4/21/2021 0 Comments Sandstone Depositional Environment
Enlarged intergranular porosity resulted from the dissolution of detrital illite matrix.Peter Sandstone in the Michigan basin was deposited in marine peritidal to storm-dominated, outer shelf depositional environments that evolved in a regionally significant transgressive pattern.The formation is bounded by carbonate and shaly clastic strata of the Prairie du Chien Group below and is transitional to condensed sequence clastics and carbonates of the Glenwood Formation above.
Sedimentologic and petrographic analysis of conventional core from 25 wells suggests that reservoir quality in the formation is strongly dependent on a complex diagenetic history, especially the nature and subsequent dissolution of intergranular carbonate in the sandstone. Petrographic evidence indicates that porosity in the formation formed by dissolution of precursor dolomite of various origins and, locally, the formation of pore-filling authigenic clay (chlorite-illite). Authigenic clay is the incongruent dissolution product of dolomite, detrital K-feldspar, and, possibly, muscovite and results in diminished reservoir quality where abundant in the St. Peter Sandstone. Authigenic clay is volumetrically more significant in the upper portions of the formation and is associated with higher concentrations of detrital K-feldspar. Depositional facies controlled the distribution and types of intergranular carbonate (now dolomite) and detrital K-feldspar in the St. Peter Sandstone and hence reservoir quality; both components were more more significant in storm-shelf sandstone facies. Peter sandstone, Michigan basin, author Lundgren, Jr, C E and Barnes, D A, abstractNote The Middle Ordovician St. Peter Sandstone and hence reservoir quality; both components were more significant in storm-shelf sandstone facies., doi, url. Library patrons may search WorldCat to identify libraries that hold this conference proceeding. Within the Lewis genetic interval, six dip-elongate, river-dominated, cratonic delta lobes comprise the principal coarse-grained clastic units. However, in the higher Evans interval, five strike-elongate (cuspate) wave-dominated lobes are present on the northwestern rim of the basin. Petrographic evidence from four Mississippi cores associated with delta-plain and delta-front facies in the two sandstone unites indicates a dominance of monocrystalline quartz and chert rock fragments and more a relative absence of orogenic indicators such as polycrystalline quartz, muscovite, and metamorphic rock fragments. Porosity development results largely from the formation of moldic secondary porosity and enlarged intergranular porosity. ![]() Secondary moldic porosity was generated through the dissolution of feldspars and shale fragments.
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