Numerical Investigation of Hydrocarbon Transport by Solitary Waves in the Eugene Island Field, Gulf of Mexico Basin

Joshi, Ajit; Appold, Martin S.; Nunn, Jeffrey

Hydrocarbons hosted by shallow Plio-Pleistocene sand reservoirs in the Eugene Island field in the northern Gulf of Mexico basin are thought to have ascended distances of 1.5 to four kilometers from overpressured Tertiary source sediments at rates as high as 100's of m/yr. Most of the hydrocarbon transport appears to have occurred episodically along the Red growth fault despite its relatively low permeability. Solitary waves are a plausible mechanism for hydrocarbon transport in a geologic setting like Eugene Island in that they have the potential to travel at rates much greater than the rates of flow through porous media predicted from Darcy's law. The present study has sought to quantify the behavior of solitary waves for the geologic conditions found at Eugene Island.

The initial focus of the research was on solitary wave transport of oil. This research showed that solitary waves could arise in sediments undergoing steady pore pressure increase due to compaction disequilibrium and hydrocarbon generation, provided that permeability was a sensitive function of effective stress and overall was very low (10⁻²⁵ to 10⁻²⁴ m²), and that pore fluid pressures reached levels equal to 91-93% of lithostatic pressure. The solitary waves were found to reach maximum velocities on the order of 10⁻³ m/yr and could ascend 1-2 km before dissipating into the background. Although solitary waves could transport oil much more quickly than possible through the prevailing background flow regime, they seem unlikely to have been able to travel the vertical distances and at the velocities observed at Eugene Island, though they could have been important oil transport agents in other fields where source rocks and reservoirs are closer together.

Current research is focused on methane transport by solitary waves. The scenario investigated thus far is for an instantaneous increase in pore fluid pressure in the source rock and one-dimensional transport in a methane-saturated porous medium. Methane saturated solitary waves could travel further than oil saturated waves at rates on the order of tens of meters per year or more. Methane saturated solitary waves could also form under higher and much less restrictive permeability of up to about 10⁻¹⁸ m². The results suggest that solitary waves may be much more effective agents of methane transport than oil transport.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013