- 學位論文
高解析度海洋地熱量測設備之研發
The Development of Seafloor High-Resolution Heat Flow Instruments
摘要
地球表面的熱流量大小是由地球生成時的熱、內部的熱源、不同區域間熱量的轉移、以及不同地球內部物質之間的熱傳導能力差異等因素所決定。大地熱流的研究可以幫助暸解地球內部熱源及溫度的分佈，提供了解地殼和岩石圏構造以及其演化有用的資訊，作為研究地球物理、化學與地質現象的一個基本資料。所以大地熱流探測為研究全球性及區域性熱流的重要步驟。本論文主要說明三種存在不同類型海洋地熱流探測設備的設計、製造和資料處理，以及改進儀器性能，和改善海洋地熱流探測的正確性及作業效率。另外，由於海洋探測儀器的損耗率及購置成本都很高，自製儀器不但可以大幅降低探測所需經費，同時可增加儀器使用以及提高探測作業的成功率。 本研究所研發的海洋地熱流探測設備包含(1)HR-3利氏探針、(2)CHTL自錄式小型溫度計以及(3)NP-1細針式熱傳導探針。HR-3利氏探針的研發，主要是沿續台大海洋研究所過去多年研製利氏探針的經驗，更新電路板設計、增强儀器性能及加入新的作業功能，使儀器可靠性提高、作業更為便利。CHTL自錄式小型溫度計的設計，主要用於附著於岩心取樣器上，以數個小溫度計組成自主托架式地熱探針，並利用岩心取樣器有較深沉積物穿透能力的特性，測量海床下較深處的溫度梯度。NP-1細針式熱傳導探針應用於量測由岩心取樣器取回沉積物樣本的熱傳導係數。這些儀器已完成設計及生產製造，並有多次實際的海上現場作業測試，證實這些儀器的功能及性能均可逹設計時的要求，部份技術並取得國內外的專利權。 傳導熱流是溫度梯度與熱傳導係數的乘積。海洋熱傳導性的地熱探測只能在海床下十米左右的深度測量溫度梯度，而且地表地層內的平均溫度梯度僅約30 mK/m，因此測量儀器的溫度解析能力是非常重要的性能。過去受限於溫度探棒的構造及測量方法，各式海洋地熱探測設備的溫度解析度大約在1 mK左右。本研究針對利氏探針的長溫度探棒所設計的比例式測量電路，以及共地迴路多工三線式的熱敏電阻測量連接法，可以將利氏探針測量溫度的解析度提高至0.1 mK。為目前同類型的儀器中最高者。自錄式小型溫度計也採用比例式測量電路，它的溫度解析度也可以逹到0.1 mK的水準。 針對各個儀器的構造、施測作業方式不同，這三種儀器的研發重點分別為： HR-3利氏探針的研發重點為高溫度解析能力的多通道長溫度探棒測量電路架構； CHTL自錄式小型溫度計的研發重點為機構的便利性及堅固性； NP-1細針式熱傳導探針主要訴求為攜帶及施測的便利性及速度。 地熱探針插入沉積物中產生的摩擦熱會使得探針以及其周圍沉積物的溫度上升，產生暫態溫度干擾。要在海床上等待摩擦熱消散，回復至沉積物原有的背景溫度需要很久的時間，在實務上並不可行。我們使用探針插入沉積物時短時間內的高解析度的資料，以圓柱形溫度衰減函數建立摩擦熱的溫度模型，然後以外插計算，預測因摩擦熱所提高的溫度至無限長的時間，推算背景溫度及計算溫度梯度。利氏探針以及自主托架式地熱探針的小溫度計資料都可以用這種方法處理，但由於小型溫度計的溫度探頭並非理想圓柱體，直接推算的誤差較大。改善的方法是直接從原始的溫度梯度資料，用上述模型來推求最終之背景溫度梯度，並加上經驗式修正，可以得到較佳的結果。
並列摘要
Heat flow at various regions of the Earth’s surface is affected by primordial heat, interior heat sources and heat transfer between different regions. The geothermal heat flow information can be used to understand the Earth’s interior heat source and the lithospheric structures. The thermal structure can also play an important clue for understanding geophysical, geochemical, and geological processes. For that, this thesis is mainly aimed to develop a reliable tool for marine heat flow measurement. The development, construction and data reduction of different types of the marine heat flow measurements will also be compared. Because of high loss and damage rate and the high cost of the marine instruments, the capability of building in-house instruments can significantly reduce the cost of scientific experiments. In this thesis, three major invented parts of the marine geothermal instrument are presented: (1) the Lister-type heat probe, (2) the compact high-resolution temperature logger and (3) the needle probe. The development of the Lister-type heat probe includes the updating of the design of circuit boards, the improvement in performance, and the additionally new functional features. It makes the new design more reliable and efficient. Compact high- resolution temperature logger is used to attach to a piston or gravity corer in order to have a deeper penetration ability of the corer and to measure the temperature gradient beneath the seafloor. Finally, the needle probe is used to measure the thermal conductivity of a core sample. The completed design and production of the instruments was made, and utilized in many field operations at sea. A conductive heat flow is the product of a temperature gradient and a thermal conductivity. In reality, the measurement of a conductive heat flow can only be made in few meters below the seafloor; whereas, a thermal gradient of the crust is only about 30 mK per meter. Thus, the heat flow measurement needs a high temperature resolution of the instrument. However, the existing marine heat probes had only about 1 mK of temperature resolution. In this study, taking into account the features of the three developed instruments and optimizing measurement schemes, we will develop the state-of-the-art temperature measurement instruments. Particularly for the long temperature probe of the Lister-type heat probe, using ratiometric measurement and Common-Ground, Multiplexed-Three-Wires measuring scheme (CGMTW), the HR-3 can have temperature resolution of 0.1 mK, which is the highest resolution amongst the Lister-type heat probes so far. Taking into account different construction and operation of instrument, we develop three designs of heat flow instruments: HR-3 Lister-type heat probe, emphasizing on the high temperature resolution measuring scheme of the multi-channel long temperature probe; CHTL temperature logger, emphasizing on durability and convenience mechanic structure; NP-1 needle probe, emphasizing on mobility, portability and measuring speed. When the heat probe penetrates into the sediments, the friction heat will raise the temperature of the probe and its surrounding sediments and generate transient temperature interfere. It takes a considerable span of time for waiting the dissipation of friction heat and the return to the background temperature. In fact, this may not be realistic, especially when one considers the research ship’s operation time and cost. A more practical way is to use the high-resolution frictional heat data caused by the frictional penetration into the sediments, and to numerically simulate the friction heat dissipation by using cylindrical temperature decay function to predict the friction-raised temperatures to infinite time. Accordingly, both the background temperatures and temperature gradients of the sediments can be obtained. Such kind of data reduction can be used for the Lister-type heat probe and the autonomous outrigger probe. However, the small temperature loggers that are attached to an autonomous outrigger probe may be not suitable for such a reduction because the temperature probe is far from an ideally cylindrical body. In that case, the reduction directly from the original thermal gradient data and an empirical correction formula could be adopted to obtain better background thermal gradients.