PDC bit designs for directional drilling typically sacrifice penetration rate for steering performance, resulting in a higher cost per foot. This paper discusses a process for modeling the drilling behavior of PDC bits, insights gained regarding bit efficiency when steering with various motorized and non-motorized rotary steerable systems (RSS), and field experience with the resulting bit design.
Prediction and analyses of PDC bit behavior used a bridgeable software platform to integrate various design applications. This allowed the combined analyses of performance objectives and criteria, including cutting structure, rock type, application, well profiles, drives, and 3D contact. Simulations were then run to examine the performance of different cutting structures relative to various drilling parameters, and matched to a specific drive system. An optimized PDC bit design was developed and manufactured, and its field performance was compared to the model and to PDC bit performance in offset wellbores.
The optimized design was manufactured in a 6 1/8-in PDC bit and run on motorized and non-motorized RSS. It resulted in significant ROP increases and a lower cost per foot compared to offset wells, while retaining a high level of steering response. In one well, the ROP was increased to 48.43 ft/hr versus a target of 35 ft/hr based on offset performance. The resulting cost per foot was reduced from $11.40 KD to $8.59 KD.
The paper examines bit performance and dull condition for the runs and compares them with offset runs. Field performance results validate the bit design modeling and simulation process, and emphasize the importance of integrating various performance analyses to improve bit efficiency without degrading critical steering characteristics.
Extensive development of cutting structures that "drilled on paper" combined with full scale bit laboratory testing has resulted in the development of a design process that combines multiple design objectives and criteria to model and simulate bit behavior during drilling. As shown by field results, this process of balancing the design provides the means to optimize overall performance and lower costs for many different bit applications.