A Busted Flush in the Santos Basin (Brazil) Becomes a Winning Hand—Hydrocarbon Generation and Multi-Path Migration on Shallow and Deepwater Flanks of the Basin

William G. Dickson¹, Craig F. Schiefelbein², and A. G. Requejo^2
1 DIGs, Stafford, TX
² Geochemical Solutions International, The Woodlands, TX

Combining data sets to interpret better results faster is a common E&P task that can take a few lessons from poker players. First, you can't play poker alone; several disciplines have contributed to this work. Next, winners take advantage of unexpected turns of the cards. The Santos Basin has been viewed as gas-prone, due either to the nature of the source rock or later flushing. We now see substantial oil potential along the southern flank of the basin. We addressed the following questions (as new data "cards" turned up):

- Look at charge from marine & lacustrine sources. How far will each migrate, do they overlap and where will the oils concentrate? - Was an early migration from lacustrine source displaced by late gas generation, causing the basin to look gas-prone? Can we verify that basin asymmetry "tilted" the hydrocarbon phase to gas on the north flank? - Can integrating geochemistry with detailed g&g mapping reveal potential for oil trapping on the unexplored south flank of the basin? - Which passive margin basins, along strike or across the ocean are similar, providing examples or inviting extrapolation of our initial results?

Local answers in the Santos Basin include: - Oils migrate both vertically and horizontally - salt welds or windows permit vertical migration from the pre-salt source to the post-salt section but do not represent chimneys right to the surface. - Post-salt lithology can provide carrier beds and top seals to move hydrocarbons 20 - 100 km laterally, perhaps 10x the lateral distances seen within the pre-salt in Campos Basin.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005