ENVIRONMENTAL IMPACTS OF OIL AND GAS EXPLORATION AND PRODUCTION: GROUND WATER IMPACTS AT OSPER SITES, OSAGE COUNTY, OKLAHOMA

Starting in the 1950s, oil and natural gas became the main sources of primary energy for the increasing World population. The clear benefits of petroleum consumption, however, carry major environmental impacts that range from local to global in scale, including air pollution, global climate change and water contamination. Exploration and production of petroleum have caused detrimental impacts to soils, surface and ground waters, and ecosystems in the 36 producing states in the USA. These impacts arose primarily from the improper disposal of some of the large volumes (~20 billion bbl/yr total) of saline water, with toxic organic and inorganic components, produced with oil and gas; from accidental hydrocarbon and produced water releases; and from the large number (> 2.5 million) of abandoned petroleum wells, some of which were ‘orphaned' or not correctly plugged. Impacts to ground-surface can arise from related activities, such as site clearance, construction of roads, tank batteries, brine pits and pipelines, and other necessary land modifications. For the last five years, we have been investigating the transport, fate, natural attenuation and ecosystem impacts of inorganic and organic compounds in releases of produced water and associated hydrocarbons at the Osage-Skiatook Petroleum Environmental Research (OSPER) sites, located in NE Oklahoma. Approximately 1.0 ha of land at both OSPER “A” (inactive lease) and “B” (active lease) sites, are visibly affected by salt scarring, tree kills, soil salinization, and brine and petroleum contamination. Geochemical data from nearby oil wells show that the produced water source is a Na-Ca-Cl brine (~150,000 mg/L TDS), with high Mg, but low SO₄ and dissolved organic concentrations. Groundwater impacts are being investigated using a variety of methodologies, including detailed chemical analyses of water from repeated sampling of 85 boreholes, 1–71 m deep. The most important results are: 1- A plume of high-salinity water (2,000–30,000 mg/L TDS) extends beyond the visibly impacted areas at OSPER “A”, indicating a large amount of salt remains in the rocks after more than 65 years of natural attenuation; and, 2- produced-water brine and minor dissolved organics have penetrated the thick (3.5-6 m) shale units at OSPER “B”, resulting in three saline ground water plumes.