3-D Modelling of Hydrocarbon and CO2 Generation and Migration, Gulf of Gabes, Offshore Tunisia

Grimmer, Joerg O.¹; Benbrahim, Abderrazak ²; Hamdi, Ali ²; Nadin, Phil ¹; McQuilken, Jonathan ¹
(1) BG Group, Reading, United Kingdom. (2) Exploration, BG Tunisia, Tunis, Tunisia.

3D petroleum systems modeling utilizing the 3D PetroMod software has been used to constrain the generation and migration of both hydrocarbons and CO2 in the Gulf of Gabes, offshore Tunisia with a focus on the Jugurtha discovery and the Miskar Field. The objective of the study was to define the source of the hydrocarbons and the CO2, their concentrations, volumes and filling history of the R1 Inferior and R1 Superior reservoirs. A twenty-seven layer petroleum systems model incorporating ninety faults with two source rocks (Bahloul and Bou Dabbous Formations), a deep Fahdene Formation CO2 source and an additional CO2 source defined by a Late Cretaceous intrusion was constructed.

Overall the modeling shows: Most of the CO2 is generated by a late Cretaceous intrusion.

7-8 km burial depth of the thick Fahdene Formation “carbonates” are needed for this formation to reach temperatures that are high enough for the thermal cracking of carbonates and the release of large masses of CO2.

The late Cretaceous intrusion causes early generation of both hydrocarbons and large masses of CO2. This is prior to Late Eocene peak hydrocarbon generation from the Bahloul Fm and further generation of CO2 from the deep burial of the Fahdene Formation.

Hydrocarbon and CO2 migration is vertically through the petroleum system and the faults are closed as modeling scenarios show that open faults are unlikely.

The modeled masses of hydrocarbons and CO2 are consistent with the masses present in the Jugurtha discovery and the Miskar Field.

The Bahloul Formation is inferred to be a Type III kerogen source rock; otherwise a greater amount of liquids would be present in the petroleum system.

The outcome and the benefits of this project are a better understanding of the petroleum system and the origin and spatial distribution of hydrocarbons and CO2 in the Gulf of Gabes.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.