Standard Test Method for Determining Transmissivity and Storage Coefficient of Low-Permeability Rocks by In Situ Measurements Using the Constant Head Injection Test

Test Method—The constant pressure injection test method is used to determine the transmissivity and storativity of low-permeability formations surrounding packed-off intervals. Advantages of the method are: (a) it avoids the effect of well-bore storage, (b) it may be employed over a wide range of rock mass permeabilities, and (c) it is considerably shorter in duration than the conventional pump and slug tests used in more permeable rocks.

Analysis—The transient water flow rate data obtained using the suggested test method are evaluated by the curve-matching technique described by Jacob and Lohman (1)² and extended to analysis of single fractures by Doe et al. (2). If the water flow rate attains steady state, it may be used to calculate the transmissivity of the test interval (3).

Units:

4.3.1 Conversions—The permeability of a formation is often expressed in terms of the unit darcy. A porous medium has a permeability of 1 darcy when a fluid of viscosity 1 cp (1 mPa·s) flows through it at a rate of 1 cm³/s (10−6 m³/s)/1 cm² (10−4 m²) cross-sectional area at a pressure differential of 1 atm (101.4 kPa)/1 cm (10 mm) of length. One darcy corresponds to 0.987 μm². For water as the flowing fluid at 20°C, a hydraulic conductivity of 9.66 μm/s corresponds to a permeability of 1 darcy.