Today, drill bits and mud motor issues often account for more than half of the reasons for pulling out of hole before total depth (TD) on typical directional drilling wells. In this paper, we present a comprehensive methodology designed for optimally matching drill bits, mud motors, and bottomhole assembly (BHA) components for reduced failure risks and improved drilling performance.

The methodology consists of combining the design characteristics of drill bits, mud motors, and the rest of the BHA. Each crucial component, like the drill bit, the mud motor, or the rotary steerable system, is analyzed with a particular simulation software made for the component itself before combining the components into a system analysis tool that considers all the detailed features. For example, the simulation software for the mud motor and power section optimizes for the type of elastomer, the mud compatibility, and the fit used. Cutter types and geometries, hydraulics, rocks, and the back and side rake angles are all included in the drill bit simulation. A full drillstring and wellbore simulation takes care of the rest of the components and the link to the top drive. The workflow smartly combines physics-based simulation and data analytics to achieve the necessary level of accuracy with reasonable computation time.

The new methodology presented here enables performing joint simulations of performance, durability, and stability for the first time. The performance simulation involved rate of penetration (ROP) prediction, motor power output, and available downhole torque. The durability consists of estimating the motor fatigue life, the bit wear over time, and the fatigue estimation of BHA components. The stability simulation analysis risks of lateral vibration, axial vibration, stick/slip, and bit and BHA whirl. All these are done on a system level with interdependences between different components considered. It enables matching the best bit with the best motor under the best possible BHA. The full workflow was evaluated with the drilling of a typical section in the Permian with significant improvement in both the ROP and reliability.

In summary, this paper describes a collective simulation capability that enables matching the bit, motor, and BHA by evaluating the design characteristics of each component and combining them into a system-level simulation tool. It enables joint evaluation of the ROP capability, bit wear, motor fatigue life, and BHA shock and vibration. At the end, we can perform fast drilling without compromising durability or reliability.

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