Giant Bubbles Could Sink Ships Anna Salleh, ABC Science Online Stormy Gaseous Seas
Oct. 24, 2003 — Methane bubbles from the sea floor could be responsible for the mysterious sinking of ships in areas like the Bermuda Triangle and the North Sea, new Australian research confirmed. Computational mathematics honors student David May and supervisor, Professor Joseph Monaghan of Monash University in Melbourne, Australia, reported their research in the American Journal of Physics. Their modeling suggests that giant bubbles are much more likely to sink ships than previously thought, adding new weight to warnings about ships traveling in areas where bubbles are likely to be.
Huge bubbles can erupt from undersea deposits of solid methane, known as gas hydrates. The methane — found as an odorless gas in swamps and mines — becomes solid under the enormous pressures at the deep sea floor. Under the sea, however, the ice-like methane deposits can break off and become gaseous as they rise, creating bubbles at the surface
Ryskin is a professor at Northwestern University, where he teaches chemical engineering. On his Web site he notes, "I became interested in geology and geophysics a few years ago." Putting together two facts, he built a grim picture.
The first fact is that the seafloor continuously leaks methane, the same thing we burn as natural gas. Some comes from serpentinization and some from the action of microbes. As the bubbles rise, the gas dissolves into the deep seawater, where oxygen and microbes in the water consume it.
The second fact is that at times in Earth history, the ocean currents have failed to stir the deepest waters. That's true today of the entire Black Sea, for instance. At other times, whole ocean basins have stagnated. Conditions there quickly become anoxic as the oxygen in the water disappears.
Ryskin asked what would happen to that gas in a stagnant ocean basin. His answer, in the September 2003 Geology, is an oceanic eruption driven by explosive methane. The scenario is horrifying in several ways.
Enough methane dissolves in deep, cold water (about 0.4 percent by molar volume) if that water were to rise, the gas would come out of solution and create a mist whose volume is seven times greater than pure water. The resulting eruption would quickly spread and release the whole ocean basin's worth of natural gas in great clouds. These would inevitably ignite. The amounts of gas would be enormous, and the worldwide fires and explosions would be catastrophic. Even the formation of fullerene compounds, now considered a sure sign of asteroid impacts, is plausible. Land organisms would suffer mass extinction.
The seafloor off Santa Barbara just burped up a huge eruption of methane – and scientists caught it on video. Now, at about 5,000 cubic feet at the surface, this methane cloud was huge by people-watching-with-videocameras standards. That’s not to say massive by vast-limitless-ocean standards. But still, it gave the scientists a chance to do some number-crunching on an imaginary massive eruption of methane.
And why are the scientists stretching their imaginations in this way, you might ask? Well, it turns out that there are actually massive (not just huge) deposits of methane on the ocean floor (and in Arctic permafrost, too, but that’s another story). The ocean deposits are quiescent at the moment, frozen into sort of waterlogged crystals called methane hydrates, a.k.a. clathrates (here’s a bit more blogging on clathrates). But it takes a lot of cold combined with a lot of pressure to persuade methane gas to lead a quiet life as a crystal.
At a glance, ocean bottoms are great places for cold and pressure. Except in a warming world. There’s evidence from studies of the last 100,000 years or more that methane has fizzed en masse into the atmosphere at the same time that the Earth’s temperature has warmed dramatically.
So, the problem of methane hydrate release is potentially serious and there may be other potential horrible short term catastrophic possibilities also.
Countries (including ours) and companies are trying to determine if they can drill for and use methane hydrates as a new source of clean energy. But, what if they have an accident in the research or production stage that cause the release massive amounts of methane into the atmosphere?
Was there a recent methane hydrate release into the atmosphere that caused deaths? Reportedly, last decade, a Japanese Research Ship was conducting research about methane hydrates in a purported methane hydrates area. The ship’s radio operator was talking to someone in Japan. The person on shore said the talk suddenly stopped in the middle of the conversation. No one could make contact with the ship. Planes flying to find the ship found some floating debris, but not the ship.
