Some of the most important oil reservoirs located at the Maracaibo Lake Basin are produced by a waterdrive mechanism. After four decades since the beginning of production, oil rates have declined mainly due to a continuous increase in water production.
These reservoirs are characterized by highly heterogeneous sandstone formations in which water channeling through high permeability strakes is a very common cause of water production. Another type of problem affecting production in these reservoirs is behind casing communication between producing sand and nearby water sands. Both problems have caused a rapid increase in the water-oil ratio of the wells, which in most of the cases were abandoned affecting considerably the oil recovery of the reservoirs.
This paper describes four successful selective water shutoff applications in producing wells from mature reservoirs at Maracaibo Lake Basin performed during the last seven years. The aim was to correct problems of channeling and behind casing communication. An elastic gel system of variable consistency with easily controlled gelling times was used. In some applications a gel-cement combination was necessary to improve results. Reservoir and well characteristics, diagnostic analysis and the different types of selective placement used are shown as key factors for success.
Using the elastic gel system the water production has been reduced to a minimum, obtaining an increase in wells productive life-time, which in global terms reaches a volume higher than 2 millions barrels of additional oil recovered.