The Ketch, Schooner and Topaz fields, Blocks 44/26, 44/28, 49/1a and 49/2a, UK North Sea

Abstract

AbstractThe Ketch, Schooner and Topaz fields were discovered between 1984 and 1987 and produced from Upper Carboniferous, Westphalian C/D (Bolsovian/Asturian) reservoirs. Gas production began in 1996, 1999 and 2009 for Schooner, Ketch and Topaz respectively. The low net-to-gross reservoir consists of discrete, low sinuosity fluvio-deltaic channels evolving upwards into an aggradational, distal fluvial fan setting, dominated by braided channels. Fault compartmentalization and variable sandbody extent mean that reservoir connectivity was a key subsurface uncertainty. The Ketch and Schooner fields gas-in-place estimates at development approval of 956 and 1021 bcf are now modelled as 581 and 654 bcf respectively. This reduction is due mainly to remapping (Schooner) and revised reservoir modelling reflecting production experience. Generally poor reservoir connectivity is demonstrated by the lower connected gas-in-place volumes, estimated at 351 and 481 bcf respectively, based on production data. Field recovery to cessation of production in 2018 was 263 (Ketch) and 310 bcf (Schooner) or 75 and 64% of the in-place volume connected to production wells. Topaz has 139 bcf gas in place, with recovery of 10.4 bcf from a connected volume of 14 bcf, equating to 74% recovery of connected volumes or 7.5% full field recovery.