Another ship sent to the scene to determine what happened, found the ship on the sea bottom, completely intact. It was speculated that a giant methane bubble came up from the seabed and encapsulated the entire ship. This displaced all the water from beneath the ship, the buoyancy that allowed it to float and it immediately sank like a falling brick to the ocean bottom. Sounds absolutely crazy, doesn’t it?
However, some scientists feel that methane hydrate bubbles are the cause and answer to the ships that have so mysteriously sunk in the Bermuda Triangle, although there is a lot of skepticism about this belief. A New York Times August 28th article described “Giant Methane Burps” as seen from a research plane. Hypothetically, assume the Japanese ship discussed above was 150 feet long (for comparison think of a 15 story high building lying down) and that a methane bubble came up from the sea bottom and encapsulated the ship. Think, for example, how you sometimes see a ship inside a bottle.
Given the Arctic Ocean methane release situation into the atmosphere as described last summer, President Barack Obama, must order our Country and also respectfully ask the other nations and companies to initiate a 2 year moratorium on physical methane hydrate research, the actual drilling, etc., but to continue with laboratory experiments, in order to obtain a better understanding of the situation.
Am I being an alarmist? I say no, but you can judge for yourself. A 2001 (My emphasis) U.S. Geological Survey report about methane hydrates included one small section concerning Hazards.
“Gas (Methane) Hydrates represent a hazard to conventional oil and gas production. In the Gulf of Mexico, oil and gas exploration is extending into water depths where gas (Methane) hydrates occur at the sea floor. Pumping hot oil from great depths through drill pipes can cause warming of sediments and dissociation of (Methane) hydrate, liberating large amounts of methane, weakening sediments, and perhaps generating pockets of highly pressured gas.
The result might be gas blowouts, loss of support for pipelines, and sea-floor failure that could lead to underwater landslides and the release of methane from hydrates.” (My emphasis) See more about underwater landslides below.
The fact sheet’s final sentence was “Natural gas hydrates may also become economically extractable.”
A 2001 (My emphasis) The Geological Society of London (World’s oldest association of earth scientists) short summary discussing tsunamis caused by underwater landslides (and other causes) “A major submarine (landslide) slope failure in the N. Atlantic could give rise to a tsunami large enough to flood major cities on the coast of America or Europe.”
For comparison of the tsunami’s wave height described in the Summary, imagine an 11 or 12 story high building racing toward you.
The decision by BP and many other energy companies to drill through areas of unusual ice-like crystals -- called methane hydrates -- is a risky one fraught with huge consequences for failure.
"Methane hydrates are a geological hazard, and it's been well established for decades that they are dangerous," said Richard Charter, head of the Defenders of Wildlife marine program and member of the Department of Energy's methane hydrates advisory panel. "Until 10 or 15 years ago, the industry would avoid them no matter what."
Now, Charter said, the rush to produce more oil for domestic consumption has forced companies like BP to take bigger risks by drilling in deep waters that are a breeding ground of hydrates. And they worry that a new drilling push into the Arctic Ocean -- which President Barack Obama has authorized to begin next month -- could expose a fragile and remote environment to additional risks from catastrophic oil spills.
Methane hydrates only exist in cold water -- just above or below freezing -- and at the undersea pressures found in deep water off the continental shelf. "It's a lot like ice," said William Dillon, a retired marine geologist with the U.S. Geological Survey in Woods Hole, Mass. "The conditions that form them exist at the seafloor and in the sediments below."
This slushy mixture of sea water and methane gas makes drilling more complicated. For one, the presence of methane hydrates in sediment makes the seafloor unstable. That's why BP was using a high-tech drilling rig that was positioned like a helicopter on the surface.
And if hydrates are warmed by oil moving through pipes, they can turn into methane gas (known as "kicks" to drillers) that can shoot back up the drilling pipe and ignite the rig. Investigators are already focused on that scenario as a possible cause of the blast aboard the Deepwater Horizon rig on April 20.
