溶质离子扩散条件下泥页岩力学与化学井眼稳定模型研究

井壁失稳是钻井工程中经常遇到的一个十分复杂的问题，影响井壁稳定的因素是多方面的。以往建立的化学力学井眼稳定模型认为泥页岩表面有一层半透膜，通过引入膜效率系数，把钻井液与泥页岩相互作用所产生的力效应和纯力学结合起来。笔者认为水和溶质离子的流动改变了井壁孔隙压力，从而导致井壁失稳，在建立近井壁孔隙压力传递模型的基础上，考虑钻井液与泥页岩之间的水和离子的流动，建立了一个评价泥页岩化学与力学井眼稳定的新模型。模型计算结果表明：井眼失稳既可以发生在井壁，也可以发生在泥页岩内部，并具有时间效应；同时表明水的活度与溶液的性质是影响泥页岩井眼稳定的重要因素。

A Mechanical-Chemical Model for Shale Wellbore Stability Under Solute Diffusion

Wellbore instability is a very complex problem encountered while drilling. The factors of affecting wellbore stability are various and much complicated. In the previous studies, wellbore stability models have introduced chemical effects by adding an osmotic potential modified with a membrane efficiency to the pressure acting at the well wall. In this paper, an entirely different approach is adopted. In which the fluxes of water and solutes are supposed to play an important role in determining the pore pressure profile in shale and a model of pore pressure propagation is presented. The fluxes of water and ions into and out of the shale are accounted for. A model that combines chemical effects with mechanical ones and provides a quantitative tool for evaluating wellbore stability is also presented. Calculation results of the model show that wellbore failure can not only occur close to well wall but also occur inside the shale. The failure process is time-depended. The activity of the water and properties of the solutes are two significant factors affecting wellbore instability in shale.