The influence of thermal history on hydrocarbon prospectivity in the Central Irish Sea Basin

Abstract

AbstractThermal history reconstruction studies of four hydrocarbon exploration wells located in the Central Irish Sea Basin (CISB) reveal three major regional episodes of heating and cooling. Units throughout the pre-Quaternary section intersected in wells 42/12-1, 42/16-1 and 42/17-1 began to cool from their maximum post-depositional palaeotemperatures in Early Cretaceous time, between 120 and 115 Ma. Cooling from subsequent palaeotemperature peaks began in Late Cretaceous-Early Tertiary (70–55 Ma) and Late Tertiary (25–0 Ma) time. Results from well 42/21-1 are dominated by the two more recent episodes, and show no evidence of the Early Cretaceous episode. This is thought to reflect a different structural setting of this well, within a North Celtic Sea-Cardigan Bay trend. Palaeotemperature profiles suggest that heating in each episode was due largely to deeper burial, with subsequent cooling caused mainly by uplift and erosion. A maximum of c. 3 km of additional Late Triassic to Early Cretaceous section is required to explain the observed Early Cretaceous palaeotemperatures. Appropriate values for the Late Cretaceous-Early Tertiary and Late Tertiary episoders are c. 2 km and c. 1 km, respectively. All of these cooling episodes correlate closely with similar episodes recognized from previous studies in surrounding regions, from onshore Ireland, Scotland, South Wales and northern, eastern, central and SW England, and each appears to be of truly regional extent. Exploration risk in the CISB generation can be significantly reduced through recognition of the major palaeothermal episodes that have affected the region, and the variation in the magnitude of their effects across the region. The challenge for future exploration in the region is to identify regions where the main phase of hydrocarbon generation post-dated structuring.