A Drilling Rate Model for Roller Cone Bits and Its Application

Abstract

Abstract Modeling bit performance is a scientific approach to optimizing drilling performance. Drilling rate or rate of penetration (ROP) is one of bit performance indexes. Several ROP models for roller cone bits have been developed over the years. However, there exist errors to some extent between these models and the field. This is because of the technical complexity of the bit-rock interaction. This paper introduces a new ROP model based on the interaction mechanism between drill bit and rock. The ROP model takes into account bit structure, especially cutting structure, and drilling parameters, such as WOB, RPM, and bit wear. The paper then focuses on applications of the ROP model in predicting drilling rate and rock compressive strength with drilling well data from Western Canada. Simulations were carried out using the ROP model for roller cone bits with two sets of offset well drilling data. The predicted ROP and rock strength when the model is used in an inverted mode were compared with field data or results from log rock strength data respectively. The comparison shows the ROP model can predict drilling operational ROP and rock compressive strength well. The ROP model is different from others in that it takes into account the bit cutting structure in more detail. The model can reflect the effects of different number of inserts and insert shape on ROP. The model is especially useful when selecting a roller cone bit with same IADC code but with different insert features and designs, and can be used in optimizing the drilling parameters in a planning mode and predicting the unconfined compressive strength in an inverted mode.