What are the issues?

One of the first questions is where are the magma bodies that are most easily tapped. In a general sense these have been mapped by the United States Geological Survey (USGS), but the ability to trace and predict the flow and circulation of these bodies is needed and has yet to be well developed. The investigations by various Icelandic groups have shown that magma movement and circulation can be traced and levels of activity measured. Particularly those underlying the Icelandic Krafla Geothermal Power station which annually produces 170 GWh[4] from geothermal steam wells. The science feasibility of magma movement tracing has been shown, but it is currently expensive and time consuming.[5]

One would like a clear picture of how specific magma types react to the introduction of water to produce steam and hydrogen plus biomass introduction to produce natural gas. Just what such a heat transfer structure and chemical process environment might look like will help to reduce uncertainty and aid wellhead designs. The chemical equations are known, but how the materials dynamically interact over years is needed to build confidence in designs and estimated operating costs.

The many well holes penetrating a working region of magma for energy extraction can be disrupted or destroyed by Earth movements or quakes. The Icelandic Krafla geothermal power station mentioned earlier has currently 19 boreholes. Quakes have destroyed some of then in an earlier period. Knowledge of the quake potential and locations of possible mantle movements is needed to give reliability to magma based power plant investments. Note that the Krafla station calmly sits on a volcano and has managed the situation beautifully for the past 17 years.

The geothermal wells that yield commercial steam at the Geysers in Northern California have to be periodically re-drilled because of changes in the under-structure of the water and hot rock interfaces. The Geysers wells do not reach into the magma underlying the area at greater depths. It is assumed that the steam producing interface of a well reaching into the magma would have a changing interface that would periodically require an upgrade, but no one knows much about well maintenance of this type. The rate of heat flow or heat rate, as it is commonly called, is also one of the uncertainties holding back major energy companies from exploring magma energy extraction development.[6] Heat flow is also affected by the circulation or non-circulation of the magma over time.

Loss of the pumped-in fluids and the possibility that resultant steam may migrate to other locations in the magma chamber not accessible to the return boreholes is a concern. Mapping the heat transfer structure for a magma body and the magma circulation around this heat exchanger is certainly feasible but has not yet been done. Additionally, how to design or craft the heat exchanger would certainly be a valued technology. One of the Sandia experiments in a magma lake showed the loss of fluids not to be a problem, but this is only one case.

Northrup, et all. (1978) Outlined two methods for generating storable gaseous fuels in a high-temperature magmatic environment: (1) hydrogen generation by the interaction of water with ferrous iron oxide in magma or very hot rock, and (2) hydrogen, natural gas and carbon monoxide generation by conversion of a water-biomass mixtures at high temperatures in a magmatic environment. The risk here for the non-biomass case is the rate of depletion of ferrous oxide in the magma. The risks for the biomass-case are the accumulation of ash and sulfur in the interface structure. Both of these problems are solvable.

The Icelandic State Power organization has had dramatic experience with corrosive vapors while drilling steam wells for their Krafla power station. Largely due to seismic activity which caused corrosive magma vapors to enter the geothermal steam system, thus destroying the borehole linings of several wells from corrosion. The seismic activity numbered nine volcanic eruptions near the station beginning in 1975 and lasting until 1984. Moving to corrosion resistant materials reduced that problem to manageable levels. Another form of corrosion problems arise from electrolysis the details of which are not well documented.

How does the gas get out of molten rock in order for the rock—the magma—not to blow itself to bits when it approaches the surface? We know that some magma contains more than 1,000 atmospheres of gas pressure when it’s below ground and if that stuff were to come right up to the surface, you’d have an ash eruption, but instead we often have a lava eruption and we only have a gas pressure of a few atmospheres when the stuff comes out, so the gas must somehow escape and we think it escapes into the volcano itself—leaks out of this central pipe—at about the depth we’ll be looking at the pipe. All the strategies for extracting energy from magma do not include bringing the magma to the surface where this pressure problem would present itself. This is a non-issue.

Lost circulation is the loss of drilling fluid from the well bore to the surrounding rock formation while drilling a geothermal well. This fluid loss must be brought under control before the well can be properly cased. Conventional loss-zone treatments can be expensive and inefficient. Because of the fractured, void filled nature of rock types usually associated with geothermal resources, lost circulation is a very persistent and costly problem in geothermal drilling. To help reduce the cost of geothermal energy, the US DOE Geothermal Drilling Technology Program has sponsored research and development work at Sandia to develop new technology for detection, characterization and treatment of lost circulation.

It is known that magma from various sites around the world and under the ocean have different magma chemistries, surrounding structure and pressures. These differences may mean that a technology solution in one region will not apply to another, thus upping the cost and risks for commercialization.