The Three Forks First Bench (TF1) in the Williston Basin is attractive to operators for its production qualities; however, the formation is problematic for drilling with polycrystalline diamond compact (PDC) bits. TF1 is an interbedded dolostone, 30 to 40 ft thick, capped by the abrasive Pronghorn/Sanish formation with high stress variations/spikes and laminations. These formation characteristics lead to cutter damage and vibration, which cause slow rates of penetration (ROP) and additional trips due to bit/bottomhole assembly (BHA) failure.
In response to these challenges, a revolutionary rock-removal system has been designed. The system implements conical diamond elements (CDE) to work in unison with the PDC cutters. Conventional PDC bits complete a typical 10,000-ft TF1 lateral in a one-bit/BHA in only one out of five wells. The most common reason for tripping is bit/BHA failure due to the harsh characteristics of the TF1. The CDE's unique geometry applies a concentrated point load to fracture formation more efficiently, and its ultra-thick diamond layer provides superior impact strength and wear resistance. Bits utilizing CDEs in conjunction with PDC cutters are known as CDE bits. They are able to withstand the demands of the application where conventional PDC bits cannot.
CDE bits average 5,447 ft at 83 ft per IADC hour when placed as the first bit in a lateral. That performance is 10% farther and 15% faster than conventional PDC bit offsets. Analyzing measurement while drilling (MWD) tool vibration data, CDE bits have proven to mitigate BHA vibrations compared to conventional PDC bits. These performance step changes have helped operators improve their one-bit/BHA TF1 lateral success rate from one out of five wells with conventional PDC bits to an astounding one out of three with CDE bits.
One operator in particular has utilized CDE bits to their full potential. From September 2014 to September 2015, the operator's one-bit/BHA total depth (TD) rate using conventional PDC bits was only 13%. However, the 1-bit/BHA rate when CDE bits were used was 83%, which provided a considerable savings in eliminating the nonproductive time (NPT) in tripping. Depending on the depth, a trip could cost the operator USD 80,000 and 16 hours in NPT. The average performance of CDE bit drillouts has been 9,538 ft at 137 ft per on-bottom hour, providing a 74% improvement in footage and a 2% improvement in ROP over conventional PDC bits for the operator. The reduction in NPT in tripping and improvement in drilling performance has led the operator to prefer drilling with CDE bits.