Reservoir Compartmentalization through Geochemical and Sedimentological Investigations; Example from Sirt Basin oil field, Libya

By

 Alain Noyau¹, Louai Machhour²

(1) TOTALFINAELF, PAU Cedex, France (2) TOTALFINAELF, PARIS la Défense Cedex, France

 The oil field studied (Sirt Basin, Libya) is represented by two structures (West & East). The west structure can be separated into 3 depositional areas (Northern, central and southern).

Uncertainties in the lateral continuity of the reservoir unit are suspected in each area. However, an extensive continuity of this reservoir from the North to the South of the West structure is not clearly demonstrated. A reservoir sedimentology and geochemistry studies was performed on several core wells and production oil samples collected from the West and the East structures with the following objectives:

-         To clarify the lateral continuity and communication of the reservoir unit in each area from the West structure. If lateral barriers can be highlighted, the different hinge points suspected to correspond to reservoir discontinuities would be proposed,

-         To evaluate the lateral continuity/discontinuity of the reservoir between the West and East structures. In the West structure the analysis suggests that the oil collected in the reservoir unit exhibits 3 distinct geochemical signatures probably due to reservoir disconnection or compartmentalization.

From a sedimentological viewpoint, this reservoir heterogeneity can have two different origins: 1) Tectonic origin (faults) and/or 2) Sedimentary origin (disconnected reservoir bodies, diagenetical events, etc.).

The East structure does not show any difference in the oil composition. This result seems to show that the reservoirs are laterally connected. Sedimentological analyses reveal that all the wells of the East structure do not exactly correspond to the same depositional environments but contrasts in facies and reservoir characteristics are not important enough to induce lateral compartmentalization of the carbonate reservoir unit.