非彈性應變回復法之三維應力測量應用於宜蘭地熱探勘之評估

Abstract

世界上的化石能源逐年面臨匱乏的危機，這將對人類的生活與經濟發展造成衝擊，因此開發替代能源為全球必行的趨勢，考慮環境保護、永續利用、經濟發展與資源優勢之因素，地熱能為適合臺灣發展的替代能源之一。 位於太平洋火環帶西緣的臺灣，是個富含地熱資源的國家，其中宜蘭地區地下水充足，若能在該地深處找到熱源與水源富集之區域，該地則即為理想的地熱電廠場址。 本研究以宜蘭紅柴林地熱潛能區紅柴林1號井(HCL01)與紅柴林2號井(HCL02)之岩心為樣本，進行非彈性應變回復法（ASR）實驗，量測現地的三維應力場，並以岩心描述取得現地導水裂隙與弱面位態的資料，利用三維應力與裂隙位態評估現地裂隙的滑動與擴張趨勢以及導水效果的好壞，作為地熱開發潛能的評估依據。 紅柴林1號井樣本所解算出的三軸應變場結果顯示，各樣本的三軸應變場沒有特定的規律，每個深度之樣本所對應的應力場型式也不相同。HCL01-01樣本結果不屬於安德森斷層理論的任一種斷層型式的應力場，水平最大應力的擠壓方向為西北-東南向，解算三為主應力之規模由大到小分別為46.05、41.06、34.29 MPa；HCL01-02樣本結果趨近於逆斷層型式的應力場，水平最大應力的擠壓方向為北北西-南南東向，解算三為主應力之規模由大到小分別為57.86、34.03、29.3 MPa；HCL01-03樣本結果趨近於正斷層型式的應力場，水平最大應力的擠壓方向為北北東-南南西向，解算三為主應力之規模由大到小分別為41.35、34.46、27.96 MPa；HCL01-04樣本結果趨近於逆斷層型式的應力場，水平最大應力的擠壓方向為北北東-南南西向，解算三為主應力之規模由大到小分別為68.58、61.16、51.09 MPa。整體而言，各樣本ASR實驗顯示的應力場結果並不一致，但有水平最大主應力的擠壓方向皆趨近為南北向擠壓的共通點。 紅柴林2號井樣本所解算出的三軸應變場結果顯示，各樣本的三軸應變場沒有特定的規律，每個樣本所對應的應力場型式也不同。HCL02-06樣本結果趨近於正與走向滑移間過渡斷層型式的應力場，水平最大應力的擠壓方向為西北西-東南東向，解算三為主應力之規模由大到小分別為65.09、56.46、34.96 MPa；HCL02-07樣本結果趨近於走向滑移斷層型式的應力場，水平最大應力的擠壓方向為西北-東南向，解算三為主應力之規模由大到小分別為80.08、60.79、46.8 MPa。HCL02-6、7樣本水平最大主應力的擠壓方向趨近於西北東南向擠壓，彼此間有水平最大應力擠壓方向雷同的共通點。 紅柴林1號井樣本解算出的滑動趨勢皆小於0.6，各位態的構造弱面均不容易錯動活化。紅柴林1號井樣本解算出的擴張趨勢顯示，深度約1492公尺西北-東南走向、向東北傾斜之中到高傾角的構造弱面有高的擴張趨勢；深度約1560公尺東北-西南走向、向東南傾斜之中傾斜程度傾角的構造弱面有高的擴張趨勢；深度約1579公尺南北走向、向東或向南傾斜之高傾角的構造弱面有高的擴張趨勢；深度約2222公尺西北-東南走向、向東北傾斜之中到低傾角的構造弱面有高的擴張趨勢。 本研究由紅柴林1號井岩心樣本所計算的擴張趨勢與附近深度構造弱面位態進行比對，分析的結果為大部分的構造弱面(如: 層面、劈理、裂隙、礦脈、斷層擦痕面、導水裂隙)位態都沒有高擴張趨勢，於現今應力場下不利於以擴張撐裂的方式發展成為導水裂隙。只有1491.5~1555.7公尺深朝西南方傾沒的礦脈群擁有高擴張趨勢，較有機會以張裂的方式發展成為現今的導水裂隙。 若能由其他資料，例如井測資料，證實該位置導水裂隙的存在，將有利於加強型地熱電廠之注入井與生產井的設井相對位置之評估。The world's fossil energy is facing a crisis of scarcity year by year, which will impact human life and economic development. Therefore, the development of alternative energy is a global imperative trend. Considering environmental protection, sustainable utilization, economic development and resource advantages, geothermal energy is one of the alternative energy sources suitable for Taiwan's development. Taiwan, located in the western margin of the Pacific Ring of Fire, is a country rich in geothermal resources. Among them, the groundwater in Yilan area is abundant. If we can find an area rich in heat sources and water sources deep in the area, it will be an ideal geothermal power plant site. In this study, the core of Hongchailin No. 1 (HCL01) and Hongchailin No. 2 (HCL02) in Yilan Hongchailin geothermal potential area was taken as samples, and the non-elastic strain recovery method (ASR) experiment was carried out to measure the three-dimensional stress field in situ. The data of water conduction fracture and weak surface state were obtained by core description, and the three-dimensional stress and fracture position state were evaluated by using the three-dimensional stress and fracture position state. The trend of slip and expansion of ground fissures and the effect of water diversion are estimated as the basis for evaluating the potential of geothermal development. The results of triaxial strain field calculated from well Hongchailin 1 show that the triaxial strain field of each sample has no specific law, and the stress field pattern corresponding to each depth sample is also different. HCL01-01 sample results do not belong to the stress field of any fault type in Anderson fault theory. The compression direction of the horizontal maximum stress is northwest-southeast, and the magnitude of the three main stresses calculated is 46.05, 41.06 and 34.29 MPa, respectively. HCL01-02 sample results tend to the stress field of the reverse fault type, and the horizontal maximum stress should be calculated. The compression direction of the force is NNW-SE, and the magnitude of the three principal stresses calculated is 57.86, 34.03 and 29.3 MPa from large to small, respectively. The results of HCL01-03 samples tend to normal fault-type stress field. The compression direction of the horizontal maximum stress is NNE-SW, and the magnitude of the three principal stresses calculated is 41. 