Choice of production strategy in modern reservoir management relies heavily on numerical simulation. Large fields may require prohibitively large computer times. New techniques were developed to save computer and engineering time: local grid refinement with small timesteps and flux boundary conditions for simulating regions of special interest. The combined use of these techniques allowed flexible, non-time-consuming, user-friendly reservoir simulation of a variety of reservoir management scenarios for Troll field.

The small Yme oil field offshore Norway was discovered in 1987, but the Plan for Development and Operation (PDO) was first submitted in 1993 due to the field's marginal character. The recoverable oil reserves as basis for the PDO were only 3,4 mill. Sm3. With the field located far from infrastructure, the development decision required a dedicated effort from the license owners. Focus was put on increasing and firming up the reserves basis while maintaining acceptable production costs. Accordingly, a jack-up drilling rig was leased and modified for simultaneous drilling and production. An oil tanker was leased for storage and field off-loading. The time from contract awards to first oil from the main structure, Yme Gamma Vest, in February 1996 was only 13 months. An important part of the development strategy in order to improve profitability was active exploration of mapped prospects in the license area in parallel with field development activities and production. The first subsea satellite development, Yme Beta Ost, was put on production in June 1996. This was only nine months alter submitting the PDO to the authorities and three months after production start for the main field. During the production phase three more exploration wells have been drilled. Overall, these have increased the reserves basis and prolonged the field lifetime. The Yme reservoirs comprise several challenges such as low reservoir pressure and solution gas content, special fluid properties such as high salinity of the formation water with dissolved solids of 190.000 ppm, and high asphaltene content of the oil. Artificial lift using ESPs and subsea gas lift was installed from the start. A compact water injection unit contributes to improved oil recovery. Barefoot open hole multilateral horizontal completions and hydraulic fracturing of vertical wells have also been used to improve drainage from the reservoir which has large permeability contrasts. The Yme field development shows how a marginal offshore field development can be initiated and improved using decision making under risk and application of unconventional techniques. P. 447

This paper was prepared for presentation at the SPE/ICoTA Coiled Tubing Roundtable held in Houston, U.S.A., 15-16 April 1998.

Thm papar was salected for prewntation by an SPE ProgramCommittee fol~ng revkw of infomtion mntained "man abstracf submitted by the author(s), tintents of the paper, as presen~d. have not been reviewed by the Sociity of Wtroleum Engineers and are subject to corrdo by the author(s), The material, as pmsanted, does not necessarily reflect anỹ tion of the Wety of Petro!eum Enginmrq i~o~cars, or mmbers. %pars presented at SPE meetings am sub~fo pub~cation re~w by Editorial Committees of the Society of Petroleum Engineers. Electronic reproduction, diatribu~rr, or storage of any part of this papar for commercial pur~sas Wout the wmen conaant of the Wety of Petroleum Engineers is prohibited. %rmission to reprdu~in print k restricted to an abstract of not more than W wr@ illu~ahns may not k copkd The abstract must wntain umspicuous achMe@mnt of Were and by Mom the paper was presented Wife Librarkn, SW. PO. Sox 833t33e, Richardson, TX~3.3838, Q, fax 01.972.952.9435. AbstractThe small Yme oil field offshore Norway was discovered in 1987,but the Plan for Development and Operation (PDO) was first submitted in 1993 due to the field's marginal character, The recoverable oil reserves as basis for the PDO were only 3,4 milL Sm3. With the field located far from infmtructure, the development decision required a dedicated effort from the license owners.