Thicknesses of Chemically Altered Zones in Shale Matrices Resulting from Interactions with Hydraulic Fracturing Fluid

Hydraulic fracturing of unconventional shale reservoirs increases the fracture network surface area to access hydrocarbons from the low permeability rock matrix. Porosity and permeability of the matrix, through which hydrocarbons migrate to fractures, are important for determining production efficiency and can be altered by chemical interactions between shale and hydraulic fracturing fluids (HFFs). Here, we present results from an experimental study that characterizes the thickness of the alteration zone in the shale matrix after shale–HFF interactions. Experiments were conducted with whole cores submerged in HFF both with and without added barium and sulfate to promote barite scale formation. After 3 weeks of reaction at 77 bar and 80 °C, the cores were characterized using X-ray microtomography, synchrotron X-ray fluorescence microprobe imaging, and synchrotron X-ray absorption spectroscopy. Our results show that the thickness of the altered zone depends on shale mineralogical composition and varies for ...