Conductor Design To prevent formation breakdown while drilling

We need to calculate the minimum conductor setting depth based on the following data:

  1. Formation strength gradient p FSG
  2. Sea water gradient p sw
  3. Return mud gradient pm
  4. Water depth Dw
  5. Flow line height above seabed Fh

Let X = the casing setting depth below seabed, then, (X x pFSG) + (Dw x psw) - (Fh 4 X) pm Example given p FSG = 0.67 psi/ft Dw = 175 ft psw = 0.445 psi/ft Fh = 240 ft pm* = 0.48 psi/ft

Depth of conductor BDF = 10 4 65 + 175 4 200 - 450 ft

* Mud weight in annulus based on calculated maximum drilling rate to avoid overloading.

Maximum Drilling Rate to avoid overloading of annulus

The maximum drilling rate can be calculated based on the following data:

  1. Pump rate Q ( ft^min or m^min)
  2. Volume of cuttings V ( ft^mln or ms/min)
  3. Maximum annulus mud weight Pa (density Da = lb/ft3or kg/m3)
  4. Density of drilled formation Dfm (lb/ft3or kg/m3)
  5. Density of drilling mud Dm ( lb/ft3or kg/m3 )

Then,

Example

Let V = Volume of formation drilled where: Q = 100ft3/min or 2.83 m3/min

In a 26" hole the volume of formation cut per foot (m)drilled = 3.687 ft30r 0.032 m3

The maximum drilling rate then becomes

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