Rop modeling of rollercone and pdc drill bits
Creators: name: Rashidi, Behrad
Publisher: name: University of Calgary
Year: 2012

description: Bibliography: p. 142-148
description: Most pages are in colour.
description: Drilling simulation technology has been used extensively to optimize the drilling operation so as to minimize the associated costs and risks. Optimum bit types and designs with corresponding drilling parameters can be recommended for the entire bit runs through simulation studies utilizing rate of penetration (ROP) models. Therefore, availability of the developed ROP models is a key concern in drilling simulation and the performance analysis of drill bits. Rollercone and Polycrystalline Diamond Compact (PDC) are the two most common and widely used drill bits in the drilling industry; and they can generally be served as the best fit in any drilling situation. Therefore, comprehensively developed ROP models for these bits play an important role in generating reliable outcomes required for the pre-planning, real-time, and the post-analysis phases of drilling a well. There have been several attempts to introduce ROP models for the rollercone and PDC bits in order to implement them at any drilling operational mode using any combination of drilling parameters, bit designs and lithological information. However, due to the existing complexities in mathematical modelling of the rock/bit interaction phenomenon, previous attempts have not been successful and never lead to develop a perfect model for each bit type. These complexities can be classified as: Mathematically modeling the forces applied to the formation by the cutters of the bits.? Mathematically modeling the generated rock volume by each single cutter of the bit to obtain the cumulative generated cutting volume considering rotating action of the bit. ? Taking into account the integrated effect of the operational and bit design parameters, not only their individual effects, as well as considering the entire existing variables/effects in modeling the drilling rate of the bits. ? Developing invertible ROP models that can be used to estimate formation strength values using any sets of drilling parameters. Therefore, in this study, the most applicable ROP models for the rollercone and the PDC drill bits are developed with properly including the abovementioned shortcomings of the previously developed and published models. For the rollercone bits, a totally new and comprehensive ROP models are established based on a unique approach of single cutter­rock interaction. This novel ROP model perfectly integrates the effect of the drilling variables, cutters' geometry and the design structure of the bit. The bit wear and hydraulic effects are also integrated, mathematically modeled, in order to precisely reflect the effect of the worn cutters as well as the available hydraulic level at the bit (required for the bottom hole cleaning) on the newly introduced ROP models respectively. For the PDC bits, since the most recent proposed ROP model by Motahari et. al., (2008) properly takes into account only the effect of the operational and bit design parameters, new bit wear and hydraulic models are also developed and introduced to that model so as to generate valuable results through performance analysis of PDC bits. One of the most important features of the newly introduced ROP models, after they are fully developed, is that they can be easily inverted and utilized to generate accurate rock strength values using offset/real-time field data. This unique characteristic of the ROP models makes them perfect candidates for drilling simulation studies to optimize the drilling operation in the most cost effective manner. Therefore, herein, a thorough systematic simulation method is established by incorporating the comprehensively developed drilling rate models for conducting performance evaluation studies of rollercone and PDC drill bits. The introduced simulation method is capable of recommending optimum sets of drilling, bit types and design parameters through analysing of various drilling scenarios. The verification of the introduced simulation method is performed by comparing the created rock unconfined compressive strength (UCS) logs through employing the inverted ROP models, using offset well data, as well as the outputs of a commercially available drilling simulator (Drops) (Bratli et al., 1997). Also, the bit wear trends generated by implementing the new wear function of the PDC bits utilizing offset well data are compared and verified with the corresponding results of the drilling simulator (Drops) (Bratli et al., 1997) for testing and verification purposes. The comparison of the results obtained from the models with the simulator outputs as well as the field data has been quite encouraging which signifies the application of the introduced simulation method in determining the best case scenario in planning of the future wells with the lowest possible expenditures.