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A new method for assessing stage-based hydraulic fracturing quality in Wolfcamp formation of Permian Basin

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In 2018 US Geological Survey assessed Wolfcamp formation in Permian Basin at west Texas and southwest New Mexico, USA as the world's largest tight oil play that has the most technically recoverable reserves. This is the result of favorable combination of tectonic activities and the depositional environments in the Paleozoic period. Three major cycles of tectonic movements controlled the creation of Permian Basin and its sub-basins. Frequent seawater inundations and retreats caused cyclic changes in depositional environments from Pennsylvania to early Permian ages, leading to the formation of an organic rich, tight and thick formation, the highly heterogeneous Wolfcamp play. Advanced completion technology of combining horizontal drilling with multi-stage massive hydraulic fracturing is needed for the commercial development of Wolfcamp play. Successful application of advanced completion technology in Wolfcamp faces two challenges: stage-after-stage cumulative stress-shadow effects and localized heterogeneity in lithofacies and reservoir quality. The “one-for-all” fracturing design needs to be able to fine-tune stage-by-stage based on real-time feedback from fracturing quality of previous stage. Existing methods, from production logging to micro-seismic mapping, cannot provide real-time feedback of stage-based treatment quality. We propose a new method in this paper. The new method is based on the assumption that constant density of slick-water at shut-in intervals during hydraulic fracturing allows an accurate calculation of bottom-hole pressure from surface treatment pressure and true vertical depth at each stage. Using real-time on-site monitored surface treatment pressures during shut-in intervals at the end of pad and flush injections, stage-by-stage fracturing quality are calculated. Two Wolfcamp case studies in Midland Basin at Reagan County, Texas show that the new method can be used to quantify stage-based treatment qualities. Stage-based fracturing qualities from this new method are consistent with stage-based treatment results evaluated using other methods.