Troll Oseberg Gas Injection (TOGI) Development

ABSTRACT In 1986 the Oseberg partners decided to replace the planned water injection scheme by gas injection. Pressure maintenance by gas of the Oseberg reservoir instead of water is estimated to increase the overall oil recovery by approximately 7% or 75 mill bbls. In addition 21 water injection wells are saved. Approximately 75% of the injected gas will be recovered. The Troll-Oseberg Gas Injection (TOGI) development was initiated to supply gas to Oseberg from the nearby Troll field. The gas is produced by a subsea station with 5 wells, and transported unprocessed through a 48 km long pipeline to Oseberg. The subsea station is remotely controlled and monitored from Oseberg. This 3 bill NOK project operated by Norsk Hydro started production in January 1991 after 4 1/2 years development. INTRODUCTION In order to further improve the oil recovery from the Oseberg field reservoir an external gas supply for injection purposes was sought for to replace a planned and comprehensive water injection scheme for the Oseberg reservoir. This triggered a study directed towards a deepwater development of part of the nearby giant Troll field gas reserves for injection gas delivery to Oseberg, 48 km away, for improved reservoir pressure maintenance. The Troll-Oseberg Gas Injection (TOGI) development was initiated by Norsk Hydro and presented to the Oseberg and Troll field partners in the spring of 1986, and was met with their approval. 4 1/2 years of novel technology development, testing, installation and completion work has now passed and the TOGI development is preesently in operation and gas is being produced from the Troll deepwater station in 303 meters of water by the Troll field licensees, and transported and sold to the Oseberg field licensees to enhance the Oseberg oil recovery with approx. 7%. Two percent, up to one trillion scf. of the large Troll reserves will be injected into Oseberg over a twelve year period. 75% of this gas will be recovered and sold after year 2002, when Oseberg goes into its gas production phase. This paper will addressThe impact on Oseberg of gas injection vs. water injection.A brief presentation of the contractual agreements between the two license groups.A conceptual description of the TOGI development.a presentation of TOGI project contracts and organization principles. Norsk Hydro is the operator of both the Oseberg project and the TOGI project. This paper is one in a series of six which are presented at the OTC 1991. Impact on Oseberg - Advantage of Gas Infection The Oseberg field is located approximately 140 km west of Bergen, Norway, fig. 1. The phase I development of this field consisted of a field centre (the 'A' and the 'B' platforms), an oil pipeline (28") to shore and an oil terminal onshore for storage and export of the crude oil. Phase I also included two subsea wells. The main Oseberg reservoir is split in three different structures, the Alpha structure, The Alpha North structure and the Gamma structure, fig. 2.