Fracturing fluids are chemically reactive and can interact with shale once injected into subsurface. The chemical interactions between shale and fracturing fluids cause dissolution of primary minerals and precipitation of secondary minerals. These chemical reactions do not only affect the permeability of the shale fractures, but also alter porosity, permeability, and diffusivity of the shale matrix. It is important to understand the lengths and extents of shale matrix alteration, because hydrocarbon needs to migrate through the matrix to the fracture in order to be collected. Here we show a study that quantifies the alteration zone depths in shale matrices after reacting with fracturing fluids at 80 <sup>o</sup>C and 77 bars for three weeks. We focus on carbonate dissolution, barite precipitation, and pyrite oxidation in clay-rich Marcellus and carbonate-rich Eagle Ford shale samples. Our results show that the reaction zones are generally larger than we expected for low-permeable shale. The depths of reaction penetration vary from a couple of micrometers to centimeters, depending on reaction types and mineralogical compositions of the shale. Our results provide insights into predicting hydrocarbon migration through shale matrices and improving unconventional simulation processes.

Alteration depths from the shale surface into the matrix

2019 Spring National Meeting

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