Estimating Reservoir Pressure Gradient from Stage-By-Stage Pressure Fall off Analysis in Shale Horizontal Wells

The pressure fall-off data at the end of pumping a hydraulic fracture stage is typically recorded for 15 to 30 minutes and, in some cases, could be extended to an hour. However, this data is never analyzed and often ignored due to the lack of suitable models for estimating the fracture characteristics. This paper introduces a method to analyze these fall-off data to diagnose each frac stage by calculating stimulated surface area, stage permeability, stage fracture half-length, and stage productivity index (Ibrahim et al 2020). In this study, we present a novel approach to estimate reservoir pressure for each stage from the fall-off data analysis. A new method has been developed to estimate the final frac stage pressure gradient after the frac is complete. This method is based on using pumping and leak-off data to calculate each stage pressure which will be used to match frac stage geometry from fracture half-length, fracture conductivity, fracture face skin, and stage productivity index. The estimated stage pressure gradient will help in estimating the amount of depletion from well to well. A field case for three shale oil wells will be presented and calibrated with the existence of the Diagnostic Fracture Injection Test or DFIT method to confirm the accuracy of this method in estimating each frac stage pressure gradient. This new method can be used to help minimize Fracture Driven Interactions (FDIs) between parent and child wells. This paper proposes a novel, low-cost method for estimating all frac stage pressure gradients without performing actual DFIT tests which could cut cost and time of completion. The findings of this paper help improve the efficiency of multistage hydraulic fracturing stimulation of horizontal wells.