1. n. [Formation Evaluation]

A technique for measuring the grain volume of a core sample by observing the change in pressure of helium introduced into a chamber containing the sample. The rock sample is placed in a chamber of known volume. Helium is held in a reference chamber at known volume and pressure, typically 100 to 200 psi [689 to 1,379 kPa]. The two chambers are connected, causing the helium to drop in pressure as it fills the sample chamber and the pores in the sample. The only volume not filled is the grain volume and the isolated pores. Neglecting the latter, the grain volume can then be calculated from Boyle's Law using the pressure before and after connecting the chambers and the chamber volumes.

See: Boyle's Law Single Cell,  buoyancy,  core plug,  liquid saturation method,  mercury displacement method,  porosimeter,  routine core analysis,  summation of fluids method