Compressibility of Sandstones at Low to Moderate Pressures

Bulk volume compressibilities of petroleum-bearing sandstones were measured in the range, 0-15,000 psi. Compressibilities were found to be function of pressure, rock composition, and texture. If sandstones are divided into two classes; one with well sorted, well rounded grains, the other with poorly sorted, angular grains; then within a class the compressibility is a linear function of the amount of intergranular material. A useful model for a sandstone is the sphere pack composed of a mixture of very hard and very soft spheres. This model correctly predicts (a) the pressure at which grains crush, (b) the compressibility of the intergranular material, and (c) the relation between compressibility and pressure.