A Cost-Effective Pump-Down Falloff Pressure Test for Pore Pressure and Closure Pressure Evaluation
Authors: Lolon E. , Mayerhofer M. , Griffin L. , Pearson M. , McChesney J. , Strickland S. 
Published: September 2024

High resolution surface pressure data is increasingly being acquired not only during the hydraulic fracture treatment, but also during and after the wireline pump-down and perforating phases. While pump-down falloff pressure data recently became more accessible, it has not commonly been analyzed as a Diagnostic Fracture Injection Test (DFIT) because the pump-down procedure doesn't follow standard DFIT practices. It is common that after perforating the first stage, pump-down operation is immediately followed by a hydraulic fracture treatment to increase operating efficiency. The immediacy of this practice forfeits an opportunity to collect important post-perforation falloff pressure data which may be analyzed to understand rock properties.

This paper introduces a cost-effective procedure to evaluate pore pressure and closure pressure by introducing small changes to pump-down practices. The method begins with a wireline pump-down at 2-15 bpm to the toe of the lateral, then continues with an injection usually at 2 bpm while perforating the first stage, concluding with an extended shut-in. The operator perforates the toe stage with a wet casing shoe at least 7 to 10 days before frac fleet arrival to ensure there is no issue pumping into the well for the first stage. Duration of the extended shut-in (falloff) and volume of water pumped while perforating do not significantly differ from the duration and injected volume for a DFIT. But, unlike DFITs where a pump truck is mobilized to location after the toe prep is completed, the pump-down falloff test is performed as an integral part of the pump-down operations, therefore eliminating the need to dispatch pumping personnel and equipment to perform a separate DFIT pump-down. The test can be done during the first stage perforating operation of plug-and-perf completed horizontal wells using real-time high-resolution pressure gauges that record pump-down injection rates and pressures.

The operator has successfully performed the extended pump-down falloff pressure tests in 12 horizontal wells in the Williston Basin. The results of these tests were validated with offset DFITs. The closure and pore pressure results from both methods were in good agreement, but with some depletion observed in the most recent wells drilled. This paper shows that not only can we estimate pore pressure (p¯), but also closure pressure for the "total rock system" affected by the injection using the first stage's pump-down and perforating falloff pressure data without conducting a conventional DFIT. The authors also analyzed pump-down pressure decline data for all other stages to identify stages with reservoir pressure depletion or potential communications with offset fracs or prior stages (stress shadow) along the lateral allowing the frac design to be adjusted if needed prior to pumping the stages (e.g., pump a smaller treatment when a stage is depleted). The proposed pump-down falloff tests are operationally practical and may be used as an alternative option in evaluating pore pressure and closure pressure differences among wells on multi-well pads.