Coupled geochemical-geomechanical alterations in shale fracture systems

Shales are typified by low permeability, where geochemically-induced permeability alterations to shales serving as energy sources or waste repositories can hinder or shut down operations. In this work, we explored the influence of key physical and chemical controls (temperature, fracture geometry, fluid saturation) on barite precipitation in shale under representative subsurface conditions, as well as the effects of induced barite precipitation on fracture permeability. A series of triaxial direct shear experiments was designed to promote barite precipitation in fractured shale cores, where continuous x-ray radiography and periodic x-ray computed tomography was applied to monitor the onset and development of barite precipitation resulting from mixing of incompatible fluids. The results confirm that precipitation becomes more favorable at increasing temperatures and barite saturation indices, and particularly with elevated [Ba²⁺] relative to [SO₄^2-]. No significant permeability reductions were observed, due primarily to the fact that precipitates preferentially filled offshoot fractures and coated fracture walls, leaving primary flow paths uninhibited. The results have direct implications for minimizing and preventing barite scaling in shale oil and gas reservoirs, as well as important implications for predicting fluid transport in tight subsurface systems that are susceptible to geochemical alterations.