Dispersed shaly sand

For dispersed shaly sand, a relatively monotonic decrease of permeability with increasing clay content can be expected as a result of the decrease of effective pore space. 

For dispersed shaly sand, there are various relationships and models that describe the dependence of permeability on porosity, shale content, and shale properties. Examples are ... 

Schon and Georgi (2003) developed a capillary-based model for dispersed shaly sand that shows an analogy to the Waxman-Smits equation (Section 8.5.3) for electrical properties. This model (Fig. 2.32) accounts for the reduction in porosity and decrease in the pore cross-sectional area with the content of clay and the associated immobile water. Starting with Hagen-Poiseuille s law, the flow rate for a cross-section is reduced by a film of clay particles. Permeability for dispersed shaly sand can be written as a functimi of the clean sand permeability sd and the dispersed shale content Fsh... 

FIGURE 2.32 Capillary tube model for dispersed shaly sand. Clay reduces pore radius from r to r-d. Schon and Georgi (2003). 

Dispersed Shaly Sand—The Waxman-Smits Equation... 

In case of dispersed shale, the shale conductivity is added to the pore fluid conductivity. With this idea, Waxman and Smits (1967, 1968) and Waxman and Thomas (1974) developed the dispersed shaly sand model They implemented the fundamental mechanisms of the shale conductivity based on cation exchange processes at the clay mineral-electrolyte (water) interface. 

Permeability of shaly sands is controlled by shale/clay content, type of shale distribution (laminated, dispersed, stmctural), porosity, and confining stress. A general impression is given by Fig. 2.18. 

Schon et al. (2005) applied a modular model concept for electrical, hydraulic, and elastic anisotropy studies that allows a joint interpretatiOTi of anisotropic formations. The model crmsideration and analysis of real logging data show that shear wave velocities depend strongly on the shale distribution and that the difference of the velocity of shear waves with different polarization can be related to the shale distributirHi (laminar or dispersed, structural). A shear wave-based method can discriminate between laminated and dispersed shaly zones and provide an estimate of the sand reservoir properties. 

Schon, J.H., Georgi, D.T., 2003. Dispersed shale, shaly-sand permeability—a hydraulic analog to the Waxman-Smits equation. In Presented at the SPWLA 44th Annual Logging Symposium, 22-25 June. Paper S. 

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