The Heidrun Field - Challenges in Resetvoir Development and Production

Abstract Geological, reservoir and well-technology related challenges have been overcome in the planning and pre-drilling phases of Heidrun and, although additional challenges remain in the future, the field has come rapidly to plateau production, mainly through high-rate gravel packed oil producers from the highest quality and most homogeneous reservoir, the Fangst, An extensive data acquisition program in the pre-drilling phase has laid the groundwork for improved reservoir description of the complex Tile and Are Formations, which are heterogeneous reservoirs containing barriers to fluid flow and having complex fluid systems. These formations have the potential of contributing large reserves from this giant oil field. Plans are in place for a pilot water flood in these reservoirs and strategies are being evaluated to realize the value of the undeveloped gas reserves and/or use the gas in secondary recovery of oil from Tllje and Are. Introduction The Heidrun Field is located in the prolific Haltenbank area, 190 Km from the Norwegian coast in 350 m of water. (Fig. 1) The field was discovered in 1985 with the drilling of Well 6507/7-2 and appraised from 1985 to 1987 with a total of seven weils. The field covers an area of 14 mi.' and was unitized in 1991 with 75"A of the resource in Block 6707/7 and the remaining 25%. in Block 6707/8. Conoco was the operator in the exploration anddevelopment phase, and the operator ship was transferred from Conoco to Statoil in October 1995 at start of fieid oii production. The reservoir development responsibility was transferred to Statoil in January 1994, but still remained an integral part of the overall development project. The recoverable reserves are located in three reservoirs of Jurassic age; the Fangst Group with exceptionally good reservoir characteristics, and the more heterogeneous Tile and Are Formations, which are of substantially lesser reservoir quality and represent the major challenge in the current development planning. All reservoirs contain saturated acidic crude oil and free gas, however a heavier and more viscous crude oil is foundin the Tile and Are Formations than in the Fangst Group. Reservoir data, fluid properties and in-place hydrocarbon volumes are given in Tables I and 2. The Heidrun Field was developed with a concrete Tension Leg Platform (TLP) and two sub sea water injection templates. Oil export is achieved through a direct shuttle loading (DSL) concept allowing shuttle tankers to dock directly with the export lines, thus avoiding the requirement for in-field crude storagefacilities. Gas export will be via a gas pipeline to Tjeidbergodden in mid-Norway, starting in late 1996. Production from the field commenced in October 1995, along with the water injection. Regular injection of gas started in December of the same year. Ire reservoir development includes acceleration of oil production through an extensive pre-drilling program'. A total of 16 development wells were pre-drilled and some partly completed before the Heidrun TLP was installed in the field during June 1995.