Vertical and Lateral Reservoir Inhomogeneities of a Big-River Bar Deposit, Mississippi River, Missouri

Douglas W. Jordan, Wayne A. Pryor

The Bryant bar, located on the Mississippi River in southeastern Missouri, is a potential sandstone reservoir that is 18,500 ft long, 3,000 ft wide, and 55 ft thick (70,082 ac-ft). A river-meander belt reservoir model was developed from an extensive drilling, coring, trenching, and mapping program. Approximately 2,100 horizontal and vertical gas permeability measurements were made of bedding units in trenches, vibracores, and Shelby and splitspoon cores from a variety of depositional environments within this major sand body.

Permeability increases with an increase in mean grain size, although the presence of infiltrated mud is an important factor in reducing permeabilities. Avalanche sand and gravel foreset beds in large, laterally continuous, sand waves have permeabilities that range from 91 to 138 darcys. Lower bounding surfaces of foreset laminae are typically not as well sorted, and permeabilities are reduced by 10-50%. Tangential foresets of the laterally restricted, lunate sand dunes have permeabilities that range from 90 to 160 darcys.

Permeabilities measured in the interbedded muddy sand, silt, and sandy silt beds from the levee, crevasse, and abandoned channel fill have widely varying permeabilities ranging from 0 to 50 darcys.

Mud and silt beds and laminae are very common between and within bedding units in the point-bar and surrounding environments, and are effective permeability barriers to vertical and horizontal fluid migration within point-bar deposits. The distribution patterns of these permeability barriers significantly control effective reservoir continuity. This river-meander belt reservoir model will enhance the understanding of vertical and lateral inhomogeneities in hydrocarbon and water reservoirs.

AAPG Search and Discovery Article #91041©1987 AAPG Eastern Section Meeting, Columbus, Ohio, October 7-10, 1987.