Dynamic Simulation of Drilling Vibrations for Design of Drill Strings and Downhole Tools

在加拿大近海等恶劣环境中，石油钻井平台的停机时间代价极其高昂(接近每天100万美元)。与振动有关的管道和井下工具故障很常见，极端可达定向井带来了与直井不同的挑战。这项研究将得到一个计算效率高的斜井动态振动模型。该模型将用于改进井下部件的设计，并研究有意振动的潜在好处。振动可分为轴向振动(沿管道长度)、扭转振动(扭转)或横向振动(管道弯曲)。因为这些振动是相互依赖的，所以需要一个能够预测所有这三种振动的模型。为了简单性和计算时间，许多先前的模拟对所考虑的振动类型进行了限制；然而，这样的模型不会捕捉到对预测部件寿命和钻井性能很重要的某些现象。钻柱由相对较细的受拉管组成，过渡到弯曲的“建造”部分，最后是较重的钻柱，称为钻箍，与钻头、传感器和导向钻头的工具一起组成“井底组件”，即BHA。垂直和建造部分将被模拟为刚性质量和旋转惯性之间的一系列集总轴向和扭转弹簧，以及钻井液的减振。在构建部分，将通过考虑各种摩擦和接触力的数学模型来完善扭矩和阻力预测。由于钻具组合管柱最容易受到与轴向和扭转运动高度耦合的横向振动的影响，因此钻具组合将被建模为一系列受弹簧约束的三维振动圆柱体，以及井筒摩擦、冲击和接触力。一旦这种更简单、运行速度更快的模拟方法通过实验和更复杂但速度更慢的有限元模型得到验证，它将被用于预测管道和其他部件从表面到最终深度的载荷。载荷将被用于更详细的部件级有限元模型，以预测局部应力和应变，之后将预测其疲劳寿命。疲劳破坏是指由于重复或变化的载荷而导致的早期破坏。该模型还将用于研究故意引入的振动的可能性，以减少摩擦扭矩和向前移动管道的阻力，增加钻头和岩石之间的钻削力，或减少可能导致管道粘连的岩石岩屑堆积。提高油井钻探效率将增加盈利能力，并使资源密集型加拿大经济受益。钻井失败的减少和油井质量的提高将减少所需的钻探总量，并减轻对地面的环境影响。

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.