Spatial Distribution of Clay Minerals in the Neogene Sediments of North Kuwait and its Impact on Thermal Production

Abstract

Clay minerals are commonly observed in the Neogene succession of North Kuwait, both in the two viscous oil rich sandstone reservoirs (S1, S2) and intervening shale layers. SEM and XRD analysis of the core samples explain that Smectite is the dominant and Palygorskite, Illite and Kaolinite as minor clay mineral constituents. The paper describes the vertical and lateral distribution of these minerals in different sedimentary facies from bottom to top and the impact of steam on them. The bottom and second channel-dominated sand and intervening shale (S2B sand, S2 Shale, S2A sand) layers show variation in total average clay content, as well as the swelling clay (smectite, illite-smectite) and fibrous palygorskite, with a low content in the north and center (2-4.6%), a moderate content in the east (6.7-7.3%) and a high content in the south (11.2-14.4%). The Middle shale layer (MShale), is recognized as a flooding surface, observed at base of muddy interdistributory bay/lagoonal or floodplain deposits, sharply overlaying the channel-filled sandstones. Smectite –Illite is the dominant clay constituent. The first channel-dominated sand and intervening shale (S1B sand and S1 Shale) layers contain predominantly smectite, illite-smectite and palygorskite content. The northern, southwestern and southeastern parts of the field, with more argillaceous channels and floodplain facies associations, have a high average total clay content (9.6-20%). The central part of the field, which is predominantly contains clean channel sand bodies, has a lower, average total clay content (4.9-12.6%). The topmost sand (S1A sand) layer contains higher proportion of muddier channels and interdistributary bay facies, in the northern part and has high (>7%) total clay content, but generally <2% swelling clays and palygorskite. The central part of the field, with clean channel sands, has relatively low (<7%) total clay content, with 0.8-3.2% swelling clays and palygorskite. The southern part of the field, with argillaceous channels, has a relatively high (>7%) total clay content, with 2.2-6.3% swelling clays and palygorskite. The sealing Cap Shale (bound by maximum flooding surface at the base and an erosive surface at the top) comprises of marine and restricted marine shales capping the underlying S1A sandstones. The clay mineral comprises of illite-smectite, kaolinite and chlorite, with no palygorskite content, As this viscous oil is planned to be produced by thermal applications, Clay stabilization experiments were conducted to ascertain the permeability reduction in the reservoir due to swelling of clay minerals and changes after exposure to steam. The steam flood experiments are conducted at 32, 65 and 232°C on actual core plugs and the conversion of Illite-smectite to smectite was observed, reducing the permeability. Chemical stabilizers were suggested for controlling these damaging effects at higher temperature.