Diagnostic Fracture Injection Tests (DFITs) are used to estimate stress, pore pressure, and permeability. The term “DFIT” is often used broadly to refer to any injection/shut-in test designed to create a hydraulic fracture. However, it usually refers to a test performed in a low permeability formation (<10s of microdarcy), performed after the well has been drilled, and with the intention of performing an extended shut-in (one week is most common).

This course covers the DFIT interpretation procedure from the paper URTeC-2019-123. The procedure was developed as part of a collaborative industry study sponsored by a group of six operators and one service company.

The course starts by stepping through the basic physics of a DFIT – near-wellbore tortuosity, the ideal Nolte period, the effect of the contacting of the fracture walls, and the late-time impulse period. We show how these behaviors can be diagnosed from a handful of key plots. Then, the course covers estimation of stress, pore pressure, and permeability. Finally, the course concludes by providing practical tips for interpretation.

In formations with permeability greater than 10s to 100s of microdarcy, fracture closure has a fundamentally different effect on the shape of the pressure transient response than in formations with lower permeabilities. This course is focused on interpretation of DFITs in low permeability formations (<10s of microdarcy).

The URTeC-2019-123 procedure has been validated by direct in-situ deformation measurements and detailed numerical modeling matches to field data, and it can be derived analytically from first-principles. Compared with the ‘holistic’ DFIT interpretation procedure, it gives somewhat higher estimates for stress, and often much lower estimates of permeability. The procedures differ in other ways. For example, they use different equations for ‘frac efficiency’ from ‘time to closure.’ This course discusses the empirical and theoretical reasons why the URTeC-2019-123 procedure yields more accurate parameter estimates.