Geochemical Interpretation of Flowback Fluids to Assess Fracking Efficiency and Reservoir Compartmentalization

The geochemical assessment of flowback fluids from hydraulic fracturing represents an effective tool to quantify recovery rates of fracturing fluids and the provenance of recovered water, to assess the functionality of fracturing stages, to evaluate lateral reservoir compartmentalization between structural blocks, and to provide evidences for the functionality and efficiency of natural or hydraulic fractures on gas mobilization. As a practical benefit, geochemical fingerprinting of recovered fluids can improve strategic decisions for performed fracturing technologies by avoiding water-pay zones, to minimize volumes of required fracturing fluids for injection purposes, and to economize the recycling process for recoverable flowback fluids. For the present study, hydraulic fracturing projects of an open hole (well O-1) and cased hole (well C-1) completion were targeted to correlate geochemical time trends of flowback fluids between both well types. As a major result, exclusively 17% (6,948 barrels, abbreviated as bbl) and 2% (552 bbl) of injected fracturing fluid were recovered from the open and cased hole cases, respectively, during the post-fracturing period. In both cases, main portions of flowback water were composed of formation water from the clastic horizon close or adjacent to the fractured zone. The low recovery rate for the cased well suggests major losses of injected fluids through induced fractures. Flowback rates and volumes are more elevated for well O-1 prior to the milling out of the ball seats, which implies flowback along the balls. Heterogeneities between formation water salinities from well O-1 (TDS = 165,000 mg/L) and C-1 (TDS = 65,000 mg/L) indicate the presence of two independent hydraulic systems with compartmentalized structures between two reservoir blocks of the studied exploration field. Further studies are needed to isolate the weighting of well design (open hole vs. cased hole), fracturing techniques (number of fracturing stages and periods), and variations in formation water composition.