Millennium EMS Solutions Ltd.
March 2017
Executive Summary
This report was funded by Petroleum Technology Alliance Canada (PTAC) under project # 16-SGRC-02. It builds upon research from a former PTAC Project, 13-AU-SGRC-04, and the reader is referred to that report for additional supporting detail.
Current analytical techniques allow for convenient and simultaneous analysis of a wide range of metals in environmental samples. Groundwater monitoring programs at upstream oil and gas wellsites in Alberta often track a large number of individual metals. Some of these metals may be present in significant concentrations in oilfield drilling fluids or in produced formation waters. Oilfield drilling fluids may remain on site after well drilling is complete, and accidental releases of produced formation waters may occur. Accordingly, metals that are typically present at higher concentrations in oilfield drilling fluids or in produced formation waters are more likely to result in anthropogenic increases in metal concentrations in shallow wellsite groundwater than other metals. In addition, certain metals may be mobilized into groundwater as a natural by-product of the biodegradation of hydrocarbons or other organic chemicals that may be present on an oilfield wellsite as a result of anthropogenic activities. This summary report identifies groundwater metals that have a plausible source related to anthropogenic activities at oilfield wellsites.
A concentration of a metal in shallow groundwater that exceeds the Tier 1 groundwater guideline does not necessarily imply an anthropogenic source. For many metals, the natural range of background concentrations in shallow groundwater exceeds the Tier 1 groundwater guideline value. A related PTAC project, # 16-SGRC-05, being completed by Millennium EMS Solutions Ltd., is currently developing statistical distributions for natural concentrations of trace metals in shallow Alberta groundwater, and will be helpful in distinguishing anthropogenic from natural influences on groundwater metals concentrations.
This project gave consideration to which metals in shallow groundwater could potentially have an anthropogenic source at a typical oil or gas wellsite. Metals that could have sufficiently high concentrations in drilling mud components and/or formation waters to be of concern were identified. Metals that could potentially be released into shallow groundwater as a by-product of the biodegradation of organic compounds were also considered. The potential issue of the mobilization of metals into groundwater as a result of a release of saline produced water and the associated ion exchange of metal ions from clay surfaces was investigated but shown not to be a concern.
A total of 10 metals were identified as having the potential for significantly elevated groundwater concentrations resulting from anthropogenic activities at oilfield wellsites. These metals are summarized in Table A.
It should be noted that the presence of any one of these metals in shallow groundwater at an oilfield wellsite at a concentration above the Tier 1 guideline does not necessarily imply an anthropogenic source, since background concentrations of these metals frequently exceed Tier 1 guideline values. Some qualitative information relating to this issue was summarized in this report, but the reader is directed to a parallel project (PTAC 16-SGRC-05) for more quantitative information on the range of background metal concentrations in shallow groundwater.
# 16-SGRC-02 / 17-SGRC-07