Patent ID: 7024930

Claim:
A method for determining a termination condition for a drawdown operation using a formation tester in a formation penetrated by a borehole, comprising: setting a probe of the formation tester against a wall of the borehole so that a pretest chamber is in fluid communication with the formation, a drilling fluid in the pretest chamber having a higher pressure than the formation pressure; decompressing the drilling fluid in the pretest chamber by withdrawing a pretest piston at a constant drawdown rate; collecting data points representing fluid pressures in the pretest chamber as a function of time; identifying a range of consecutive data points that fit a line of pressure versus time with a fixed slope, the fixed slope being based on a compressibility of the drilling fluid, the constant drawdown rate, and a volume of the pretest chamber; and terminating the drawdown operation based on a termination criterion after the range of the consecutive data points is identified.