RE: lithostatic pressure2 Jul 2021 00:44
Struggling with this subject...its complicated to put into the right context..
Overburden or lithostatic pressure is a term used in geology to denote the pressure imposed on a stratigraphic layer by the weight of overlying layers of material.
It is the pressure on the rock from the weight of the rock and earth above the formation. When the overburden pressure exceeds the fluid pressure in the pore space, the formation is compacted. The porosity, permeability, and compressibility are reduced. To illustrate the effect of net overburden pressure, consider an unconsolidated sandstone. At low net overburden pressures, the formation is loosely packed, and there is a lot of space for sand grains to realign under pressure. In general, the pore throats are relatively large. Hence, the compressibility, porosity, and permeability are high. As the net overburden pressure increases, the sand grains are forced into close contact, and there is less space for realignment. Hence, the porosity and compressibility decrease. The compaction of the sand grains also reduces the size of the pore throats. Therefore, the permeability is also reduced.