Effective porosity

Effective porosity is most commonly considered to represent the porosity of a rock or sediment available to contribute to fluid flow through the rock or sediment, or often in terms of "flow to a borehole". Porosity that is not considered "effective porosity" includes water bound to clay particles (known as bound water) and isolated "vuggy" porosity (vugs not connected to other pores). The effective porosity is of great importance in considering the suitability of rocks or sediments as oil or gas reservoirs, or as aquifers.

The term lacks a single or straightforward definition. Even some of the terms used in its mathematical description ("${\displaystyle V_{cl}}$” and “${\displaystyle V_{sh}}$”) have multiple definitions.

Figure 1 illustrates core and log derivations of porosity for a sandstone and infers (some) different definitions of effective porosity.

The figure is discussed below going from left to right along the strip.

"Quartz" (more aptly termed “non-clay minerals”) forms part of the matrix, or in core analysis terms, part of the grain volume.

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