THE NORPHLET SANDSTONE AND OTHER PETROLEUM PLAYS ALONG AND OUTBOARD OF THE FLORIDA ESCARPMENT, EASTERN GULF OF MEXICO Glyn Roberts 1, Joe Erickson 2 1 Consultant, Bedford, UK; 2 Spectrum, Houston, TX. USA An analysis of modern seismic data (Spectrum s Big Wave 2D Multi-Client seismic survey) along and outboard of the Florida Escarpment in the waters of the Eastern Gulf of Mexico has revealed a number of plays both on the platform area and in the deeper waters; whilst the application of Pre Stack Depth Migration (PSDM) and the display of the data in the depth domain gives a better understanding of the geology of the survey area (Fig1a, 1b and 2), which in the main survey area, with the exception of a limited number of shallow water wells on the Florida platform, is unexplored by the drill-bit.? Figure 1a) Example Line 1: Pre Stack Time Migrated Section shows difficulty in correlating data from deep to shallow water depths. Figure 1b) Example Line 1: Pre Stack Depth Migrated version (displayed in Depth) shows that the correlation from deepwater to shallow water is easier to make.
Figure 2: Example Line 2: Pre Stack Depth Migration (displayed in Depth) showing base salt (at 8500 metres on the left hand side) running from the deepwater area onto the platform area where it pinches out on basement. Also of note is a high amplitude event at approx 3600m below SL this can be mapped over 10 s of km and is a potential reservoir. Plays recognised in the area include: A) Platform Cretaceous Shelf Edge reefs and fans Patch reefs Thrombolitic reefs Stratigraphic pinch-outs Broad structural plays Buried channels B) Deepwater Jurassic horst/graben (buried hill) plays Jurassic/Cretaceous plays associated with salt and salt tectonics e.g mini-basins, drape-over and onlap plays. Plays associated with the Cretaceous/Tertiary Boundary e.g onlap plays Oligocene and Miocene clastic plays (including onlap and drape-over plays) Particularly notable is: 1) The existence of a thick (5000 metre plus) Jurassic/Cretaceous section in the deepwater outboard of the escarpment showing all the plays associated with an autochthonous salt basin (Figs 2, 3 & 4). This is in contrast with the expectations of a number of authors that this area would be made up of Oceanic crust.
Figure 3: PSDM Section (width 110 km) showing extensive salt basin West of the Escarpment Figure 4: Zoom in on previous figure: PSDM Section (width 40 km) showing mini basement development in this case, a 2000m deep basin in the Middle-Upper Jurassic showing fan deposits on the edge of the basin and central inversion (turtle-back); capped by bright basin floor fan deposits further enlargement shown on the next page.
Figure 5: Mini basin development (Section width = 15 kms) 2) The evidence for an extension of the Norphlet Sandstone play, tested successfully in the North Eastern part of the GOM at the Vicksburg and Shiloh wells (Fig 6 & 7), tens of kilometers South Eastwards into virgin territory along the foot of the Escarpment in the northern part of the survey area.(fig 8). Figure 6: Location of Vicksburg and Shiloh wells in relation to Spectrum s survey areas
Figure 7: Pre Stack Depth Migration (Plotted in depth) in the vicinity of the Vicksburg and Shiloh oil discoveries. Vicksburg was drilled to 7741m with a reported 300 foot net sand pay in the Norphlet Sandstone. In Shiloh, these sands have been reported to be aeolian (Godo 2006). salt Figure 8: PSDM section showing Vicksburg/Shiloh analogue 100 kms to SE of those discoveries. Arrows indicate suggested movement and expulsion of salt to create structures in which hydrocarbons could be trapped within the Norphlet sandstone (McDonough et al 2008).
References: Godo, T: Norphlet Aeolian Dunes in the Deepwater Eastern Gulf of Mexico AAPG 2006 and HGS Dinner Presentation (Abstracts only) K. Gohrbandt : West Florida shelf and slope prime target for gas, oil in eastern Gulf of Mexico: OGJ 11/6/01 K. Gohrbandt: Eastern Gulf of Mexico-1: A look at regional deposition under W. Florida shelf, slope: OGJ 21/1/02 K. Gohrbandt: Eastern Gulf of Mexico-2 : Here is habitat of oil and gas under W. Florida shelf, slope: OGJ 28/1/02 K. Gohrbandt: Eastern Gulf of Mexico-3: New assessment offered for W. Florida shelf, slope: OGJ 4/2/02 McDonough et al: A deepwater Frontier in the North Eastern Gulf of Mexico: The Jurassic Norphlet Sandstone Oil Play. AAPG 2008, Capetown (Poster) Roberts, GF & Finstad, KG: Survey suggests numerous petroleum plays in the eastern Gulf of Mexico First Break, April 2006 Roberts, GF & Finstad, KG: Eastern GoM seismic survey indicates numerous petroleum plays Offshore Magazine, June 2006 www.spectrumasa.com