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Mississippian sedimentology, depositional and diagenetic control on the Kisbey sandstone petroleum reservoir development, Williston basin

University of British Columbia

The Mississippian, Kisbey Sandstone, of the Williston Basin comprises the siliciclastic component of the mixed carbonate-siliciclastic-evaporitic ramp deposits of the Frobisher-Alida beds. The Kisbey Sandstone comprises multiple laterally and stratigraphically discontinuous intervals of quartz arenite which are regionally uncorrectable. Sandstone thickness ranges from <1 to 20 metres with the thicker intervals (3-20 metres) trending NE-SW, perpendicular to the inferred shoreline of Frobisher-Alida beds. A full geophysical log suite consisting of the gamma ray, photoelectric, density and neutron logs are necessary for identification and mapping of the sandstone. The sandstone is predominately massive with rare planar cross bedding and parallel laminations. The massive texture of the sandstone makes depositional interpretations ambiguous. The carbonate lithofacies associated with the Kisbey Sandstone provide a depositional framework for interpretation of the Kisbey Sandstone depositional environments. The primary carbonate lithofacies and depositional environments are open marine crinoidal grainstone and mudstone, pisolitic-ooilitic shoals, protected peloidal grainstone and mudstone Three depositional environments of the sandstone are recognized: 1) wave influenced sandstone shoals; 2) storm-transported sandstone to the open marine environment; and 3) tidal channel sandstone. The interpreted depositional environments reflect autocyclic influences acting on the Frobisher-Alida ramp. Allocyclic influences, such as a relative drop in sea level, do not directly influence the deposition of the Kisbey Sandstone, but did lead to progradation of the restricted marine and evaporitic environments on the Frobisher-Alida ramp. An allocyclic influence is however necessary to transport the Kisbey Sandstone tb the Frobisher-Alida ramp. Eolian transport, analogous with the modern southeast coast of Qatar, is a possible mechanism that controls the initial influx of the Kisbey Sandstone onto the Frobisher-Alida ramp. The Kisbey Sandstone average porosity is 17% and average permeability is 140 md; however, the porosity and permeability values vary greatly in a seemingly unpredictable fashion. The apparent non-uniform distribution of porosity and permeability is characteristic of most sandstone intervals in the study area. Core descriptions, petrographic and scanning electron microscope examination of the Kisbey Sandstone indicates sandstone cements consist only of dolomite and anhydrite. Dolomite is pervasive in the Kisbey Sandstone, but due to abundant intercrystalline porosity the sandstone remains porous and permeable. Anhydrite occurs as patchy zones 2 cm in diameter and along individual lamina, completely occluding pores, has a random distribution at the core sample scale, and correlates with zones of low permeability and porosity. Both dolomite and anhydrite are interpreted to have cemented the Kisbey Sandstone during the early marine stage of diagenesis. Dissolution occurred during subaerial exposure and development of the sub-Mesozoic Unconformity and is responsible for partial dissolution and random distribution of the anhydrite cement. Although the Kisbey Sandstone intervals have an arbitrary distribution of low porosity and permeability zones, most sandstone intervals in the study area have good reservoir potential.

Thesis/Dissertation

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2009-07-08

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http://hdl.handle.net/2429/10406

Geological Sciences

University of British Columbia

UBCV

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