Oligocene source and reservoir rocks evaluation using a multi-disciplinary approach within eastern offshore Nile Delta province

Document Type : Original Article

Authors

1 Egyptian Natural Gas Holding Company

2 Geology Department, Faculty of Science, Al-Azhar University

3 PetroSannan petroleum company

Abstract

Nile Delta Basin in the Eastern Mediterranean has been one of the most important hydrocarbon areas, with estimated undiscovered natural gas reserves 800+ trillion cubic feet. In favor of increasing certainty and giving the current study more confidence, a multi-disciplinary approach was applied to evaluate the Oligocene potentiality as a hydrocarbon source and reservoir by integrating Sequence stratigraphy concept, petrophysical evaluation and Basin modeling workflow.

Interpreting sequence stratigraphy framework would explain the spatial and temporal distribution of reservoir along the study area and consider the effect of various deposition process and deposional elements. On the other hand, petrophysical evaluation sheds light on the reservoir quality and track the changes of reservoir criteria and facies and proves that the effective porosity values directly affected by overburden thickness, average effective porosity in the shallowest cycle Ch_B is 15 % decreasing to 12% within the deeper cycle Ch_A and reached its lowest value 10% within the deepest cycle and maximum overburden. The turbidity channelized system - which is widely distributed in the region- and the predominant reservoirs of the Oligocene with wide range of reservoir thickness, from 1.6 m within Ch_B cycle at Helm-1st1 well location and reaches its maximum 68 m within Ch_B cycle at X-1 well location. In parallel with 1D basin modeling was applied as source rock evaluation technique to figure out the Oligocene source rock potentiality for hydrocarbon generation. A wide range of maturity levels marked, starting from the lowest mature source rock unit marked by low amount of total generated hydrocarbon 0.04 Mtone and recent critical moment 1.1 Ma within Ch_B cycle at Salamat-1 well location, to the most mature source rock unit with high amount of total generated hydrocarbon 0.74 Mtone with old critical moment 15.5 Ma within Ch_B cycle at Notus-1st2 well location. The results of this integrated work proved that, the Oligocene shale is the main source rock for both Oligocene and Miocene with total 1D generated hydrocarbon mass 4.84 Mton. Oligocene deposits proved a successful combined stratigraphical and structural hydrocarbon exploration play supported by various gas discoveries.

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