Dynamic Characteristics of a Large Fluid Filled Crack for Pollution Free Use of the Earth's Crust

地壳无污染利用的大型充液裂缝动态特性

基本信息

批准号：
15560061
负责人：
HAYASHI Kazuo
金额：
$ 1.34万
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：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-15560061/
关键词：
subsurface crack subsurface space Micro Seismicity AE Elastic wave hydraulic fracturing characterization of crack Non-destructive inspection

项目摘要

In characterizing reservoir cracks, most crucial factors are initial crack aperture, crack size and interface stiffness. In order to estimate these three parameters, the present method compares the peak frequencies obtained from field experiments with the expectation provided by analyzing theoretically a dynamic problem of a fluid-filled crack. The crack is modeled as a penny shaped crack under an axisymmetric deformation mode with fluid leakage from its periphery. The analysis is performed with the aid of Boundary Integral Equation Method. In the first fiscal year, the basic nature of the influences of factors, such as viscosity, compressibility, Young's modulus and so on, is investigated, emphasizing the effect of damaged zone surrounding the crack. In the second fiscal year, the method is applied to two demonstration sites to examine the applicability. Firstly, the method is applied to Higashi-hachimantai HDR test site, Tohoku University. In the test site, there is a water circulation subsurface system consisting of two wells crossing through a predominant crack created by hydraulic fracturing. Drilling noise of a nearby well is employed as artificial seismic source to activate the fluid within the crack. It is found that the radius of the crack is about 40m. The aperture is dependent on the reservoir pressure. It is about 0.3mm for the reservoir pressure less than 2MPa at wellhead, whereas it is about 0.5mm for the reservoir pressure larger than 2MPa. The change is very sharp; it seems to change almost step wisely at 2MPa. Secondly, the method is applied to a seismic event observed at Australian HDR site. The event is about 4000m deep. The attenuation is very weak and the signal continues over 100sec. The radius and the aperture are estimated to be 160m and 17mm, respectively. The interfacial stiffness is very small. This suggests that the crack is almost completely open.

在表征储层裂纹时，大多数关键因素是初始裂纹孔径，裂纹尺寸和界面刚度。为了估计这三个参数，本方法将从现场实验获得的峰值频率与通过理论上分析流体填充裂纹的动态问题所提供的期望。裂纹在轴对称变形模式下建模为一分钱裂纹，其外围流体泄漏。分析是借助边界积分方程方法进行的。在第一个会计年度，研究了因素影响的基本性质，例如粘度，可压缩性，Young的模量等，强调了裂纹周围受损区域的影响。在第二会计年度，该方法适用于两个示范地点以检查适用性。首先，该方法适用于Tohoku University的Hachi-Hachimantai HDR测试网站。在测试地点，有一个水循环地下系统，该系统由两个孔通过液压压裂产生的主要裂缝组成。附近井的钻孔被用作人工地震来源，以激活裂缝内的流体。发现裂缝的半径约为40m。孔径取决于储层压力。储层压力小于2MPA的储层压力约为0.3mm，而大于2MPA的储层压力约为0.5mm。变化非常敏锐；似乎在2MPA上明智地改变了步骤。其次，该方法应用于在澳大利亚HDR站点观察到的地震事件。该活动深约4000m。衰减非常弱，信号持续100秒以上。半径和孔径估计分别为160m和17mm。界面刚度很小。这表明裂缝几乎完全开放。