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.