Natural Oil and Gas Seepages
The USGS is involved in a number of geochemical and geophysical activities funded by and of interest to MMS in Southern California. One such activity is the work being conducted near Point Conception, California.
Tar and oil residues are prevalent on California beaches, especially in southern California where natural oil seeps are common. To manage the offshore production of oil and gas, baseline information on tar and oil accumulations from natural seepages and spills are being investigated. Baseline tar and oil deposits on beaches are an important management tool to differentiate between the environmental impact of natural oil seepage versus possible oil spills or illegal dumping at sea.
The USGS, in collaboration with the MMS, is conducting a 3-year organic geochemistry study to assess the interrelations among oil seeps, tarballs, and produced crude oils in the offshore southern Santa Maria Basin of southern California, from Point Arguello to Point Conception. Monitoring of the beaches periodically will help provide the details of tar composition, amount, and possible transport pathways through time.
The major goal of the Sources, Transportation, and Fate of Natural Oil and Gas Seepages project is to identify the geologic setting, source(s), and ultimate dispersal of natural oil and gas seeps in the area. The surveys will focus on likely areas of hydrocarbon seepage over the Point Arguello oil field. The project will:
- Document the locations and determine the geochemical fingerprint of natural seepages within the offshore southern Santa Maria Basin;
- Determine geochemical fingerprint of coastal tar residues and potential sources, both onshore and offshore in this region and compare these data with the existing database for the coastal regions of California;
- Establish chemical correlations between offshore active seeps and coastal residues to link seep sources to oil residues;
- Measure the rate of natural seepage of different seeps and try to assess regional natural oil and gas seepage rates;
- Predict transport pathways of oil from seep sources to the coastline;
- Interpret the petroleum system history for the natural seeps;
- Extend the coastal tar residue study to include beaches of Santa Barbara County.
USGS scientists conduct fieldwork at Boathouse Beach to monitor the amount of tar residue
Thus far, the USGS scientists have reached the following conclusions:
- All collected coastal tar residues and oils are derived from the Miocene Monterey Formation;
- Tar residues are geochemically distinct from crude oils collected from platforms in the study area;
- Tar residues can be geochemically placed into five groups based on differences in chemical fingerprints;
- A preliminary conclusion is that tar is being transported north along the California coastline from sources in the southern California area.
The USGS and MMS have jointly funded a three-year effort for a sidescan sonar survey of selected areas northwest and east of Point Conception to identify the most active seep areas. The initial survey completed in June 2003 as part of a cruise for the southern California earthquake hazards work. Four of the thirteen survey days were for the MMS effort. The USGS is in the process of identifying the most active seep areas, which will then be resampled by remotely operated vehicle (ROV) and any hydrocarbons recovered will be tagged by USGS scientists.
