Replicating pore topology/structure of tight gas reservoirs is essential for modeling fluid flow through such porous media. Constitutive relationships between the macroscopic properties of the medium can often help with such modeling efforts. This research demonstrates the validity of physically constructing a pore network for tight media based on Weibull lognormal skewed distributions.
A randomized construction approach was developed to generate a realistic three-dimensional (3D) pore network of tight porous media to visualize fluid flow at the pore scale level. This approach offers flexibility in studying macroscopic property relationships with a pore throat structure. Further, the model was validated by generating an equivalent 3D pore network according to an experimentally derived throat size distribution. The distribution was obtained from an ambient mercury injection capillary pressure (MICP) analysis for 17 selected core samples from three Mesaverde tight gas sandstones basins in the U.S. The model used Weibull distributions to estimate other network properties, such as aspect ratio, throat length, and coordination number.
Sensitivity analysis was performed to assess the effects of certain pore structures, including pore and throat radius, and coordination number, and geometries, such as square, circle and triangle, on the petrophysical and electrical properties of the physical representation of permeable and tight media. The study shows the importance of taking into consideration the internal pore structure to estimate the petrophysical and electrical properties.
The estimated porosity, and simulated absolute liquid permeability and formation factor of the physically equivalent networks were in good agreement with the measured data
obtained by Byrnes et al. (2009). A variation between the simulated absolute permeability to liquid and the measured routine gas permeability was encountered in core samples that have measured gas permeability and porosity smaller than 0.1md and 8%, respectively. Computed capillary pressure curves were in good agreement with lab measurements. It is concluded that pore – throat size distribution is important as pore connectivity in describing fluid flow properties and capacity of tight porous media.