Abstract

A new technique for numerical reconstruction of porous media is proposed that combines the flexibility and easy data conditioning of pixel-based multiple point statistics (MPS) along with robustness of object-base algorithms. Single phase gas flow simulations that consider slippage effects through a network of slots and micro-fractures extracted from petrographic work in tight porous media of the Nikanassin Group in the Western Canada Sedimentary Basin (WCSB) have been conducted. Furthermore, correlations between Klinkenberg slippage effect and absolute permeability have been developed. This leads to a new unified flow model in which Knudsen number acts implicitly as a flow regime indicator.

A detailed understanding of fluid flow at the micro scale level in tight porous media is essential to establish and develop techniques for economic flow rate and recovery. Direct available imaging techniques cannot capture all the details of tight formations at the pore level. Choosing an appropriate equation for flow through a single element of the network is crucial; this equation must include geometry and other structural features that affect the flow as well as all variation of fluid properties with pressure. Disregarding these details in a single element of porous media can easily lead to flow misinterpretation at the macroscopic scale.

Due to the wide flow-path-size distribution in tight porous media, a variety of flow regimes can exist in the equivalent network. Two distinct flow regimes, viscous flow and free molecular flow, are in either side of this flow regime spectrum. Since the nature of these two types of flow is categorically different, finding/adjusting a unified flow model is problematic. The complication stems from the fact that the viscosity concept misses its meaning as the flow regime changes from viscous to free molecular flow in which a diffusion-like flow mechanism dominates. For each specified flow regime, the appropriate equations for different geometries are studied. Also, different unified flow models available in the literature are critically investigated.

Simulation of gas flow through the constructed network at different mean flow pressures leads to investigate the functionality of Klinkenberg factor with permeability of the porous media and pore-level structure. It is concluded that for tight formations the slippage effects is more pronounced and cannot be neglected in the flow equations.

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