Using the Cone Penetrometer Tool to Evaluate Depositional Character: Examples from the South Carolina Coastal Plain

Wyatt, Douglas E.¹, Frank H. Syms², Randy Cumbest³ (1) Washington Group International, Aiken, SC (2) Lettis and Associates, North Augusta, SC (3) Washington Savannah River Company, Aiken, SC

The cone penetrometer technique is widely used in shallow geotechnical and engineering geology studies. This technique is effective primarily in unconsolidated sediments but provides a high resolution profile of independent measurements that can yield lithologic and depositional data. These data can be interpreted to develop detailed stratigraphic and depositional models of sand and clay bodies, lithologic interfaces, and possibly indicate depositional and diagenetic character that may not be typically available. The high vertical resolution provides a significant advantage that is not preserved in unconsolidated sediment core recovery or visible from coastal plain style outcrop examples.

A cone penetrometer data set includes three parameters; tip resistance: a direct resistance to penetration that can be related to the strength; sleeve friction: an indication of the stiffness or cohesive nature of the sediment; pore pressure: an indication of the tightness of the formation that can be related to hydrologic properties. These parameters can be used to interpret lithologic information that can then be extrapolated into depositional patterns as a basis for building a high resolution depositional model. Additionally, electrical resistivity, acoustic data, moisture or dielectric, and natural gamma data are collected. These data allow unique internal maps of sand body relationships and features to be made. This level of detail is usually not available for deeper reservoir studies.

Examples are presented from the tidal, subtidal, deltaic, Miocene and Eocene Coastal Plain of South Carolina. Detailed characteristics are found in these sediments that might be preserved during deeper burial and reservoir charging.