Abstract: Depositional Processes and Predictive Modelling of Deep Water Turbidite Sands of the Britannia Formation, Britannia Field, U.K. North Sea
M. Guy, D. R. Lowe
The Britannia Field is a large gas condensate accumulation located 125 miles northeast of Aberdeen in the U.K. North Sea. The reservoir formation is Lower Cretaceous in age, and is composed of a wide variety of "deep" water turbidite sands. These were shed off surrounding highs and temporarily stored in a shelfal setting before being fed axially into the asymmetrical Wytch Ground Graben. Depositional compartmentalization resulted from sand input from both the east and west. The sands represent a localized regression associated with the Austrian Orogeny, set in an overall transgressive regime.
Detailed core examination has resulted in the recognition of an unusual variety of facies types arising from sediment gravity flow processes that span the spectrum between turbidity current and debris flow. Sandy high density turbidity (HDT) flows give rise to "conventional" HDT deposits. With the addition of mud, cohesion becomes an important factor, and its amount, nature, and distribution governs the behavior of the flow. The resulting flows are termed "Slurry flows," and their deposits exhibit a spectrum of internal structures and properties that reflect the changing dynamics of clay/sand interactions.
Understanding the depositional processes, within the framework of a chronostratigraphically sub-divided reservoir, has enabled predictive mapping of the facies distribution across the Field. Depositional pattern models are being tested by predrilling producing wells. Since there is an intimate link between lithotype, permeability, and gas saturation, the development of a predictive model has greatly increased the confidence in OGIP estimation.
AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France