Several marine geologists told Discovery News that the location of methane hydrate fields are well-mapped by petroleum companies and the Minerals Management Service, which regulates the industry. Researchers aboard scientific drilling ships say they avoid methane hydrate fields because of the inherent risks.
In 2003, Unocal abandoned plans to drill in the deep water off Indonesia for the same reason. China has delayed plans for offshore oil development after finding large hydrate fields, but many industry officials say they can engineer proper safeguards.
There are also large amounts of methane gas below the ocean floors. Many kilometers underwater – where light never reaches – there are large stores of methane called clathrates frozen into the sediments along ocean margins. It has been estimated as much as 2000 to 4000 gigatons (Gt) of carbon are stored in these sediments. As a result of changing ocean chemistry caused by global warming, methane from clathrates may be released into the water and eventually the atmosphere . With our current 6 Gt/year output of greenhouse gases worldwide this type of release would have devastating impacts on our climate. Melting of deep-sea methane stores has happened before, millions of years ago, when ocean acidity increased and the climate was affected for the next 100,000 years . With atmospheric carbon dioxide making the oceans more acidic each year, the idea of frozen methane dissolving on the ocean floor is not so far fetched.
A team of university scientists using a mini research submarine on a NOAA-funded research cruise has discovered, photographed, and sampled what appears to be a new species of centipede-like worms living on and within mounds of methane ice on the floor of the Gulf of Mexico, about 150 miles south of New Orleans.
Although scientists had hypothesized that bacteria might colonize methane ice mounds, called gas hydrates, this is the first time animals have been found living in the mounds.
The discovery of dense colonies of these one-to-two-inch-long, flat, pinkish worms burrowing into a mushroom-shaped mound of methane seeping up from the sea floor raises speculation that the worms may be a new species with a pervasive and as yet unknown influence on these energy-rich gas deposits.
The worms were observed using their two rows of oar-like appendages to move about the honeycombed, yellow and white surface of the icy mound. The researchers speculate that the worms may be grazing off chemosynthetic bacteria that grow on the methane or are otherwise living symbiotically with them.
Recent work by a number of laboratories suggests that free gas streaming through the seafloor or seafloor hydrate deposits may constitute yet another large oceanic methane source. On the northern continental slope of the Gulf of Mexico, for instance, a process known as “gas washing” fills subsurface petroleum reservoirs with natural gas that flows upward from even deeper reservoirs in the Earth’s crust.
It has been estimated that less than 2 percent of generated oil and gas ever makes its way into commercial reservoirs. Of the residual oil, about half remains dispersed in the source rock and sediments.
The residual oil and organic matter in deeper sediments is subjected to more heating and natural processing and is broken down into natural gas. The gas streams upward, washing out clogged pore spaces and recharging many fuel reservoirs. Evidence comes from oil wells in the northern Gulf of Mexico, where we have observed significant changes in oil compositions over time scales as short as 10 years. The wells continue to produce long after their expected lifetimes.
The other half of the residual oil leaks upward and out of the sediments into ocean bottom waters. Remarkable satellite photographs of the Gulf of Mexico and other regions reveal slicks extending for miles in areas where no oil production is occurring. Similar photographs are now being used to locate new oil and gas accumulations.
Beyond the geological “cooking and squeezing” processes that produce petroleum and gas, large quantities of gas also are being produced biologically. Many gas hydrate accumulations and ocean-floor gas seeps consist of methane largely derived from microorganisms.
Bacteria living in oxygen-poor areas beneath deep-sea sediments on the seafloor produce methane as a major product of their metabolism. Some models suggest that bacteria in sediments may account for 10 percent of the living biomass on Earth. In addition, microbial communities beneath the seafloor, whose numbers are entirely unknown, may also be producing vast amounts of methane.
Global warming and tsunamis
The pervasive and ongoing movement of methane gas—from seeps, decomposing hydrates, gas washing, and microbial sources—leads to some fascinating phenomena and important questions.
Methane is a greenhouse gas that traps heat about 20 times more effectively than carbon dioxide. If methane deposits and seeps prove to be ubiquitous in the oceans, they are a potentially significant contributor to global warming.
