The Caister Fields, Block 44/23a, UK North Sea

The Caister Gas Fields are located in Block 44/23a, within the Silver Pit Basin area of the Southern North Sea Basin and comprise a Bunter accumulation overlying a Carboniferous accumulation. The Carboniferous structure is a faulted northwest–southeast-trending anticline, bounded to the northeast by a major reverse fault. The reservoir is formed of early Westphalian B braided channel sandstones, the thickness of which varies from 20–50 m over the field. Porosity is fair with an average of 11%. Average horizontal permeability is 5 mD, although permeabilities up to 400 mD are measured. The Bunter structure is a simple, unfaulted, elongate northwest–southeast-trending dome, with seal provided by the overlying Haisborough Group saliferous shales. The sheet-flood reservoir sandstones, with a thickness of 150 m over the field, have an average porosity of 21% and an average horizontal permeability of 100 mD. Combined initial gas in place is estimated at approximately 400 BCF with recoverable reserves in the order of 300 BCF.