Field Trial of a Modified DFIT (Pump-in/Flowback) Designed to Accelerate Estimates of Closure Pressure, Reservoir Pressure and Well Productivity Index

ABSTRACT A problem with the conventional diagnostic fracture injection test (DFIT) design, which involves analysis of the pressure falloff after the pump is shut-off, is the long test times required to achieve closure pressure ( p c ), a proxy for minimum in-situ stress, and after-closure flow regimes that can be analyzed for reservoir pressure in ( p r ) and transmissibility. An alternative approach to DFIT implementation is to flowback the injected fluid immediately after the pump is shutdown. Historically this approach has been to accelerate closure only, but recently the authors have demonstrated that careful design of the flowback procedure can yield accelerated p c estimates and possibly reservoir information. The new DFIT is referred to as ‘DFIT-FBA’, where FBA refers to the flowback analysis component to the test. p c is estimated using a Cartesian plot of flowing pressure versus flowback time. p r is determined through flowback data flow regime identification. The well productivity index for the studied reservoir interval is derived using the flowing material balance method. With constraints applied on created fracture properties, reservoir permeability may be determined. The practical application of the DFIT-FBA method is demonstrated with a field trial performed in a western Canadian tight oil reservoir. The resulting DFIT-FBA data quality is excellent yielding both closure and reservoir pressures due to accurate flow rate measurement. Both pressure estimates are in excellent agreement with a conventional DFIT performed on the same zone in the same area, but were obtained in a fraction of the time. In addition, application of the flowing material balance equation to after-closure data yielded an estimate of well productivity index for the tested interval. The DFIT-FBA demonstrated herein allows estimation of properties of interest to completions and reservoir engineers in a fraction of the time of the conventional DFIT.