Surface and Downhole Geophysics for Determination of Light Non-Aqueous Phase Liquid Migration in Faulted Dolomite
Monday, December 4, 2017
The determination of LNAPL migration and groundwater flow patterns by identifying and mapping subsurface preferential pathways such as faults, fractures, air/water-filled voids, or solution cavities that may impact groundwater movement is crucial from both an environmental and engineering perspective. The primary goal of this research was to determine the feasibility of detecting LNAPL migration in a highly-weathered and faulted dolomitic environment through a combination of surface electrical resistivity imaging (ERI) and induced polarization (IP) methods, and a detailed suite of borehole geophysical logs. Appropriate ERI and IP electrode geometries have been taken into account for a target depth of approximately 130-feet bgs. Surface geophysical data have been integrated with downhole geophysical data from eight wells that include electric (8”, 16”, 32”, and 64” normal resistivity), natural gamma, fluid resistivity, temperature, optical televiewer, caliper, and heat pulse flow meter logs. These data were compared to structural geologic features identified with ERI and IP data to determine preferential pathways in which both groundwater and LNAPL likely migrate throughout this site. A second goal of this research was examine the observe any variations in ERI, IP, and borehole geophysical responses over areas which contain documented LNAPL in large, known volumes, and infer whether these variations in geophysical responses are caused by the significant LNAPL presence. This research discusses observed variations in both surface and downhole geophysical responses and how these variations relate to interpreted subsurface structural features and LNAPL migration.