SUBSURFACE ANALYSIS OF TRIPOLITIC CHERT IN NORTHWEST ARKANSAS

This project involves the subsurface analysis of tripolitic chert using wireline data from gas wells in Northwest Arkansas. The analysis of wireline data (gamma ray, neutron porosity, and resistivity logs) from approximately 75 wells across a 4000 square mile area. The primary project goal is to characterize the Mississippian system with a specific focus on the subsurface distribution of tripolitic chert. Secondary project goals are the correlation of Mississippian gas production to tripolitic chert occurrence and the correlation of subsurface data with adjacent outcrop data.

The Boone Formation of Northwest Arkansas displays a high level of heterogeneity in both the dispersion and the type of chert present within exposed outcrops. Some outcrops consist of mostly limestone with little to no chert present, other outcrops contain 50% ­to 60% chert, and a few outcrops consist of mostly chert with little to no limestone present. There are three different types of chert found within the Boone formation. The three chert types are penecontemporaneous chert (Lower Boone), later diagenetic chert (Upper Boone), and tripolitic chert (Historically placed in Upper Boone).

Although historically the tripolitic chert has been said to occur at the top of the Boone formation recent outcrop studies have raised questions to whether the tripolitic chert occurs in the Upper Boone, Lower Boone, or in the interval between the two. Despite decades of outcrop study, the stratigraphic position of tripolite within the Boone is ambiguous. This difficulty arises from the fact that the complete Boone section is not exposed at any location within the study area. Mapping Boone tripolitic chert in the subsurface has the potential to resolve this long standing problem.