Short note: Formation fracturing caused by excessive borehole fluid pressures during drilling in unconsolidated or coastal-plain sediments may be an unknown problem on your project

Abstract

Doug Wyatt was formerly a fellow scientist at the Savannah River Site, working in regional characterizations, facility siting, geotechnical and geophysical studies, and environmental characterization. Wyatt received his Ph.D. in geological sciences from the University of South Carolina and his M.S. degree in geology and geophysics from Vanderbilt University. Wyatt is currently a senior scientist and technical advisor at the National Energy Technology Laboratory.Frank Syms is currently a principal geologist at the Savannah River Site, specializing in geotechnical exploration and characterization. Frank received an M.S. degree and a Ph.D. from the University of South Carolina. During the initial characterization and engineering studies of the Savannah River Site (SRS), performed by the Corps of Engineers, numerous zones of lost circulation, grout take, and rod drop were noted in the unconsolidated coastal-plain sediments. Large foundation-grouting programs (pressure grouting) discovered that intervals of microchanneling and fracturing occurred during pumped grout programs (Aadland et al., 1995; Wyatt, 2000). Ongoing drilling activities at the SRS commonly report zones of lost circulation and rod drop, generally thought to be soft zones (Aadland et al., 1995). In many cases, rod drops and lost circulation are caused by soft zones and possible microchanneling; however, an abundance of cone penetrometer test (CPT) data, combined and correlated with borehole geophysical logs, suggests that many coastal-plain sediments may be subject to hydraulic fracturing during drilling operations. In many cases, environmental drilling contractors or rig site personnel do not routinely measure their drilling fluid pressures or weights, add pump pressures to calculations, or calculate grout pressure on key stratigraphic zones. Hydraulic fracturing may be the cause of some of the lost circulation problems in unconsolidated sediments and may cause problems if key aquitards or confining units are damaged. Comparing and using data from CPT and geophysical data, particularly the formation multitester …