Publication Date:
2022-05-26
Description:
Author Posting. © The Authors, 2004. This is the author's version of the work. It is
posted here by permission of Elsevier B. V. for personal use, not for redistribution. The
definitive version was published in Marine and Petroleum Geology 22 (2005): 479-497, doi:10.1016/j.marpetgeo.2004.08.008.
Description:
Large volumes of gas have vented through a north-south transect of the offshore northern Gulf of Mexico. An overview of surface and subsurface manifestations of this gas venting is presented. This gas movement has caused extensive alteration of reservoired oils to the north of the transect which are estimated to have equilibrated with, or been gas washed by, as much as 30 volumes of gas for every volume of oil. This gas washing entrains and carries upward the most volatile oil components depositing them in either shallower reservoirs or venting them to the overlying sediments and the water column. A significant amount of this gas bypasses the reservoirs and vents upward into the overlying sediments and waters. In spite of the significant amounts of the gas involved, the venting at the seafloor appears to occur primarily through highly localized faults and fractures. This gas discharge is spatially and temporally heterogeneous, making it difficult to estimate the actual hydrocarbon fluxes involved. This upward gas movement leaves characteristic signatures at the sediment water interface including carbonate pavements in older seep areas, and chemosynthetic biological communities, methane hydrates, and gas seeps in more recent long-term seep areas. In some cases where gas venting is very recent, massive disruption of surface and subsurface sediments is observed to be occasionally accompanied by mud volcanoes. Venting can be vigorous enough to produce methane gas bubbles, which appear to be injected rapidly into surface waters and which may constitute a significant source of methane, a greenhouse gas, to the atmosphere.
In the northern Gulf of Mexico, gas venting is sometimes accompanied by natural oil slicks at the sea surface, which can be tracked for many miles in non-productive areas. These gas-venting signatures are not unique to the Gulf of Mexico; similar seep features are observed in sediments worldwide. The widespread occurrence of these seep features, which may or may not be related to subsurface oil and gas deposits, may explain why use of surface seeps has often proved to be so controversial in oil exploration. Indeed, most seeps are probably not linked with economic subsurface petroleum reservoirs.
The relationships between surface seep features and productive subsurface reservoirs along a N-S transect of the Northern Gulf of Mexico are presented as an example of how all surface and subsurface geochemical, geological, geophysical data might be used together to better constrain interpretations regarding the nature and dynamics of subsurface oil and gas deposits and their plumbing in frontier areas.
Description:
Support for this work was provided by the Department of Energy, Grant No. DE-FG02-86EF13466 and U.S. Department of Energy Grant No. DE-FC26-00NT40920 through the University of Mississippi to Jean Whelan and; Gas Research Institute Contract GRI50972603787 to Larry Cathles, Cornell University with a subcontract to Jean Whelan.
Keywords:
Methane
;
Hydrate
;
Seep
;
Migration
;
Petroleum
;
Gas
;
Biodegradation
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
410907 bytes
Format:
1938672 bytes
Format:
431909 bytes
Format:
447165 bytes
Format:
1698446 bytes
Format:
3350588 bytes
Format:
8748656 bytes
Format:
1787740 bytes
Format:
6720580 bytes
Format:
6616164 bytes
Format:
796614 bytes
Format:
1321398 bytes
Format:
350228 bytes
Format:
3654480 bytes
Format:
943534 bytes
Format:
946396 bytes
Format:
189440 bytes
Format:
application/postscript
Format:
application/postscript
Format:
application/postscript
Format:
application/postscript
Format:
image/jpeg
Format:
image/tiff
Format:
image/tiff
Format:
image/tiff
Format:
image/tiff
Format:
image/tiff
Format:
image/jpeg
Format:
image/jpeg
Format:
application/postscript
Format:
image/tiff
Format:
application/postscript
Format:
application/postscript
Format:
application/msword
Permalink
