First production from the Viking fields began in 1972 and at its peak a total of 13 platforms produced at rates up to 930 million cubic feet per day from 20 wells and was supplying 12% of the United Kingdom's natural gas requirements. In addition, several prospects were drilled in the early 1970's but, due to disappointing results, were viewed as un-economic and consequently were not pursued for development. Since discovery in the late 1960's of the Viking A and B fields and associated satellites, exploration and appraisal within the Viking contract area has identified five possible new gas accumulations named the Viking Extensions. Appraisal of these extensions commenced with the remapping of the Viking contract area with proprietary 2D seismic data acquired in 1983 and 1987, supplemented with traded seismic data from adjacent block operators. However it was only the re-negotiation of the gas sales contract and the removal or the Gas Levy in 1992 that provided favourable marketing conditions for the development of additional Viking gas production and initiated the current appraisal programme for remaining reserves. This programme began with acquisition of a 3D seismic survey in 1993 and these data and subsequent drilling have resulted in very promising initial results. It is expected that as this latest evaluation of the Viking extensions and remaining exploration prospects reaches it's full conclusion, between 730 and 1000 Bcf or additional gas reserves will have been realised. This will provide the opportunity for many more years of renewed life from one of the oldest producing areas in the North Sea. Viking Field History The Viking field area is located in the gas basin or the Southern North Sea approximately 140 km offshore from the Lincolnshire coast of England (Fig. 1). The blocks covered by the Viking area include 49/12a and 49/16 and 49/17 (Licence P033) and were originally awarded to Continental Oil Company in Licensing Round 1 in September 1964. Current licensees are the operator Conoco (U.K.) Limited, and B.P. Exploration each holding a 50% equity. Producing Reservoirs. Nine accumulations of gas, Viking A, B, C, D, E, F, G, Gn, and H have been discovered and put on production (Fig. 1) since the first well, 49/12-1 was drilled in 1969. All reservoirs comprise the Lower Permian Leman Sandstone Formation of the Rotliegendes Group with producing zone porosities and permeability's ranging from 7% to 25% and 0.1 mD to over 1000 mD), respectively. Two central gas gathering complexes, A and B, receive gas from the nine accumulations. Gas is gathered at the B complex from its own field and satellites C, D, E, G and H and piped 11 kilometres to the A complex through a 24 inch diameter pipeline. It then enters the Viking Transportation System's (VTS) 28 inch pipeline to be transported onshore to the Theddlethorpe gas terminal on the Lincolnshire coast. All wells in the A and F reservoirs were permanently abandoned in 1995. Initial gas in place (IGIP) and Reserves. The IGIP for all Viking area producing fields has been estimated at 3,230 Bcf or which approximately 2,750 Bcf have been produced (as of March, 1995) reflecting a recovery of 85%. The three largest fields have produced 76% or the total reserves from the A (970 Bcf), E (620 Bcf) and C (515 Bcf) reservoirs whilst the B, H and G reservoirs have produced an additional 17 % and the D, F and Gn represent the remaining 7%. Geologic Setting and Stratigraphy The Leman Sandstone consists of stacked aeolian sands ranging in thickness from around 500 to over 800 feet. These were deposited under arid conditions in a large, predominantly east-west trending basin, initiated by thermal subsidence at the end of the Variscan orogeny.