油页岩热损伤演化特性及损伤模型研究

发布时间：2018-01-30 23:21

本文关键词： 油页岩热损伤 CT SEM 分形理论力学性能损伤模型二次开发　出处：《吉林大学》2015年博士论文　论文类型：学位论文

【摘要】：油页岩资源丰富，全世界油页岩资源折算成页岩油高达4000亿t以上，是天然原油探明可采储量的3倍左右。我国油页岩资源预测储量高达7199亿t，排在全世界第四位，折算成页岩油资源为476亿t。由于经济与人口的快速增长，能源需求正在急剧增加，而常规油气资源却在日益减少，在能源危机的背景下，油页岩资源以其巨大的资源储量以及光明的开发前景，得到越来越多的关注。在油页岩的开采方式中，原位开采技术虽然开始较晚，但是发展较快，目前已经有十几种之多，核心都是通过对地下油页岩储层进行加热，使油页岩中的干酪根热解产生油气。对油页岩层进行加热，就必然会导致其出现热损伤现象，力学性质产生劣化。由于油页岩层处在地下一定深度，受到较为复杂的地应力作用，当热损伤出现时，就可能导致油页岩层出现较大变形甚至是破坏，对安全生产产生不利影响。因此，有必要对油页岩的热损伤过程展开研究，增加对油页岩热损伤劣化特性的认识。本研究结果可用于油页岩原位开采过程中预测可能出现的地表沉降，防范可能出现的不利情况等方面，具有一定的理论意义和实际应用价值。本研究选取吉林农安油页岩作为研究对象，首先应用热重分析仪测得油页岩试样的热解失重曲线，通过对油页岩试样的热解失重规律进行分析，确定了所要研究的温度区间为常温到700℃，在此区间内，选择了8个温度水平进行试验，8个温度水平分别为25℃（常温）、100℃、200℃、300℃、400℃、500℃、600℃、700℃。按照确定的温度水平对油页岩试样进行加热，然后分别采用CT扫描以及SEM技术测得不同温度油页岩试样的细观结构图像。通过测得图像对试样孔隙、裂隙以及矿物颗粒的形态特征进行定性分析和定量计算，分析温度作用下油页岩试样的损伤演化特性，在此过程中得到如下结论：随着温度的升高，油页岩中的矿物发生了较大变化，矿物的数量出现减少，矿物形状发生改变且尺寸在变小；与此同时，油页岩中较大孔隙的数量在增加，其形状也由长条形向椭圆形转化，定向性逐渐明显。这些变化都使得油页岩内部的热损伤逐渐加剧，力学性能逐渐劣化。应用数字图像盒维数算法对不同温度油页岩的CT图像以及SEM图像进行分形分析，发现在25-700℃之间，分形维数D随温度升高呈现出先增大后减小的变化趋势，并在400℃时达到最大值，说明400℃时油页岩内部的孔隙形态最为复杂。对加热到不同温度水平的油页岩试样进行物理力学性能测试，结合纵波波速、弹性模量、峰值强度等参数对油页岩在温度作用下的宏观损伤劣化特性进行分析，研究发现：在温度作用下，纵波波速和弹性模量出现了持续的下降，而峰值强度出现了先增大后减小的变化趋势，并在400℃达到最大值，400℃是油页岩宏观力学性能发生改变的特殊温度节点。分别根据纵波波速以及弹性模量定义了损伤变量，研究发现：损伤变量随温度升高而逐渐增大，两者正相关。700℃时损伤变量最大，，两种方法计算的损伤变量值分别为0.936和0.785，比较真实的反应了油页岩的损伤情况。最后，在实测试验数据的基础上，结合岩石损伤理论，推导出了针对油页岩的热损伤本构方程，然后应用Flac3D软件进行二次开发，在软件中自定义出考虑热损伤的油页岩本构模型（OsTd模型），并通过与单轴压缩试验的结果进行比较，验证了OsTd模型的正确性。
[Abstract]:Oil shale is rich in resources, the world oil shale resources converted into shale oil up to more than 400 billion T, is a natural crude oil proven recoverable reserves of about 3 times. China's oil shale resources forecast reserves of up to 719 billion 900 million T, ranked in the world fourth, converted into shale oil resources for the 47 billion 600 million T. due to the rapid growth of economy and population, energy demand is increasing rapidly, while the conventional oil and gas resources are dwindling, in the context of the energy crisis, the oil shale resources to reserves its huge resources and a bright development prospect, has gained more and more attention.
In the oil shale mining method, in situ mining technology although started late, but rapid development, currently has more than a dozen, the core is through the heating of the underground oil shale reservoir, the pyrolysis of kerogen in oil shale to produce oil and gas. The oil shale layer is heated, it will inevitably lead to the the thermal damage phenomenon, caused deterioration of mechanical properties. The oil shale layer in certain depth underground, under stress is complex, when thermal damage occurs, it may cause the oil shale strata appear larger deformation or even destruction of production safety is adversely affected. Therefore, it is necessary to study the thermal damage process of oil shale the increase in understanding degradation characteristics of oil shale thermal injury. The results of this study can be used for surface subsidence prediction may occur in oil shale in the mining process, prevent the possible unfavorable situation. It has a certain theoretical significance and practical application value.
This study selected Jilin Nong'an oil shale pyrolysis as the research object, firstly the measured oil shale samples using TGA curves of weight loss, through the pyrolysis of oil shale samples were analyzed to determine the weight loss, the temperature range of the research is at room temperature to 700 DEG C, in this range, select 8 temperature level test, 8 temperature levels were 25 DEG C (normal temperature), 100 C, 200 c, 300 C, 400 C, 500 C, 600 C, 700 C.
Heating of the oil shale samples to determine the level of temperature, then using CT scanning and SEM technology of oil shale samples measured at different temperature. The microscopic structure of image obtained by the image on the porosity of samples, morphology of fracture and mineral particles by qualitative analysis and quantitative calculation, analyze the evolution characteristics of oil shale sample damage the effect of temperature, get the following conclusion: in this process, with the increase of temperature, changes in oil shale mineral, mineral quantity decreased, the change of the shape and size of minerals in smaller; and at the same time, the number of oil shale in the larger pores increase in its shape from strip to oval the transformation, directional gradually obvious. These changes make the thermal damage of oil shale inside gradually increased, gradually deterioration of mechanical properties. The application of digital image box dimension algorithm for different temperature The fractal analysis of CT images and SEM images of oil shale revealed that the fractal dimension D showed a trend of increasing first and then decreasing with increasing temperature at 25-700 D, reaching the maximum at 400 C, indicating that the pore morphology of oil shale is the most complex.
The physical mechanical performance test of oil shale samples with different temperature levels of heating, combined with the longitudinal wave velocity, elastic modulus, peak strength parameter analysis of oil shale under temperature macro damage deterioration found in temperature, the longitudinal wave velocity and elastic modulus has decreased continuously, and the peak intensity appeared first increased and then decreased, and reached a maximum value at 400 C, 400 C is a special node temperature of oil shale macro mechanical properties changes. According to the longitudinal wave velocity and elastic modulus of the damage variable is defined, the research found that the damage variable gradually increases with increasing temperature, a positive correlation between.700 DEG C when the maximum damage variable, damage variable values computed by two methods were 0.936 and 0.785, compared to the real response to the damage of oil shale.
Finally, based on experimental data, combined with the rock damage theory, deduced the damage constitutive equation for oil shale, then two times the development of application of Flac3D software in the software custom considering the thermal damage of the oil shale constitutive model (OsTd model), and compared with the results of compression tests the single axis, the OsTd model is verified.

【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TE662

【参考文献】