各向异性地层钻井井斜问题研究

在实验室内以全尺寸实物钻头破岩,系统地研究各向异性地层对井斜影响程度的成本较高。随着计算机硬件和数值模拟计算软件，尤其是有限元软件的发展，使得有限元仿真模拟各向异性地层钻井井斜是经济可行的。在弹塑性力学、岩石破碎力学的理论基础上，建立了三牙轮钻头齿面与井底岩石接触问题的动态模拟的有限元模型，模型中地层岩石力学特性建立为各向异性材料模式。提出了以岩石临界塑性应变为判据，来判断岩石材料是否被切削或剥落，并在动态仿真模拟过程中，将这些剥落的单元去掉，形成钻井井眼和新的井底表面。用文中建立的模型，动态模拟、分析了钻头钻进时，在各向异性地层和地层倾角的干扰下，钻头与井壁间产生不对称的侧向力，使钻头产生侧向偏移，累积形成井斜，给出了定量的模拟结果。调整参数可以模拟和分析不同钻井参数、各向异性地层以及地层倾角对井斜的影响关系，从而为各向异性地层以及高陡构造地层防斜打快提供理论参考，同时为防斜工具的设计、改进以及井眼轨迹控制提供理论基础。

Research on borehole deviation in drilling anisotropy formations

It will spend a lot to conduct systematic research on the effect of various anisotropic formations on borehole deviation by using full-size drill bits to break the rock in the lab. Along with the development of computer hardware and numerical simulation software, in particular the development of finite element software, it gets feasible to simulate the borehole deviation in all anisotropic formations. On the basis of the elastic-plastic mechanics and the rock fragment mechanics, the finite element model dynamically simulating the contact of the tooth surface of tri-cone bits and the downhole rock is established, in which the patterns of anisotropic materials are established representing the rock mechanics characteristics. It is proposed that the critical rock plastic strain value be used to judge whether rock materials are cut or flaked off. Well bore and new borehole surface develop after the units flaked off are removed during the process of dynamic simulation. While dynamically simulating and analyzing the drilling based on the newly established model, lateral force of drill bits and borehole wall is produced due to the interference of anisotropic formations and the formation dip. As a result, lateral deviation of drill bits is caused, and finally borehole deviation is caused. Quantitative simulation results are given. Parameters can be adjusted to simulate and analyze the effect of the different drilling parameters, the anisotropic formations, and the formation dip on borehole deviation. It will provide anti-deviation and fast penetration in anisotropic formations and high inclined formations with theoretical references. In addition, it offers theoretical basis for the design and improvement of anti-deviation devices and the wellbore trajectory control. 