冰岛南部Bodmodsstadir地热田的概念模型和自然状态模型

THE CONCEPTUAL MODEL AND NATURAL-STATE MODEL OF THE BODMODSSTADIR GEOTHERMALFIELDIN SOUTHERN ICELAND

Ｂｏｄｍｏｄｓｓｔａｄｉｒ地热田是冰岛南部低温地热田之一．１９７４年以来，已完成１０口钻井．根据温度测井、井中压力和水位测量和一些地质地球物理资料研究，本文建立了它的概念模型．为了进一步建立该地热田的自然状态模型，本文进行了稳态和非稳态地温场模拟．通过假定一倾向北西的主断裂，模拟计算地温与观测地温吻合得很好．非稳态模拟还表明象这样的地热系统形成后５０００ａ就能达到准稳态（自然状态）．进一步通过求解质量和能量传输方程表明，该地热田深部补给在１０．０Ｌ／Ｓ，深部补给通道（断裂）的渗透率０．８达西．建立的自然状态模型能够用于这个地热田的评价和开发．

Iceland is situated on the Mid-Altantic Ocean Ridge. The constructiveboundaries between the north AmeriCan and Eurasian plates follow the Mid-AtlanticRidge and cross Iceland from southwest to northeast. In Iceland the boundaries are charac-terized by a central zone of rifting and volcanic actibity which represent the extension andaccretion of the crust. During the processes of rifting and volcanic actitity, manyextensional fractures are formed, and basaltic magmas raised from asthenosphere eruptsand intrudes intensively so that the crust beneath this rifting zone is very hot and its shallowtempeaturb is over 150C / km. Many high temperature and midde-low temperaturegeothermal fields are formed in this processes. In order to exploit and utilize the resourcesof geothermal energy, it is essential to establish the conceptual model and natural-statemodel. ThiS is also helpful for understanding the processes of heat diffusion from the earthinterior in ocean ridges,The Bodmodsstadir geothermal field is one of the low temperature geothermal fieldslocated just outside the neovolcanic zone in southern Iceland. Ten wells have been drilled inthis area since 1974. Well BS-1 is the only Producer and the water from it is used for green. houses and heating on the Bodmodssadir farms. Repeated temperature and water-levelmeasurements have been made in these boreholes. The formation temperature- distributionin the area, the location of aquifers, a deduced fracture and a conceptual model of theg6othermal field are presented in this paper based on temperature logs, water levelmeasurement and pressure in the wells and other geological and geophysical data. To further develop the natural -state model of the Bodmodsstadir geothermal system,steady-state temperature simulations were performed first. When assuming a fracture situated between wells BS-2. and BS-10, dipping 82 ° and striking N 40 °E in thesteady-state simulation, the calculated temperature distribution matChes well the observedt6mperature in the wells. The results from steady-state show that the presented conceptualis reasonable. The following is non-steady state temperature simulation, which by solvingonly the equation of energy transport, indicates that it took about 5000 years for this system to reach quasi-steady state (natual state). Furthermore, when solving both the massand the energy transport equations in the non-steady-state simulation, the recharge raterate from depth has to be in the range of 1-10kg/ s, with permeability of the fracture betWeen 0.1-0.8 Darcy to match the observed temperature data, The natural state model developed in this study could be used to evaluate thisgeothermal system and for planning its development. The results of this also show that themid-ocean ridge is the important region of heat diffusion from earth interior, where . theheat diffusion is mainly in convection unlike the interior of plates where the heat diffusionis mainly in conduction.