The Ravenspurn North Field, Blocks 42/30, 43/26a, UK North Sea

Abstract

Abstract The Ravenspurn North Field is a gas accumulation located in the Southern North Sea, Permian Gas Basin which was discovered in October 1984. It has undergone four years of appraisal well drilling culminating in the approval of the development plan in 1988. Development wells are currently being drilled and three offshore installations are planned; first gas production began in July 1990. The Ravenspurn North Field is a combined structural and stratigraphic trap. The reservoir is fault closed along a series of anastomosing oblique strike-slip and normal faults. Seals along the faults are provided by the Silverpit Formation mudstones and Zechstein Group evaporites. The reservoir deteriorates to the northwest because of thinning, facies change and increasing authigenic clay content. The Lower Leman Sandstone Formation of the Rotliegendes Group forms the reservoir. It consists of a sequence of aeolian dune, fluvial sheetflood, fluvial channels and lake margin sabkha deposits. Non-reservoir intervals are formed by playa lake mudstone sequences. Fluvial and sabkha facies dominate in the northwest while aeolian facies dominate in the southeast parts of the Field. Reservoir quality was initially controlled by lithofacies distribution. Subsequent diagenesis further modified the reservoir rock resulting in variations in the porosity and permeability. Deliverability is a function of variable permeability with two areas identified; the high deliverability area where gas wells have tested sufficient quantities for commercial production without artificial stimulation and a low deliverability area where gaswells require hydraulic fracture stimulation before significant commercial production rates are achieved.