Control of Geothermal Reservoirs Consisting of Multiple Cracks

本项目的主要目标是阐明地热工程水库，如HDR/HWR水库，在具有多个软弱面的岩体中的力学响应。为此，我们建立了储集层由无数节理组成的情况和储集层由主要储集层裂缝组成的情况的模型。我们已经阐明了这类油藏的基本特征。然后，我们成功地将它们应用于在Fenton Hill HDR油田和Yuomori HWR油田进行的大规模水力压裂/增产的结果。可取的是，利用从钻孔深度反演的岩心样品中裂缝的几何和力学特征来估计模型的基本特征是可取的。因此，我们开发了基于Labato…的从裂隙表面的分维特征估计裂隙水力性质的新方法。在三轴应力条件下进行了更多的实验。此外，我们在神冈矿的一条巷道上进行了小型水力压裂，制造了一个人造裂缝，并对水力压裂产生的表面的分形特征进行了表征，发现水力压裂产生的表面与爆炸产生的裂隙表面和受剪切运动影响的松动边表面的分维特征不同。我们还开发了井间地震测量、钻孔雷达测量和精密声发射测量等新技术，以估计多机架地热储层的结构和围岩地应力状态。我们分析了在地热田观测到的数据集，并利用这些新技术估计了储层特征。研究发现，水库人工裂缝很可能普遍伴有多条或多条小的次生裂缝。采用立方体填充床模拟含二次裂缝的岩石，通过室内试验研究了含二次裂缝的储集层裂缝的水力和传热特性。较少

The main objective of the present project is to clarify the mechanical response of geothermal engineered reservoirs, such as HDR/HWR reservoirs, within a rock mass with many planes of weakness. To this end, we have constructed models for the case that the reservoir consists of innumerable joints and for the case that the reservoir consists of predominant reservoir cracks. We have clarified the basic characteristics of such reservoirs. Then, we have applied them successfully to the results of massive hydraulic fracturing/stimulation conducted at the Fenton Hill HDR field and at the Yunomori HWR field. It is preferable that the basic characteristics of the models can be estimated by using the geometrical and mechanical characteristics of fracture surfaces of fractures within core samples retrieved from the depth of boreholes. Therefore, we developed new methods for estimating the hydraulic properties of fractures from the fractal characteristics of fracture surfaces based on the laborato … More ry experiments under tri-axial stress conditions. Furthermore, we conducted mini-hydraulic fracturings in a driftway at the Kamioka mine to make a man-made fracture and to characterize the fractal characteristics of the surfaces created by hydraulic fracturing to find that the fractal characteristics are different from those of surfaces of fractures made by explosion and of slicken sides which are the surfaces subjected to shear movements. We have also developed new techniques on crosshole seismic measurement, borehole radar measurement and precise AE measurement for estimating the structure of multicrack geothermal reservoirs and the in-situ stress state of surrounding rocks. We have analyzed data sets observed at geothermal fields and have estimated reservoir characteristics by using these new techniques. It was found that it is highly probable that man-made reservoir cracks are accompanied by many-small secondary cracks generally. The hydraulic and heat transfer properties have been investigated for reservoir cracks accompanied by the secondary cracks by conducting laboratory experiments, where the rock with secondary cracks is simulated by a packed cube bed. Less