Establishing
Controls on Reservoir
Quality in the Cambro-Ordovician of the Tiguentourine
Field, Illizi Basin, Algeria
Haddad, Sasha1, Craig Smalley2, Alasdair Hutchison2 (1) University of Liverpool, Liverpool, United Kingdom (2) BP Exploration, Sunbury on Thames, United Kingdom
Sonatrach, Statoil and BP have initiated exploitation of the gas-condensate bearing, Cambro-Ordovician reservoirs of the Tiguentourine and La Reculee (TLR) structures in the Illizi basin of southern Algeria.
Well test results during pre-drilling have been variable, largely driven by variable reservoir quality (RQ). Understanding initial RQ and subsequent diagenisis is key to reducing future drilling risk.
The primary diagenetic controls are initial clay content and
quartz cementation. This project concentrated on the reservoir
facies,
eliminating clay controls by effectively using a Vsh cutoff. The project
therefore concentrated on the influence of, and controls on quartz cementation.
The process of quartz cementation was modeled in software that allows the consideration of burial/temperature/effective stress history, the resulting compaction, the kinetics of quartz formation, controls on quartz cement formation such as initial rock texture, and the effects of inhibitors such as clay rims to quartz grains and hydrocarbon charge.
The conclusions
were that early hydrocarbon charge is necessary in order to explain the
distribution of RQ, the natural state of the reservoir
otherwise being entirely
quartz cemented. Unrealistically high values of Ea are needed otherwise.
Initial rock texture overprints this control, best original quality having best
ultimate quality relative to rocks in a similar location
diagenetically
.
Presence of a common palaeo-hydrocarbon contact is supported by bitumen
presence, good wells located palaeohighs/closures on the palaeostructure map,
and trends in variation in overprediction of quartz cement with depth.