Landing the wellbore into the target zone is critical when drilling Bakken or Three Forks wells in the Williston Basin. The main performance criterion of the curve section is to ensure the directional objectives are met while minimizing shale exposure. In general, Polycrystalline Diamond Compact (PDC) drill bits designed for higher Rates of Penetration (ROP) are too difficult to control in this section and risk landing the curve above the target zone. In such cases, a costly BHA trip would be required to pick up a less aggressive bit.
The new bit design allowed a higher Weight on Bit (WOB) to be applied while holding the high side toolface, thus achieving higher ROP and maintaining the required build rates throughout the curve section. The combination of high fixed bend motors with the new designed bit allowed drillers to plan sections with higher build rates; thereby shortening the build section, reducing drilling time and improving the economics of the well.
The introduction of PDC cutters featuring unprecedented thermal stability, combined with a holistic approach to solving the challenges of drilling faster while maintaining steerability were major contributions to the successful implementation of the new bit design. The traditional approach of using a heavier set blade and cutting structure coverage to improve stability and prevent cutter overload was challenged following the development of PDC cutter technology that focused on thermal resistance rather than toughness. The improved directional control exhibited by the new design resulted from extensive iterations and detailed analysis of the cutting structure, torque control components, fluid impingement angles, and blade arrangements. Collectively, these individual features combined to increase stability of the bit and improve its response to changes in WOB.
The success of the new design proved that improving the thermal resistance of a cutter while maintaining its toughness allows for a lighter set bit to drill the curve section in record time while maintaining toolface. In conjunction with a high performance motor, this delivered a winning combination of speed and stability, setting several field records by drilling significantly faster while maintaining the well path.
