宜蘭紅柴林地區現地應力與導水裂隙關係之研究

Abstract

臺灣東北部宜蘭平原歷經造山擠壓與弧後張裂的影響，有較高的地溫梯度，因而產生豐富的地熱資源。透過現地應力場評估可以瞭解現今應力狀態，有助於地熱資源探開與開發，同時也對地熱鑽井工程提供重要資訊。導水裂隙發育與現地應力有密不可分的關係，為了使地熱發電達到最高產能。本研究利用非彈性應變回復法(Anelastic Strain Recovery )評估現地應力狀態進，而瞭解三維應力方向與大小，同時也對結元井200米岩心與養鴨場150米岩心進行岩心中視構造分析，詳細觀察並測量記錄岩心中各個地質構造的特徵與位態，探討地質構造於地底下的分布狀況。最後整合應力場評估與岩心中視構造分析結果，探討其地下構造與應力之關係。 研究結果指出ASR實驗明顯單純受到板劈理異向性的影響，推測岩心板劈理中水分的逸散會使岩心體積收縮，ASR紀錄並非現地應力釋放所產生之應變。岩心中視構造分析結果指出，結元井底下板劈理構造發達，因此大多數非充填裂隙與斷層泥主要順著板劈理面發育，而開口充填裂隙具有平行板劈理及垂直板劈理兩個群集。養鴨場井中開口充填裂隙亦具有兩群集分佈，與結元井不同的是，養鴨場井岩心有急折帶的產生。斷層擦痕反演指出，結元井過去曾有南-北方向拉張之正斷層應力場，以及南-北擠壓之逆斷層應力場。為了探現地應力與導水裂隙之關係，本研究利用DCDA、應力多邊形及斷層擦痕反演提供現地應力大小及方向，並透過3D-stress分析不同情境下開口充填裂隙成為導水裂隙之潛能。結元井與養鴨場開口充填裂隙屬於高擴張趨勢之開口充填裂隙，意味著現地應力具有高潛能使結元井與養鴨場井中切過劈理之開口充填裂隙成為導水裂隙。 綜合上述成果，斷層擦痕結果中逆斷層可能與早期板劈理同時形成；蘭陽平原正斷層應力場可能為沖繩海槽向西南延伸至之後所致，將應力場由南-北方向擠壓之逆斷層應力場轉變為南-北向拉張正斷層應力場；應力演化推測為早期劈理之逆斷層應力場演變至現今正斷層與走向滑移斷層應力場混合帶。

Ilan plan in northeastern Taiwan possesses abundant geothermal resources resulted from a higher geothermal gradient due to the influences of compression of mountain building and extension of back-arc rifting. Understanding in-situ stress field can evaluate current stress state for benefiting geothermal exploration and development and providing important information to geothermal engineering. Because development of geothermal fluid conduits is highly depended on in-situ stress, for enhancing geothermal productivity, this study conducted Anelastic Strain Recovery (ASR) to evaluate direction and magnitude of in-situ stress. Simultaneously, core description and investigated structure characteristic in JY-01 and 102-01 wells. At last, integrate in-situ stress and core description to figure out relation of in-situ stress and underground structure. Based on results of ASR experiment, samples were affected by slaty cleavage.We speculate shrinkage of core due to dry out of core water escape from core that induce core volume shrink. Core descriptions indicate slaty cleavage were well development in JY-01. Therefore, most fracture and gouge were along slaty cleavage to develop. And open-filling fractures across and parallel to slaty cleavage in JY-01 well. Well 102-01 havs two open-filling groups, and well 102-01 also has kink structure. According to stress inversion of fault slip, there reverse and normal faulting stress states in JY-01. We exploit DCDA, stress polygon and slickenside inversion to provide direction and magnitude of in-situ stress, Then, 3D-stress analysis potential of slip and dilation tendency of open filling become fluid conduits in different stress regime. Open- filling fractures high dilation tendency in JY-01 and 102-01. This result signify that in-situ stress has high potential to make fracture perpendicular to slaty cleavage becoming fluid conduits. In summary, we speculate reverse faulting and early stage slaty cleavage were develop in same time. Okinawa trough elongate to S-W induce normal faulting stress regime in Ilan plain that induce S-N reverse faulting stress state turn into S-N normal faulting stress state. We speculate earlier reverse faulting evolution to normal and strike-slip faulting stress state.