Abstract Successful management of geothermal energy requires detailed understanding of physical and chemical conditions within the field prior to exploitation. It is thus crucial to identify fluids involved and their residence times, as well as the heat source, so as to assess the potential of the resource in terms of energy production. To this end, a geochemical study of relatively undisturbed fluids from the newly-developed Theistareykir geothermal field, Northern Volcanic Zone, Iceland was carried out on production wells, fumaroles, and mud pots. Noble gas (He, Ne, Ar, Kr, and Xe) elemental and isotopic abundances and stable isotopes (δ18O and δ2H) were measured to determine the system fluid sources and dynamics as exploitation proceeds. Results of this study, together with previously published data, show that four fluid sources are present: modern and local meteoric water (48.9%); sub-modern meteoric water from regional highlands precipitation (10.6%); pre-Holocene glaciated meteoric water (40.4%) with strongly depleted δ2H values of −127‰, calculated 40K-40Ar* fluid residence times from 57 ± 20 ka to 92 ± 30 ka and a (U/Th)-4He fluid residence times from 96 ± 50 ka to 160 ± 80 ka; and, finally, 3He-rich magmatic fluids. Concomitant enrichment in 18O and radiogenic 4He suggests that some fluids reside a long time in the reservoir, exchanging O and He with reservoir rocks. Maximum estimated helium isotopic ratios, 3He/4He (R), of 11.45 Ra (Ra = atmospheric ratio) show that the magma beneath Theistareykir is a depleted mid-ocean ridge basalt (MORB) mantle (DMM), with less influence (8.7 to 12.7%) of the Icelandic mantle plume source. Calculated heat (Q)/3He ratios plotted vs. R/Ra and 4He/36Ar ratios suggest that convective heat transport dominates the eastern part of the field where the magmatic heat source is located, while in other parts of the field, heat conduction seems to be dominant. Boiling and phase separation exists in the field, as indicated by δ18O values which fall to the left of the Global Meteoric Water Line in a δ18O vs. δ2H plot, but Q/3He ratios indicate that boiling affects only 1–10% of the fluid reservoir. With this obtained knowledge, any subsequent changes in the field conditions during the exploitation phase of Theistareykir can be better understood, helping to sustainably manage the resource.

中文翻译：

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冰岛新开发的 Theistareykir 地热田的流体和热量的来源和输送

摘要 地热能的成功管理需要在开采前详细了解现场的物理和化学条件。因此，确定所涉及的流体及其停留时间以及热源至关重要，以便评估资源在能源生产方面的潜力。为此，对来自冰岛北部火山区新开发的 Theistareykir 地热田的相对未受干扰的流体进行了地球化学研究，研究人员对生产井、喷气孔和泥浆罐进行了研究。测量稀有气体（He、Ne、Ar、Kr 和 Xe）元素和同位素丰度以及稳定同位素（δ18O 和 δ2H）以确定系统流体源和随着开采的进行动力学。这项研究的结果与之前公布的数据一起表明存在四种流体源：现代和本地大气水（48.9%）；来自区域高地降水的亚现代大气水（10.6%）；前全新世冰川大气水 (40.4%) 具有 -127‰ 的强烈消耗的 δ2H 值，计算 40K-40Ar* 流体停留时间从 57 ± 20 ka 到 92 ± 30 ka 和 (U/Th)-4He 流体停留时间从 96 ± 50 ka 到 160 ± 80 ka；最后是富含 3He 的岩浆流体。18O 和放射成因 4He 的伴随富集表明一些流体在储层中存在很长时间，与储层岩石交换 O 和 He。最大估计的氦同位素比 3He/4He (R) 为 11.45 Ra（Ra = 大气比）表明 Theistareykir 下方的岩浆是枯竭的洋中脊玄武岩 (MORB) 地幔 (DMM)，其影响较小（8.7 至12.7%）的冰岛地幔柱源。计算出的热量 (Q)/3He 比率与 R/Ra 和 4He/36Ar 比值表明对流热传输在岩浆热源所在区域的东部占主导地位，而在该区域的其他部分，热传导似乎占主导地位。现场存在沸腾和相分离，如 δ18O 值在 δ18O 与 δ2H 图中落在全球流星水线左侧所示，但 Q/3He 比率表明沸腾仅影响 1-10% 的流体水库。有了这些知识，可以更好地了解 Theistareykir 开发阶段现场条件的任何后续变化，有助于可持续地管理资源。热传导似乎占主导地位。现场存在沸腾和相分离，如 δ18O 值在 δ18O 与 δ2H 图中落在全球流星水线左侧所示，但 Q/3He 比率表明沸腾仅影响 1-10% 的流体水库。有了这些知识，可以更好地了解 Theistareykir 开发阶段现场条件的任何后续变化，有助于可持续地管理资源。热传导似乎占主导地位。现场存在沸腾和相分离，如 δ18O 值在 δ18O 与 δ2H 图中落在全球流星水线左侧所示，但 Q/3He 比率表明沸腾仅影响 1-10% 的流体水库。有了这些知识，可以更好地了解 Theistareykir 开发阶段现场条件的任何后续变化，有助于可持续地管理资源。