從地溫週期性變化推估地層原地之熱擴散係數

岩石熱擴散係數（thermal diffusivity）的測量通常都是取岩樣於實驗室內以儀器進行分析，本研究嘗試利用地表下溫度之監測資料推估地層之原地（in situ）熱擴散係數。根據熱傳導原理，地表溫度變化訊號會往地下傳遞，傳遞過程中訊號的振幅衰減和相位的變化與深度和地層的熱擴散係數有關，熱擴散係數大的地層其振幅衰減慢、相位差小，如能同時得知地表和某深度溫度訊息，則依熱傳理論可求得該深度整個地層的熱擴散係數。本文收集台灣北部大屯火山區一口地溫監測井深度1、3和13公尺之連續溫度監測資料，以及氣象局在該地區同時期之氣溫紀錄，以半空間（half space）熱擴散方程式進行試誤法演算（trial and error），將氣溫的年週期變化視為熱源，取不同的熱擴散係數數值帶入熱擴散方程式中，所得的理論與實際各深度觀測值之最小誤差，即視為地層之現地熱擴散係數，根據此方法推得該口井地表至深度1公尺、3公尺和13公尺地層之熱擴散係數分別約9.5×10^(-7) m^2s^(-1)、1.1×10^(-6)m^2s^(-1)和1.0×10^(-6)m^2s^(-1)，此數值落於一般岩石的範圍。

關鍵字

無資料

並列摘要

The thermal diffusivity of formation samples is usually measured in a laboratory. In this study we computed the in-situ rock thermal diffusivity using the measured borehole temperatures. It could be inferred that the amplitude decrease and phase change are related to the depth and thermal diffusivity. For a high thermal diffusivity formation, the amplitude decay is low and phase change is small; therefore, the rock thermal diffusivity at a certain depth can be estimated by the surface and subsurface temperature distribution at a specific time. In order to compute the thermal diffusivity of shallow formations in Tatun Volcano area, continuously monitored temperatures at the depth of 1, 3, and 13 meter and at the surface have been collected. A trial and error method was used to estimate the thermal diffusivity when the minimum difference was observed between the computed and the measured values. Results show that the rock thermal diffusivity at depths of 1, 3, and 13 meters are 9.5×10^(-7) m^2s^(-1)、1.1×10^(-6) m^2s^(-1) and 1.0×10^(-6) m^2s^(-1), respectively which fall within the range of formation thermal diffusivity.

並列關鍵字

thermal diffusivity ； trial and error

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