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TVD = 10,000 ft

Formation Pressure Gradient = 0.57 psi/ft

Mud Weight = 10 ppg

UNDERBALANCE

Do you have primary well control below?

Formation pressure works out at:

  Formation Pressure (psi) = 0.57 x 10,000 = 5,700 psi

Hydrostatic pressure works out at:

  Hydrostatic Pressure (psi)  = 10 x 0.052 x 10,000 = 5,200 psi

Hydrostatic pressure of 5,700 psi  is less than (under) the balance value of

5,200 psi, by 500 psi. The well is in a state of underbalance.

If the formation is permeable, then the well will flow and you will get a kick.

We will assume the kick comes into the annulus and moves upwards. This willdisplace mud out at surface. The driller should recognise this excess flow as akick, and close the well in using the BOPs.

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Mud Weight = 10 ppg

Choke line from BOPstack to choke manifold

TVD = 10,000 ft

Formation Pressure = 5,700 psi

Drill PipePressure Gauge

CasingPressure Gauge

BOP inclosed position

Kick inannulus

Remote Choke inclosed position

Once the BOPs have been closed, there will be no further flow of mud out of thewell. Pressure will build up. This build up can be monitored on two gauges atsurface - the drill pipe pressure gauge and the casing pressure gauge.

The drill pipe pressure gauge measures the pressure acting up the inside of thedrill string and the casing pressure gauge measures the pressure acting up theinside of the annulus.

 At some point the pressures will stabilise. These stabilised, shut in pressuresare given a number of different names. In this book they will be called Shut In

Drill Pipe Pressure (SIDPP) and Shut In Casing Pressure (SICP) respectively.

The picture above shows the well in a shut in position. This well and kick will beused as you work through many of the remaining subjects in this book.

 Assume that there is no float installed in the drill string. This means the drill pipepressure gauge will be open to pressure through the bit. Assume the bit is onbottom, the kick is all in the annulus and also on bottom.

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FORMATION PRESSURE - AGAIN

The well has been shut in on a kick and the pressures have stabilised. What will

SIDPP be equal to?

Formation pressure is pushing up the drill string with 5,700 psi  of pressure.

What is acting down the drill string? A clean column of 10 ppg mud. This gives

a hydrostatic pressure of:

  Hydrostatic Pressure (psi)  = 10 x 0.052 x 10,000 = 5,200 psi

If there is 5,700 psi  pushing up the drill string, and 5,200 psi  pushing backdown the drill string, then the pressure on the gauge at surface will read the

difference. In this case 500 psi.

For this kick, SIDPP  is 500 psi. You will be able to read this on the drill pipe

pressure gauge, once the pressures have stabilised.

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TVD = 10,000 ft

Mud Weight = 10 ppg

Formation Pressure = 5,700 psi

Drill Pipe

Pressure GaugeCasing

Pressure Gauge

BOP inclosed position

Kick inannulus

Remote Choke inclosed position

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In most kick situations, you will not know formation pressure ahead of time. Ifyou did, you should not have taken the kick!

Once you have taken a kick, however, you will be able to read SIDPP on the drill

pipe pressure gauge. You will know the well TVD, and the mud weight  youhave in the hole. From those you will be able to work out the hydrostatic

pressure acting down the drill string.

Formation pressure is the sum of SIDPP and string hydrostatic pressure - just

add them together to get formation pressure. Check that on the well opposite:

  Formation Pressure (psi) = Hydrostatic Pressure in Drill String (psi) + SIDPP (psi)

  = 5,200 + 500 = 5,700 psi

In a kick situation SIDPP is used to calculate formation pressure.

 Answer the following, to the nearest psi:

1) What is formation pressure? TVD = 13,560 ft; SIDPP = 385 psi;

Mud Weight = 11.5 ppg

2) What is formation pressure? Mud Weight = 9.9 ppg; TVD = 8,125 ft;SIDPP = 610 psi

3) What is formation pressure? Mud Gradient = 0.6968 psi/ft;SIDPP = 460 psi; TVD = 14,820 ft

4) What is SIDPP? TVD = 9,455 ft; Mud Weight = 10.3 ppg;Formation Pressure Gradient = 0.5564 psi/ft

5) What is SIDPP? TVD = 15,670 ft; Mud Weight = 14.8 ppg;Formation Pressure Gradient = 0.811 psi/ft

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