Critical Porosity Models

Anomalous velocity and porosity are often indicators of abnormal pore pressure. It is important, therefore, to be able to link velocity to porosity and rock texture in a rational, firstprinciple-based manner. The critical porosity concept allows for building such rock physics models. Critical porosity is the porosity above which the rock can exist only as a suspension. In sandstones the critical porosity is 36% 40%, that is the porosity of a random close pack of well-sorted rounded quartz grains. This pack is often the starting point for the formation of consolidated sandstones. Using this staring point for effective medium modeling, rational models can be built that relate velocity to porosity depending on rock texture and lithology.