PDC Bit Selection Through Cost Prediction Estimates Using Crossplots and Sonic Log Data

Abstract

Abstract PDC bit technology has developed into an attractive and economical alternative in many drilling scenarios. Although much has been done for bit selection and optimization for tricone bits, much is still to be done for PDC bits, due to the difficulty of modeling the PDC wear, bit whirl and account for the many types and geometrical configurations of the existing PDC in the market today. This paper presents a method to select a PDC bit through predicting the lowest drilling cost for a given situation of interest, given the shear stress level it will be subjected to. The method uses all data from the PDC bit records, therefore containing many different lithologies and rock properties. It is based on the comparison of past bit performance and correlates it to the formation's shear stress. Graphic outputs play a key role in the analysis to queue in to a particular data group of interest within an extensive bit database. The proposed procedures have been validated using data from 49 wells from 6 Brazilian fields and the results showed that the cost savings are significant. Examples are presented and discussed. Introduction As PDC bits become more and more popular with an increasing number of suppliers and types, questions are raised on how to select from such a wide variety of options. One approach to the problem has been to try and investigate at a single cutter level the parameters that determine or affect the lifetime and performance of this element and then try and predict the bits performance, considering cutter placement on its surface. Such parameters and geometrical arrangements include but are not limited to: heat generation degrading metallurgical properties, weight on bit, rotation, hydraulics, formation resistance, jet cleaning action, formation abrasiveness, differential pressure across the bit face, bit wear, bit whirl (not modeled only avoided [ref. 1]), face exposure, bit geometry (including back rake and side rake angles), element cutting size and type, cutter density, etc. Although at first there might seem to be no solution to this problem, it can be partially simplified by considering two distinct approaches regarding the purpose of what is to be accomplished. P. 525^