ELECTRICAL GEOPHYSICAL SURVEYS OF OIL FIELD SALINE WATER CONTAMINATION, OSAGE SKIATOOK PETROLEUM ENVIRONMENTAL RESEARCH SITE, NORTHEASTERN, OKLAHOMA

The first extensive field studies at the Osage Skiatook Petroleum Environmental Research Site (OSPERS), carried out in the fall of 2001, consisted of dc resistivity depth soundings and single frequency electromagnetic (EM) conductivity profiling. The dc resistivity surveys showed that subsurface plumes of contaminated water have resistivities lower than 5 ohm meters (electrical conductivity of 200 millisiemens per meter, ms/m). In contrast, background resistivities were found to be on the order of 50 ohm meters (20 ms/m). Resistivity soundings near the Skiatook Lake shoreline show there is a high conductivity layer overlain by a resistive layer. The high conductivity is likely due to the high TDS ground water in the region whereas the resistive layer is due to fresher waters of the lake and dryer sediments. The ground profiling EM measurements defined a geometrically complex, near surface (within 5m) conductivity anomaly produced by highly-soluble salts that do not always correspond to surface salt scars. Both resistivity soundings and EM measurements suggest that salts contamination has penetrated shale units normally considered aquitards. Drilling was carried out in 2002, based in part on these geophysical results and confirms the basic subsurface electrical interpretation. In August of 2003, depth imaging (multi-frequency) EM profiling and borehole logging was done. The subsurface interpretation of shallow high conductivity correlates well with geophysical induction conductivity logs and mapped the lateral extent of the shallow plumes. By chance repeat EM profiling measurements were made of part of the site before and after a rainstorm when runoff salinity was being monitored. At this time a marked increase in conductivity occurred within a narrow delta at the shore of Skiatook Lake. During May of 2005, EM profiles were completed on land and in the lake along shallows near the shore. Areas of high subsurface conductivity were mapped beneath the lake where an old, submerged, brine disposal pit is located and where previously noted high conductivities from runoff occur.