Abstract

In 1967, the Gulf Oil Company initiated a program to develop technology for locating seeps in the marine environment. By 1974, a fairly sophisticated system had been developed and installed on Gulf’s seismic vessel, the R/V Hollis Hedberg. This system was operated by Gulf from 1974 to 1983 to collect an extensive “sniffer” geochemical database in the Gulf of Mexico that contains over 191,000 dissolved gas analyses. A detailed evaluation of this database made with respect to discoveries made after the geochemical data was recorded showed that the data was 88% effective in finding new commercial production. This technology not only has the ability to predict whether a block has hydrocarbon potential, but also whether it is more likely to produce oil or gas, a very important economic factor in the evaluation of offshore blocks.

The marine sniffer database extends from Florida to the Mexican border, covering the entire Texas and Louisiana offshore shelf. Active seepage anomalies demonstrate the actual extent and variability of oil and gas seeps, defining both the spatial extent and vertical variability of hydrocarbon plumes as they rise from the seafloor sediments. Spatial and temporal changes are quite distinctive when comparing natural versus anthropogenic seeps, which are almost exclusively related to leaking well casing and/or pipelines. This marine database allows the full complexity of dissolved hydrocarbons associated with deep marine seepages from natural and anthropogenic sources to be illustrated by numerous examples that demonstrate the variability of dissolved hydrocarbon concentrations in seawater.

This hydrocarbon seepage database provides the most extensive and complete coverage of the entire Gulf of Mexico shelf that has ever been collected. Dissolved gas measurements have been made at the surface (hull inlet) and at two depths (mid-tow, 450 feet) and (deep-tow, 600 feet), allowing both vertical and temporal measurements on regional and localized grids that cover a vast expanse of the offshore Gulf of Mexico. Examples shown demonstrate the spatial, vertical, and temporal variability of natural and anthropogenic seepages.