Evaluation of single fracture stage performance with integrated rockmechanics and pressure transient analysis

The most common stimulation technique for shale production is multistage hydraulic fracturing. Estimatingfracture geometry is a focal parameter to judge the fracture operation and predict the well performance.Different direct and indirect techniques can be used for fracture diagnostics to estimates fracture geometries.The current study combines fracture measurements and pressure transient analysis to estimate fracturesurface area on each stage and to estimate production as a pseudo production log. The numbers and kinds of fractures were calculated as a function of treating pressures, injection rates,proppant concentrations, and formation properties to compute fracture surface area (FSA). Pressure transientanalyses were then conducted with the leak-off data upon completion of each frac stage to estimate theproducing surface (PSA). The fall-off data was processed first to remove the noise and water hammeringeffects. The PTA diagnostic plots were used to define the flow regime and the data were matched with ananalytical model to calculate producing surface area. Tensile and shear fractures are both created during the injection of frac fluids. Shear fractures are causedby movement in already existing natural (fluid expulsion) fractures found in all shale source rocks. Shearfractures form a pressure below the minimum horizontal stress. These shear fractures take advantage ofthe rock fabric and develop higher surface area than tensile fractures for the same given volumes of waterand sand. FSA is a measure of permeability enhanced area due to hydraulic fracturing. Producing surface area isthe resulting effective flow areaconnected to the wellbore. Diagnostic plots showed a linear and radial flowregime depending on the formation and the completion design. Good correlations were found between PSAand FSA results. In general, higher FSA produces higher PSA. In cases where producing surface area washigher than expected from fracture surface area, communication was found with offset wells. When FSAhigher than PSA were found, it was usually caused by increased stress from too close offset wells. Combining FSA and PSA measurements provides forecasts of production for each stage and helps tooptimize well spacing at the end of each frac stage.