Introducing a Customized Workflow to Analyze DFIT-FBA Post-Flowback Shut-In (Rebound) Data

Abstract DFIT-FBA (FBA = flowback analysis) offers a faster alternative to traditional diagnostic fracture injection tests (DFITs) for determining key parameters used in hydraulic fracturing design. While a method exists for estimating reservoir pressure from the flowback period of DFIT-FBA, this method could be inaccurate for certain cases. In this study, shut-in data (also called rebound) recorded after the flowback period of the DFIT-FBA test were analyzed to provide an independent estimate of reservoir pressure. An extensive DFIT-FBA post-flowback shut-in test was simulated and analyzed to interpret all pressure signatures. This detailed investigation provided valuable insights into physical mechanisms occurring during the post-flowback shut-in period of a DFIT-FBA test. Based on these findings, a customized analysis workflow was developed and then utilized to estimate reservoir pressure from post-flowback shut-in data for nine field cases. These results were then compared with the results obtained from the analysis of the flowback period of DFIT-FBA. Key observations from the simulation study include: 1) linear flow is the only reservoir flow regime observed during the post-DFIT-FBA shut-in data of the simulated case; 2) reservoir pressures estimated from the shut-in test are always higher than the actual reservoir pressure even after an extended shut-in period. The major takeaways from analyzing field examples include: 1) shut-in pressures recorded after a DFIT-FBA test reach a maximum, and will decline if pressure is monitored long enough; 2) more accurate reservoir pressure estimates will be obtained if the test is extended far beyond the point where maximum pressure is observed; 3) if the minimum horizontal stress and reservoir pressure are similar in magnitude, and/or occur close in time, the reservoir pressure signature during the flowback period of a DFIT-FBA could be masked by the fracture closure event. In such cases, the reservoir pressure estimate obtained from the analysis of DFIT-FBA flowback data should be used with caution, unless confirmed through independent estimates, such as DFIT-FBA post-flowback shut-in data.