By Cliff Montgomery – June 12th, 2010
A 2008 U.S. government study, which discussed potentially disruptive gas sediments on the Gulf Coast sea floor, may offer a clue as to what caused the explosion of BP’s Deepwater Horizon oil rig.
It’s perhaps still too early to determine any certain causes for the blast, which in turn has allowed the release of up to 50,000 barrels of oil every day.
That amount “is roughly five to six times the amount spilled in Alaskan waters in 1989 by the Exxon Valdez,” according to The Washington Post.
The Congressional Research Service (CRS) report, entitled Gas Hydrates: Resource and Hazard, clearly states its point:
“Offshore drilling operations that disturb gas hydrate-bearing sediments could fracture or disrupt the bottom sediments and compromise the wellbore, pipelines, rig supports, and other equipment involved in oil and gas production from the seafloor,” according to the study.
The American Spark quotes major segments of the report below:
“Gas hydrates occur naturally onshore in permafrost, and at or below the seafloor in sediments where water and gas combine at low temperatures and high pressures to form an ice-like solid substance.
“Methane, or natural gas, is typically the dominant gas in the hydrate structure. In a gas hydrate, frozen water molecules form a cage-like structure around high concentrations of natural gas. The gas hydrate structure [thus] is very compact.
“When heated and depressurized to temperatures and pressures typically found on the Earth’s surface (one atmosphere of pressure and 70 degrees Fahrenheit), its volume expands by 150 to 170 times. Thus, one cubic foot of solid gas hydrate found underground in permafrost or beneath the seafloor would produce between 150 to 170 cubic feet of natural gas when brought to the surface.
“Gas hydrates are a potentially huge global energy resource. The United States and other countries with territory in the Arctic or with offshore gas hydrates along their continental margins are interested in developing the resource.”
Gas Hydrate Resources
“There are several challenges to commercially exploiting gas hydrates. How much and where gas hydrate occurs in commercially viable concentrations are not well known, and how the resource can be extracted safely and economically is a current research focus.
“Estimates of global gas hydrate resources, which range from at least 100,000 TCF [Trillion Cubic Feet] to possibly much more, may greatly over-estimate how much gas can be extracted economically. Reports of vast gas hydrate resources can be misleading unless those estimates are qualified by the use of such terms such as in-place resources, technically recoverable resources, and proved reserves:
- The term in-place is used to describe an estimate of gas hydrate resources without regard for technical or economical recoverability. Generally these are the largest estimates.
- Undiscovered technically recoverable resources are producible using current technology, but this does not take into account economic viability.
- Proved reserves are estimated quantities that can be recovered under existing economic and operating conditions. […]
Gas Hydrates in the Gulf of Mexico
“On February 1, 2008, the MMS released an assessment of gas hydrate resources for the Gulf of Mexico. The report gives a statistical probability of the volume of undiscovered in-place gas hydrate resources, with a mean estimate of over 21,000 TCF.
“The MMS report estimates how much gas hydrate may occur in sandstone and shale reservoirs, using a combination of data and modeling, but does not indicate how much is recoverable with current technology.”
Gas Hydrate Hazards
“Gas hydrates are a significant hazard for drilling and production operations.
“Gas hydrate production is hazardous in itself, as well as for conventional oil and gas activities that place wells and pipelines into permafrost or marine sediments. For activities in permafrost, two general categories of problems have been identified:
(1) uncontrolled gas releases during drilling, and
(2) damage to well casing during and after installation of a well.
“Similar problems could occur during offshore drilling into gas hydrate-bearing marine sediments. Offshore drilling operations that disturb gas hydrate-bearing sediments could fracture or disrupt the bottom sediments and compromise the well bore, pipelines, rig supports, and other equipment involved in oil and gas production from the seafloor. [Emphasis added]
“Problems may differ somewhat between onshore and offshore operations, but they stem from the same characteristic of gas hydrates: decreases in pressure and/or increases in temperature can cause the gas hydrate to dissociate and rapidly release large amounts of gas into the well bore during a drilling operation.
“Oil and gas wells drilled through permafrost or offshore to reach conventional oil and gas deposits may encounter gas hydrates, which companies generally try to avoid because of a lack of detailed understanding of the mechanical and thermal properties of gas hydrate-bearing sediments.
“However, to mitigate the potential hazard in these instances, the wells are cased — typically using a steel pipe that lines the wall of the borehole — to separate and protect the well from the gas hydrates in the shallower zones as drilling continues deeper.
“Unless precautions are taken, continued drilling may heat up the sediments surrounding the well bore, causing gas from the dissociated hydrates to leak and bubble up around the casing. Once oil production begins, hot fluids flowing through the well could also warm hydrate-bearing sediments and cause dissociation. The released gas may pool and build up pressure against the well casing, possibly causing damage.
“Some observers [further] suggest that exploiting the gas hydrate resources by intentionally heating or by depressurization poses the same risks…as drilling through gas hydrates to reach deeper conventional oil and gas deposits.”
