Calculation Stages

  1. Calculate the height in the annulus occupied by the string contents, Di
  2. Calculate P, p=po - D1 Pi
  3. Calculate the pressure at the top of the influx,

4. Calculate the expanded height (h) of the influx in the annulus with V2

PiV1 = P2V2

P2 = mean pressure of influx = 2

D1 = The height of the displaced string contents in the annulus

P = Pressure at the bottom of the expanded influx

Pi = Initial mud gradient

PO = Influx gradient hb = HEIGHT OF GAS COLUMN AT THE BOTTOM OF THE HOLE, OR IF THE AREA OF THE ANNULUS CHANGES, THE EQUIVALENT HEIGHT AT THE BOTTOM BASED ON THE ANNULAR AREA AT THE POINT OF INTEREST.

PF =

hydrostatic head of influx = Po K hb

PT =

Pressure at the top of the influx

h

Height the influx occupies in the annulus

Pann =

Annulus pressure

D

Depth of hole

The final Strong - White equation now becomes:

where:

P

1

x Ln

Pwh

p1 = original mud gradient p2 = gas cut mud gradient

P = original bottom hole pressure with p mud

Pwh = atmospheric pressure i.e. 14.7 psi

AP = reduction in BHP

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