EXPERIMENTS EVALUATING GEOCHEMICAL ALTERATION OF MATRIX MATERIALS ADJACENT TO SIMULATED HYDRAULIC FRACTURES

Determining the geochemical interactions that occur during hydraulic fracturing is a non-trivial process due to the variability in both formation water and hydraulic fracturing fluid (HFF) composition. The introduction of performance additives, such as de-scaler and acid, further increases the system complexity. We have performed experiments evaluating several different novel HFF mixtures in an attempt to capture a broad view of the geochemical interactions occurring at depth. Marcellus Shale outcrop was artificially fractured and propped open using a standard 40/70 mesh sand to mimic a hydraulically fractured unit. Four HFF compositions including natural spring water without additives, natural spring water with typical hydraulic fracturing chemicals plus acid, synthetic reused produced water, and synthetic produced water with hydraulic fracturing chemicals plus acid were used in the experiments. Computed tomography scanning and scanning electron microscopy were performed on the cores before and after reaction. The imaging techniques indicate that HFF with acid resulted in net dissolution, while reused produced water resulted in barite precipitation, regardless of the application of scale inhibiter or other additives. The geochemical modeling is in agreement with the physically observed changes, accurately predicting precipitation and dissolution. The proppants appear to reduce flow in some regions of the fracture and thus residence time of fluids which will impart differential geochemical processes throughout the fracture. Experiments utilizing freshly drilled core material are ongoing to facilitate a comparison between the outcrop samples and to evaluate the interaction of proppants with flow pathing and ultimately precipitate location.