The effects of laboratory drying techniques on the permeability of tight sandstone core
Identical samples of tight Spirit River Formation sandstone were cut side-by-side from the same piece of core and dried under different conditions in the laboratory prior to permeability testing. One core plug was dried in a controlled relative humidity chamber at 60/sup 0/C and 45% relative humidity. Another plug sample and a full-diameter (10 cm) piece of core were dried at 70/sup 0/C under a vacuum of less than 0.5 mm Hg (0.07 kPa). The permeability to gas of all three samples was subsequently measured under conditions of in-situ overburden stress and reservoir pressure. Permeability values for the samples dried under controlled humidity conditions were consistently below those samples dried in a vacuum oven. Limited data suggest that this effect may be greater at lower pore pressures. The core specimens were examined under a scanning electron microscope to detect differences in the rock microstructure that could account for the marked divergence in permeability. High power (6500x) observations of the relative humidity-dried sample revealed the presence of authigenic clay minerals blocking many pore throats. This type of clay structure was absent from the vacuum-dried rocks; pore throats in these samples were coated with fine particulate debris. It appears that extensive drying of these rock samples in a vacuum oven damages or destroys pore blocking clay by drawing off lattice water and causing the material to disintegrate, thereby opening pores and increasing permeability. Relative humidity drying, on the other hand, removes free pore water but does not significantly disturb the clay. Samples in which the pore blocking clay has been destroyed will give erroneously high gas permeability values, particularly at lower pore pressures.
- Research Organization:
- Inst. of Gas Technology
- OSTI ID:
- 5199095
- Report Number(s):
- CONF-830305-
- Journal Information:
- Soc. Pet. Eng. AIME, Pap.; (United States), Vol. SPE/DOE11622; Conference: SPE symposium on low permeability, Denver, CO, USA, 14 Mar 1983
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SANDSTONES
DRYING
PERMEABILITY
THERMAL DEGRADATION
BENCH-SCALE EXPERIMENTS
DRILL CORES
HUMIDITY
NATURAL GAS FIELDS
PORE PRESSURE
RESERVOIR ROCK
SCANNING ELECTRON MICROSCOPY
TEMPERATURE EFFECTS
ELECTRON MICROSCOPY
GEOLOGIC DEPOSITS
MICROSCOPY
MINERAL RESOURCES
NATURAL GAS DEPOSITS
RESOURCES
ROCKS
SEDIMENTARY ROCKS
030200* - Natural Gas- Reserves
Geology
& Exploration