Dry Gas Reinjection In A Strong Waterdrive Gas/condensate Field Increases Condensate Recovery-case Study: The Sleipner Ost Ty Field, South Viking Grabea Norwegiannorth Sea

摘要

The Sleipner Ost Ty field is a strong waterdrive gas/condensate field, with in-place volumes of 59 ×10~9Sm~3 dry gas and 52 × 10~6Sm~3 unstabilized condensate. The reservoir consists of deepwater turbidite sandstones and associated mudstones, which act as baffles to flow. The reservoir qualities are very good, with high porosity and permeability in the range of 100 to 1,000 md.rnThe first production in the area began at the Sleipner Ost Ty field in 1993. The initial reservoir pressure of 244 bar (2.44 × 10~4 kPa) is only a few bar above the dewpoint pressure. Massive dry-gas reinjection started in 1996, and the reservoir pressure increased during the next two years, which caused an increase in the condensate-to-gas ratio. During the injection period, which lasted until 2005, 29 × 10~9Sm~3 of dry gas was injected. The main focus during these years was to obtain good vertical and areal sweep of the dry gas in order to vaporize the dropped-out condensate. Chemical gas tracers were injected and analyzed for in the production wells to monitor the movement of the dry gas through the reservoir. This knowledge was used to identify unswept areas, and to change the drainage pattern by conducting well interventions and drilling infill wells.rnThe injection was stopped primarily because of high probability of trapping gas. Compositional reservoir simulation showed that from 10 to 20% of the injected dry-gas volume could be trapped in the northern region, which has no producers. The risk of not being able to back-produce the injected dry gas was considered high, since the saddle area separating the producers in the south from the injectors in the north was invaded by the aquifer.rnThe gas cycling program has increased the condensate recovery factor substantially; from the originally planned 50% by pressure depletion, to the current estimated ultimate recovery of 81%. As of July 2007, the condensate recovery factor was 76%.