Levels of Reservoir Heterogeneity in a Mississippi River Meander Belt Sand System

Douglas W. Jordan, Wayne A. Pryor

Six levels of heterogeneity are present in a Mississippi River meander belt sand system near Dorena, Missouri, and these levels can be applied to reservoir description models. On an oil-field scale, the meander belt (13 million acre-ft of which 9 million acre-ft is sand), with its multiple abandoned channels, is the first level of heterogeneity. Level 2, represented by meander loop sands (1.2 million acre-ft) and single abandoned clay-filled channels, is on a stacked reservoir scale. Individual point bars (70,000 acre-ft) with extensive mud sheets (single reservoir or pool scale) constitute level 3. Lobe sheet units (40 acre-ft) of single well scale contain numerous reactivation surfaces and isolated mud drapes and are the fourth level of heterogeneity. Bedding units (< 10 acre-ft) with impervious bedset boundaries, of flow unit or perforated interval scale, constitute level 5. The sixth level of heterogeneity, individual laminae with variations in textural properties (cubic inches), is associated with interparticle fluid flow.

The distribution of permeability barriers and nature of bounding surfaces control vertical and lateral reservoir continuity at the various levels. Poor sorting within and between foreset lamina, as well as infiltrated clay (level 6), are responsible for reducing permeabilities 10-50%. Large planar foresets and trough cross-beds (levels 4 and 5) have permeabilities ranging from 90 to 160 darcys. Permeabilities measured in clayey sand, silt, and sandy silt beds from the levee, crevasse, and abandoned channel fill range from several millidarcys to 50 darcys, and interbedded clayey silt and clay constituting channel plugs, chute fills, and mud sheets (levels 1, 2, and 3) have essentially no permeability.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.