Reservoir Management Aspects Of Producing Oil From Thin Oil Rims In The Troll Field

Abstract

ABSTRACT The 22–26m thick oil zone in the Troll West Oil Province, offshore Norway, is planned to be developed by 18800m long horizontal wells. The viability of such wells has been proven by long-term testing. To obtain economic oil production the wells will be completed in the lower part of the oil rim close to the oil-water contact. The high water production which is expected can, to some extent, be controlled by gas reinfection. A flexible gas injection scheme will therefore be implemented. Allowing wells to produce free gas together with the oil (supercritical - production) has been shown to accelerate oil recovery and to improve lift and balance well pressures at the subsea manifolds. The complexity of the Troll field together with simultaneous oil and gas production from different parts of the field makes development planning and reservoir management a great challenge. Significant movements of the fluid contacts across the field are expected. To predict the global effects accurately in addition to local phenomena, such as gas and water coning in oil wells, very flexible simulation models have been constructed. INTRODUCTION The Troll oil and gas field is located in 300m water depth offshore Norway and covers an area of 700km2 (Fig. 11. It contains an up to 26m thick oil rim sandwiched between a large gas cap and an active aquifer. The field consists of three easterly tilted fault blocks (Fig.2). In the western most fault block, the Troll West Oil Province (TWOP), the oil column is 22- 26m thick. The estimated oil in-place in this province is 155x106m3. In the central fault block, the Troll West Gas Province (TWGP), the oil zone is 12 – 14m thick and the estimated oil in-place 440x 106Sm3. In the Troll East fault block the oil column is only O - 4m. The major gas accumulation is found in Troll East with a gas in-place estimated at 1072x109 Sm3. In the TWGP the estimated gas in-place is 570x109Sm3, and in the TWOP 2.7x109Sm3. The development of Troll is divided in three phases. Phase 1 includes gas production from Troll East and is planned to start in October 1996. Phase 2 covers development of the oil resources. A plan for development and operations(PDO) of the oil in the TWOP was prepared during 1991 and was approved in 1992. This plan assumes production startup by the beginning of 1996. Oil production from the TWGP is presently under evaluation, The TWOP development concept has flexibility to include a future development also of the oil resources in the TWGP. Phase 3 includes large scale gas production from Troll West. The gas strategy will be coordinated with the oil production and will not be settled until the extent of the oil development in the TWGP has been defined.