3D列印裂隙網絡試體於不同圍壓下裂隙力學與水力平均內寬之量測

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Title:	3D列印裂隙網絡試體於不同圍壓下裂隙力學與水力平均內寬之量測
Authors:	楊鈞凱;Yang, Chun-Kai
Contributors:	應用地質研究所
Keywords:	3D列印;裂隙網絡;滲透率;孔隙體積;力學平均內寬;水力平均內寬
Date:	2019-08-19
Issue Date:	2019-09-03 17:00:57 (UTC+8)
Publisher:	國立中央大學
Abstract:	天然氣儲存、二氧化碳封存和核廢料處置，常選擇低滲透岩石作為主要的地質障壁，低滲透岩石因其結構緻密，孔隙體積較低，滲透率主要由裂隙所主導，然而現地岩體不連續面分布複雜，加上體積過大，不利於現地試驗直接量測流體在裂隙岩體中的流動方式與裂隙受力變形特徵之關係。近年來，3D列印技術逐漸成熟，以數位模型為基礎，透過光敏樹脂和石膏粉末，以堆疊累積的方式來建構3D岩石模型，且因容易修改模型、無須製作模具、成型速度快等優點，該技術已運用在探討岩石力學領域方面。本研究利用裂隙參數(裂隙中心位置、開口寬、裂隙半徑和位態)生成裂隙網絡，並使用光固化3D列印技術列印裂隙岩體圓柱型試體，並利用高圍壓孔隙體積/滲透率量測儀進行滲透率和孔隙體積量測，以探討裂隙網絡岩體在不同圍壓下的滲透率行為以及裂隙受力閉合特性，同時也利用理論計算的方式，計算相同裂隙網絡滲透率條件下之水力平均內寬，並與透過孔隙體積量測獲得之力學平均內寬進行比較。四個試體量測到的滲透率值介於1.73×10-12 m2 ~ 2.73×10-12 m2 (圍壓介於0.3MPa ~ 4MPa)，而孔隙體積介於715.92 mm3 ~ 1331.35 mm3 (圍壓介於1MPa ~ 4MPa)。計算得到的水力平均內寬介於37.25μm ~ 43.75μm (圍壓介於0.3MPa ~ 4MPa)，其對應力的敏感性較低；而計算得到的力學平均內寬介於86.73μm ~ 161.29μm (圍壓介於1MPa ~ 4MPa)，其對應力的敏感性較高。透過雙曲線和半對數曲線兩種不同內寬閉合模型進行擬合，發現兩種模型對於力學平均內寬閉合量擬合的相關係數介於0.91 ~ 0.99之間，能良好地描述力學平均內寬閉合量與有效應力之間的關係，而對於水力平均內寬閉合量擬合的相關係數則介於0.18 ~ 0.86之間，因水力平均內寬對有效應力的敏感性較差。力學平均內寬與水力平均內寬之比值介於2.13~4.21之間。;Low-permeability rocks are often used as the main geological barrier in natural gas storage, carbon dioxide storage and nuclear waste disposal. Low-permeability rock is dense in structure, low in pore volume, and permeability mainly dominated by its fractures. However, the overly large mass and the complex discontinuity make it unfavorable in the in-situ test which measures the relationship between flow pattern of fluid in fractured rock mass and deformation characteristics of fracture. In recent years, 3D printing technology has gradually matured. Using digital model as the foundation, 3D rock model is constructed by stacking and accumulating through photosensitive resin and gypsum powder. The technology has various advantages such as easy modification, requires no molds and fast forming and has been applied in rock mechanics fields for academic exploration. In order to investigate the permeability behavior of fractured network rock mass under different confining pressures and the closure characteristics of fractured forces, this study used the fracture parameters (fracture center position, aperture, fracture radius, and orientation) to generate a fracture network; the fractured rock mass cylindrical specimen was printed using photocuring 3D printing technology, and the permeability and pore volume measurement were performed using a high confining pressure pore volume/permeability instrument. At the same time, the theoretical calculation method is used to calculate the hydraulic average aperture under the same fracture network permeability. The hydraulic average aperture is then compared with mechanical average aperture, which is found via pore volume measurement. The permeability values measured by the four specimens ranged from 1.73×10-12 m2 to 2.73×10-12 m2 (confining pressure is between 0.3 MPa and 4 MPa), while the pore volume ranged from 715.92 mm3 to 1331.35 mm3. (confining pressure is between 1MPa and 4MPa). The calculated hydraulic average aperture is between 37.25μm and 43.75μm (confining pressure is between 0.3MPa and 4MPa), which is less sensitive to stress; the calculated mechanical average aperture is between 86.73μm and 161.29μm (confining pressure is between 1MPa and 4MPa), and its sensitivity to stress is high. Through the fitting of two different aperture closure models of hyperbolic and semi-logarithmic curves, it is found that the correlation coefficient between the two models of mechanical average aperture closure is between 0.91 and 0.99, which can well describe the relationship between the mechanical average aperture closure and the effective stress. The correlation coefficient for the fitting of the hydraulic average aperture closure is between 0.18 and 0.86, because the hydraulic average aperture is less sensitive to effective stress. The ratio between mechanical average aperture and hydraulic average aperture is between 2.13 and 4.21.
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