The Richfield zone of the lower Middle Devonian Lucas Formation has been a source of significant quantities of hydrocarbons in the north-central and Saginaw Bay area of Michigan. Production through 1980 totaled 91,639,006 bbl of oil.

Prior work, which interpreted the Richfield's environment of deposition to be sabkha, neglected any detailed study of porosity type and distribution within the zone.

Integration of data from core analysis, contemporary geophysical well logs, and thin-section analysis provided a basis for delineating porosity types and porosity distribution within the fields. Porosity type and origin were determined by using the guidelines of Choquette and Pray. Patterns of porosity were mapped within producing fields and presented as "time-slice" contour maps and cross-sectional fence diagrams.

This approach will allow better understanding of the development of porosity in these sabkha carbonates and provides a more reliable method of predicting porosity trends.

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