--> --> Hydrocarbons in Deep Water: A Brief Review of Some DSDP/ODP/IODP Results, by Martin Hovland, Barry Katz, and George Claypool; #90043 (2005)

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Hydrocarbons in Deep Water: A Brief Review of Some DSDP/ODP/IODP Results

Martin Hovland1, Barry Katz2, and George Claypool3
1 Statoil, Stavanger, Norway, [email protected]
2 ChevronTexaco, Houston, Texas
3 Independent consultant, California

On the first leg of the Deep Sea Drilling Project (DSDP), petroleum-stained cores were recovered in deep water from the ‘Challenger Knoll’, a salt diapir, in the deepwater (3,000 m +) Gulf of Mexico (GoM). This led to recognition of the need for a DSDP health and hazard policy, which was instituted and later adopted by the Ocean Drilling Program (ODP) and the current IODP (Integrated ODP, as of 2004). This policy required that all proposed DSDP/ODP/IODP sites be reviewed by a ‘Environmental Protection and Safety Panel’ (EPSP), consisting of independent experts not formally associated with the drilling program.

Even though hydrocarbon-prone regions have been avoided during the 36-year history of the program, hydrocarbon shows are regularly encountered and require an onboard decision to continue drilling or abandon the hole. This decision is usually made by the operations manager, with advice from the assigned onboard geochemist together with onshore personnel from ODP and the EPSP. In most cases hydrocarbons are dominated by biogenic (microbial) gases (methane and traces of ethane, C1 and C2). Guidelines exist to assist project personnel in distinguishing the common occurrence of shallow biogenic gas from anomalous shows that may indicate the presence of migrated or in situ generated thermogenic hydrocarbons.

A quick search on the ODP/IODP website (www.oceandrilling.org), for example, brings up a total of 357 hits on “petroleum”, 57 on “butane”, and 44 on “bitumen”. The latter includes the following ODP legs: 101, Bahamas transect; 139, Sedimented Ridges I; 146B, Santa Barbara Basin; 155, Amazon deep fan; 156, Equatorial Atlantic Transform; 169, Sedimented Ridges II; 180, Woodlark Basin; and 188, Prydz Bay. Considering that the ODP normally drills relatively shallow cores in water depths greater than 1,000 m, and that only digitised results exist on the website (i.e., only legs drilled after 1981) these hits must be regarded as a high number of hydrocarbon indications. The DSDP/ODP/IODP experience thus represents a very interesting database for hydrocarbon geologists.

Of particular interest to participants at this conference may be the sites located on very young oceanic crust (e.g., Red Sea, DSDP Site 226; Guaymas Basin, DSDP Leg 64; Juan de Fuca Ridge, ODP Leg 146B; and the Gorda Ridge, ODP Leg 180). Hydrocarbons were identified at these locations. The available data from these sites clearly indicates that these hydrocarbons were not inorganically derived, but formed through natural pyrolysis reactions, largely induced by hydrothermal circulation through sediments and rocks containing organic matter.