Compressibility test

This test determines the pore volume compressibility of a rock sample under reservoir condition. The constant stress σ₁ simulates the overburden while the radial stress σ₃ is controlled in such a way that the radial deformation of the sample is zero throughout the test (uniaxial strain test). A pore pressure is injected and then varied e.g. to simulate the depletion of the reservoir.

The axial deformation of the samples gives the bulk volume change while the squeeze out of the pore fluid gives the pore volume change. Variations of this procedure like testing under a hydrostatic stress condition are also applicable.

The test can be carried out with saturated samples (water, brine, oil) from ambient conditions up to a temperature of 150°C and an operating pressure of up to 140 MPa (σ₂ = σ₃). Sample dimensions applied so far are length : diameter = 2:1 with specimen diameters of 1” to 2”.

 

Experimental setup

test	σ1	σ3	ε1	ε3	Pp	measured
pore pressure variation	constant	f(ε3)	≠ 0	= 0	variable	Δl
at prevented lateral strain		variable	free	constant