SUMMARY
The Naricual formation of the El Furrial field is a deep anticline oil reservoir. It was originally highly overpressure and the reservoir temperature was quite high. The medium-type crude oil has a large asphaltene content and the fluid properties change significantly with depth. The field is sealed off from the underlying aquifer by a 200 feet tar mat. The primary production mechanism is fluid and rock expansion.
A major data collection campaign for reservoir definition was set up right from the start of production. It resulted in a pressure maintenance programme whose objectives were the acceleration of oil production and the maximisation of the oil recovery and profitability.
The pressure maintenance project and the enhanced recovery methods that have been implemented were based on 400,000 barrel/day water injection, later to be increased to 550,000 barrel/day and 450 million standard cubic feet per day of miscible gas injection. Together with the primary recovery these projects were estimated to produce 3,210 million barrel oil, and increase the oil recovery by 33 % of the original oil in-place. An integrated reservoir management and a continuing actualisation of the reservoir model was required from the start. As an illustration, the geological model was refined eight times during the past 13 years and the ongoing exploitation plan was adjusted accordingly. Its implementation required flexibility of facilities and production operations.
This paper describes the field monitoring techniques of the water and gas injection. Tools and methods used to improve production and injection patterns have also been addressed. The application of resins, emulsions and diverting agents to control production and injection was excluded mainly due to the extreme reservoir conditions. Sand plugs have been set and intervals have been re-perforated with the aim of obtaining a more uniform injectivity and productivity. Their success ratio exceeded 70 %.
Finally, the paper provides information on current studies, whose short term implementation could lead to produce up to 55 % of the original oil in-place.
