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首页> 外文期刊>Mechanical systems and signal processing >A novel stochastic process to model the variation of rock strength in bit-rock interaction for the analysis of drill-string vibration
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A novel stochastic process to model the variation of rock strength in bit-rock interaction for the analysis of drill-string vibration

机译：一种用于模拟钻头-岩体相互作用中岩石强度变化的随机模型，用于分析钻柱振动

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摘要

A common issue faced in the oil and gas industry is the vibration of drill-strings, which are detrimental to operational efficiency and can incur in great financial losses. Because of this, a great effort has been devoted in the literature to the analysis of these vibrations. In addition, the modeling uncertainties and variations in environmental factors, like lithology, corroborates the use of stochastic models instead of deterministic ones. Therefore, the three main objectives of this work are: (ⅰ) to propose a novel stochastic model to describe the uncertainties on the rock strength by means of stochastic processes; (ⅱ) to propose a novel coupled stochastic process, which considers the bit dynamics, and; (ⅲ) to analyze the effect of such uncertainties on torsional vibration severity. The drill-string is described by a continuous axial-torsional model discretized by means of the finite element method. A coupled nonlinear bit-rock interaction model is considered, in which the cutting component of torque is modeled as a stochastic process in order to consider the variations on rock strength while drilling. Ito stochastic differential equations are used to generate two different stochastic processes: Ornstein-Uhlenbeck process and a novel coupled process. The second one considers the bit dynamics in order to describe better the physics when severe torsional vibration happens. The statistics of the response show that the uncertainties on rock strength may lead to predictive scenarios where the amplitude of vibrations at the bit are significantly larger than the ones provided by the deterministic model. Also, the differences between the processes are small when the vibration at the bit is small, but the novel process presents the worst case when severer vibrations are present.
机译：石油和天然气行业面临的一个普遍问题是钻柱的振动，这不利于作业效率，并可能导致巨大的财务损失。因此，文献中已经对这些振动进行了巨大的努力。此外，建模的不确定性和环境因素（如岩性）的变化也证实了使用随机模型而不是确定性模型。因此，这项工作的三个主要目标是：（ⅰ）提出一种新颖的随机模型，通过随机过程描述岩石强度的不确定性; （ⅱ）提出一种新颖的耦合随机过程，该过程考虑了位动态，并且; （ⅲ）分析这种不确定性对扭转振动严重性的影响。钻柱由一个连续的轴向扭转模型描述，该模型通过有限元方法离散化。考虑了耦合的非线性钻头-岩石相互作用模型，其中将扭矩的切削分量建模为随机过程，以便考虑钻井时岩石强度的变化。伊藤随机微分方程用于生成两个不同的随机过程：Ornstein-Uhlenbeck过程和一个新颖的耦合过程。第二个考虑了钻头动力学，以便更好地描述发生严重扭转振动时的物理特性。响应的统计数据表明，岩石强度的不确定性可能会导致预测性情况，其中钻头处的振动幅度明显大于确定性模型提供的幅度。同样，当钻头处的振动较小时，这些过程之间的差异也较小，但是当存在更严重的振动时，该新型过程将呈现最坏的情况。

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