Specific yield can be close to effective porosity, but there are several subtle things which make this value more complicated than it seems.
12.
The effective porosity is of great importance in considering the suitability of rocks or sediments as oil or gas reservoirs, or as aquifers.
13.
However, there is also a concept of closed porosity and effective porosity, i . e ., the pore space accessible to flow.
14.
The difference is the glauconitic microporosity which contains water at reservoir conditions and is included as part of the Vsh ( non-effective porosity ) by log analysis.
15.
"' Sonic logging "'is a well logging tool that provides a lithology and rock textures, most notably decreasing with an increasing effective porosity.
16.
Therefore it is essential to have a core-or at least a good understanding of the geology-before invoking total " vs " effective porosity relationships.
17.
More importantly for the consideration of effective porosity, though, glauconite grains ( part of the Vsh ) have intra-particular microporous pore space which retains capillary-bound water.
18.
Although shales have low permeability and low effective porosity, shale gas is usually considered separate from tight gas, which is contained most commonly in sandstone, but sometimes in limestone.
19.
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 ).
20.
In essence, total porosity minus shale water, where solid minerals and the volume of shale ( Vsh ) constitute the matrix ( non-effective porosity ) and the remaining volume constitutes the effective porosity.
