Monte Carlo Simulation of Bottomhole Coordinates in Directional Drilling
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Increasing interest is now focused on directional survey and on the uncertainty inherent in the calculation of the bottom
hole coordinates because many wells are drilled from offshore platforms and urban drill sites. These uncertainties may
result from errors due to the limitation on instrument accuracy, unconcentric positioning of the tools with the borehole and
may include reading errors. It is therefore necessary to develop methods for determining the cumulative effect of these
errors on the bottomhole coordinates and reducing such effects. In this study, Monte Carlo simulation method is adopted as
a technique of achieving this objective. The inclination angle, Ii and the azimuthal angle, Ai are treated as random variables
with their associated probability density function P(Ii) and P(Ai) respectively. These represent the distributions of the
potential survey measurements in a given well. The parameter Si which represents the linear segment constituting the
curvilinear axis of the wellbore is treated deterministically since its values can be measured accurately. Treating Ii and Ai as
random variables in a wellbore model is justified by the fact that both of them, though deterministic, can hardly ever be
measured accurately in any subsurface survey. The results of the study show that the probability of the estimated
bottomhole positions being true is nearly unity for vertical well and slightly less for directional well.
Keywords
TJ Mechanical engineering and machinery