calculate the changes in surface profile. Calcite content is determined by X-Ray Diffraction analyses. Conductivity tests are performed on the samples up to a closure stress of 4000 psi, as integrity permits. Based on the results obtained from this study, acid fracturing the Eagle Ford Shale could provide optimistic impact on production. Acid fracturing treatments in high calcite containing zones of the Eagle Ford Shale are expected to result in an increase in productivity. For the Eagle Ford Shale, the surface etching patterns that may provide sustained conductivity are channeling and roughness. A direct correlation is shown between calcite content of the shale and resultant surface etching volume. Furthermore, the higher the calcite content of the samples, the more likely the etching pattern is channeling or surface roughness. Brinell Hardness tests are completed on Eagle Ford samples, showing that, on average, the higher the Brinell Hardness number, the better the resulting surface etching pattern and sustained acid fracture conductivity.
