North sea formation waters atlas / Атлас морских формаций Северного моря

Discovered in 1972, the Amethyst Field is a group of five gas accumulations covering an area of 97 km 2 in the southern North Sea in blocks 47/8a, 47/9a, 47/13a, 47/14a and 47/15a. It is one of the closest fields to the Humberside coast. Gas production started in October 1990.
The field comprises a NW- SE-trending faulted anticline structure, with a crest at 8800 ft sub-sea. Gas-water contacts are at 9049 ft in Amethyst East and 9017 ft in Amethyst West (see map). The main reservoir rock is the Permian Leman Sandstone of the Upper Rotliegendes Group. Three main lithofacies types are present, which are, in order of decreasing reservoir quality: aeolian dune sands, sheet sand and interdune sediments, and wadi deposits. Reworked equivalents of these sediments are also present.
The dune sands were originally clean and quartzose, with < 10% feldspar. The main diagenetic minerals are early calcite (calcrete), dolomite cement, late illite (K-Ar date of c. 100-150 Ma) and late anhydrite cement. <...>