Abstract
The model presented in this paper is a new approach to predicting the performance of full-hole and core drag bits. The model is based on theoretical considerations of single-cutter rock interaction, lithology coefficients and bit wear. Several new modeling features are introduced, these include "equivalent bit radius", "dynamic cutter action", "lithology coefficients" and "cutter wear". The model is applicable to all types of drag bits (Natural Diamond Bits (NDB), Polycrystalline Diamond Compact Bits (PDC) and any Geoset Bits) with correct cutter geometrical description. The model is useful for pre-planning, day to day and post drilling analysis, as well as drilling optimization.
Application of the model to evaluate drag-bit performance has shown good results in several lab and field cases. The advantages of this model include, optimization of operating parameters, optimization of bit parameters and support of a total drilling system for penetration rate, solids control and hydraulics optimization. In addition, use of the model is simple and straight forward, data requirements are standard and readily available. Lithology coefficients can be obtained from lab data or one set of drill-off and/or bit performance test in the field. Penetration rates can be predicted by the model for different lithologiεs using rock strengths obtained from offset drilling or log data. In other words, the model will predict penetration rate for any set of operating conditions, formation description and bit parameters.
