Cambrian Hydrocarbon Reservoirs in the Sirt Basin, Libya

Paul Swire¹ and Rida M. Khalil^2
1KUFPEC, Kuwait, Kuwait
²Woodside Petroleum, Tripoli, Libya

Cambrian aged hydrocarbon reservoirs in the Sirt Basin of Libya consist mainly of pre-rift quartzitic sandstones. To the east the informal PUC (Pre Upper Cretaceous) D, C and B units can be correlated to the lower Amal Group units of the nearby Amal Oilfield. Interbedded shales have yielded marine microplankton that indicate a Middle to Late Cambrian age. The top of the PUC B reservoir is identified as the Hercynian Unconformity. The units of the lower Amal Group are referred to as Amal units I, II and III. Amal Unit II is the major hydrocarbon reservoir in the Amal Field. Sedimentary core description indicates that deposition was as a high stage bar.
In the West Sirt Basin Pre Late Cretaceous sediments consist almost wholly of pre rift sediments belonging to the Cambrian or older. The type section for the Hofra Formation is the A1-11 well (Jofra Oilfield). It is represented by 2350' of fine grained well sorted sandstones interbedded with thin silty mudstones.
In the central Sirt Basin pre rift Hofra Formation is also preserved. The recovery of an acritarch assemblage from thin interbedded siltstones with quartizitc sandstones in the D2-104a well in the Hagfa Trough indicates marginal marine deposition and a Middle to Late Cambrian age. These sandstones are fractured and provide a hydrocarbon reservoir in the Wadi Field and other nearby fields (Dor Marada and Tibisti).
The Cambrian aged formations are therefore important as mainly fractured hydrocarbon reservoirs and in that they provided fault edges and highs for younger hydrocarbon reservoirs to shoal against so developing good porosities and permeabilities.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece