1

Equatorial MarginsPetroleum Systems Inferences

from Geochemistry and Geophysics with Geologic Thinking

Techniques for leveraging Information-Rich Rasters within

PaleoGIS

by William Dickson (DIGs),by William Dickson (DIGs),Craig Craig SchiefelbeinSchiefelbein (Geochemical Solutions), (Geochemical Solutions),

Mark Mark OdegardOdegard (Grizzly Geosciences),(Grizzly Geosciences),John John ZumbergeZumberge ((GeomarkGeomark Research)Research)

Talk Outline

• Issues– Plate model vectors lack granularity– Petroleum source layer (paleogeographic)

models lack control

• What we do– Gain resolution with rasters– Fix raster reconstruction problems– Incorporate oils for geochem control

UTIG “PLATES” Demo Global Model &S. America-Africa (SAM-AFR) Gravity

Many 0Ma polygons in model – detailed enough?

SAMSAM--AFR at 105Ma (AFR at 105Ma (AlbianAlbian))

Reasonable feature match

(“PLATES”demo model) to gravity at 1:40mm scale

Brazil: Plate Mismatch on Grav, Mag

“PLA

TES

”D

emo

CO

BM

AR

IMB

A C

OB

100 km

Gravity Isostatic

Residual AGC (GI-AGC)

Magnetic Intensity

Reduced-to-PoleAGC (MR-AGC)

W Africa: Senegal/Guinea &

Gabon MarginsModel Compromise:Speed vs Accuracy

124

km

124

km

2

Why does granularity matter?

• Rift basin widths ~100 – 200 km containing graben 10 – 40 km wide

• Rifts: 5% of global producing basins but 12% of global oil reserves – Landon, 1994

• Passive margins overprint rifts as sediments flood rift-generated sags

• Passive margin sags & rift basins are primary targets for petroleum exploration

Raster/Vector Mismatch

DEM Reconstruction, 2008, with South America fixed: Africa raster mismatches vector

Raster/Vector Solution

• DIGs/GrizGeo converted rasters to vectors (large point shapes) for exact recon.

• External, auxiliary process became a Bigtime-saver where rasters have common x-y extents & cell sizes

Reconstruct One, Define All

• Raster to point shape with two indices representing x, y location & RGB values

• Reconstruct shape; then export to new shape including index columns

• Generate new raster with null values for locations missing input x,y index

• Populate RGB values into xy file; write out as raster

• Swap RGB values for each data layer = Reconstruct One, Define All

Central Atlantic data at 145 Ma

C Atl DEM/G/Mrasters at 145 Ma

42 data layer batch

at 94 Ma

3

Consider Basin Development

• Containers for petroleum systems• Source the sine qua non - where is it?• Paleo-geographic reconstructions help

infer source layer deposition• Oil geochemistry provides hard controls

for paleo-models

Sediment Isopach,Basins, AOIs

SATL Geochem: Oils (Tertiary deltaic excluded), Cuttings Extracts, Seeps

Brazil Basins with Oil FamiliesBrazil Basins with Oil Families

Oil familygroups associate

with basins expressed as gravity lows

(blues)

Gabon Basins with Oil Families

Oil family groups associate Oil family groups associate with basins expressed as with basins expressed as

gravity lows (blues)gravity lows (blues)

30 km

105Ma: Oils, Seeps, Crustal Feats, GI-AGC

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Atlantic Salt Basin at 105Ma (Albian)

• Lacustrine-affinity oils – pre-Albian aged source

• Many oils correlate• Gaps (i. e., Reconcavo) can

infer unrecognized source (N Gabon)

• Other pairs: Congo Fan-Cumuruxatiba; Santos-Mocamedes

Gabon

Congo

Ang

ola

Nam

ibia

Brazil

SAM-AFR at 105Ma (Albian)•Syn-rift and Syn-rift/ Transitional oils locate on the SAM margin

CearaFoz doAmazonas

Para-Maranhao

Ivory Coast

Gha

na

Fr.

Gui

ana

Brazil

Guinea

Liberia

K

Review

• Issues– Plate models too coarse– Source models need control

• What we’ve Done– Increased data resolution– Reconstruct multiple rasters exactly– Used oils for geochem validation

Thanks for your attention

For further discussion, see lists of papers and presentations plus

contact info at:digsgeo.com

geochemsol.com