Phase I of the PETGAS (Petrophysics of Tight Gas Sandstone Reservoirs) JIP was undertaken by the University of Leeds, and sponsored by Aurelian Oil and Gas plc, BG, BP, EBN, Shell and Wintershall. A key aim of PETGAS is to create An Atlas of the Petrophysical Properties of Tight Gas Sands containing detailed descriptions of the properties of individual samples (e.g. porosity, gas and brine permeability, Hg-injection characteristics, diagenetic history, mineral composition) as well as individual sections outlining key controls on the petrophysical properties.
In total, the PETGAS sponsors provided ~25 samples each for routine core analysis (RCA) and around 35% of these were then subject to special core analysis (SCAL). In the original project proposal the RCA analysis was to involve:
- X-ray CT tomography;
- Microstructural analysis using secondary electron microscopy (SEM),
- Quantitative X-ray diffraction analysis (QXRD),
- He porosity;
- Hg-injection porosimetry;
- Gas permeability at a single effective stress
- Brine permeability at a single effective stress;
- Ultrasonic velocities (Vp, Vs1, Vs2) at a single effective stress.
- Electrical resistivity at 100% brine saturation.
- Gas permeability at a range of effective stresses up to the in situ stress
- Brine permeability at a range of effective stresses up to the in situ stress
- Ultrasonic velocities (Vp, Vs1, Vs2) at a range of effective stresses up to the in situ stress.
- NMR T2 distributions.
- Capillary pressure analysis using humidity chambers, porous plates and the centrifuge.
- Electrical resistivity measurements as a function of saturation.
- Brine permeability and electrical resistivity of 100% brine saturated samples as a function of stress.
- Gas relative permeability analysis at each capillary pressure.
- Stress dependence of relative permeability.
- NMR T2 at each saturation.
- Pore volume compressibility.
- Static elastic properties.