Energy Frontiers: The Energy Potential of Geopressurized Brine

Natural gas is largely methane, and it is considered a desirable source of energy because it contains less carbon than other fossil fuels, meaning that it produces less carbon dioxide (about 14 kg C/GJ) per unit of released energy when it is burned than oil (about 19 kg C/GJ), and far fewer than coal (about 25 kg C/GJ for bituminous coal).  It is widely used to generate electricity (most of the new electrical generating plants that have been built in the U.S. since the 1970s are fueled by natural gas), for industrial processes (e.g. steelmaking) and for commercial and residential heating.  It is used as a chemical feedstock to make most of the world's agricultural fertilizers through the Haber-Bosch process, and is the most economical source of hydrogen, the supposed "fuel of the new economy." 

As Julian Darley described so well in his recent book High Noon For Natural Gas, North America is now in the early stages of a continent-wide natural gas supply crisis.  In 2003, for example, the natural gas pipeline system in North America came within a whisker of losing pressure.  A decision was nearly made at the time to cut off supply to industrial users, in order that power generating plants and residential customers could continue to be supplied.  In order to address the growing crisis, the Bush Administration's National Energy Plan anticipates a wholesale expansion of US facilities for receiving shipments of liquefied natural gas (LNG), which must be obtained from generally the same countries that sell us oil, and for regasification of the LNG in order to maintain pressurization of the natural gas distribution pipeline.  Clearly, natural gas is not the vehicle through which the United States is going to enhance its energy independence. Importation of LNG is not a long term solution for the addition reason that while the status of global production and reserves for natural gas are marginally better than they are for crude oil, global production of natural gas is also expected to peak within the next few decades. 

The better longer term solution to the natural gas crisis, in my opinion, involves a combination of (1) taking measures to increase energy efficiency in the use of natural gas; (2) construction of a significant number of new nuclear power plants while phasing out gas-fired plants; and (3) encouraging commercial exploitation of what are termed non-conventional sources of natural gas.  Non-conventional natural gas includes methane clathrates (also called methane hydrates), coal bed methane that is trapped in coal sedimentation, tight gas that is trapped in small reservoirs, and geopressurized brine methane that is suspended within water in geopressurized underground aquifers.  Energy analyst P.R. Odell has predicted that the combined production from such non-conventional sources will overtake conventional natural gas production by about 2070.

Small amounts of coal bed methane have been in production in the U.S. since the 1950s, but efforts to produce it redoubled with the implementation of the Section 29 tax credits in the late 1970s.  Once derisively termed "moonbeam gas," it is now economical to produce, although not as much so as conventional gas because it is contained in smaller, localized deposits.  Coal bed methane figures to be an important source of natural gas in the future.  Methane hydrates also exist in abundance beneath the Arctic permafrost and the ocean floor, but are difficult to harvest safely because they tend to be unstable.  Methane is a more potent greenhouse gas than carbon dioxide, and a mishap with a large methane hydrate deposit could have disastrous environmental effects.  For these reasons, no commercial effort to produce methane hydrates is anticipated in the foreseeable future, although Japan, India and the U.S. all have active methane hydrate research programs.  In the longer term, perhaps in twenty years, methane hydrate production is possible and perhaps even likely.  Production of tight reservoir gas requires fracturing of the surrounding rock with explosives or other techniques. It has been a success story the past two decades, with wellhead recovery volume of some projects exceeding that of conventional wells, although like coal-bed methane the smaller size of the deposits limits recovery efficiency. 

Geopressured reservoirs or aquifers exist deep underground, usually as a salty solution or brine, in locations throughout the world.  The brine is typically saturated with methane, with between 30 to 80 cubic feet of methane gas contained in each barrel of fluid. Fluid pressures in such aquifers can be as much as twice the normal hydrostatic gradient, meaning that significant pressure will exist at the wellhead when the reservoir is tapped. The water is also often quite hot, with temperatures typically within the range of 90 °C - 200 °C.  Three types of energy could potentially be derived from geopressurized brine: (1) Thermal energy from the temperature of the fluid; (2) mechanical energy from the fluid pressure; and (3) chemical energy from the methane that is suspended within the fluid.

Vaclav Smil, in his outstanding book Energy at The Crossroads relies upon the work of The IAEA's H.H. Rogner to estimate that total global resources of geopressurized brine gas could as much as 110 times the world's current proved natural gas reserves.  Smil also mentioned that the Gulf of Mexico potentially contains more brine gas than the world's total natural gas reserves as estimated by Peak Oil experts Jean Leherrere and Colin Campbell.  Small amounts of brine gas have already been commercially recovered in Italy, Japan and the U.S., although the commercial motivation for the production had more to do with recovering trace minerals from the brine that it did with the methane.  However, large-scale production of brine gas is generally considered to be uneconomical at current prices by most energy experts.

In response to the energy crisis of the mid-1970s, the predecessor agency to the U.S. Department of Energy appropriated funds to study the feasibility of producing brine gas from the northern Gulf of Mexico.  The Wells of Opportunity and Design Wells program provided for a preliminary study of the extent and the characteristics of the region's geopressurized aquifers, and the feasibility of producing brine gas.  The Design Wells program culminated in the construction of a test well in Pleasant Bayou, Louisiana in 1979, and ultimately included five test wells that by the end of the 1980s had produced over 35 million barrels of hot, pressurized, methane saturated brine. The methane was stripped from the pressurized brine and the degassed brine was re-injected into shallow unconfined sands beneath the ground, with no apparent ill environmental effect.

The Design Wells program clearly demonstrated that it is feasible to produce significant amounts of thermal energy, mechanical energy and methane from geopressurized brine reservoirs. However, during the energy glut of the 1990s the technology was simply not economically competitive with other non-conventional natural gas production, let alone conventional projects.  As a result, the DOE and the energy industry lost interest in the subject.

With present market conditions being significantly different than they were in the early 1990s, there have been a few indications of renewed interest in the industry for exploring geopressurized brine projects.  A paper presented by Unocal's Jeremy Griggs at a workshop at Stanford University earlier this year made a strong case that brine gas can be economically produced under certain conditions, namely by producing brines of lower salinity from the larger bulk aquifers.  Among Griggs' recommendations is that the DOE re-open the Wells of Opportunity program.  Considering the limited expense of the program and enormous domestic reserves that could become available if this source of methane is eventually able to be successfully harnessed, I would think that the Bush Administration would leap at the chance to become less reliant on foreign sources of energy.  With today's technology, the recovery of thermal energy (Griggs suggests high efficiency binary-cycle power plants be deployed) and the efficiency at which the methane can be extracted from the saturated brine (there is some evidence that use of heavier hydrocarbons would assist in extraction) would likely be far superior today than was possible 15 years ago.         

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[Sergio]

Dear All,
I have a theory for the formation of methane hydrate and would like your comment.
One of the sources of methane hydrate is the CO2 from the eruption of volcanoes in Deep Ocean. The CO2 at very high temperature is in unstable state (from sp to sp3) and react with water to form methane hydrate and O2. At high pressure (300 bars?) and low temperature (0 C) the methane is trapped in water to form methane hydrate.
The chemical reaction is as follows:
CO2+7.75 H2O --> O2+ CH4.5.75H2O

If somebody in an expert in thermodynamics please calculates the enthalpy and entropy but remember that this is not a standard state because we have a high gradient of temperature (CO2 at 1000 to 2000 C with the environment at 0 C).
Looking forward to receiving comments I give you my best regards,
Sergio