Wednesday, June 30, 2010

Danger Lurks In The Deep Water - 2

In the first post of this series we noted that the "loop current" in the Gulf of Mexico (GOM) reached all the way up to the Deepwater Horizon area (up to "Atwater Valley").

This loop current there was first discovered when researchers did drilling to explore the extent and nature of methane hydrates on the seabed of the GOM (1999-2009).

We noted that the researchers said that, without those loop currents, drilling would have been much more dangerous, because those loop currents helped cool the drill apparatus, which was heated up intensely when friction from the bit ground through the strata beneath the sea floor.

We asked what caused the loop current to move south, if in fact it did move, as the government had said in news releases.

In this post we consider the effect that pressure and temperature could have on the stability of the seabed of the GOM.

Even without the loop current factor, the researchers pointed out early on in the ten years of research into these mysterious gulf hydrates, that they posed a threat:
Natural gas hydrate deposits are found in deep offshore environments. In some cases these deposits overlay conventional oil and gas reservoirs. There are concerns that the presence of hydrates can compromise the safety of exploration and production operations [Hovland and Gudmestad, 2001]. Serious problems related to the instability of wellbores drilled through hydrate formations have been documented by Collett and Dallimore, [2002]. A hydrate-related incident in the deep Gulf of Mexico could potentially damage the environment and have significant economic impacts.
(Hydrate Related Geohazards, 2002-2004, page 5, emphasis added). Clearly the dangers were there, were well known, and the "damage to the environment" as well as "significant economic impacts" were foreseeable.

In Is A New Age Of Pressure Upon Us - 2 we considered what changing pressures might have on these sub-sea floor deposits.

The "Hydrate Related Geohazards" report linked to above confirms that even gravity, or the instruments used to explore below the ocean, create enough impact to cause some pressure on the deposits and substrata:
Gravity waves on the sea surface produce small changes of hydrostatic pressure on the seafloor. These pressure variations produce very small deformations of near-seafloor sediments, and the resulting elevation changes can be sensed by a seafloor gravity meter. The seafloor compliance (ratio of the deformation response to the pressure drive) is sensitive to elastic properties of sediments hundreds of meters below the seafloor [Willoughby and Edwards, 1997], i.e. coincident with the GHSZ. The success of this seemingly improbable method depends on exquisitely sensitive (but commercially available) field-deployable gravimeters, and averaging times of several hours per site [Willoughby and Edwards, 2000]. Methane in the water column, where the water depth is more than 500 meters, is a strong indicator that methane hydrate is either being accumulated [Roberts and Carney, 1997], depleted [Hutnak et al., 1999; Sasaki et al., 2002], and/or redistributed [Paull et al., 1995] within the sediments below. Any of these situations can affect seafloor stability.

The stability of a hydrate-affected formation is controlled by its temperature and pressure. Thus these quantities, which have only ancillary roles in conventional oil and gas reservoir characterization, are of prime importance for monitoring hydrate deposits.
(ibid, pages 2-3, emphasis added). In the Dredd Blog posts, quoted above, we hypothesized that global warming would warm the GOM, and that as the GOM water level rises due to both warming and the ice caps melting around the globe, the pressures and temperature fluctuation on the seabed could destabilize the sub seabed areas, raising the danger level even more.

In the Dredd Blog post From Deepwater I To Deepwater II, we considered the fragmentation, which the great asteroid impact that created a ~112 mile wide crater on the seabed and the Yucatan Peninsula, could have caused.

There is evidence of substantial fragmentation that goes from the seabed level deep down into some of the reservoirs:
... the Blake Ridge deposit, which is situated on a quiescent passive margin, has a fault system extending from below the base of the bottom simulating reflector to almost the seafloor. These faults are believed to constitute efficient conduits for transport of methane [Rowe and Gettrust, 1994; Booth et al., 1998].
(ibid, page 11, emphasis added). In other words, methane hydrates can gasify, then move upward through the fractures or faults.

The report indicates that the fractures or faults go deep, as would be expected in the area around the crater caused by an asteroid impact that destroyed the dinosaurs along with much of the earth's ecosystem 65 million years ago.

The report flatly stated that the danger lasts for the entire lifetime of a well, because an entire reservoir can become dangerous:
These measurements warn of the possibility of drilling hazards, and provide inputs to wellbore stability and seafloor stability models that help predict whether the deposits will become hazards during production. However the predictive power of these stability models is still untested. Moreover, even after more experience has been acquired with them, the models are unlikely to provide totally reliable predictions of hazard events. Offshore platforms, wellheads and pipelines are very costly assets, and the environmental risks associated with disruption of hydrocarbon production in deep water are considerable. Therefore prudent engineering practice dictates that potential hazard conditions be monitored, possibly over the lifetime of the reservoir.
(ibid, page 14, emphasis added). It is likely that reservoir instability may resonate to other reservoirs near by, or to the seabed above the reservoir, and spread the instability.

Clearly the people who are crying "drill baby drill", even as a mega disaster unfolds before their eyes, are careless, reckless, and in some cases criminally insane.

The next post in this series is here.

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