- 期刊
臺南縣隆田構造淺層甲烷氣之探勘
A New Discovered Shallow Biogenic Gas Field in Lung-Tien, Tainan
摘要
中油公司於民國93年6月在臺南縣的隆田構造淺層鑽獲大量甲烷氣，並命名為官田氣田。本次適時引進DHI/AVO的概念，在四方圈合的構造內，配合震測剖面的震波異常及振幅隨支距變化(Amplitude Variation with Offset, AVO)反應，解釋其含氣範圍，鑽井結果證實於鑽深694公尺處及837公尺處各有一生產層，氣樣分析結果顯示甲烷含量高達99%以上。 有關AVO反應的分類，可以分成四種類型，嘉南平原區六雙層至二重溪層內含氣砂層之AVO震波反應歸屬第三類型，產氣層之震波反射AVO分析中，反射振幅隨支距增加而有明顯增大現象。 真振幅資料處理，需分兩階段進行。首先需依照一般的資料處理流程，求取正確的速度模型及估算各種靜態修正量、折射靜態修正量和剩餘折射靜態修正量後，第二階段再使用這些修正量及參數，利用表面一致性振幅修正法及表面一致性解迴旋法，從原始資料重新處理起，需採嚴格標凖的雜波摘除。本次AVO分析的前置處理有別於以往所做者，即利用表面一致性振幅修正法，將振幅分解成四個因素－震源因子、測站因子、支距因子及波道因子，再引用AVO技術評估，因此提高可信度。 由於甲烷氣通常存在於1,500公尺深度範圍內，而在嘉南平原區，此種深度之震測資料品質良好，適合藉由振幅異常現象迅速篩選出有油氣潜能的地區，進一步做AVO分析，此爲一有效率的探勘方法。
並列摘要
A shallow biogenic gas field has been recently discovered in Lung-Tien, Tainan. The seismic amplitude anomaly and AVO responses complied with a four-way dip structure strongly encouraged the drilling of KTN-1 well. It has been proved that there are two pay-zones at depth 694m and 837m respectively. The methane content is more than 99%. AVO responses are categorized into four types. The AVO responses of gas bearing sands in Liushuang and Erhchungchi formations belong to Type 1ff, i.e., the seismic amplitude will increase with increasing offset. An amplitude anomaly can be a pitfall of unconsolidated sediments, high porosity brine sands or tight streaks. Amplitude preservation and systematic processing sequences are essential for a reliable AVO analysis. The true amplitude processing can be separated into two phases. The first phase just follows the conventional processing sequences to acquire a correct velocity model and to accomplish various static corrections. The second phase is to apply the parameters and correction values obtained in phase-one to run a surface consistent amplitude correction and a surface consistent deconvolution. Source factor, station factor, offset factor and channel factor have been counted for the amplitude correction before conventional processing, hence the reliability of AVO evaluation is raised. The biogenic gas usually exists in the reservoirs less than 1,500m. Seismic data from these shallow formations mostly have good quality. Therefore, it's a good way to fast screen out the potential hydrocarbon accumulation and then further to be confirmed by the AVO analysis.