This paper is the first reporting of a directional drilling simulation computer program that converts side force values, generated by a three-dimensional bottom-hole assembly algorithm, to actual displacements in the x and y planes. The program can be used to simulate directional wells that have been drilled, or to predict the actual trajectory for a given bottom-hole assembly, geology, and operating conditions.

The logic for the simulation program is presented, discussing how the bottom-hole assembly program, and the bit and stabilizer side cutting data were merged to form the basis of the program. Various inputs for a simulation or prediction, and the sensitivity of each input, are discussed. Mechanisms that are not included in the algorithm are cited, explaining how the lack of these mechanisms precluded the simulation of a certain variety of directional wells.

Results from the simulation of a directional well drilled in Holland are presented. Matching of actual inclination and direction data provided the basis of showing how the program could be used in a predictive mode for the selection and operation of other bottom-hole assemblies for drilling another directional well in the same area.

A final section discusses some of the problems encountered in running simulations and how these problems equate to actual field conditions. Mechanisms that need to be added to the algorithm to increase the fidelity and the breath of the simulation are mentioned.

The existing program has been used successfully to match wellbore trajectories in areas where the geological effects are nil to moderate and the wellbore conditions can be accurately described. With further refinements and enhancements to the program, it will only be a matter of time before any directional or deviation control well can be simulated. This ultimately means a computer program can be used to aid the drilling person in making sound engineering decisions on how to drill a directional well.

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