Paleo-Oil Migration and Charge Modeling of the Murzuq Basin, Libya

By

 Daniel Barson¹, Troy Myers¹, Kaush Rakhit¹

(1) Rakhit Petroelum Consulting Ltd, Calgary, AB

 The Murzuq Basin of southwest Libya is a saucer-shaped intracratonic sag bounded on three sides by prominent structural highs, each with a wide Paleozoic outcrop belt at high topographic elevation. Basin fill is predominantly Paleozoic and Mesozoic sandstone and shale, with rare limestone. The main petroleum reservoir is the upper Ordovician Memouniat sandstone. The primary source rock is the Silurian Tanezzuft shale.

Basin modeling indicates that in the various depocentres of the basin, high TOC shales of the Tanezzuft Formation have been oil generative since late Devonian. Oil migration patterns have changed in response to evolving basin structure and patterns of water flow. Since the basin was uplifted above sea level following the Hercynian Orogeny, meteoric water recharge has complicated the pattern of oil migration and introduced the risk of flushing. Given these complexities, hydrodynamic modeling is a useful tool for reducing exploration risk.

By modeling the evolving hydrodynamic framework of the Murzuq Basin, oil migration patterns in the Memouniat reservoir were mapped for four distinct “snap shots” in the basin history:

Present Day

Holocene (10,000 y BP)

End Cretaceous (c. 65 my BP)

End Carboniferous (c.286 my BP)

Reservoir structure, hydraulic head and oil kitchens were mapped for each time step as inputs for Dynamic Oil Migration Modeling. The Dynamic Oil Migration Maps reveal charge fairways and shadow zones (regions of no-charge) for each time step. Despite the symmetrical basin geometry, charge fairways are surprisingly restricted and large parts of the basin never received oil charge.