March 2001 Vol. 222 No. 3  Exploration

Perry A. Fischer,  Engineering Editor

Creepy worms; towering chimneys; and Crazy Horse is for real

In 1997, Charles Fisher, biology professor at Penn State, discovered the creature shown here with the proverbial face that only a mother could love. It’s a flat, pink worm about an inch or so long, it lives on methane hydrate beneath 3,000 ft of ocean on the Gulf of Mexico seafloor. It crawls around the surface of the methane ice, grazing for bacteria, which, in turn, are feeding off the methane. It is speculated that the bacteria may be Archaea that have lived beneath the Earth’s crust, feeding on methane, and migrated upward with it, eventually settling on the ice. The ice worms are not ancient animals but are related to common red mud worms.

An ice worm that calls methane hydrate outcrops in the GOM home. Photo (intentionally inverted) courtesy of C. Fisher, Penn State University; research sponsored by NOAA.

The new worm species, Hesiocaeca methanicola, is an indicator of natural gas deposits on the seafloor. Since the beginning of the oil industry, seeps have been a good harbinger of oil and gas reservoirs – and that has not changed. All that’s needed now is for someone to invent a methane ice-worm detector!

The area was revisited in October 2000 using the deep-dive vessel Alvin,…operated by Woods Hole Oceanographic Institute (WHOI). A preliminary new finding was that a species of chemosynthetic tubeworm (not ice worm) that grows on the seeps has a life span of about 200 – 250 years. The tubeworms feed, in part, via symbiotic, oil- and gas-eating bacteria in their gills.

One final bit of recent marine-geology news: Scientists onboard the WHOI vessel Atlantis discovered an extraordinary area of hydrothermal vents last December. Dubbed "The Lost City," it is located near 30°N, 45°W, in the North Atlantic on the slopes of a 12,000-ft undersea mountain. The area comprises the largest vent chimneys ever found, with 30-ft diameters soaring 180 ft above the seafloor and adorned with weird spires. "If this vent field were on land, it would be a national park," said Duke University structural geologist Jeff Karson, a principal investigator on the expedition.

In addition to their size, the vents are unique because they stand on one-million-year-old ocean crust that is buried deep beneath the seafloor and several miles west of the Mid-Ocean Ridge, which is where they would normally be found. Large communities of shrimps, mussels and tubeworms typical of most other Mid-Ocean Ridge vents are absent, and they appear to be built of carbonates and glassy silica, unlike most other Mid-Ocean Ridge deposits, which are formed by iron and sulfur.

It’s official. BP’s Crazy Horse discovery, located about 125 mi south of New Orleans in the deepwater GOM, has been successfully appraised. The Crazy Horse appraisal was drilled in Mississippi Canyon Block 822 and confirmed that the field is at least a billion-bbl discovery – the largest in Gulf of Mexico history.

In addition, another well discovered 600 ft of oil pay in Mississippi Canyon Block 776, located about 5 mi northwest of the original Crazy Horse discovery. The new field will be called Crazy Horse North. A phased-development plan is underway, with first oil expected by 2005 from some type of floating production unit capable of handling 250,000 bopd(!). BP owns 75% of Crazy Horse, with ExxonMobil owning the remainder.

ExxonMobil acquired a 100% position in several key blocks north of Crazy Horse in March of 2000. The company will spud an exploration well within the next three months to test a prospect it calls Hawkes, located in Mississippi Canyon Blocks 508 and 509.

De-gas the lake. For those of you interested in CO₂ reservoirs, you may recall the 1986 outgassing of Lake Nyos in Cameroon, which killed more than 1,700 people by suffocation. Whatever the cause, Lake Nyos and a smaller companion lake appear to be unique and strange. Geologists do not agree on the mechanism for the catastrophe, with some feeling that it was caused by volcanic eruption of CO₂. Other scientists believe that CO₂ continuously bubbles from the lake bottom, causing the water to become CO₂ saturated; then, a triggering mechanism such as a landslide causes the catastrophic CO₂ release.

To avoid another disaster, a 5.5-in. 3 650-ft-long pipe was installed along the lake bottom, where the gas-saturated water is densest. The top of the pipe is 150 ft above the lake and, once degassing begins, should spout a 10% water/90% CO₂ mixture venting 600 liters of CO₂ every second. The project is a $2-million international collaboration between Cameroon, France, the U.S. and Japan.

Comments? Write: fischerp@gulfpub.com