Abstract

Foreland fold-and-thrust (FFT) belts are one of the remaining frontiers for hydrocarbon exploration where large discoveries can still be expected. A methodology is described to assess their petroleum potential. Oil generation, migration and trapping history are studied together with structural modelling. Structural reconstructions require the successive use of inverse models to restore geological or seismic sections to their initial, undeformed geometry, and forward models to simulate thrust development with time. The restoration of structural sections to their intermediate geometry, between the onset of compression and their present form, is an aid in reconstructing the burial maturation and diagenetic history of potential source rocks and reservoirs. Erosion and uplift are two competing factors that can delay hydrocarbon generation and must be accounted for in these simulations. Forward modelling is helpful in testing the validity of assumed migration pathways and traps. Complementary ID or 2D models are used to integrate the burial and thermal histories with the kinetic parameters of potential source rocks, providing the timing of oil generation and expulsion, and even simulation of fluid flow and migration processes in areas that are well constrained structurally. Coupling the kinematics of deformation of complex areas (fold-and-thrust belts) with thermal, maturation and expulsion modellings is possible. Future implementations in FFT belts will be required to address such important processes as fluid circulation and hydrocarbon migration, or dewatering and compaction of potential reservoirs. The use of these integrated techniques in regional examples is described in Neogene orogenic belts (Western Alps, Apennines, Outer Carpathians, Eastern Venezuela Basin) to explain the various habitats of oil and gas in FFT belts. Oil-source rock correlations help to identify very distinct productive horizons, either in the allochthon or in the underthrust foreland. Long migration pathways (more than 100 km) are identified during early stages of deformation, with migration of the oil toward the flexural bulge. Shorter migration pathways (10 to 20 km) toward the frontal structures of the fold-and-thrust belt are responsible for late-stage trapping.

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