The Use of Complex Wells for Reserves Optimization in the Mabruk Field

The Mabruk field, located in the Sirt Basin, is made up of four oil accumulations, namely North Mabruk, East Mabruk, Central Mabruk, and West Mabruk. The latter one, where fair reservoir characteristics were encountered, is the most extensively developed. The Mabruk carbonate reservoir, located at a depth of 3500 ft, is characterized by steep variations of facies together with a complex compartmentalization, resulting in massive reservoir heterogeneity.

Several attempts were made by various companies since the late fifties to develop the field with vertical wells. But due to the small thickness (45 ft) and low reservoir permeability, the performance of vertical wells is generally poor.

Since 1995, the approach used by Compagnie des Pétroles Total Libye (CPTL) succeeded in developing and increasing the reserves in the West Mabruk field by using sophisticated drilling techniques. The use of horizontal and multilateral wells allowed coping with the low productivity and alleviated the impact of heterogeneities. Reservoir simulation was also utilized to predict the areas that will be poorly swept, and plan infill drilling. A gradual increase of forecasted recovery from 19% in 1995 to 28% today resulted from this approach.

The next stage of the Mabruk development will be to capitalize on the knowledge gained in West Mabruk, to adapt in the other parts of the Mabruk field (particularly the East and Central areas). Also, a review of the well performance and the improvement in geological understanding should lead to further improvements in future well design, including: well geometry, spacing, simulation and intervention strategy, and water injection scheme.

This paper discusses the development philosophy followed so far, and the foreseen improvements currently under study to further improve the ultimate recovery factor in the field. Preliminary results from the ongoing investigations are also presented.