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ABSTRACT: Hydrocarbon Shows in the Scientific Ocean Drilling Programs

B. J. Katz, K.-C. Emeis

For more than 20 yr, two major programs, the Deep Sea Drilling Project (DSDP) and the Ocean Drilling Program (ODP), have been coring the deep oceans for scientific purposes. For technological as well as financial reasons, drilling was and is performed without a riser. Precruise preparation, therefore, is aimed at preventing an accidental hydrocarbon discovery. During the course of drilling, at the more than 700 locations studied to date, numerous black shales of various ages were encountered. Many of these represent thermally immature hydrocarbon source rocks. Although these organic-rich rocks (up to 34 wt.% total organic carbon) by themselves did not pose a safety problem, hydrocarbon shows were detected on no less than ten legs. These shows represent heavy (C15+), thermally generated hydrocarbons. Commonly, these shows can be attributed to migration through a porous and permeable network into the penetrated section. In these situations, migration commonly occurs over distances on the order of several tens of miles from a more mature, structurally deeper section (e.g., Challenger Knoll, DSDP Site 2). There are, however, instances where there is strong geochemical evidence for in-situ hydrocarbon generation. In-situ hydrocarbon generation appears to be the result of anomalous thermal conditions associated with high heat flow, igneous and/or hydrothermal activity (e.g., Tyrrhenian Sea, ODP Site 652). Such conditions are more commonly associated with young

marginal basins. The distribution of these shows provides valuable information on the long-term exploratory potential of the deep oceans and continental margins.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990