Permeability changes due to pore pressure discharge (laboratory study)

Abstract

If saturated porous medium has a boundary where it contacts with fluid under high pressure and the pressure is dropped at that boundary, the conditions for tensile cracks could be achieved in the medium. One can expect, that if micro-cracks appear, the permeability of that medium will increase. In the paper, the results of experimental laboratory study of fracturing of the porous saturated medium due to pore pressure rapid drop are presented. The artificial porous samples were saturated by oil and had a boundary directly contacted with fluid under the high pressure. At some moment, the pressure at that boundary was dropped. Pore pressures and acoustic emission (AE) were registered by the sensors located at the sample ends. It was found by pore pressure diffusion equation numerical solution in comparison with experimental data that permeability is high immediately after the pore pressure discharge beginning and it diminishes rapidly during the pore pressure dropping. It was shown that the AE variation is governed by the pore pressure gradient. In it was found, that in the series of subsequent pressure discharges the sample permeability increased with every next pressure discharge due to the sample micro-fracturing.