- GeoRef, Copyright 2004, American Geological Institute.
The Glauconitic sandstone consists of six lithological facies interpreted to represent the lower-middle shoreface, middle shoreface, upper shoreface-foreshore, backshore, marsh, and lagoonal zones of a progradational, barrier-island system. Tidal inlet and/or later stage fluvial channel deposits cutting through the sandstone trend form discontinuities in the reservoir. The hydrocarbon trapping mechanism is stratigraphic but with some structural influence. Deep faults, active during the deposition of upper Manneville sediments, caused differential subsidence and local thickening of sediment. This activity resulted in the apparent lateral juxtaposition of different facies. Parts of the Glauconitic sandstone form an exceptionally thck beach-shoreface sequence (up to 45 m or 148 ft thick.) Faulting of sub-Cretaceous units may have controlled the rate of subsidence and the amount of sediment accumulation during deposition of the Glauconitic sandstone. The abundance of clay, mostly kaolinite, largely controls reservoir quality. Argillaceous backshore sandstone, which contain abundant detritial kaolinite, are poor reservoirs; clean foreshore deposits are good reservoirs. Porosity and permeability are only slightly reduced in the clean sandstone by formation of diagenetic phases such as kaolinite and quartz. During the wet forward-combustion recovery process, migration of kaolinite and dissolution-reprecipitation of silica could cause formation change.--Modified journal abstract.