| 摘要: | 地熱能源是臺灣近幾年積極開發的綠能之一，而要能夠有效使用地熱能源，岩體的流體儲存及移棲特性扮演重要的角色，流體儲存由岩體之孔隙率及力學內寬所決定，流體移棲特性由岩體之滲透率及水力內寬所決定。本研究利用實驗室實驗，對大屯火山地區五指山層砂岩和紅葉地區紅葉層板岩進行四項物理參數的量測，孔隙率及力學內寬透過波以耳定律來測量，對於砂岩試體來說，滲透率及水力內寬使用穩態流法；板岩試體因為屬於低滲透率岩石（k < 10⁻¹⁸ m²），超出穩態流法的測量範圍，因此使用脈衝衰減法來做測量。
砂岩完整試體孔隙率在圍壓3MPa～120MPa下，孔隙率範圍為2.7%～4.7%，滲透率範圍為 1.9 × 10⁻¹⁷ m² ～ 2.0 × 10⁻¹⁶ m²，砂岩節理在圍壓3MPa～60MPa下，力學內寬範圍為45.5μm～126.4μm，水力內寬範圍為25.9μm～8.7μm；板岩完整試體孔隙率在圍壓3MPa～20MPa下，孔隙率範圍為0.0%～5.1%，滲透率範圍為 2.3 × 10⁻²⁰ m² ～ 9.7 × 10⁻¹⁸ m²，板岩節理在圍壓3MPa～60MPa下，力學內寬範圍為72.7μm～506.5μm，水力內寬範圍為1.7μm～16.8μm。
實驗結果說明，節理對流體流動之貢獻遠大於完整岩石，本研究根據實驗室實驗的結果，估計在含節理岩體的節理間距為1公尺時，其等效滲透率與完整岩石滲透率之差異，另外板岩也進行剪應力場的不密合節理模擬，來比較密合節理與不密合節理的差異。結果顯示，在節理間距為1公尺時，節理砂岩的等效滲透率是完整砂岩的2.2～4.5倍；密合節理板岩的等效滲透率是完整平行葉理板岩的12～18倍；不密合節理板岩的等效滲透率是密合節理板岩的133～300倍。
完整砂岩和完整板岩之孔隙率與滲透率關係皆可以用指數律來描述，而節理砂岩與天然劈理密合板岩之力學內寬與水力內寬關係，其力學內寬和水力內寬之比值（E/e）有隨著水力內寬減少而增加的趨勢，天然不密合劈理板岩則呈現相反趨勢。
透過實驗結果，力學內寬要扣掉完整岩石在相同有效應力下的孔隙體積，但是水力內寬則不需考慮完整岩石滲透率之貢獻，在對於低滲透率岩石，透過脈衝衰減法（PDB）進行力學內寬量測時，是否可以忽略完整岩石孔隙率之貢獻，尚需進一步探討。
;Geothermal energy has been actively developed as one of the major renewable energy resources in Taiwan in recent years. To effectively utilize geothermal energy, the fluid storage and migration characteristics of rock masses play a crucial role. Fluid storage is controlled by rock porosity and mechanical aperture, whereas fluid migration characteristics are governed by permeability and hydraulic aperture. In this study, laboratory experiments were conducted to measure four physical parameters—porosity, permeability, mechanical aperture, and hydraulic aperture—of sandstone from the Wuchishan Formation in the Tatun volcanic area and slate from the Hongye Formation in the Hongye area. Porosity and mechanical aperture were measured using Boyle’s law. For sandstone specimens, permeability and hydraulic aperture were determined using the Steady State method. Slate specimens, however, are classified as low-permeability rocks (k < 10⁻¹⁸ m²), which exceed the measurable range of the Steady State method; therefore, the Pulse Decay Balance (PDB) method was employed.
For intact sandstone specimens under confining pressures ranging from 3 to 120 MPa, porosity varied between 2.7% and 4.7%, and permeability ranged from 1.9 × 10⁻¹⁷ m² to 2.0 × 10⁻¹⁶ m². For jointed sandstone under confining pressures of 3–60 MPa, mechanical aperture ranged from 45.5 μm to 126.4 μm, while hydraulic aperture ranged from 25.9 μm to 8.7 μm. For intact slate specimens under confining pressures of 3–20 MPa, porosity ranged from 0.0% to 5.1%, and permeability ranged from 2.3 × 10⁻²⁰ m² to 9.7 × 10⁻¹⁸ m². For jointed slate under confining pressures of 3–60 MPa, mechanical aperture ranged from 72.7 μm to 506.5 μm, whereas hydraulic aperture ranged from 1.7 μm to 16.8 μm.
The experimental results indicate that joints contribute far more significantly to fluid flow than intact rock. Based on laboratory results, this study further estimated the differences in equivalent permeability between jointed rock masses with a joint spacing of 1 m and intact rocks. In addition, numerical simulations of non-mated joints under shear stress conditions were conducted for slate to compare mated and unmated joint conditions. The results show that, with a joint spacing of 1 m, the equivalent permeability of jointed sandstone is 2.2–4.5 times that of intact sandstone; the equivalent permeability of mated joint slate is 12–18 times that of intact slate with parallel cleavage; and the equivalent permeability of unmated joint slate is 133–300 times that of mated joint slate.
The relationships between porosity and permeability for both intact sandstone and intact slate can be described by exponential laws. For jointed sandstone and naturally mated cleaved slate, the ratio of mechanical aperture to hydraulic aperture (E/e) increases with decreasing hydraulic aperture, whereas naturally unmated cleaved slate exhibits an opposite trend. Experimental results suggest that mechanical aperture should be corrected by subtracting the pore volume of intact rock under the same effective stress, while hydraulic aperture does not require consideration of the permeability contribution from intact rock. For low-permeability rocks, whether the pore volume contribution of intact rock can be neglected when measuring mechanical aperture using the Pulse Decay Balance method requires further investigation. |
