Oil rig downtime is extremely costly (approaching $1M/day) in harsh Canadian environments such as the offshore. Vibration-related failures of pipes and downhole tools are common, with extreme reach directional wells imposing different challenges than vertical wells. This research will result in a computationally-efficient dynamic vibration model for deviated wells. The model will be used for improved design of downhole components, and to study the potential benefits of intentional vibration. Vibration can be classified as axial (along the pipe length), torsional (twisting), or lateral (bending of the pipes). Because these vibrations are interdependent, a model is needed that can predict all three. Many prior simulations place restrictions on the types of vibration considered, in the interests of simplicity and computation time; however, such models will not capture certain phenomena important for predicting component life and drilling performance.
The drillstring consists of a vertical portion made of relatively thin pipes in tension, transitioning into a "build" section that is curved, and ending with heavier pipes called drill collars that, along with the bit, sensors, and tools for steering the bit, make up the "bottom-hole assembly", or BHA. The vertical and build sections will be modeled with a series of lumped axial and torsional springs between rigid masses and rotary inertias, with damping due to drilling fluid. In the build section torque and drag force prediction will be refined by consideration of various mathematical models of friction and contact force. Because the BHA pipes are most susceptible to lateral vibrations that are highly coupled to axial and torsional motion, the BHA will be modeled as a series of three-dimensionally vibrating cylinders constrained with springs, along with wellbore friction, impact, and contact forces. Once this simpler, faster-running simulation method is validated with experiments and more complex but slower finite element models, it will be used to predict the loads on pipes and other components as they progress from the surface to their final depth. The loads will be used in a more detailed component-level finite element model to predict local stresses and strains, after which their fatigue life will predicted. Fatigue failure refers to premature failure due to repeated or varying loads. The model will also be used to study the potential for intentionally-introduced vibration to reduce friction torque and resistance to moving the pipes forward, to increase drilling force between the bit and rock, or to reduce the buildup of rock cuttings that can cause the pipe to stick. Improving the efficiency of oil well drilling will increase profitability and benefit the resource-intensive Canadian economy. Reduced drilling failures and improved well quality will reduce the total amount of drilling required and lessen environmental impact at the surface.