Relatively modest changes in global ocean temperatures or sea level could trigger a massive release of oceanic methane. If a change in ocean bottom pressure or a rise in water temperatures passes a certain threshold, sizable methane hydrate deposits could decompose rapidly and release a large quantity of heat-trapping gas back into the atmosphere. This scenario has been proposed as a possible cause for some past episodes of rapid global warming.
Evidence from the past suggests that upward-seeping methane may pose another threat: underwater avalanches. Landslides at the edge of the continental slope just off the East Coast of the United States may have been triggered by pockets of methane gas that had built up pressure under a lid of overlying sediments and exploded. Similar landslides today might generate tsunamis that would hit the U.S. coast. An offshore oil-drilling platform that accidentally hit such a gas pocket would also be endangered.
On May 6, 2009, the U.S. Department of Energy (DOE) National Energy Technology Laboratory (NETL)in collaboration with the U.S. Geological Survey (USGS), the U.S. Minerals Management Service, an industry research consortium led by Chevron, and others completed a landmark gas hydrate drilling expedition. The objective of the 21-day expedition was to confirm that gas hydrate can and does occur at high saturations within reservoir-quality sands in the Gulf of Mexico. This objective was fully met, with highly saturated hydrate-bearing sands discovered in at least in two of three sites drilled.
Gas hydrate is a unique substance comprised of natural gas (almost exclusively methane) in combination with water. Gas hydrate is thought to exist in great abundance in nature and has the potential to be a significant new energy source to meet future energy needs. However, prior to this expedition, there was little documentation that gas hydrate occurred in resource-quality accumulations in the marine environment.
The Gulf of Mexico Gas Hydrate Joint Industry Project (JIP) Leg II expedition follows a 2005 JIP Leg I drilling program that focused on possible drilling hazards related to gas hydrate in fine-grained sediments. Leg II was designed to expand the understanding of gas hydrate in the Gulf of Mexico by specifically targeting systems thought to include high-quality (thick, porous, and permeable) sands.
Site Summary – Walker Ridge Block 313
The drill sites at Walker Ridge 313 lies in ~6,500 ft of water within the western part of the “Terrebonne” mini-basin in the northern Gulf of Mexico. The primary target of drilling were a series of strong seismic anomaly that lay approximately 3,000 fbsf (feet below the seafloor). These anomalies exhibit strong “positive” amplitude response, indicating a horizon in the subsurface across which the speed of sound waves significantly increases. In addition, these same horizons, when traced deeper to the west, are observed to switch “polarity” to a strong negative response. Pre-drill interpretations determined that this collection of seismic responses was indicative of free gas accumulations (the negative anomalies) being trapped within porous and permeable sand horizons by significant accumulations of overlying gas hydrate within the sediment pore space. The primary goal of JIP drilling at this site was to test the validity of this interpretation through drilling and logging of wells at this site.
Site Summary – Green Canyon Block 955
The gas hydrates JIP site selection team identified numerous potential targets in Green Canyon block 955. Three of these sites were drilled in Leg II. The wells are located in over 6,500 ft of water near the foot of the Sigsbee Escarpment. The locations are near a major embayment into the Escarpment (“Green Canyon”) which has served as a persistent focal point for sediment delivery into the deep Gulf of Mexico.
Green Canyon block 995 includes a prominent channel/levee complex that has transported and deposited large volumes of sandy sediment from the canyon to the deep Gulf of Mexico abyssal plain. The southwest corner of the block includes a recently developed structural high caused by deeper mobilization of salt. The crest of the structural high is cut by complex network of faults that can provide pathways for migrating fluids and gases. Geophysical data reviewed during assessment of the site revealed a complex array of geophysical responses near the inferred base of gas hydrate stability. Some of these responses are suggestive of free gas and some indicative of gas hydrate, but all are limited to depths that are near or below the inferred base of gas hydrate stability.
