Pore-Level Analysis of the Relationship Between Porosity, Irreducible Water Saturation, and Permeability of Clastic Rocks

Abstract

fax 01-972-952-9435. AbstractPermeability is one of the most important, most spatially variable, most uncertain, and hence least predictable transport properties of porous media. Various empirical models, such as Tixier's, Timur's and Coates' equations, are widely used to quantify permeability from welllog calculations of porosity and irreducible water saturation. However, these models do not explicitly include the role played by rock structure, spatial fluid distribution in the pore space, wettability, or clay mineral distribution on permeability. We present a pore-scale approach to investigate the influence of these factors on the permeability of clastic rocks for explicit pore geometries of brine-saturated granular rocks.Synthetic pore-scale models are constructed to represent granular sands with variable grain-size distributions. These models include the structural effects of compaction, cementation, and distribution of dispersed hydrated clay minerals. Irreducible water is geometrically distributed on grain surfaces of the synthetic rocks. Permeability is calculated from lattice-Boltzmann flow simulations. A nonlinear relationship between permeability, porosity, and irre-ducible water saturation is established for these computergenerated rocks. We compare calculated permeability values of computer-generated rocks and laboratory measurements of core samples to those estimated from different empirical approaches, such as Tixier, Coates, and Timur models. It is found that the latter models cannot be applied to general cases of clastic rocks even if their free parameters are adjusted to fit core measurements. Our simulations also show that spatial distributions of clay minerals and irreducible water play a fundamental role in establishing an accurate correlation between permeability, porosity, and irreducible water saturation. Specific deterministic equations must be established for rock formations that exhibit distinct grain-size distributions, clay types, structural clay distributions, and grain cementation.

Pore network modeling of thin water film and its influence on relative permeability curves in tight formations

“…As average pore size decreases, the water saturation increases which is more conspicuous in small pores. This finding is consistent with previous research by Torskaya et al [97]. Using lattice-Boltzmann method, they studied the relationship between irreducible water saturation and permeability.…”

Permeability from Microscopy: Review of a Dream

“…There is a general consensus [48] that irreducible water is distributed on the wetted areas of the grain surface (directly on the grain surface, or inside the grain-lining clay layer), that is we can assume that S wi = cS p where S p is surface area per unit volume of pore space, and c is a constant. This Fig.…”

“…For a review of Timur's equation ([2,3]) see [48] (that also lists further similar equations such as Tixier [49], Wyllie and Rose [46] to estimate permeability from measured irreducible water saturation S wi or vice versa). In Timur's equation permeability k and S wi are connected as k = 0.136Φ 4.4…”

Experimental Investigation on Sandstone Rock Permeability of Pakistan Gas Fields

“…Their common conclusion was that the increase in gravel and coarse grain size types of particle in sandstone causes an increase in permeability whereas reducing the porosity. Many relationships of permeability with the porosity; irreducible water saturation and sorting are presented in literature [10,11,12].…”