Evaluation of Formation Permeability Using Minifrac Pre-closure Data - Case Study

Hydraulic Fracture Design relies strongly on formation permeability. For the fixed quantity of proppant, higher formation permeability will lead to higher optimal fracture width and lower optimal half-length. Low permeability and tight formations, however, in many cases would not flow without fracturing and thus cannot be tested for permeability using conventional techniques such as Pressure Transient Analysis. This is why a practical way to determine permeability for fracture design in such formations is Minifrac, or, Diagnostic Fracture Injection Test (DFIT).

Conventionally, Minifrac pre-closure data is used for determination of leak-off coefficient and fluid efficiency. After-closure data is in turn used for formation permeability evaluation. Low permeability formations, however, exhibit radial flow only after a considerable time after shut-in. This makes permeability evaluation using after-closure data not practically applicable in many cases.

In this study we propose a new approach to DFIT design and evaluation using pre-closure data for determination of formation permeability. The approach is based on the fact, that if water is used as an injection fluid, the dominant leak off mechanism will be reservoir fluid compressibility. This enables to explicitly relate permeability and leak-off coefficient. The leak-off coefficient can be determined using pre-closure data, which reduces required minifrac time considerably.