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Determination of formation pressure during a drilling operation

  • US 7,765,862 B2
  • Filed: 11/30/2007
  • Issued: 08/03/2010
  • Est. Priority Date: 11/30/2007
  • Status: Active Grant
First Claim
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1. A method for determining true formation pressure while drilling in an earth formation, using recirculating fluid that flows downward through a drill string and returns to a surface in a void between the drill string and the earth formation that has a portion of mudcake thereon, the method comprising:

  • a) providing a measurement device with a probe on the drill string;

    b) controlling a mud flow rate to obtain a first measured borehole pressure and measuring a corresponding first probe pressure with the probe wherein the corresponding first probe pressure is the pressure in the earth formation adjacent the mudcake;

    c) controlling the mud flow rate to obtain a second measured borehole pressure and measuring a corresponding second probe pressure with the probe wherein the corresponding second probe pressure is the pressure in the earth formation adjacent the mudcake;

    d) deriving the true formation pressure from calculating a first ratio from the first and second measured borehole pressures and the first and second probe pressures.

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