The Distribution of Chlorite-Precursor Phases in Cores Through a Modern Tidal Bar: Towards Prediction of Chlorite in Reservoir Sandstones

Abstract

Chlorite cement can have profound effects on reservoir quality in deeply buried ancient sandstones since it inhibits the growth of pore-filling quartz cement. There are no satisfactory models to predict the occurrence and distribution of chlorite in sandstone frustrating attempts at reservoir quality prediction during field exploration, appraisal and management. We have drilled deep cores in a tidal bar in the Ravenglass Estuary in the UK to help reveal chlorite distribution in a modern sedimentary system. The cores, drilled by a geotechnical contractor are high quality and have facilitated detail analysis of sedimentology, mineralogy and mineral distribution in the sediment and geochemical analysis. The cores have been analysed by sedimentary logging, laser particle size, XRF, XRD and SEM-EDS analyses and a range of statistical approaches to determine the controls on chlorite distribution. The work has shown that chlorite in the tidal bar sediments is limited to specific depositional facies (depositional sub-environments) and is controlled by a combination of specific provenance and hydrodynamic processes. High resolution XRF logging has shown that high concentrations of iron, linked to diagenetic chlorite, are strictly limited to specific bed types from sediment deposited in tightly constrained sub-environments. Post depositional processes such as infiltration seem to be unimportant in these sediments. The data produced in this and related studies are fast moving towards well-defined sedimentological and diagenetic models capable of predicting reservoir quality in deeply buried marginal marine sandstones.

AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019