Laboratory Study of Microseismicity Due to Rapid Fluid Pressure Drop

One type of the porous medium fracturing is related with rapid pore pressure drop. In case of the fluid pressure discharge at some fracture or a borehole boundary, the conditions for tensile cracks could be achieved. One can expect, that if micro-cracks appear in the porous medium, the permeability of that medium will increase. In the paper, the results of experimental laboratory study of fracturing of the porous medium saturated by fluid 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 time, the pressure at that boundary was discharged. Pore pressures and acoustic emission (AE) were registered by the sensors located at the sample ends. It was found that multiple microfracturing occurred during the pore pressure dropping. It was shown that the AE is governed by pore pressure gradient. In the series of subsequent pressure discharges it was found, that the sample permeability increased with every next pressure discharge. The permeability was estimated on the basis of pore-elasticity equation.