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Abstract: Quantitative Evaluation of the Geologic Evolution and Hydrocarbon Potential of the Gulf of Gabes, Tunisia

M. A. Yukler, A. Moumen, I. Daadouch, H. Bouhlel, A. Meskini, M. Saidi, H. Jarraya

A quantitative basin modelling study is carried out, using YUKLERPCR software and all the available data in ETAP, Tunis, to provide the necessary data for the ranking prospects within the permits in and around the Gulf of Gabes, Tunisia, and to aid in the selection of drilling target(s).

Fifty-eight wells with pressure, porosity, temperature and maturity data are modelled to construct the conceptual model in terms of paleoenvironments, lithofacies, type of geologic events and their durations, and heat flow. The oil/condensate and gas shows are used as checks on the generation of hydrocarbons. The conceptual model is then used in the modelling of fifty-one pseudo-wells, together with the real wells, to quantity the geologic evolution and hydrocarbon potential of the gulf within a continuous three-dimensional geological framework.

The computed subsidence and the optimized heat flow histories show that the subsidence of the subbasins within and around the Gulf of Gabes from the Callovian to the Berriasian, from the Aptian to the Paleocene and from the Langhian to Recent were the result of tensional forces. The heat flow values first increased and then decreased during these times. The subsidence from the mid Paleocene to the Oligocene was not controlled by tensional forces. The optimized heat flow values were constant during this time and the seismic data show that the Eocene sediments are onlapping onto the underlying older formations. The subbasins were subjected to more than one compressional event from the Langhian to Recent. Major uplift and erosion took place during the Tortonian and the mid-late Pliocene which altered the subsurface topography and affected the timing of trap formation and trap size.

The last heat flow increase and the late Tertiary sedimentation were the controlling factors for the generation and migration of hydrocarbons. The effective hydrocarbon generation and migration took place only during the last 4 my within and around the Gulf of Gabes. The occurrence of economic hydrocarbon accumulations, however, are directly related to the pressure histories during the last 5 my. In the areas where high abnormal pressures took place, the carbonate reservoirs are fractured and have good reservoir properties. In the areas where major uplift and erosion took place during the 3 to 1 mybp, subnormal pressures occurred leading to seal failures and, thus, resulted in non-economical accumulations.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France