The Green Canyon site combines many of the features required for the formation of significant gas hydrate accumulations, including sources of gas and migration pathways (the faults) for that gas into the gas hydrate stability zone as well as porous sands within the stability zone in which gas hydrate can accumulate. A motivation behind the JIP’s selection of the site for Leg II drilling was to test the hypothesis that gas hydrate accumulations within sands at the base of gas hydrate stability restrict the vertical migration of gas into shallower units within the structure.
Site Summary – Alaminos Canyon block 21 and East Breaks block 992
The final site tested by the Gulf of Mexico Gas Hydrates JIP during Leg II lies in roughly 4900 ft of water within the East Breaks (EB) 992 and Alaminos Canyon (AC) 21 protraction areas. This area is known as the “Diana” sub-basin, and contains several prolific oil and gas fields. The targets for JIP Leg II are shallow sand packages that occur approximately 600 feet below the seafloor and 800 feet above the inferred base of gas hydrate stability. The sands are distributed widely across AC 21 and adjoining areas, and also occur as more isolated units in blocks EB992 and AC24. A small isolated sand body within the target interval was penetrated by the 1995 ExxonMobil “Rockefeller” well (EB992 #001). Log data from that well indicated a sand ~130 ft thick with elevated, but low (~2 ohm-m) resistivity. If that data were correct (and the validity of shallow log data taken in boreholes designed to reach deeper targets are always somewhat suspect), the unit would be expected to contain a low saturation of gas hydrate (~30% Sgh).
Regional seismic data showed the sand to have a highly irregular top and relatively flat base with small, local incisement into subjacent units. The seismic data also suggests that the unit transmits sound waves at significant greater speed than the surrounding shales, consistent with, but not conclusive of, the presence of gas hydrate. Throughout the area, the geophysical expression of the interval is relatively consistent, with few features that reveal the sources or migration pathways for gas. The sediments are also very young (< 0.2 million years), being late Pleistocene in age.
Gas hydrate is a crystalline energy mineral that occurs globally along deep continental margins at high pressure and low temperatures (1). The Mississippi Canyon (MC) 118 gas hydrate site (Fig. 1; 28.852295 N and -88.491950 W) was first discovered during dives of the Johnson Sea Link (JSL) research submersible late in 2002. Maximum water depth at the site during measured during dives of the Johnson Sea-Link (JSL) research submersible is ?890 meters and measured seafloor temperature is ?5.7 °C. Hydrocarbon gases vent at the site because of fault migration-conduits that are related to an isolated salt body at relatively shallow depth in the sediment section.
The present paper synthesizes the preliminary results of multidisciplinary investigations at the MC 118 gas hydrate site (Fig. 1). Initial questions include the source of gas that vents to the water column and its relation to gas hydrate outcrops. In addition, it appears that hydrocarbon-driven microbial processes have greatly modified the seafloor over time (Fig. 2). The MC 118 site is characterized by enormous volumes of carbonate rock that strongly modifies the seafloor over an area of ?1 km2. The carbonate rock is the result of complex consortia of microbes which drive carbon and sulfur cycles in an isolated lightless environment.
Complex chemosynthetic communities have developed in association with gas vents, gas hydrate, and authigenic carbonate rock. It is remarkable that microbes have so strongly affected the seafloor because of abundant hydrocarbons. The main objective of this paper is to begin the process of understanding how the isolated MC 118 site developed from episodic venting of hydrocarbons over a considerable span of time. The site is a valuable natural laboratory that warrants further research by means of a seafloor observatory because so many questions remain unanswered.
