Multi-Modal Assessment of Salt Contamination from Commercial Hydrocarbon Production

摘要

The largest waste stream in the production of oil and natural gas is co-produced saltwater. Inadequate management of this waste has left an unfortunate and enduring legacy of extensive brine-scarred landscapes in hydrocarbon producing areas of the United States and elsewhere. Assessment of the spatial distribution of soil salinity in areas potentially subjected to saltwater contamination from various oil and gas activities is important for: (1) identifying the origin of contamination and (2) evaluating the size of the impacted area; knowledge essential to designing an effective remedial approach for the salt damage. Such an assessment is accomplished in several ways, including: (1) visual assessment of soil and vegetation characteristics, (2) terrain conductivity surveys, (3) electrical resistivity soundings and (4) soil sampling and analysis. Visual assessment can be useful in identifying areas soil contamination within the root zone; heavily contaminated areas are often devoid of vegetation, less heavily contaminated areas possess vegetation that differs in growth and/or biological diversity from uncontaminated area; areas with somewhat deeper contamination may be unable to support more deeply rooted species. Soil sampling and analysis provides quantitative data concerning the content and constituency of salts present in the sample. Terrain conductivity survey data provides spatially extensive information on soil conductivity averaged over a depth interval of between about three and six meters. Resistivity sounding data provides information on the depth of contamination and its possible impact on local groundwater. Visual assessment is rapid and inexpensive, but can only identify contamination within the root zone. Soil sampling provides specific quantitative data, but can only reflect the soil sampled; mapping of large areas will required a large number of samples. Terrain conductivity surveys and resistivity soundings can be conducted rapidly but require specialized equipment. The most effective assessment of the spatial distribution of salt contamination uses each of the assessment methods to its best advantage. Visual assessment is used to identify probable salt contamination sources and the most heavily contaminated areas. Terrain conductivity surveys and resistivity soundings are used to confirm the visual assessment and to map the geophysically sensible limits of salt contamination. Soil sampling is used to relate the results of the visual assessment and the conductivity survey to specific quantitative salinity data. Here a case study is described that shows how this multi-modal assessment approach was used to develop a soil salinity maps that was used to reach a successful settlement discussion with an oil and gas operator.