US EPA

4287564 

Journal Article 

Phase fractionation and oil-condensate mass balance in the South Marsh Island Block 208-239 area, offshore Louisiana 

Losh, S; Cathles, L III 

2010 

1 

Marine and Petroleum Geology
ISSN: 0264-8172 

27 

2 

467-475 

10.1016/j.marpetgeo.2009.10.004 

WOS:000274564400010 

Phase fractionation can strongly deplete oil of its volatile compounds in a regular and characteristic fashion. This process has affected oils to a remarkably uniform extent throughout the 30 x 15 km South Marsh Island 208-239 and Vermilion 30-31 area (including the Tiger Shoal Starfak Mound Point,,, Lighthouse Point, Amber, Trinity Shoal, and Aquamarine fields) just offshore Louisiana. Fractionation of the original "parent" oil likely occurred in the deep, relatively flat-lying Rob L sand that underlies the area, and produced gas-washed oils (mean API 33 degrees) and gas condensates (mean API 50 degrees) in a volume ratio of 1:3.5. Both fractionated oil and vapor migrated from the fractionation site to shallower reservoirs. However, the estimated ultimate production ratio of gas-washed oil to gas condensate in this group of fields is 1:0.32, about 11 times higher than would be expected on mass balance considerations alone. Thus, there is an apparent deficiency of producible gas condensate relative to the amount of producible oil for the entire study area and for every field in that area. In the case of the Tiger Shoal field, the ratio of industry-estimated ultimately producible oil to gas condensate is 1:1.1. Based on the production data, we conclude that either there is an additional 6.4 x 10(6) m(3) (43 MMbbl) of undiscovered and/or unproduced condensate in the area or that condensate has escaped preferentially in vapor form to the seafloor. The well-studied and nearly depleted Tiger Shoal field provides a good example of how chemical data can be analyzed in a way that contributes insight into the phase fractionation process and the remaining exploration potential of an area. (C) 2009 Elsevier Ltd. All rights reserved. 

Gulf of Mexico; Tiger Shoal; Gas washing; Evaporative fractionation; Gas condensate; Migration