The upper continental slope, Mississippi Canyon, northern Gulf of Mexico, is a region characterized by dynamic geology, including subsidence, uplift, and prograding. It contains producing gas fields, salt ridges, hydrate formations exposed on the seafloor, and an interpreted hydrated and underlying free gas zone. High-resolution seismic reflection data collected from this area reveal widespread geologic features that can be identified in the shallow subsurface from disparate locations and on different data sets but that remain unsatisfactorily interpreted or explained. Unexplained reflector patterns, apparently associated with gas hydrates, are here presented. Heat-flow data, collected from an area of numerous normal faults, include widely ranging values with greater heat-flow possibly representing "open faults" conducting geo-thermal fluids to the surface. However, accompanying high-resolution seismic data do not differentiate suspected open faults from non-open faults. High-resolution data reveal vertical lineaments in the shallow sub-surface in areas of regional inclination. Each lineament extends vertically through the same sequence of horizontal reflectors and terminates as reflectors become indistinct. These "broom" features have been interpreted as short-lived faults originating as sediments descend the inclination, as zones of escaping free natural gas, or both. High-resolution seismic data show both homogeneity and heterogeneity of reflector characteristics in the upper slope environment. Both the shallowest and the deepest of the ubiquitous shallow reflectors remain relatively homogeneous throughout the region. An intermediate unit, however, shows variability in both thickness and reflector pattern, the latter being so unique that the unit can be correlated across faults and from one profile to another. Remarkable variability in vertical extent suggests that this unit may be accommodating volume changes, possibly due to hydrate expansion. This entire sequence, by analogy with a 28.35m piston core interpretation in the same physiographic province, appears to represent an interval of, at most, Upper Pleistocene time, and possibly as brief as a single Holocene-glacial couplet.
A carbonate/hydrate mound in Mississippi Canyon Block 118 has been chosen by the Gulf of Mexico Hydrates Research Consortium to be the site of a sea-floor observatory. It will include seismo-acoustic, geochemical and micro-biologic sensors to monitor ambient noise, fluid venting and environmental conditions. The observations are expected to promote a better understanding of how fluids migrate within the mound and affect the formation/dissociation of gas hydrates. A number of preliminary studies have been done in preparation for installing the observatory. The mound is approximately one kilometer in diameter and is located on the continental slope in about 900m of water. Its surface has been imaged by multi-beam bathymetric sonar from an AUV 40m above the sea floor and by cameras at, or a few meters above, the sea floor. Also, direct visual observations have been made from manned submersibles. The interior of the mound and the underlying hydrate stability zone have been imaged seismically, electromagnetically and by direct-current resistivity. Proprietary 3-D seismic volumes show nearly vertical normal faults that connect deep salt formations with soft fine-grained sediments near the sea floor. It is hypothesized that these faults act as conduits for brines and hydrocarbon fluids, including petroleum and natural gas, to migrate upward and form the carbonate and hydrate constituents of the mound. Gas samples have been collected from vents and outcropping hydrate. Chemical analyses show the vent gas to be thermogenic from deep hot source rocks and to average 95% methane, 3% ethane 1% propane with minor other gases. There is no significant biogenic component. The outcropping hydrate is Structure II with gas composition 70% methane, 7.5% ethane, 15.9% propane with minor other gases. The difference between gas compositions from vents and hydrate appears to be due to molecular fractionation during hydrate crystallization. Results of geochemical studies indicate that vents formed at different times in various places on the surface of the mound. It is hypothesized that hydrate accumulations fill the faults to the point of blocking the flow and then divert the fluids into other migration routes. The mound may also be influenced by geologic structures on a larger scale than fluid migration. On 18 April, 2006, an earthquake occurred in the vicinity of Mississippi Canyon Block 122, about 15km east of the observatory site. It was characterized by anomalously weak P-waves and was not detected by USGS algorithms that rely on P-wave first arrivals to trigger them. It did produce long-period surface waves which allowed it to be detected and studied by other researchers. On the basis of surface waves, its magnitude was 4.8, a significant event. And it was not an isolated event. A similar earthquake occurred on the continental slope near Green Canyon Block 210, about 200km south-west of the observatory site, on 10 February, 2006. It had a 5.3 surface-wave magnitude. The weakness of P-wave arrivals is thought to indicate that such events are generated by gravity-driven slumping in soft sediments. If so, they may be symptoms of the instability of the continental slope offshore of the Mississippi River delta.
Originally posted by apacheman
The first fact is that the seafloor continuously leaks methane, the same thing we burn as natural gas. Some comes from serpentinization and some from the action of microbes. As the bubbles rise, the gas dissolves into the deep seawater, where oxygen and microbes in the water consume it.