Patent ID: 7753118

Claim:
A method of determining an estimate of the permeability of a cement annulus in a formation traversed by a wellbore having a casing around which the cement annulus is located, using a tool having a hydraulic probe and a pressure sensor, comprising: a) locating the tool at a depth inside the wellbore; b) drilling a hole through the casing and partially into the cement annulus; c) locating the hydraulic probe in hydraulic contact with the cement annulus; d) using the pressure sensor to measure the pressure in the hydraulic probe over a period of time in order to obtain pressure data; e) finding a relaxation time constant estimate of the pressure data by fitting the pressure data to an exponential curve which is a function of the relaxation time constant, and a difference between a starting pressure in the hydraulic probe and the formation pressure; and f) determining an estimate of the permeability of the cement annulus according to an equation which relates said permeability of the cement annulus to said relaxation time constant estimate.