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Dynamic Response of a Fluid-filled 3-D Crack and its Application to Characterization of Geothermal Reservoir Cracks

充液三维裂纹的动态响应及其在地热储层裂纹表征中的应用

基本信息

批准号：
10650070
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：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-10650070/
关键词：
Geothermal Energy HDR Geothermal Reservoir Crack Crack Characterization AE Elastic Wave

项目摘要

The dynamic response of a fluid-filled penny shaped crack, which was a typical example of 3-D cracks, was analyzed in detail in the framework of the theory of elasto-dynamics. It was revealed that the response was divided into tree types (Type I, II and III). Type I is the group that does not have any clear peaks in the power spectrum of the oscillation of the crack surface, and Type III is the group that has very clear peaks of fundamental modes in the power spectrum. Type II is in between Type I and Type III. Type III appears under the condition that attenuation of the wave traveling along the crack surfaces is weak and thus standing wave can be easily formed due to the reflection of the elastic wave at the crack periphery. Since Type III is far more informative than the other two and thus is preferable for the estimation of the crack parameters, it can be recommended that the reservoir pressure should be kept as higher as possible during the field experiments of active acoustic techniques.A new method is proposed for estimating the crack size, aperture and interfacial stiffness which is caused due to the asperity contact between the two crack surfaces. The method compares the frequencies of the fundamental modes of the standing wave, that are theoretically determined by the analyses just mentioned above, with the peak frequencies of the elastic waves observed during the field experiments such as hydraulic fracturing. The method was successfully applied to the field data obtained during hydraulic fracturing conducted in Hijiori and Ogachi HDR/HWR fields. Crack size and aperture in Hijiori field were estimated to be 5-11m and 1-44mm, respectively. Those in the Ogachi field are 4-28n and 10-22mm.

在弹性动力学理论的框架内，对三维裂纹的典型实例-充液硬币形裂纹的动力响应进行了详细的分析。结果表明，响应分为树型（类型I，II和III）。类型I是在裂纹表面振荡的功率谱中没有任何明显峰的组，类型III是在功率谱中具有非常明显的基模峰的组。II型介于I型和III型之间。III型出现在波沿裂纹表面沿着传播的衰减弱的条件下，从而由于弹性波在裂纹周边的反射而容易形成驻波。由于第三类模型的信息量远大于其他两类模型，因而更适合于裂缝参数的估算，因此建议在现场主动声技术试验中应尽可能保持较高的储层压力，并提出了一种新的方法来估算裂缝尺寸、孔径以及由于裂缝表面粗糙接触而引起的界面刚度。该方法将驻波的基本模式的频率（其在理论上由上述分析确定）与在诸如水力压裂的现场实验期间观察到的弹性波的峰值频率进行比较。该方法成功地应用于在Hijiori和Ogachi HDR/HWR油田进行水力压裂期间获得的现场数据。Hijiori气田的裂缝尺寸和孔径估计分别为5- 11 m和1- 44 mm。Ogachi场的平均直径为4- 28 mm，平均直径为10- 22 mm。