New Insights on the Mauddud Formation (Upper Albian): Characterisation of Sedimentology, Diagenesis and Reservoir Quality

Abstract

This paper integrates the sedimentological, petrographical and reservoir quality results from a multiwell study on the characterisation of the Mauddud Fm. (Upper Albian) in an onshore field in North Kuwait. The Mauddud Fm. is a complex mixed clastic/carbonate system dominated by shallow-water carbonates describing a complete 3rd order transgressive-regressive cycle. Muddy carbonates and fine-grained clastics occur in the transgressive interval overlain by cleaner/grainier carbonate lithologies in the regressive section. The lithofacies are interpreted to have been deposited in a shallow lagoonal setting with variably developed shoals and minor clastic inputs from land. The interpreted depositional setting is much more proximal than what has been previously interpreted in the North Kuwait area. An complex diagenetic sequence affected the Mauddud Fm. An early, pervasive dissolution event was the most important process in pore volume creation, resulting in a common mixed micro/macropore system in matrix-supported textures, and a macropore-dominated system in coarse-grained textures. A later calcite cement phase had a strong detrimental effect on the smaller macropores, while its effect on larger macropores was variable, as it is mainly a pore-lining phase, having an overall moderately negative control on reservoir quality development. This study refined our understanding of the strong links existing between the depositional textures, stratigraphic framework, diagenetic overprint and reservoir quality distribution, which allow to split the Mauddud Fm. in two main reservoir intervals that are recognisable across the field: a lower part with overall poor reservoir quality (partially controlled by depositional factors) due to the presence of muddy, clastic-prone and strongly cemented facies, and an upper interval with moderate to good reservoir quality, as a result of reduced cementation and increased occurrence of an early dissolution phase. the diagenetic overprint resulted in a large-scale homogenisation of this upper part of the reservoir. At the field scale, the south-western areas are likely to host reduced reservoir quality, as clastic and tight lagoonal facies are more abundant. Enhanced reservoir quality is expected in central and northern sectors, where a thicker section of cleaner, more open marine facies is present. This reservoir architecture is thus likely to improve future reservoir modelling and prediction of reservoir quality sweet spots.

AAPG Datapages/Search and Discovery Article #90194 © 2014 International Conference & Exhibition, Istanbul, Turkey, September 14-17, 2014