Datapages, Inc.Print this page

Abstract: Abstract: Regional Diagenetic Trends in Lower Cretaceous Muddy Sandstone, Powder River Basin, Wyoming

William R. Almon, David K. Davies

Lower Cretaceous sandstones of the Muddy Formation have produced significant hydrocarbon reservoirs in the Powder River basin. These reservoir sandstones accumulated in a variety of fluvial, deltaic, and shallow-marine environments. The porosity and permeability of Muddy sandstones are affected significantly by the amount and composition of diagenetic materials. Diagenetic assemblages within the Muddy are time controlled. Oldest Muddy sandstones (zones 5, 6) are characterized by a kaolinite-chlorite-illite-quartz assemblage. Intermediate Muddy sandstones (zones 3, 4) are characterized by a kaolinite-quartz assemblage with sporadic chlorite and illite. Youngest Muddy sandstones (zones 1, 2) are characterized by a kaolinite-quartz assemblage. This diagenetic time trend is m tched by a change in the composition of detrital components. Older Muddy sandstones are more feldspathic and contain more rock fragments and less quartz than the younger sandstones.

Well-stimulation and completion treatments should take into account the diagenetic assemblages present in the reservoir sandstones. In the oldest Muddy sandstones, the rocks tend to be acid sensitive or, occasionally, freshwater sensitive, and there will be migration of fines (kaolinite booklets) during production. In the younger Muddy sandstones, the principal problems will be migration of the fines and stabilizing of the kaolinite.

AAPG Search and Discovery Article #90969©1977 AAPG-SEPM Rocky Mountain Sections Meeting, Denver, Colorado