台灣錦水氣田深部儲集岩層序地層研究

Abstract

錦水氣田位於台灣西北部麓山帶，為一南北兩端傾沒的不對稱背斜構造，歷經多年鑽探發現是一個油氣蘊藏豐富的氣田，近年來產自淺部中新世及上新世地層的油氣逐漸枯竭，而深部漸新世地層的油氣蘊藏量尚未明瞭。由於震測資料品質欠佳對於深部地層的解析有限，故本研究藉由鑽探錦水構造所獲得之井下岩心及井測資料，進行沉積相研究，分析其沉積循環的變化，建立本區域的層序地層架構，進而探討本區域儲集層之特性及分布。 本研究蒐集統整了10口井岩心資料與井測資料，並建立包括汶水層與五指山層上部之一千分之一地層柱。經由井下岩心觀察及汶水溪上島剖面野外地質調查共分類出9種岩相，經由岩相組合解析沉積環境。透過井測資料與井下岩心岩性的比對，根據井測資料進行岩石物理特性分析，檢視綜合柱狀圖所建立的岩性(砂岩、泥質砂岩、頁岩)分別有良好的群聚現象，岩石物理特性的區別驗證岩性劃分的可信度。孔隙率經由岩心實驗及井測計算進行比對分析，結果顯示砂岩孔隙率約為2.3%~8.3%；泥質砂岩則為0.8%~5.2%。 經由建立連續的岩性地層柱，並由井測資料分類4種井測相，歸納井測相與沉積相之關係，建立了潮汐作用為主的海岸平原及波浪作用為主的淺海陸棚環境。五指山層上部主要以海岸平原環境為主，汶水層下部亦以海岸平原環境為主，上部則以淺海陸棚環境為主，自漸新世晚期至中新世早期形成三次沉積循環。 層序地層劃分為4大層序，汶水層包含兩組完整層序，可合理與文獻報導之台灣中部剖面的劃分對比，結果顯示層序UO、層序一及層序二由下而上可分別對比至3級的全球海水面變化，TB1.3、TB1.4及TB1.5。由東西及南北剖面層序側向對比結果顯示，古海岸線大致為東北-西南向，沉積物由西北側供應至東南側堆積。層序對比顯示於層序界線上部之海進砂體常平行於古海岸線連續性良好可作為良好儲集層，可為探勘的主要標的。層序界線之下的高水位體系域，以外伸堆積的砂體為主常垂直於古海岸線，探勘可朝其西北物源方向著力。

Chinshui structure is located in the northwestern of Taiwan Foothills, for a north-south dumping asymmetric anticline structure, after years of drilling as a rich oil and gas fields. By means of the core and log data from the wells in Chinshui structure, this study analyzed the sedimentary facies and sedimentary cycle, established the regional sequence stratigraphy framework, further discussed the characteristics and distribution of the reservoir. The study collected 10 well core data and well log data, and established the stratigraphic column including the Wenshui formation and the upper part of the Wuzhishan formation. Nine kinds of lithofacies were classified through the observation of the core and the field section, and the sedimentary environment was analyzed through the combination of lithofacies. Through the comparison between the well log data and the lithology of the core, the petrophysical characteristics are analyzed according to the well log data, and the lithology (sandstone, shaly sandstone, shale) established by the cross-plot is observed to have good clustering phenomenon. The difference in petrophysical properties verifies the credibility of lithological division. The porosity is analyzed by core experiments and well calculations. The results show that the sandstone porosity is about 2.3%~8.3%; the shaly sandstone is 0.8%~5.2%. By establishing a continuous lithologic stratigraphic column and classifying the four types by well log data, the relationship between the log type and the sedimentary facies is summarized. The coastal plain environment is dominated by tidal, and the shallow marine shelf environment is dominated by waves. The environment of upper part of the Wuzhishan formation and the lower part of the Wenshui formation are coastal plain environment, and the upper part of the Wenshui formation is shallow marine shelf . Three sedimentary cycles were accumulated from the late Oligocene to the early Miocene. The sequence stratigraphy is divided into four major sequences. The Wenshui layer contains two complete sequences, which can be reasonably compared with the literature of the central Taiwan section. The results show that the sequence UO, sequence one and sequence two can compare to the third order global sea level changes, TB1.3, TB1.4 and TB1.5. The lateral comparison of the sequence of the east-west and the north-south section shows that the ancient coastline is roughly northeast - southwest, and the sediment is supplied from the northwest side to the southeast side. The sequence comparison shows that the transgressive sand above the sequence boundary is often parallel to the ancient coastline and has good continuity as a good reservoir, which can be the main target of exploration；highstand system tract below the sequence boundary, the progradation sand are mainly perpendicular to the ancient coastline, and the exploration can be directed toward the northwest source.