Abstract

Increasing the life of PDC bits without compromising on bit performance is crucial in drilling operations. It allows the operator to reduce non-productive time and the bit manufacturer to increase the reliability and the repairability of its products. This paper introduces a new PDC bit selection method designed to maximize the durability of the selected bit based on simulations of 3D realistic cutter damage.

During PDC bit drilling operations, any damage caused to one cutter tends to overload others and compromise the balancing and the durability of the whole cutting structure. The impact of various kinds of bit failure and cutter damage on the performance of different cutting structures is estimated. The analysis is performed with the help of a 3D bit-rock interaction model which simulates the drilling process considering both the drill bit and the hole being drilled as 3D meshed surfaces. The simulator is based on a generic computational geometry algorithm which estimates the exact volume of rock removed by each cutter while making minimal assumptions on the geometry of the cutter. Any cutter shape, including damaged ones can be simulated based on this model. Thus, realistic dull conditions can be applied to PDC cutters to analyse how the bit performs once damaged.

A series of simulation scenarios involving different failure mechanisms like abrasive wear, broken cutters, or lost cutters, have been conducted on a series of targeted 9 ¼ in. bit designs aimed to be run in an application in South East Kuwait. Bit designs have been ranked with respect to simulated performance indicators like drillability, steerability, stability, tool face control and also to their ability to withstand mild to catastrophic failure events. Based on this analysis, the top ranked bit design has been selected, manufactured and successfully run in the field. For the first time in the area, the bit achieved two sections (9 ¼ and 6 ½) in one, showing both a high durability and a good compatibility with the directional system used along the formation sequence drilled.

While the classical bit selection process is usually limited to the comparison of different bit designs in a given drilling scenario, the present paper demonstrates how this process can be further optimized by selecting the bit which also guarantees a maximum level of performance when subjected to worst case failure scenarios. This new method should benefit both the operator and the bit manufacturer as it is designed to achieve longer intervals, reduce operating costs and increase the global bit performance.

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