大地電磁與重力法應用於台灣西北部關西構造研究

Study of the Guansi structure in northwestern Taiwan by using MT and Gravity methods

游峻一(Chun-Yi Yu) ； 黃旭燦(Shiuh-Tsann Huang) ； 楊潔豪(Chieh-Hou Yang) ； 施輝煌(Huei-Huang Shih)

《健行學報》 36卷4期 (2017/01) Pp. 1-22

摘要

台灣西北部之內麓山帶地質非常複雜，石油業以傳統探勘法描繪細部地下構造較困難，特別是複雜封閉儲油構造，故必須藉構造地質和整合地球物理的資料與解釋，方能建立較佳的地質構造模型。本研究利用本團隊開發之重力軟體及大地電磁法測勘結果，探討關西背斜附近地區地下地質構造。開發之重力軟體的特色為同時考量不同之地質參數限制條件，包括地層之密度、深度與傾角及斷層之位置與傾角、地層及地層密度之連續性、等斷層距、固定模型參數等亦考量在內。針對複雜地質構造地區，參考震測剖面及不同之地質解釋剖面，以基元建構地質模型，作為初始密度模型。固定基元大小，應用開發之多變量重力逆推軟體，以不同方式調整地層物理參數方式作逆推，以求出重力之理論值與觀測值密合度最佳之地下密度摸型，可作為最佳之地質解釋模型，其地質構造模型大致與重力逆推結果相當；大地電磁法分析結果，發現沿張渝龍1-1'測線附近，在背斜軸西側2公里，深度約2,500公尺處，有局部地層呈現高電阻率狀態，推測在桂竹林層內，此高電阻率團往下逐漸擴大至深度6,000公尺，推測經過地層為河排層、打鹿層、北寮層，含油氣潛能機會較高，但此區塊並未向南延伸，由此研判關西背斜較具油氣潛能之地區應在背斜北側附近地區。

關鍵字

重力逆推 ； 大地電磁法 ； 關西背斜

並列摘要

The foothill belt of northwestern Taiwan has a complex subsurface geological structure; the detailed subsurface structure is hard to be delineated by using the conventional exploration techniques; especially for a complex reservoir. Therefore combination of the structural geology, various geophysical data and effective interpretation techniques must be used to establish a better geological structure model. The aim of this study is combined the gravity result using our gravity inversion program with MT survey result for delineating a complex subsurface geological structure area in Guansi anticline. The features of our multi-source inverse program encompass the functions of allowing the variation of geological constraints such as bed densities, depths and dips, and locations and dips. The continuity of layering densities and boundaries, constant fault throws, and some fixed model parameters are also included. In order to increase the efficiency of an inversion in the gravity data, we use blocks to construct an initial density model by referring the seismic section and/or geological interpreted model and then fix the size of each block. By using our multi-source program, we observe that the physical parameters of the blocks are continuously being modified during inversion. The best-fitting interpreted geological model is the one that the observed and the computed gravity anomalies are well-matched, and the subsurface geological model. The gravity inversion result is comparable to the geological structure model. MT results indicate that a local high resistivity zone within the Kueichulin Formation, it starts at a depth of 2500 m along the line chang1-1, 2 km west of Guansi anticline. Then the zone passes through the Hopai formation, Talu shale and Peiliao formations and gradient large with the depth, it ended in the depth of 6000 m. It is being considered to be a potential reservoir. Since the zone is not extended southward, a potential reservoir may confine in the north of Guansi anticline.

並列關鍵字

gravity inversion ； MT ； Guansi anticline