含瓦斯煤流固耦合数学模型及其应用

  本文关键词：含瓦斯煤流固耦合数学模型及其应用，由笔耕文化传播整理发布。

含瓦斯煤流固耦合数学模型及其应用

重庆大学硕士学位论文

（学术学位）

学生姓名：莫道平

指导教师：万 玲 教 授

专 业：力 学

学科门类：工 学

重庆大学航空航天学院

二O一四年五月

Coal Containing Methane Fluid-solid

Coupling Mathematical Model and Its

Application

A Thesis Submitted Chongqing University

in Partial Fulfillment of the Requirement for the

Master’s Degree of Engineering

By

Mo Daoping

Supervised by Prof. Wan Ling

Specialty: Mechanics

College of Aeronautics and Astronautics of Chongqing University,

Chongqing, China

May 2014

摘 要

为了研究含瓦斯煤岩中瓦斯运移规律，以多孔介质有效应力原理为基础，考虑含瓦斯煤岩的孔隙率、渗透率动态变化规律以及煤岩的弹塑性本构关系，建立起了含瓦斯煤弹塑性流固耦合数学模型。借助于COMSOL Multiphysics 多场耦合数值分析软件对模型的正确性予以验证，同时分析了煤岩中瓦斯钻孔抽放影响因素。本文取得了以下研究成果：

(1) 建立起了含瓦斯煤弹塑性流固耦合数学模型。该模型能够充分反映煤岩变形条件下的煤岩孔隙率和渗透率的动态变化规律、弹塑性本构关系；气体的可压缩性以及气体渗流的滑脱效应；瓦斯渗流与煤岩变形之间的耦合关系。并通过实验室含瓦斯煤岩常规三轴试验结果与模拟结果进行对比，结果表明：本文所建立的模型能够较好的反映含瓦斯煤在三轴应力作用下瓦斯的渗流规律和煤岩的变形特性。

(2) 对含瓦斯煤瓦斯钻孔抽放的影响因素进行了模拟分析，得出了以下结论：

①煤层内瓦斯压力会随着钻孔抽放时间的增加而降低，而且在钻孔抽放初始阶段瓦斯压力下降明显，随着抽放时间的增加煤层内瓦斯压力下降速度降低。

②瓦斯钻孔抽放的过程会煤岩骨架受到的有效应力增加，从而导致煤岩的孔隙率和渗透率下降，正是由于这个原因才使煤层瓦斯钻孔抽放后期瓦斯压力下降速度明显减缓。

③围压对煤岩内瓦斯压力的分布有影响，当增加围压时，煤岩内瓦斯压力分布会高于低围压条件下的瓦斯压力，同时，煤岩内的孔隙率和渗透率都会下降，而且在靠近钻孔的地方下降得更为明显。煤岩卸压状态下有利于瓦斯的抽放。

④负压抽放对于煤层内瓦斯压力的改变是非常有限的，负压抽采只是使钻孔周围局部区域的瓦斯压力略低于常用抽采，对于远离钻孔的大部分区域来说，负压抽放对煤层内瓦斯压力分布的影响几乎可以忽略不计。

⑤增大钻孔半径有利于煤层内部瓦斯下降、扩大有效抽放半径，在同一时刻，瓦斯的有效抽放半径会随着钻孔半径的增加而增大，但是随着钻孔半径的增加，这种增加的趋势会不断的放缓。

⑥多孔抽放过程中，在靠近钻孔的地方单一钻孔对煤层内瓦斯压力影响较大，越靠近钻孔瓦斯压力越低；在远离钻孔的地方，单一钻孔对瓦斯压力的影响作用降低，，沿多个钻孔的周围形成了一个集中的瓦斯降压区。

关键词：含瓦斯煤，流固耦合，数值分析，渗透率

ABSTRACT

In order to study the migration law of gas in the coal containing methane. Based on the principle of effective stress in porous media, considering the porosity, the dynamic variation of the permeability and the elastic-plastic constitutive relationship of coal containing gas, establish a elastic-plastic fluid solid coupling mathematical model of coal containing gas. Use COMSOL Multiphysics to verify the correctness of the model. At the same time, we analysis the factors affecting of gas boreholes in coal containing gas. This paper has made the following findings:

(1) The elastic-plastic fluid solid coupling mathematical model of coal containing gas is established. Compared to the laboratory results and simulation results，The results show that: the model established in this paper can reflect the seepage law of gas and deformation characteristics of coal.

(2) By analysis the factors affecting of gas boreholes in coal containing gas, draws the following conclusion:

① Coal seam gas pressure will decrease with the increase of time, and at the initial stage of drilling pump gas pressure decreased significantly, with the drainage time increase of coal seam gas pressure is reduced fall velocity.

② Gas drilling drainage process will make the coal and rock skeleton effective stress should be increased, resulting in the coal and rock porosity and permeability decreasing, it is for this reason that coal seam gas drainage gas pressure, the rate of decline slowed down significantly in late.

③ Confining pressure will affect the distribution of gas pressure, with the increase of confining pressure, the gas pressure will increase, and porosity and permeability will decrease, but near the drainage hole pressure drop obviously. Coal unloading conditions will conducive to gas drainage.

④ The effect of negative pressure pumping is very limited to coal seam inner gas pressure change. Negative pressure drainage is just slightly reducing gas pressure around the borehole. For away from the drilling drainage region, the negative pressure pumping effect on coal seam gas pressure distribution is almost negligible.

⑤ Increase the borehole radius is helpful to reduce the coal inner gas pressure and expand the effective drainage radius; at one time, effective drainage radius increases with the hole radius, but with the increase of hole radius, this increased trend will

continue to slow down.

⑥ In the process of multi boreholes, near the borehole, a single borehole has greater influence on the gas pressure of coal seam. The more close to the borehole gas pressure is low. Away from the borehole, a single borehole has less influence on the gas pressure of coal seam，around the drilling area forms a centralized gas depressor area.

Keywords: Coal containing methane, Fluid solid coupling, Numerical analysis,

Permeability

  本文关键词：含瓦斯煤流固耦合数学模型及其应用，由笔耕文化传播整理发布。