Enhanced oil production of the Varg Field, through revising the geological understanding area PL038, Central North Sea

The Varg Field, license Pl 038, is situated approximately 240 kilometres offshore Stavanger. August 2002 the PL038 operatorship was taken over by Pertra AS (a PGS owned oil company) from Norsk Hydro ASA, thus becoming a new oil producing company on the Norwegian shelf. The reservoir succession comprises of Oxfordian shallow marine, highly bioturbated mudstones and muddy siltstones to sandstones reflecting a depositional range from offshore transition to upper shoreface conditions. The detailed understanding of the Varg Field comes from the numerous cores taken. The cores selected for this workshop are from three wells illustrating the importance of having a good coring program. A new image logging tool from Haliburton called the ALD tool has been shown to be extremely useful in situations where coring is difficult when such logs are correlated to cores in near by wells. Together the ALD log and cores create a formidable interpretation tool for understanding the reservoir. The second set of cores illustrates the importance of understanding the biogenetic sedimentary structures to achieve a more correct interpretation of the deposition environment, thus yielding a better predictability of the reservoir away from the wells. With this detailed predictability one can aid in improving seismic facies analysis and be able to perform quality control of calculated reservoir parameters. The third core set shows the importance of a good coring program to solve productions problems. Well 15/12-A-5 T2 began producing water from the middle of the oil zone. Without core the reason for this water production could never be explained and an elimination program could not be initiated. The core shows coarse gravel bed in the middle of the reservoir from which water break through occurred all the while oil was produced above and below.