Formation Strength Tests Calculations


This article presents the following Formation Strength Tests Calculations:

- Formation Intake Gradient (FIG)

- Effective Mud Gradient (EMG)

- Maximum Allowable Annular Surface Pressure (MAASP)

Formation Intake Gradient (FIG)

FIG (psi/ft) = LOP + (CSD x MG)

                      (CSD - RKB)

Effective Mud Gradient (EMG)

EMG (psi/ft) = LOP + (CSD x MG)


Maximum Allowable Annular Surface Pressure (MAASP)

MAASP (psi) = LOP - (CSD x MG)   (@ initial condition)



  • CSD = Shoe Depth last set casing (ft TVD - RKB)
  • MG = Mud Gradient (psi/ft)
  • RKB = Rotary Kelly Bushings Elevation above ground level (ft)
  • FBP = Formation Breakdown Pressure (psi)
  • LOP = Leak - Off Pressure = Surface pressure recorded during the test (psi)


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