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.