Evaluation of solitary waves as a mechanism for oil transport in poroelastic media: A case study of the South Eugene Island field, Gulf of Mexico basin Ajit Joshi a, * , Martin S. Appold a, 1 , Jeffrey A. Nunn b a Department of Geological Sciences, University of MissouridColumbia,101 Geological Sciences Building, Columbia, MO 65211, USA b Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803, USA article info Article history: Received 30 January 2012 Received in revised form 2 June 2012 Accepted 9 June 2012 Available online 28 June 2012 Keywords: Solitary waves Petroleum migration Eugene Island Gulf of Mexico basin Numerical modeling abstract Hydrocarbons in shallow reservoirs of the Eugene Island 330 field in the Gulf of Mexico basin are thought to have migrated rapidly along low permeability sediments of the Red fault zone as discrete pressure pulses from source rocks at depths of about 4.5 km. The aim of this research was to evaluate the hypothesis that these pressure pulses represent solitary waves by investigating the mechanics of solitary wave formation and motion and wave oil transport capability. A two-dimensional numerical model of Eugene Island minibasin formation predicted overpressures at the hydrocarbon source depth to increase at an average rate of 30 Pa/yr, reaching 52 MPa by the present day and oil velocities of 10 12 m/yr, far too low for kilometer scale oil transport to fill shallow Plio-Pleistocene reservoirs within the 3.6 million year minibasin history. Calculations from a separate one-dimensional model that used the pressure genera- tion rate from the two-dimensional model showed that solitary waves could only form and migrate within sediments that have very low permeabilities between 10 25 and 10 24 m 2 and that are highly overpressured to 91e93% of lithostatic pressure. Solitary waves were found to have a maximum pore volume of 10 5 m 3 , to travel a maximum distance of 1e2 km, and to have a maximum velocity of 10 3 m/ yr. Based on these results, solitary waves are unlikely to have transported oil to the shallowest reservoirs in the Eugene Island field in a poroelastic fault gouge rheology at the pressure generation rates likely to have been caused by disequilibrium compaction and hydrocarbon generation. However, solitary waves could perhaps be important agents for oil transport in other locations where reservoirs are closer to the source rocks, where the pore space is occupied by more than one fluid, or where sudden fracturing of overpressured hydrocarbon source sediments would allow the solitary waves to propagate as shock waves. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Hydrocarbon reservoirs and sources are commonly separated by kilometer-scale thicknesses of low permeability sediments that can be traversed by fluids in remarkably short periods of time (Holland et al., 1990; Whelan et al., 1994; Losh et al., 1999; Revil and Cathles, 2002a,b). For example, in the northern Gulf of Mexico basin, most hydrocarbon production has come from thermally immature Tertiary and Quaternary reservoirs into which the hydrocarbons have migrated from sources typically 2 to 4 km deeper shortly after reservoir deposition and trap formation (Young et al., 1977; Dow, 1984; Curtis, 1991). In the Eugene Island minibasin, historically one of the most productive hydrocarbon fields on the outer conti- nental shelf of the Gulf of Mexico basin, hydrocarbons are concentrated in shallow PlioceneePleistocene sand reservoirs but migrated from early Tertiary sediments lying at depths of about 4.5 km. These Tertiary sediments may have been the source of the hydrocarbons (Holland et al., 1990), or alternatively, temporary reservoirs that were originally charged from deeper JurassiceCretaceous source sediments (Thompson, 1988, 1991; Whelan et al., 1994). Stratigraphic, structural, and fluid pressure relations indicate that the PlioceneePleistocene reservoirs were charged within the past 0.7 million years (Holland et al., 1990; Alexander and Handschy, 1998; Losh et al., 1999), indicating flow rates on the order of at least 10 3 m/yr. However, flow rates could have been much greater than that. For example, Whelan et al. (2001) documented changes in hydrocarbon composition in shallow reservoirs at Eugene Island on the order of several years, which they attributed to recharge from deeper sources with a smaller contribution from biodegradation. High fluid flow rates are commonly made possible by the existence of permeable faults, which in the case of Eugene Island appears * Corresponding author. Tel.: þ1 573 882 6785; fax: þ1 573 882 5458. E-mail address: aj2v4@mail.missouri.edu (A. Joshi). 1 Tel.: þ1 573 882 6785; fax: þ1 573 882 5458. Contents lists available at SciVerse ScienceDirect Marine and Petroleum Geology journal homepage: www.elsevier.com/locate/marpetgeo 0264-8172/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.marpetgeo.2012.06.011 Marine and Petroleum Geology 37 (2012) 53e69