本研究主要進行宜蘭地區斷層再活動性之評估工作。考慮在宜蘭三星地區若進行增強型地熱系統(EGS)，灌注流體於地層中可造成孔隙液壓上升，因而作用在斷層面上的有效正應力將減少，導致斷層再活動之可能性增加。應力場資料來自三星地區結元井之鑽井資料，假設孔隙液壓為靜水壓梯度；以岩心密度積分求得現地的鉛直應力；由水力破裂試驗測得最小水平應力數值；以應力多邊形推估最大水平應力隨深度的變化，其上界值利用安德森臨界斷層摩擦理論求得；並利用清水IC21號井之井徑電測(Caliper log)判釋最大水平應力的方位。接著研究並蒐集震測剖面及地質剖面，利用GOCAD軟體建構宜蘭三星與清水地區地下地層及斷層的三維構造，再使用3DStress和Traptester軟體計算斷層面上各區塊因灌注流體引發重新滑動的潛勢(slip tendency, Ts & dilation tendency, Td)及臨界孔隙液壓差值(Pcp)。分析結果顯示宜蘭三星地區的應力梯度分別為鉛直應力21.6MPa/km，最小水平應力18.0MPa/km，最大水平應力之上界值根據臨界應力斷層摩擦理論(μ=0.6)求得34.2 MPa/km。依據井徑電測判釋的最大水平應力方位約為30°。假設斷層靜摩擦係數μ=0.6情況下，濁水斷層滑移潛勢最高，但低於0.6，所以在目前現地應力作用下屬於穩定狀態，擴張潛勢最高的斷層亦為濁水斷層。另評估各參數對斷層臨界孔隙液壓差之敏感度，影響最大的參數為最小水平應力。最後考量三星地區在不同應力機制下，以隨機參數取樣估算濁水斷層之臨界孔隙液壓差。若應力機制為正斷層系統，濁水斷層在滑動前所能承受臨界孔隙液壓差之最保守估計值為2.6MPa；若應力機制為走向滑移斷層系統，濁水斷層在滑動前所能承受臨界孔隙液壓差之最保守估計值為2.4MPa。;The aim of this study is to analyze the possibility of the fault reactivation in Sansing Area of Ilan. The scenario assumes the possible fluid injection activitis for Enhanced Geothermal System (EGS), which may generate high fluid pressure and trigger slip along fault planes. We determined the in-situ stress states with core logging data from the HongChaiLin(HCL) and IC21 wells,. We estimated the pore pressures from the hydrostatic pressure gradient (10.37MPa/km). The vertical stresses (SV) were calculated from core density logs of the HCL well. The gradient of the vertical stress is 21.63MPa/km. The minimum horizontal stress (Shmin) is measured with hydraulic fracture test, and its gradient is 18.01MPa/km. The maximum horizontal stress (SHmax) is estimated with stress polygon method, and its upper bound is estimated using Anderson faulting theory. The upper bound gradient of SHmax is 34.20 MPa/km. The orientation of the maximum horizontal stress is 30° from the Caliper logs of IC21 well. We also construct the 3-D geological structure model of Sansing and Chigshui area, and using the model for assessing the risk of fault reactivation with 3DStress and Traptester softwares. Under current in-situ stress state, Zhuosui fault has higher slip tendency than other faults. We also concluded that the Zhuosui fault has higher dilation tendency than others from the dialation analysis. In addition, The sensitivity analysis shows that the minimum horizontal stress is the main factor influence on the critical pressure perturbation (Pcp). The scenarios tests of fluid injection upon the Zhuosui fault show that the critical pressure perturbation allowed is 2.566MPa, assuming the normal faulting stress regime, and the critical pressure perturbation is 2.417MPa for strike-slip faulting stress states.
