Gas Cap Behavior Implications on Strategies to Improve Oil Recovery in a Mature Field: a Case History

By

 C. Monico¹, A. Fedullo¹, G. Jawadi²

(1) ENI-Agip Division, S. Donato Milanese (Milan), Italy (2) Agip Oil Comp. Ltd, Tripoli, Libya

 The exploitation of a saturated oil reservoir normally involves a variation in the gas cap. This paper deals with the offshore Libyan oil field of Bouri, on production for fourteen years, where the evolution of the gas cap consisted in an enlargement followed by a restriction. Fluid production and pressure were reproduced in all the wells through a 3D black oil model, confirming the gas cap evolution. When the enlarged gas cap reached the wells, a large quantity of free gas started to be produced. The consequence was that the mass of free gas in place started to reduce and the aquifer activity moved both the water oil contact and the gas oil contact up, causing a shrinkage effect on the gas cap. The process reflected in the behaviour of the wells in the area affected by gas cap expansion-contraction, showing a GOR increase followed by a reduction. Since the scope of work was to analyse additional development scenarios, some infilling wells and work-overs were considered in a zone previously affected by gas cap expansion. The model showed encouraging results if new drainage points were located in the upper layers of the reservoir. The correct simulation of the gas cap evolution was a powerful way to improve the field development with a positive impact on oil recovery. The proposed case history represents a significant issue on the production optimisation in a mature field.