• 作者： 蕭寶宗; 胡錦城
• 作者服務機構： 中國石油股份有限公司
• 中文摘要： 為明暸臺南一高雄平原區磁性基盤之形貌，及其與西邊海域產油氣區磁性基盤之關係，以期在本區找到大量之油氣。遂在此區用質子磁力儀量取地球全磁力絕對值，做地磁日變化之修正後，繪製該區的全磁力圖。 研討IGRF地球主磁場之準確性，據電信研究所崙坪地磁觀測站之報告算出臺彎附近自1968至1974年間地磁場平均每年降低約10伽瑪，而IGRF預測為每年增加2伽瑪，顯然有誤。故加以修正該地球主磁場，用以計繪剩餘磁力圖。 用二次元模型計算其磁力異常，並導出一公式表示磁力異常最高點與最低點偏離磁體之距離，在臺灣附近之垂直磁體，其磁力最高點偏向磁體之南邊約為磁體深度1.4倍之距離，其磁力最低點則偏北約為磁體深度0.7借之距離。磁力異常之主波長約為該磁體深度之4.3倍。應用此種關係解釋本區之獨立磁力異常，效果很好。 討論二次元力場向下延伸之問題： (1)波長小於磁體深度三至四借之波向下延伸時，會引起延伸值產生振盪。 (2)補救邊端之誤差，於剖面之兩端向外增加數據，再行計算。或用模型計算之。應 用此種方法，計算本區磁性基盤深度圖。 由前面磁力資料之分析顯出： (1)本區磁力異常起伏小且平緩，表示無淺部火成岩之凸出體。 (2)磁性基盤之最高區位於中洲西面海邊。 (3)有二條狹長形之磁性基盤高區平行於臺南、中洲構造，但分別位於此二構造之東 側約四公里處，另一條狹長形磁性基盤高區平行於半屏山構造，但位於此構造之 西北側。由此可知磁力詳測可探知磁性基盤局部性之起伏，此起伏可能影響深部 構造之形貌，故磁力詳測對於探勘深部之油氣有很大的幫助。 磁力資料配合震測、重力與井下地質資料做綜合解釋，作者認為臺南和中洲構造之形成過程如下三點： (1)泥岩之重力滑動。 (2)沉積中心之西移。由此二過程造成類似 Diapir 之初期形貌。 (3)以後由來自東方之橫擠壓力造成現今背斜構造且具有之初期形貌。此區構造之走 向由東邊之近南北走向，往西漸變成近東西走向，作者認為其因係此區位於來自 東方之橫擠壓力向西減弱之漸變帶。 研究老探井之井下地質及磁性基盤，認為未獲經濟價值的油氣之原因為： (1)所鑽遇之古亭坑泥岩內無良好之砂岩或石灰岩。 (2)有些井雖然位於淺層構造高區，但位於磁性基盤之低區，故鑽至深部變為構造低 區。 由本區與西面海域之磁性基盤綜台得知，本區係位於海域產油氣區之構造之延伸部份，故狠有希望找到大量之油氣，探井應選在磁性基盤高區且震波反射良好之處。 由此研究獲知，在實施震測前若先做磁力詳測，可使探勘石油更為有效且更為經濟。
• 英文摘要： The total intensity geomagnetic field over the Tainan-Kaohsiung plainwas measured by the proton magnetometer and the diurnal correction wasmade as usual. The International Geomagnetic Reference Field (IGRF)was applied to remove the main geomagnetic field to obtain the residualmagnetic field. Then the IGRF was compared with the observed geomag-netic field at Lungpin Observatory Magnetism, Tauyuan, and a correctionwas proposed for the annual change in the IGRF. A total intensity mapand residual magnetic maps were made. They show gentle and smoothfluctuations of the magnetic anomalies, which may have originated fromthe deeper basement, but not from any igneous intrusive in the shallow.In the western part of the area, there are large areal anomalies, trendingENE-WSW, with an amplitude of about 40 gammas. In the central andeastern parts of the area, there are many small areal anomalies, trendingNE-SW or NNE-SSW, with an amplitude of 10 to 20 gammas. The magnetic anomalies of different dyke models were calculated. Aformula was derived to express the distances to which the magneticmaximum Xmαx and minimum Xmln of the dyke have shifted from thecenter of the dyke. The relation of the wavelength of the main componentwave of the dyke magnetic anomaly to the depth of the dyke was derived.The formula and relation were easily and effectively applied to interpretany isolated magnetic anomaly. Fourier's series was applied to interpret the continuous magnetic ano-malies to get the configuration of the magnetic basement. The optimumnumber of terms that should be taken into the Fourier's series was foundby comparison. The errors occuring on both ends of the profile are des-cribed and the profile is improved. The magnetic basement depth map shows that the highest part of themagnetic basement lies on shore west of the Chungchou town. There arethree main trends of magnetic basement highs each nearly parallel to theaxis of a shallow structural high with the offset a few kilometers. Thusthe detailed magnetic survey not only can detect the generalized basementconfiguration of a rather large area, but also detect the local reliefs of themagnetic basement. The magnetic basement was interpretated with respect to geology andcorrelated with the other data. The causes for the present configurationof the Tainan and Chungchou structures are attributed to（1）gravity tec-tonics，(2) displacing of deposition basin, (3) compressional tectonic force.The change of structural trends in the area are explained as due to thearea being located in the transitional：one of the tectonic force. The locations and subsurface geology of the old exploratory test wells,wherein no economic oil or gas was encountered, were reviewed withreference to the magnetic data. Although the Tainan TN-I and TN-2 andthe Chungchou CC-2 wells were drilled in the axial part of the shallowstructural high, they are located at the magnetic basement lows. Themassive mudstone encountered in the wells thus reach very great thickness. Part of the Tainan-Kaohsiung plain has been correlated as thenortheastward extension of any offshore magnetic basement high trendwhere abundant gas has been found. It is very possible to find oil or gasunder this plain. The test well should be selected where the magneticbasement high exists with good seismic reflection. Exploration for petroleum can be more economic, effective, andquickly done by conducting such detailed magnetic survey before conductingthe seismic survey.
• 中文關鍵字： --
• 英文關鍵字： --