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.

在直接从岩浆中提取热量的系统中，工作流体（水）通过流经凝固岩浆的热收缩产生的裂缝来提取热量，即流体路径和热交换表面。这些裂缝的特征是至关重要的，在本研究中，假设岩浆室比热交换系统大得多，采用以下条件作为基本情况。的深度系统长7km，固相线温度800℃，杨氏模量乘以线膨胀系数4.5X10^5(Pa/℃)，应力场由三个场组成，一是作用在外边界上的超载压力场。首先是凝固区域，其次是作用在凝固区域内边界上的压力引起的应力场，最后是热应力场。根据断裂力学进行分析，发现增长。基础情况下，前两个断裂发生在 463℃，随后发生第九个断裂的扩展温度为 457℃，这意味着两个温度之间仅相差 6℃。裂缝的扩展和裂缝网络的形成几乎是同时发生的，因此是我们无法控制的。影响裂缝网络形成的因素似乎有很多，如断裂韧性、井筒半径、弹性常数等。在这些因素中，热交换系统的深度对断裂韧性的影响最为显着。