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Electric logs from wells in southwestern Clarke County, Mississippi, illustrate the structural and stratigraphic relations which affect hydrocarbon production. The fields studied (West Nancy, Nancy, East Nancy, Prairie Branch, and Lake Utopia) are coincident with salt-cored structures and are aligned from northwest to southeast, parallel with the updip limit of the salt. Production depths increase basinward and southwesterly. The fields produce from primary porosity in oolitic grainstones of the upper Smackover Formation. Prairie Branch and East Nancy also produce from siliciclastic sands of the underlying Norphlet Formation, whereas West Nancy has additional production from oolitic grainstones of the overlying Buckner Member of the Haynesville Formation.
The general depositional sequence that controlled hydrocarbon accumulations is: deposition of siliciclastic sands of the Norphlet; accumulation of carbonate muds of the lower Smackover and initiation of salt movement; and formation of offlapping shingles of oolite sands of the upper Smackover on faulted salt-cored structures. Structural movement was complete by the end of Haynesville deposition. Hydrocarbon migration most likely occurred during Haynesville deposition, because most Smackover and Norphlet pay zones coincide with Smackover highs and not with Haynesville structures.
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