全球海水面升降變遷曲線對比井測資料研究

Abstract

層序地層學理論認為在海相的碎屑岩地層中，沉積物粒度變化主要受控於全球海水面升降變遷；而珈瑪井測紀錄是推估沉積物顆粒大小排列變化時，常用的一種工具。依照上述性質，全球海水面升降變遷將主導珈瑪井測紀錄的數值變化。本研究選用二筆被廣泛使用的全球海水面變遷曲線作為標準，對比來自三個不同海洋沉積環境的珈瑪井測紀錄。研究證實只要慎選研究地點，層序地層學理論應該都能適用。 決定地層的年代是地質學研究與地質資源探勘的重要課題，地質資料對比是其中一個常用的方法；由於海水面升降變化是全球一致的，全球海水面升降變遷可以作為全球地層對比的標準；更進一步，透過井測資料對比全球海水面變遷可以有效率地評估出地層的沉積年代。 面對兩筆取樣的時間或空間差異大的資料時，可以透過濾波降低對比的難度。本研究採取經驗模組拆解法，藉著信號拆解與重構，可以將井測資料與海水面變遷曲線中，具有已知地質意義或波型適合對比的分量獨立出來討論；此外，透過信號拆解與重構，能讓人工直覺對比，工作速率加快且結果較為客觀。由井測資料對比全球海水面變遷曲線的成果，基本上可以發現：在大陸邊緣具有穩定沉積速率的地層中，大多數探測井的珈瑪射線紀錄，皆可能反應大尺度的海水面升降週期變化。此外，即便理論基礎或牽涉到的變因都不是很清楚，此技術可以快速且有效率地評估地層的沉積年代；就經濟效益觀點而言，應該可以廣泛地運用到全球的探勘工作上。Sequence stratigraphic theory attributes the changes of sediment stacking patterns mainly to the global sea-level fluctuation. The gamma ray logs normally can reflect the shale content of the formation. Combine these two statements, the value of gamma ray logs may reflect the global sea-level changes. Global sea-level changes could have been used as the standard for establishing a stratigraphic correlation technique. The correlation between sea-level change curves and gamma ray logs may be an efficient and economically feasible method for obtaining chronological age of the sedimentary strata. In this study, we chose two global sea-level change curves and three gamma ray logs from three wells located at different oceanic environments. To improve the efficiency of the correlating process and the accuracy of the result, we use digital signal processing methods. For choosing suitable component of the data for correlation, we decompose and reconstruct the signals by empirical mode decomposition which is an adaptive filter. It is possible to prove that the pattern of gamma ray logs in ideal sedimentary environments is similar to the pattern of global sea-level curves. Therefore, global sea-level change curves can be used as a universal standard for the correlation of gamma ray logs. The correlation between global sea-level change curves and gamma ray logs can be develop as an efficient practice for deciphering the age of the strata and applying to resource exploration.