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.