Changes

===Effects of confining pressure on porosity===

===Effects of confining pressure on porosity===

Porosity decreases with increasing net overburden pressure ([[Geostatic and lithostatic pressure|lithostatic pressure]] minus [http://www.glossary.oilfield.slb.com/en/Terms/p/pore_pressure.aspx pore pressure]), and in clastic rocks, stress sensitivity generally increases with increasing clay and decreasing cement content.<ref name=pt05r8>Amaefule, J. O., Keelan, D. K., Kersey, D. G., Marschall, D. M., 1988, Reservoir description—a practical synergistic engineering and geological approach based on analysis of core data: 63rd SPE Annual Technical Conference and Exhibition of the Society of Petroleum Engineers, Houston, TX, October 2–5, SPE 18167.</ref> Because porosity is stress dependent, laboratory measurements should be made at stress conditions whenever possible. These measurements are done with specially designed Boyle's law (pore volume) porosimeters, similar to that shown in [[:file:porosity_fig5.png|Figure 5]], which apply hydrostatic stress to the sample. In the reservoir, however, the resolved stress component is uniaxial. Uniaxial stress is less than hydrostatic stress, and consequently, the hydrostatic strain measured in the laboratory should be converted to an equivalent reservoir (uniaxial) strain.

Porosity decreases with increasing net overburden pressure ([[Geostatic and lithostatic pressure|lithostatic pressure]] minus [http://www.glossary.oilfield.slb.com/en/Terms/p/pore_pressure.aspx pore pressure]), and in clastic rocks, stress sensitivity generally increases with increasing clay and decreasing cement content.<ref name=pt05r8>Amaefule, J. O., D. K. Keelan, D. G. Kersey, and D. M. Marschall, 1988, Reservoir description—a practical synergistic engineering and geological approach based on analysis of core data: 63rd SPE Annual Technical Conference and Exhibition of the Society of Petroleum Engineers, Houston, TX, October 2–5, SPE 18167.</ref> Because porosity is stress dependent, laboratory measurements should be made at stress conditions whenever possible. These measurements are done with specially designed Boyle's law (pore volume) porosimeters, similar to that shown in [[:file:porosity_fig5.png|Figure 5]], which apply hydrostatic stress to the sample. In the reservoir, however, the resolved stress component is uniaxial. Uniaxial stress is less than hydrostatic stress, and consequently, the hydrostatic strain measured in the laboratory should be converted to an equivalent reservoir (uniaxial) strain.

==See also==

==See also==