井周煤岩蠕变力学特性及其对井壁稳定的影响研究

发布时间：2018-04-25 03:15

本文选题：煤岩 + 煤层气　；参考：《西南石油大学》2015年硕士论文

【摘要】：煤层气是一种清洁能源,我国煤层气储量丰富,开发利用煤层气资源不仅能有效遏制煤矿瓦斯灾害,降低甲烷气体对大气环境的温室效应,而且可以优化我国能源结构、缓解能源短缺问题。然而,由于煤岩的特殊力学性质和煤层气储层所处复杂地质环境特征,煤层气井壁稳定问题严重制约了我国煤层气资源的勘探开发,其中因煤岩蠕变造成煤层气井缩径、卡钻,甚至井壁的坍塌失稳现象尤为突出。本文采用室内岩石物理力学实验、蠕变模型理论研究及数值模拟研究等方法,系统和深入地研究了煤层气储层井壁煤岩的物理力学特性、蠕变力学特性,建立了煤岩弹-粘-塑蠕变模型和基于能量角度的蠕变模型,同时将其与现有岩石蠕变模型进行对比,优选得到适合描述煤岩蠕变特性的模型。最后,采用COMSOL数值模拟软件,分析了受煤岩弹性模量、泊松比、地应力分布和井径变化影响的煤层气井蠕变规律。获得主要结论如下:(1)通过室内物理实验测试,得到了煤岩的干密度、天然密度、含水率、比表面积、总孔隙体积、平均孔径等物理性质指标。分析发现,煤岩总孔体积与比表面积有关,且基本呈线性正相关。(2)煤岩单轴蠕变力学实验显示,当轴向应力从0.98MPa增加至5.98MPa时,煤样试件蠕变过程表现为衰减蠕变;当轴向应力为6.49MPa时,煤样试件蠕变过程表现为非衰减蠕变,煤岩的长期强度在5.98~6.49MPa之间。(3)根据煤岩蠕变力学实验结果,对西原模型进行了改进,获得了基于煤岩弹-粘-塑性特性的蠕变力学模型,并推导得到了本构方程和蠕变方程。改进的西原模型能够反映煤岩蠕变曲线的二次指数衰减特征。(4)基于能量角度,提出了煤岩蠕变力学模型,该模型在西原模型的基础上串联一个绕组δ元件,该元件的特点是在受力情况下应变与时间呈t3关系。并且推导出了基于能量角度的煤岩蠕变力学模型本构方程和蠕变方程。(5)煤层气储层井壁煤岩最大蠕变变形方向均为最大水平地应力方向,井眼变形呈现出最大主应力方向受压缩而产生大幅缩径现象。随着弹性模量的减小,煤层气井壁煤岩蠕变变形量逐渐增大;泊松比小于0.25时,井壁煤岩蠕变变形不明显,而后随着泊松比的增大,井壁煤岩蠕变变形显著增大;随着井径的增大,井壁煤岩蠕变逐渐呈现非线性增大;随着最大水平地应力的增加,煤层气井壁煤岩蠕变变形逐渐增大。本文所提出的煤岩蠕变力学模型,建立的煤层气井壁煤岩蠕变规律数值模拟方法,有助于认识煤岩蠕变造成煤层气井壁失稳机制,同时对于煤层气开采安全钻井和有效开展完井与固井施工等均具有重要的实际意义。
[Abstract]:Coal bed gas is a kind of clean energy, China has rich coal bed gas reserves. The exploitation and utilization of coal bed gas resources can not only effectively contain coal mine gas disaster, reduce the greenhouse effect of methane gas to the atmosphere environment, but also optimize the energy structure of China and alleviate the problem of energy shortage. However, because of the special mechanical properties of coal and rock and coal bed gas reservoir With the characteristics of complex geological environment, the problem of coalbed gas well wall stability seriously restricts the exploration and development of coal bed gas resources in China. In this paper, the phenomenon of coalbed gas well shrinkage, drilling and even wall collapse is particularly prominent because of coal and rock creep. This paper uses indoor petrophysics Li Xueshi test, creep model theory research and numerical simulation research, etc. Methods, the physical and mechanical properties of the coal rock and the Creep Mechanics Characteristics of the coal seam gas reservoir rock are systematically and deeply studied. The model of coal rock elastic viscoplastic creep and the creep model based on the energy angle are established. At the same time, the model is compared with the existing rock creep model, and the suitable model is optimized to describe the creep characteristics of the coal and rock. Finally, the COMSO is adopted. L numerical simulation software is used to analyze the creep law of coal bed gas well affected by the elastic modulus of coal and rock, the Poisson's ratio, the distribution of ground stress and the change of well diameter. The main conclusions are as follows: (1) the physical properties of coal and rock, such as dry density, natural density, water content, specific surface area, total pore volume, average pore size and so on, are obtained as follows. It is found that the total pore volume of coal and rock is related to specific surface area, and it is basically linear and positive correlation. (2) the uniaxial creep mechanical experiment of coal rock shows that when the axial stress increases from 0.98MPa to 5.98MPa, the creep process of coal sample is decaying creep, and when the axial stress is 6.49MPa, the creep process of coal sample is non attenuated creep, coal rock. The long-term strength is between 5.98~6.49MPa. (3) according to the experimental results of Coal Rock Creep Mechanics, the western original model has been improved, and the Creep Mechanics Model Based on the viscoelastic properties of coal and rock is obtained, and the constitutive equation and the creep equation are derived. The improved western original model can reflect the two exponential attenuation characteristics of the creep curve of the coal rock. (4) At the energy point of view, a creep mechanical model of coal and rock is proposed. The model is based on the West original model with a winding delta element, which is characterized by the T3 relationship between strain and time under the stress condition. The constitutive equation and the creep equation of the Coal Rock Creep Mechanics Model Based on the energy angle are derived. (5) coal seam gas reservoir wall coal. The maximum creep deformation direction of the rock is the maximum horizontal stress direction, and the borehole deformation presents the maximum main stress direction and produces the large shrinkage diameter. With the decrease of the modulus of elasticity, the creep deformation of coal bed coal rock increases gradually. When the Poisson's ratio is less than 0.25, the creep deformation of the coal rock is not obvious, and then with Poisson's ratio The creep deformation of coal and rock increases significantly, with the increase of the diameter of the well, the creep of the coal and rock gradually increases, and with the increase of the maximum horizontal stress, the creep deformation of the coal bed coal rock increases gradually. It is helpful to understand the mechanism of coalbed methane well wall instability caused by the creep of coal and rock, and it is of great practical significance for the safe drilling of coal bed gas exploitation and the effective completion and cementing construction.

【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TD842

【参考文献】