The impact of deformation timing on the prospectivity of the Middle Magdalena sub-thrust, Colombia
Published:January 01, 2007
William Sassi, Rod Graham, Ralph Gillcrist, Mike Adams, Ramon Gómez, 2007. "The impact of deformation timing on the prospectivity of the Middle Magdalena sub-thrust, Colombia", Deformation of the Continental Crust: The Legacy of Mike Coward, A. C. Ries, R. W. H. Butler, R. H. Graham
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Once deeply buried rocks are elevated in thrust belts, the resulting effects on reservoir evolution, source-rock maturity, hydrocarbon phase and charge history pose major problems for thrust belt exploration. To understand the geometrical evolution and burial history of thrust belts, successive structural restorations and dynamic basin modelling are needed. The forward modelling program ‘Thrustpack’ provides a semi-quantitative way forward, and this paper presents a ‘Thrustpack’ case study. The area considered is Rio Horta in the western foothills of the Colombian Eastern Cordillera, where westward-directed frontal structures break out onto the foreland basin of the Middle Magdalena Valley. A large sub-thrust anticline underlies the frontal thrusts and provides a substantial exploration lead. Following conventional models of back-thrusting and ‘fish-tailing’, the structure can be interpreted as entirely late, post-dating the overlying thrusts and once buried by the entire sedimentary megasequence of the Magdalena foreland basin. This would imply that the prospective section had been buried to a depth of about 12 km before uplift, and suggest a hydrocarbon graveyard, or, at best, dry gas in fractured, tight rock and potential overpressure. If the structure formed early, there is a chance of preserving both original porosity and liquid hydrocarbon in the structure, and charge risk is lessened because hydrocarbons were able to migrate into a structure that already existed. Hints from geological maps and the (generally poor quality) seismic data suggest that this is the more likely situation. It is consistent with the idea of an evolving palaeo-landscape and a mountain front with a very long history, where the structure remained relatively elevated during later sedimentation and thrusting. The modelling of these two alternative possible structural histories in ‘Thrustpack’ tests their viability and quantifies the hydrocarbon maturation, migration history and porosity evolution. The model in which the structure develops early presents real exploration opportunity whereas the alternative presents unacceptable exploration risk.
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Deformation of the Continental Crust: The Legacy of Mike Coward
This Special Publication, in memory and celebration of the work of Professor Mike Coward, is about the deformation of the continental lithosphere. The collected papers discuss geometry, structural principles, processes and problems in a wide range of tectonic settings and thereby reflect the breadth of Coward's interests. They encompass the evolution of Precambrian basement gneiss terrains, the geometry and evolution of thrust systems, basement involvement and structural inheritance in basins, syn-orogenic extension, salt tectonics, the implication of structural evolution on hydrocarbon prospectivity and structural controls on mineralization. Examples are drawn from the Lewisian and Moine Thrust Belt of NW Scotland, the Italian Apennines, NW Himalayas, the Cyclades, Oman, Zagros Mountains, Colombian Cordillera, Carpathians, North Sea, offshore Brazil, regional studies of the Irumide Belt (central Africa), Taurus Mountains (Turkey), greater South America, and from the Witwatersrand Basin of South Africa and the Antler Orogeny of SW USA.