Standard Test Method for Determining Transmissivity and Storativity of Low Permeability Rocks by In Situ Measurements Using Pressure Pulse Technique
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:
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:
5.3 storativity, S—the storativity (or storage coefficient) of a formation of thickness, b, is defined as follows:
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.
5.5.1 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.
1.1 This test method covers a field procedure for determining the transmissivity and storativity of geological formations having permeabilities lower than 10−3 μm2 (1 millidarcy) using the pressure pulse technique.
1.2 The transmissivity and storativity values determined by this test method provide a good approximation of the capacity of the zone of interest to transmit water, if the test intervals are representative of the entire zone and the surrounding rock is fully water saturated.
1.3 Units—The values stated in SI units are to be regarded as the standard. The values in parentheses are mathematical conversions provided for information only and are not considered standard. Reporting of test results in units other than SI shall not be regarded as nonconformance with this standard.
1.4 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026, unless superseded by this standard.
1.4.1 For purposes of comparing a measured or calculated value(s) with specified limits, the measured or calculated value(s) shall be rounded to the nearest decimal or significant digits in the specified limits.
1.4.2 The procedures used to specify how data are collected/recorded or calculated in this standard are regarded as the industry standard. In addition, they are representative of the significant digits that generally should be retained. The procedures used do not consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the user’s objectives; and it is common practice to increase or reduce significant digits of reported data to be commensurate with these conditions. It is beyond the scope of this standard to consider significant digits used in analysis methods for engineering design.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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