The Iceland Deep Drilling Project (IDDP) will study the interaction of high-temperature (~ 450oC) hydrothermal fluids with oceanic crust on the Reykjanes Peninsula, at the southwestern tip of Iceland, where the Mid-Atlantic Ridge emerges from the ocean. The requested funds would be highly leveraged because most of the cost of drilling a 5km deep borehole will be borne by industry and the Icelandic government, with participation from the International Continental Scientific Drilling Program. An Icelandic geothermal power company is providing an existing ~ 3 km deep well for deepening to 5 km depth. This project will provide the first opportunity worldwide to investigate the deep, high temperature reaction zone of a mid-ocean ridge hydrothermal system, which has been a long-standing goal of the Ocean Drilling Program. This drill site is ideally situated for a broad array of scientific studies involving reactions between basalt and seawater at high temperatures, reaching supercritical conditions. Such active processes in the deep, high temperature reaction zones that control fluid compositions of black smokers have never before been available for comprehensive direct study and sampling. Ocean drilling has penetrated only 2 km into 5 Ma old ocean crust. where temperatures were ~ 180 oC. In contrast, the IDDP collaboration with industry in Iceland will produce fluid samples from the flow tests at 3, 4, and 5 km, drill cuttings and spot cores down to 4.0 km depth, and 1.0 km of continuous drill core from 4.0 to 5.0 km depth. These samples will reveal the integrated record of basalt-seawater interactions at >400oC. The study of these materials will permit a quantum leap in our understanding of active hydrothermal processes that are important on a global scale,
The funds provided will be used for: (1) coring for scientific purposes; (2) support for the scientific program at the well site, for fluid sampling, for core handling, and for basic petrologic characterization of the cores, and distribution of sub-samples and data to an approved list of international scientists; and (3) support for a coordinated group of US Co-PI's investigating hydrothermal water/rock interactions and geochemical modeling. The core and fluids that will be retrieved may characterize the lower boundary of a major hydrothermal system and thus provide important evidence about what controls the upper temperature limits of hydrothermal systems.
The overarching goal of the Iceland Deep Drilling Project (IDDP) is to examine the geothermal energy potential of high-temperature (~ 450?C) hydrothermal fluids in northern Iceland at Krafla and on the Reykjanes Peninsula, at the southwestern tip of Iceland. In both locations, the Mid-Atlantic Ridge emerges from the ocean and produces active volcanism with consequent active hydrothermal systems on the island. The IDDP has been a collaborative project involving Icelandic power companies, the Icelandic government, and several US investigators funded by NSF, all focused on understanding the technical issues involved in possible production of electricity from deep, very high temperature geothermal fluids – much higher temperature than any previously successfully used for power production. The key technical question is whether there exists a sufficiently large body of fluid at ~450?C in a sufficiently permeable setting to enable sustained production at economically viable rates. The major goals of the Oregon part of the overall project were (a) develop a device to collect fluids in situ from the deep, high-enthalpy part of a hydrothermal system and analyze the fluids collected, (b) develop computer software to model chemical conditions up to T= 600?C and P = 500MPa, providing for retrieval thermodynamic data for arbitrary P-T pairs, (c) model fluids collected from successful wells to understand their chemical properties with respect to engineering issues and geologic origins. For in situ fluid sampling, we developed and tested the FIT (fluid inclusion tool), which consists of fractured synthetic quartz (Figure 1) held in a stainless steel housing (Figure 2) that is suspended by wire line in an active well where the fractures heal, trapping geothermal fluid in fluid inclusions. In the field test, we obtained a large number of fluid inclusions on healed fractures as shown in Figure 3. Measurements show that the retrieved inclusions match the expected salinity and temperature of the field setting. We obtained crush-leach bulk analyses of cations and anions by ion chromatography, and we obtained gas analyses by thermal decrepitation with mass spectrometry, however, in both instances, the quantity of fluid was small enough that the chemical analyses are subject to large errors. We are now devising a way to make larger inclusions. To understand the properties and behavior of the very high temperature geothermal fluids, we developed computer programs to model the chemical thermodynamic properties of hydrothermal fluids and minerals at temperatures up to 600?C and pressure up to 500 MPa. Using these programs and the data base we assembled to go with them, we examined 350? to 400? fluids sampled in the past from black smoker seafloor hot springs. If we could determine whether 450?C fluid exist in large quantities beneath the mid-ocean ridge system, then it is likely we can drill into them in Iceland. By computing the solubility properties of hydrothermal alteration minerals in seafloor basalt in the smoker fluids, we determined that 450?C fluids do exist in large quantities and that they form where seawater circulates to depths of about two kilometers beneath the seafloor. These conclusions are indicated by the intersection of mineral saturation curves in a graph of pressure against temperature (Figure 4). This is the first time that hydrothermal reservoir pressure has been estimated from hydrothermal fluid compositions. In combination with the estimates of temperature, this capability opens opportunity to determine the temperatures and depths of origin of a wide range of hot fluids on the planet. One major goal of the project has eluded us: drilling into a very high-heat geothermal reservoir – one where temperature and pressure in the range of 450?C and 40 MPa. In one instance a well caved in at 1000m depth; in another, we intersected magma at 2100m depth. Our goal is 4000 to 4500m. Thus, the large goal of the project remains, and is the object of another planned IDDP drilling project.
