Navigating DFIT Pressure Transients: Storage, leakoff, near-wellbore tortuosity, and postclosure

Diagnostic Fracture Injection Tests (DFITs) are used to measure stress, permeability, and fluid pressure in low permeability formations. A relatively small volume of water is injected, fracturing the formation. The well is shut-in, and pressure is monitored for days or weeks. The pressure transient is interpreted to estimate formation properties. Preclosure interpretations are aided by G-function plots, and postclosure interpretations are aided by log-log derivative plots or other specialized plots. In this talk, I introduce the basics of DFIT interpretation and describe key physical processes that impact transient behavior. Near-wellbore tortuosity can distort the transient at early time, and in severe cases can make the transient uninterpretable. When the fracture walls come into contact (mechanical closure). the storage coefficient of the system decreases as the fracture stiffens, causing an increase in the pressure derivative. Leakoff transitions from early-time Carter to late-time impulse flow, causing a peak in the logarithmic derivative. Recent research suggests that industry-standard methods of interpreting DFITs have not fully accounted for these effects and can lead to significant inaccuracy in stress and permeabilitv estimates. Conventional fracturing simulators do not handle fracture closure, and so conventional DFIT interpretations have been based on 'preclosure' and 'postclosure' calculations that skip over the closure process itself. I review results from a fracturing simulator designed to realistically describe fracture closure. For the first time, this enables an entire realistic DFIT pressure transient to be matched with a single continuous calculation. Results from these simulations have inspired a rethinking of interpretation strategy. I review recent SPE papers and paths forward.

Speaker: Mark McClure, McClure Geodynamics