(475f) Reactive Transport in Shale Matrix after Fracturing Fluid Imbibition

The porosity and permeability of shale matrices are critical for hydrocarbon transport, and thus directly impact production efficiency. After hydraulic fracturing fluid is injected, it is imbibed by shale and cause a series of chemical reactions, including dissolution of primary minerals that increases porosity, and precipitation of scale minerals that occludes porosity, both impacting hydrocarbon flows through the matrix. Our previous experimental work shows that these chemical reactions extend from the fracture into the matrix by micrometers to centimeters, varying with respect to shale mineralogy, fluid composition, and reaction types. Based on our experimental findings, we built a reactive transport model as part of this study. After successfully matching the modeling results with the experimental observations, we obtained the chemical reaction network governing shale-fluid interactions, which can be readily incorporated into shale transport models to explore the effects of chemical reactions. Using our model, we further explored the influence of various factors on chemical alteration. The modeling results strikingly show the difference between domains with and without continuous injection of fracturing fluid With continuous fluid flow in the main fracture, barite (BaSO₄) scale is a high concern because it significantly reduces porosity. Iron-bearing scale formation is negligible because the high fluid-to-solid ratio dilutes the iron concentration. In contrast, with less fluid flow, the shale matrix experiences less barite scale formation, but iron concentration can increase locally resulting in iron(III)-hydroxide precipitation in the matrix as well as in the fluid phase occupying pore space in the fractures/microcracks. The fundamental understanding of reactive transport processes gained from this study helps us to evaluate chemical damage in unconventional reservoirs due to fluid imbibition. The numerical modeling framework will be used to explore basin-specific scale-control strategies.