35, 34.46, 27.96 MPa; HCL01-04 sample results tend to stress field of reverse fault type. The compression direction of horizontal maximum stress is NNE-SW. The magnitude of the three main stresses calculated is 68.58, 61.16 and 51.09 MPa, respectively. On the whole, the results of ASR experiments show that the stress field of each sample is not consistent, but the extrusion direction of the maximum horizontal principal stress tends to be the common point of the North-South extrusion. The results of triaxial strain field calculated from well Hongchailin No. 2 show that there is no specific rule in triaxial strain field of each sample, and the corresponding stress field pattern of each sample is different. The results of HCL02-06 samples tend to be the stress field of transition fault type between positive and strike-slip. The compression direction of horizontal maximum stress is northwest west-southeast-east. The magnitude of the three main stresses calculated is 65.09, 56.46 and 34.96 MPa, respectively. The results of HCL02-07 samples tend to be the stress field of strike-slip fault type, and the magnitude of the three main stresses calculated is 65.09, 56.46 and 34.96 MPa. The extrusion direction of the maximum stress is from northwest to southeast, and the magnitude of the three principal stresses is 80.08, 60.79 and 46.8 MPa, respectively. The direction of horizontal maximum principal stress in HCL02-6 and 7 samples tends to be northwest and southeast, and there are common points in the direction of horizontal maximum stress extrusion between HCL02-6 and 7 samples. The slip trend calculated from well Hongchailin 1 is less than 0.6, and the weak facets of each state are not easy to be distorted and activated. The expansion trend calculated from well Hongchailin 1 shows that there is a high expansion trend in the weak tectonic plane with a depth of about 1492 meters northwest-southeast and a middle-to-high dip in the Northeast direction, and a high expansion trend in the weak tectonic plane with a depth of about 1560 meters northeast-southwest direction and a middle-dip dip in the Southeast direction. Structural weak planes with a high dip angle of 9 meters north-south, east or South incline have a high trend of expansion, while those with a depth of about 222 meters northwest-southeast and a middle-to-low dip angle inclined northeast have a high trend of expansion. Comparing the dilatation trend calculated by core samples of Well Hongchailin No. 1 with the position of weak plane of deep structure nearby, the results show that most of the structural weak planes (such as bedding, cleavage, fissure, vein, fault scratch surface and water conduction fissure) have no high dilatation trend, which is not conducive to dilatation under the present stress field. The way of bracing crack develops into water conduction crack. Only 1491.5-1555.7 meters of vein group, which has a tendency of high expansion, has a better chance to develop into current water conduction fissures in the form of tension fissures. If other data, such as well logging data, can confirm the existence of water-conducting fissures at this location, it will be helpful to evaluate the relative location of injection wells and production wells in enhanced geothermal power plants.