Abstract: James Limestone in Winn and Natchitoches Parishes, Louisiana

Leo A. Herrman

The James Formation of Early Cretaceous age exhibits certain reef-like characteristics within an arcuate trend in Winn and Natchitoches Parishes, Louisiana. The principal limestone varieties within this trend are light-colored pelletal-miliolid calcarenite, pelletal calcarenite, pelmicrite, and caprinid biosparite. On electric logs the limestone is characterized by a leftward excursion of the spontaneous-potential curve giving the zone the massive look of a reef section as much as 300 ft (91 m) thick in one test well. However, the limestone appears to be nonreef in origin. Isopach studies show that it is a detrital deposit which accumulated in low areas. The trend probably contains local patch-reef developments as indicated by the presence of a few caprinid zones, but it oes not appear to be a true reef trend as generally defined.

Southwest, south, and east of the massive trend the James consists principally of interbedded gray argillaceous micrite and gray shale, and on the north and northwest it consists of some combination of interbedded gray micrite, oomicrite, oosparite, quartz sandstone, and gray shale.

The few test wells that have cored the James massive-limestone interval indicate that porosity is generally less than 10 percent, with a range of approximately 4 to 16 percent. Calcite-lined vugs and intergranular openings are the main porosity types. Permeability likewise is generally low, commonly being less than 0.1 md but reaching as high as 50 md in small intervals.

Significant gas shows have been reported from test wells in the James massive-limestone interval. Several combination stratigraphic-structural anomalies are present in the area, making the James a valid target for additional wildcat drilling.

AAPG Search and Discovery Article #90975©1976 GCAGS- GC Section SEPM Annual Meeting Shreveport, Louisiana