Rapid estimation of fracture half-length and fracture propagation-rate for individual hydraulic fracturing stages using post-frac-job reports: benchmark results from Eagle Ford case study well

This study presents a practical method for estimating the propagation-rate and half-length of hydraulic fractures created in the individual fracturing Stages, using operational data recorded in so-called post-frac reports. The fluid volumes and pressures used during the actual pumping of individual fracturing Stages are routinely recorded in post-frac reports. However, these data are rarely analyzed in detail, and mostly serve as work-completion reports, based on which the service company that executed the hydraulic fracturing treatment will invoice the well owner. The new method elaborated here uses the hydraulic pressures and pumped volumes of frac fluid, as detailed in the frac-job reports. The required post-frac report data (from the actual completion job) and historic production rates were kindly availed by the operator, for this comprehensive case study using Eagle Ford well data. Starting from the pressures recorded at the wellhead, all the subsequent pressure gains and losses are computed as fluid moves toward the evolving fractures. The fluid pump-rate at the wellhead is also used in mass-balance calculations, considering fluid losses (if any) due to leak-off. The fracture propagation-rate and associated incremental growth of the fracture half-length and fracture width are quantified for all of the 22 Stages in the study well. The fracture half-lengths vary between 110 and 240 ft; the average fracture half-length is 157 ft. A back-check for accuracy of the new method is applied by comparing the average fracture half-length for the well obtained by averaging the Stage-based solutions (based on frac-report data) with independent solutions (based on history-matching production data), which gave 144 ft fracture-half-length (revealing a limited mismatch of 9.5%). The difference can be largely attributed to fracture closure prior to the production from which data was used to estimate the 144 ft fracture half-length. Other major insights from our in-depth analysis are (1) fluid leak-off over the time of the fracturing in the shale well studied is negligibly small, and (2) pressure-loss occurring in the fracture slots cannot be accurately computed by a Cubic Law equation, for reasons first detailed in the present study.