Fracture Mechanics Approach to the Growth Process of Fracture Network for Direct Heat Heat Extraction from Magma

直接加热岩浆热提取裂缝网络生长过程的断裂力学方法

基本信息

批准号：
13650981
负责人：
HAYASHI Kazuo
金额：
$ 1.6万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13650981/
关键词：
Geothermal Heat Magma Magma Energy Extraction Fracture Network Crack Crack Growth Thermal Contraction Thermal Stress

项目摘要

In the system of direct heat extraction from magma, working fluid (water) extracts heat by flowing through fractures, which are created by thermal contraction of solidified magma. Role of fractures is two fold, i.e., fluid path and heat exchange surfaces. Thus, the characteristics of these fractures are crucial. In the present research, the process of fracture growth is studied. It is supposed that the magma chamber is significantly large compared with the heat exchange system. The following condition is adopted as the base case, i.e., depth of the system is 7km, solidus temperature 800℃ and the Young's modulus times linear expansion coefficient 4.5X10^5(Pa/℃). The stress field consists of three fields, i.e., firstly the one due to over burden pressure acting on the outer boundary of the solidified region, secondly the one induced by pressure acting on the inner boundary of the solidified region and lastly the thermal stress field. The analysis is performed based on the Fracture Mechanics. It is found that growth of the first two fractures takes place at 463℃ in the base case and is followed by sequential fracture growth. The temperature at which the growth of ninth fracture takes place, is 457℃. The difference is only 6℃ between the two temperatures. This implies that the fracture growth and formation of fracture network would be almost simultaneous and thus be out of our control. There seem to be many factors which have effects on the formation of fracture network, such as fracture toughness, radius of wellbore, elastic constants and so on. Among these factors, depth of the heat exchange system has most significant effect, regarding the fracture size. Fracture toughness is less effective.

在从岩浆中直接提取热量的系统中，工作流体（水）通过流过裂缝来提取热，这些裂缝是通过固化岩浆的热收缩产生的。裂缝的作用是两个倍，即流体路径和热交换表面。这是这些裂缝的特征至关重要。在本研究中，裂缝生长的过程是研究的。预计与热交换系统相比，岩浆腔室明显大。采用以下条件作为基本情况，即系统的深度为7公里，固相物温度800℃，而年轻的模量时间线性膨胀系数4.5x10^5（PA/℃）。应力场由三个磁场，即首先是由于覆盖压力作用在固化区域的外边界上的一个场，其次是由压力作用在固化区域内部边界和最后一个热应力场的压力引起的。分析是根据断裂力学进行的。发现前两个断裂的生长发生在基本情况下的463℃，然后是顺序裂缝生长。第九骨折生长的温度为457℃。两个温度之间的差异仅为6℃。这意味着断裂网络的断裂生长和形成几乎是同时发生的，因此无法控制。似乎有许多因素会对断裂网络的形成产生影响，例如断裂韧性，井眼半径，弹性常数等。在这些因素中，热交换系统的深度对断裂大小具有最大的影响。断裂韧性的效果较差。