ASTM D4630
Full Name
ASTM D4630 – Standard Test Method for Determining Transmissivity and Storage Coefficient of Low-Permeability Rocks by In Situ Measurements Using the Constant Head Injection Test
Scope
ASTM D4630 outlines a field procedure for determining the transmissivity and storativity of geological formations with low permeability (less than 10⁻³ µm² or 1 millidarcy) using a constant head injection test.
Test procedure summary:
- Borehole preparation: a borehole is drilled into the rock formation, targeting the specific zones of interest. Coring is performed through these zones to gather geological information, which is supplemented by geophysical borehole logging. The borehole should be smooth to ensure proper packer seating and minimize formation damage.
- Packer installation: inflatable packers are attached to high-pressure steel tubing and used to isolate the test interval within the borehole. This isolates the test section from other parts of the borehole.
- Constant head injection: a constant pressure is rapidly applied to the water within the packed-off interval and tubing string.
- Flow rate measurement: the resulting changes in water flow rate are meticulously recorded using flow meters of varying sensitivities located at the surface. The initial transient flow rate depends on the transmissivity and storativity of the rock around the test interval, as well as the volume of water within the packed-off section and tubing.
- Data analysis: the collected transient water flow rate data is analyzed using curve-matching techniques to determine the transmissivity and storativity. If a steady-state flow rate is achieved, it can be used to directly calculate the transmissivity.
Key parameters and calculations:
- Transmissivity (T): represents the ability of a formation to transmit water and is calculated as T = K * b, where K is hydraulic conductivity and b is formation thickness. Hydraulic conductivity (K) is related to permeability (k) by K = (kρg)/µ, where ρ is fluid density, g is acceleration due to gravity, and µ is fluid viscosity.
- Storativity (S) or Storage Coefficient: represents the volume of water a formation releases from storage per unit surface area per unit decline in hydraulic head. It is calculated as S = Ss * b, where Ss is specific storage. Specific storage is a measure of how much water is stored in a unit volume of a formation under a unit change in pressure.
Advantages of the constant head injection test:
- Minimizes the influence of well-bore storage.
- Applicable to a wide range of rock mass permeabilities.
- Significantly shorter duration compared to traditional pump and slug tests used in more permeable formations.
Important considerations:
- Water quality is crucial. Even small amounts of solids in the injection water can clog the rock face, leading to inaccurately low transmissivity measurements.
- The temperature of the injection water should be at least 5°C lower than the rock mass to prevent air from coming out of solution and affecting the results.
- The number and orientation of test holes should be sufficient to capture the required detail for the project. Test holes should ideally intersect major fracture sets at right angles.
ASTM D4630 Accredited Laboratory
Applied Testing & Geosciences, LLC is accredited for performing tests using the ASTM D4630 standard. Contact us today to discuss your project requirements and receive a customized quote.
Resources
Keywords
transmissivity; storativity; permeability; constant head testing; in situ; low-permeability rocks; hydraulic conductivity; specific storage; borehole; injection test; pressure testing; flow rate; water saturation; viscosity; fracture aperture