Determination of the uncertainities involved in hitting subsurface target

03 August 2009 Dear Members,
I should be most grateful, if any one with experience on how to model or calculate the uncertainities involved in hitting planned subsurface target, should kindly guide and advice me on how to calculate the probability of hitting my planned subsurface target. Information involved in the extended reach well path design is as below:Torque and drag analysis allows a shallow KOP of 2100m to minimise axial stress with in the vertical depth that might cause axial vibration, my stress regime and fracture orientation allows the use of a simple build -- hold trajectory and from torque and drag analysis a sail angle of 76 degrees was calculated to minimize axial tension and friction with in the curved hole section, also my analysis called for the use of 6- 5/8in drill pipe in the upper 2755m and 5.5 in drillpipe down to the bottom hole assembly so as to minimize hydraulic friction that would limit flow rate that might lead to poor hole cleaning ,also provide the needed push to TD. Wellbore stability analysis calls for a mud weight of 1.56s.g to stabilize the trajectory, the target is located at 3033m TVD, and the horizontal departure is 2155m.
Thanks.
Divine Somiari.

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