Formula Sheet Overpressure CourseFormula Sheet Overpressure Course

S = Overburden stressS = Overburden stressP = Pore pressureP = Pore pressurev = Effective verticalv = Effective vertical stressstress

Pressure Gradient = Density (ppg) x 0.0520.052 is a conversion constant used to convert ppg to a gradientThe units of 0.052 are psi/ft/ppgFresh water has a gradient of 0.433psi/ft0.433 / 0.052 = 8.338.33ppg is the density of fresh water

PHYD = MW x FT x 0.052This can be rearranged to:EMW = PHYD / (FT x 0.052)

PPG x FT x 0.052 = PSISG x FT x 0.433 = PSISG x MT x 1.420 = PSIPPG x MT x 0.171 = PSI

PHYD = (D2 x Pf) – ((D2-D1)Pg)Where PHYD = Pressure at reservoir top (psi)Pf = Water fluid gradient (psi/ft)Pg = Gas gradient (psi/ft)D2 = Depth of bottom of reservoir (ft)D1 = Depth of top of reservoir (ft)

Si = ρb x 0.433 x DIWhere Si = Interval Overburden in PSIρb = Interval density in SG0.433 = Conversion ConstantDI = Depth of interval in FeetSo = (ƩSi) / DWhere So = Overburden Gradient in PSI/FTƩSi = Cumulative SiD = Vertical Depth

AGIP Formula

Ρb = 2.75 – 2.11 ((ET – 47) / (ET + 200))For unconsolidated formations

Ρb = 3.28 – (ET / 89)For consolidated formations

Where: Ρb = Formation density in SGET = Sonic Transit time in µsec/ft

D Exponent

R = ROP (ft/hr)N = RPMW = WOB (lbs)D = Bit Size (ins)

DxC

dc = modified d ExponentMW1 = Normal Hydrostatic PressureMW2 = Mud Weight (pref. ECD)Pn = MW1

Either ppg or SG

Ratio Method

Use formula:Where:Po = actual pore fluid pressurePn = normal pore pressure dco = observed dc exponent dcn = dc exponent from normal trend

Eaton

P = So – ((So – Pn) (Dco / Dcn)1.2)Where:P = Formation PressureSo = Overburden PressurePn = Normal Pore PressureDco = DxC ObservedDcn = DxC from NCT

Note the 1.2 is the beta factor and may change Note units are psi/ft, ppg or SG for pressures

Daines

FP = σT + ((S – P)((µ / 1- µ)) + P)Where:FP = Fracture Pressureµ = Poissons RatioσT = Superimposed Tectonic StressS = Overburden PressureP = Pore PressureUnits ppg – EMW, SG or psi/ft

σT = LOT - ((S – P)((µ / 1- µ)) + P)

MAASP = (LOT EMW – MW) x 0.052 x TVD @Shoe(For ppg calculations)

WellKIll

FP = (MW x 0.052 x TVD) + SIDPPKMW = SIDPP / (0.052 x TVD) + OMWInf. Grad. = (MW x 0.052) – ((CSIP – SIDPP) / HT)HT = Gain / Ann. Vol.Where:FP = Formation PressureSIDPP = Shut in Drill Pipe PressureKMW = Kill Mud Weight, OMW = Original Mud WeightCSIP = Casing Shut in PressureHT = Height of influxInf. Grad. = Influx gradient

Using ppg, ft and psi