Contractional natural fractures and slot porosity play and will continue to play an important role in commercial gas production from tight sands. The process that leads to these types of porosities starts with deposition of sand grains. As the grains get progressively buried inelastically the net stress increases continuously. Eventually the sand grains reach their maximum depth of burial and at this stage the vast majority of the porosity and permeability has been destroyed. Uplift leads to a cooling effect and thermo-elastic stresses that create contractional fractures and slot porosity.
Throughout these processes the sand grains get deformed and as a result there are continuous variations in volumes and areas of pendular rings, which lead to variations in porosities, permeabilities and water saturations.
This paper discusses models that can be used for estimating these variations for zero and non-zero contact angles in tight gas sands.
The subject is significant because historically oil and gas companies have gone, rightly, after tectonic fractures associated with folding and faulting in tight gas sands. The present work discusses a different possibility as the contractional fractures discussed above are not restricted to areas dominated by major tectonic events.