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Computer-Aided Exploration with THEMISED Software: Pressure, Maturation Analyses, and Migration Studies in Various Geological Environments, Rifts (North Sea), Intracratonic Basins (Paris), Tertiary Deltas (Indonesia)

P. Y. Chenet, B. Doligez, G. Bessereau, P. Ungerer, E. Brosse

The THEMISED software describes on a geologic cross section the progressive compaction of the sediments due to water expulsion, the formation of hydrocarbons as a result of temperature increase with burial, their expulsion from the source rocks, and their migration as a separate flow within the carrier beds toward the traps. This tool points out the main geological factors leading to hydrocarbon accumulation (oil and/or gas) in relatively quiet tectonic settings. It gives an objective geological interpretation on the basis of the geological hypotheses made by the explorationist.

In the North Sea basin, the writers show how the difference of behavior of the various source rocks during maturation may affect the distribution and kind of hydrocarbon accumulation. In addition, the pressure buildup within the impervious shaly seal and within the reservoir may lead to hydrocarbon dismigration, because of the seal leakage, or hydrocarbon accumulation per descensum within the reservoirs.

In some intracratonic basins like the Paris basin, the hydrodynamic conditions may perturb hydrocarbon migration. The timing of hydrocarbon expulsion is also crucial when considering the timing of traps' structuring.

In thick, recent sedimentary basins such as the Mahakam Tertiary delta (Indonesia), the rapid sedimentation causes a specific pressure buildup and a perturbation of the heat flow. The possibilities of carrier bed connections within the delta also influence the pressure regime. As a consequence, the distribution of hydrocarbon accumulations is linked both with the source beds' relations to the carrier beds and the general pressure and temperature history of the basin.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.