The effect of pore structure on the permeability of tight sandstones

The estimation of permeability is essential as it is closely related to the production rate in hydrocarbon reservoirs. In general, permeability increases with reservoir porosity. However, recent studies have shown that porosity is not a particularly reliable indicator of permeability and the effect of pore structure (pore aspect ratio and distribution) should be considered. In this study, four samples of tight sandstones were collected from the Q area of the Ordos Basin, China, including two samples with the same porosity but different permeabilities, and two samples with the same permeability but different porosities. X-ray-diffraction and thin-section analyses and experiments, under variable pressure for ultrasonic waves and permeability, were carried out. Based on rock-physics modelling, the volume fraction, aspect ratio, and radius of pores/cracks are inverted and estimated with the P- and S-wave velocities and permeability as constraints. The results show good agreement between model predictions and measurements. A comparative analysis indicates that the pore/crack density, the distribution of the aspect ratio, and the radius jointly affect the permeability.