Book Description
The ability to reuse produced waters in hydraulic fracturing operations will not only conserve freshwater resources but potentially enhance production in some cases as well. This study assesses the effects of pH and ionic strength on fluid-rock interactions associated with using produced water for hydraulic fracturing. Frontier Formation core samples (consisting of interbedded shales and sandstones) used in experiments were collected from the Hornbuckle 1-11H well within the Powder River Basin of Wyoming. A simplified fracturing fluid was constructed based on information retrieved from the Hornbuckle 1-11H completion report and includes HCl, methanol, a clay stabilizer, and an iron chelating agent. Make up water for the fracturing fluid was geochemically modeled to represent formation waters that naturally exist in the Frontier Formation. Experiments react core samples and hydraulic fracturing fluids at ionic strengths of ~ 0.015, ~ 0.15, and ~ 1.5 molal as well as near-neutral and acidic pH at 115°C (~240°F) and 35 MPa (~5000 psi) for ~ 28 days to replicate in-situ reservoir conditions. Results show significant changes in the aqueous concentrations of calcium, strontium, potassium, magnesium, lithium, and silica. Acidic pH as well as high ionic strength begins to dissolve carbonates and feldspars. Aqueous potassium concentrations increase with higher ionic strengths and shows no effect from pH, potentially due to sodium substitution in illite clays. Magnesium trends are similar to potassium, however significant decreases in aqueous magnesium occur in near-neutral pH conditions. Relative increases in aqueous silica are fastest in acidic pH conditions and unaffected by initial ionic strength. Combining these findings to already existing research has the potential to optimize well production while simultaneously conserving freshwater resources in the future.