The Effect of the Northern Drilling

A deep subsurface rock core for paleoclimate reconstruction was collected in October and November 2007 during the South McMurdo Sound Project (SMS) of the Antarctic Geological Drilling Program (ANDRILL). To allow for deeper penetration and more efficient core recovery, water-based saline drilling fluids were utilized. A total of 5.6x105 L of fluids was lost in the subsurface. The fluid was comprised of surface seawater from the sound, as the wetting agent mixed with densifying compounds (mainly potassium chloride and small amounts of fourteen other compounds including biodegradable organics). When exploring pristine locations a main goal needs to be minimizing the amount of biological and chemical contamination. Introducing a contaminant such as drilling fluids could negatively alter the in situ conditions; affecting the environment even after the exploring party has departed the system. The fate of contamination on the subsurface environment from invasive exploration methods into pristine environments is not well known. In this study, computer models (MODFLOW, SEAWAT) that are used by hydrogeologists to establish the fate and transport of contamination were utilized to determine the extent of the drilling fluid contamination from the sea floor to 1100 mbsf. In these models, previously collected logs for lithology, porosity, fracture density, drilling fluid loss, drilling fluid characteristics, and temperature were used as different parameters in the model. In addition, biodegradation and sorption constants for the drilling fluid were determined. These factors are important to determine the extent and half-life of the drilling fluids in the subsurface. Samples of drilling fluids used during coring and return fluids were collected from the drill site and were used to determine the biodegradation of the drilling fluids. The overall goal of this research project is to utilize the rich data set provided by SMS ANDRILL and some basic