Post-frac flowback water chemistry matching in a shale development

Shale developments are normally hydraulic fractured to stimulate the low permeability of the reservoirs, in order to allow fluid to flow to the wellbore. The most common fluid fracture deployed in shale developments is slickwater; which is typically composed volumetrically of approximately 95% water, 4% proppant and 1% other chemicals such as scale inhibitor, surfactant, biocide and corrosion inhibitor. Water management in shale plays accounts for 5% - 15% of total well completion costs. This study investigates the fate of fracturing fluids in shale developments and attempts to understand the effect of fracturing fluid trapped within the reservoir. Approximately 5% - 50% of fracturing fluid pumped is flowed back as the well is put on production. Scale deposition is often experienced within these wells due to the interaction of fracturing fluid lost to the formation reacting with formation brines. It is estimated that the formation of scale within the reservoir, blocks of nano-pores and reduces to some extent the fraction of fracturing fluid returned. The main purpose of this study was to simulate the post-frac flowback composition using a reactive transport model. The model simulates the injection of the fracture fluid, when in contact with the reservoirs minerals, a number of geochemical processes take place and with subsequent production further reactions are possible. The model was used to evaluate the possible causes of the high TDS content in the post-frac water, on one hand dissolution of salts present in the shale or the breaching of deep saline aquifers during fracturing. The value of this paper being to the industry is to increase the understanding of the geochemical reactions occurring during shale fracturing which will impact produced water reuse, scale inhibitor selection to prevent inorganic scale deposition resulting in better fracture performance.