Changes

===Pore volume measurement===

===Pore volume measurement===

Pore volume can be measured directly by resaturating a clean, dry rock with a fluid. Resaturation is done with either gas (Boyle's law method) or liquid (gravitational method).

Pore volume can be measured directly by resaturating a clean, dry rock with a fluid. Resaturation is done with either gas (Boyle's law method) or liquid (gravitational method).

In the ''Boyle's law method'', helium is used to saturate the sample because it is inert, not easily adsorbed onto mineral surfaces, and (due to its small molecular size) rapidly enters the micropore system. In the laboratory, the core is often placed in an apparatus consisting of a flexible rubber boot inside a core holder (Figure 5). Pressure is then applied to the outside of the rubber boot to seat it against the sample. Helium from a reference cell at known pressure is then expanded into the pore volume. The new equilibrium pressure in the system is monitored, and the pore volume is calculated from Boyle's law:

In the ''Boyle's law method'', helium is used to saturate the sample because it is inert, not easily adsorbed onto mineral surfaces, and (due to its small molecular size) rapidly enters the micropore system. In the laboratory, the core is often placed in an apparatus consisting of a flexible rubber boot inside a core holder ([[:file:porosity_fig5.png|Figure 5]]). Pressure is then applied to the outside of the rubber boot to seat it against the sample. Helium from a reference cell at known pressure is then expanded into the pore volume. The new equilibrium pressure in the system is monitored, and the pore volume is calculated from Boyle's law:

:<math>P_{1}V_{\rm r} = P_{2} (V_{\rm r} + V_{\rm L} + V_{\rm p})</math>

:<math>P_{1}V_{\rm r} = P_{2} (V_{\rm r} + V_{\rm L} + V_{\rm p})</math>

where

where