Standard Test Method for Determining Transmissivity and Storativity of Low Permeability Rocks by In Situ Measurements Using Pressure Pulse Technique

Importancia y uso:

5.1 Test Method—The pulse test method is used to determine the transmissivity and storativity of low-permeability formations surrounding the packed-off intervals. This test method is considerably shorter in duration than the pumping and slug tests used in more permeable rocks. To obtain results to the desired accuracy, pumping and slug tests in low-permeability formations are too time consuming, as indicated in Fig. 1 (from Bredehoeft and Papadopulos (1)).4

5.2 transmissivity, T—the transmissivity of a formation of thickness, b, is defined as follows:

where:

K   =   equivalent formation hydraulic conductivity (efhc).

The efhc is the hydraulic conductivity of a material if it were homogeneous and porous over the entire interval. The hydraulic conductivity, K, is related to the equivalent formation, k, as follows:

where:

ρ   =   fluid density, μ   =   fluid viscosity, and g   =   acceleration due to gravity.

5.3 storativity, S—the storativity (or storage coefficient) of a formation of thickness, b, is defined as follows:

where:

S_s   =   equivalent bulk rock specific storage (ebrss).
The ebrss is defined as the specific storage of a material if it were homogeneous and porous over the entire interval. The specific storage is given as follows:



where:

C_b   =   bulk rock compressibility, C_w   =   fluid compressibility, and n   =   formation porosity.

5.4 Analysis—The transient pressure data obtained using the suggested method are evaluated by the curve-matching technique described by Bredehoeft and Papadopulos (1), or by an analytical technique proposed by Wang et al (2). The latter is particularly useful for interpreting pulse tests when only the early-time transient pressure decay data are available.

5.5 Units: 

5.5.1 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.

Note 1: A darcy (or darcy unit) and millidarcy (md or mD) are units of permeability. They are not SI units, but are widely used in petroleum engineering and geology. A darcy has dimensional units in length.

5.5.2 Viscosity of Water—Table 1 shows the viscosity of water as a function of temperature.

Note 2: The quality of the result produced by this standard is dependent on the competence of the personnel performing it and the suitability of the equipment and facility used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing/sampling/observation/ and the like. Users of this standard are cautioned that compliance with Practice D3740 does not itself guarantee reliable results. Reliable results depend on many factors; D3740 provides a means of evaluating some of those factors.

Note 3: The function of wells in any unconfined setting in a fractured terrain might make the determination of k problematic because the wells might only intersect tributary or subsidiary channels or conduits. The problems determining the k of a channel or conduit notwithstanding, the partial penetration of tributary channels may make determination of a meaningful number difficult. If plots of k in carbonates and other fractured settings are made and compared, they may show no indication that there are conduits or channels present, except when with the lowest probability one maybe intersected by a borehole and can be verified, such problems are described by Worthington (3) Smart, 1999 (4). Additional guidance can be found in D5717.

Subcomité:

D18.21

Referida por:

D0420-18, D5876_D5876M-17R24

Volúmen:

04.08

Número ICS:

07.040 (Astronomy. Geodesy. Geography), 93.020 (Earthworks. Excavations. Foundation construction. Underground works)

Palabras clave:

borehole drilling; discontinuities; fault zones; field testing flow and flow rate; ground water; permeability; pressure testing; pulse testing; rock; saturation; storativity; transmissivity; viscosity; water; water saturation;