Partitioning of naturally-occurring radionuclides (NORM) in Marcellus Shale produced fluids influenced by chemical matrix

Threshold values for the protection of marine ecosystems from NORM in subsea oil and gas infrastructure

This modelling study uses the ERICA Tool and Bateman's equation to derive sediment threshold values for radiation protection of the marine environment relevant to NORM-contaminated products (radium-contaminated scales, ²¹⁰Pb films and ²¹⁰Po films) found in subsea oil and gas infrastructure. Threshold values are calculated as the activity concentration of the NORM-contaminated products' head of chain radionuclide (i.e., ²²⁶Ra + ²²⁸Ra, ²¹⁰Pb, or ²¹⁰Po) that will increase radiation dose rates in sediments by 10 μGy/h to the most exposed organism at a given release time. The minimum threshold value (corresponding to peak radiation dose rates from the ingrowth of progeny) were for radium-contaminated scales, 0.009 Bq/g of ²²⁶Ra, 0.029 Bq/g of ²²⁸Ra (in the absence of ²²⁶Ra) or 0.14 Bq/g of ²²⁸Ra (in the presence of ²²⁶Ra), followed by 0.015 Bq/g for ²¹⁰Pb films, and 1.6 Bq/g for ²¹⁰Po films. These may be used as default threshold values. Added activity concentrations of the NORM-contaminated products to marine sediments below these threshold values implies a low radiological risk to organisms while exceedances imply that further investigation is necessary. Using contaminated product specific parameterisations, such as K_d values derived for Ra from a BaSO₄ matrix in seawater, could greatly affect threshold values. Strong consideration should be given to deriving such data as part of specific radiological risk assessments for these products.

Estimating Radium Activity in Shale Gas Produced Brine

Shale gas reservoir-produced brines may contain elevated levels of naturally occurring radioactive material, including Ra-226 and Ra-228, which come from the decay of U-238 and Th-232 in shale. While the total Ra activity in shale gas wastewaters can vary by over 3 orders of magnitude, the parent radionuclides tend to only vary by 1 order of magnitude. The extent of Ra mobilization from the shale into produced brines is thought to be largely controlled by adsorption/desorption from the shale, which is influenced by shale cation exchange capacity (CEC) and reservoir brine salinity, often reported as the total dissolved solids (TDS). To determine how these factors lead to such large variation in Ra activity of produced brines, the U content and CEC of shale samples from the Antrim and Utica-Collingwood shales in Michigan and the Marcellus shale in Pennsylvania were evaluated. Analysis of produced brine from 17 Antrim shale gas wells was then used to develop an empirical relationship between Ra-226 activity and produced water TDS for a given U content of the shale. This correlation will provide an a priori estimate of the expected Ra activity of a produced brine from a given shale gas play when the brine salinity and U content of the shale are known. Such information can serve as a guide for optimal wastewater treatment and disposal strategies prior to any drilling activity, thereby reducing risks associated with elevated Ra activity in shale gas wastewaters.

Holistic risk assessment of surface water contamination due to Pb-210 in oil produced water from the Bakken Shale

A holistic risk assessment of surface water (SW) contamination due to lead-210 (Pb-210) in oil produced water (PW) from the Bakken Shale in North Dakota (ND) was conducted. Pb-210 is a relatively long-lived radionuclide and very mobile in water. Because of limited data on Pb-210, a simulation model was developed to determine its concentration based on its parent radium-226 and historical total dissolved solids levels in PW. Scenarios where PW spills could reach SW were analyzed by applying the four steps of the risk assessment process. These scenarios are: (1) storage tank overflow, (2) leakage in equipment, and (3) spills related to trucks used to transport PW. Furthermore, a survey was conducted in ND to quantify the risk perception of PW from different stakeholders. Findings from the study include a low probability of a PW spill reaching SW and simulated concentration of Pb-210 in drinking water higher than the recommended value established by the World Health Organization. Also, after including the results from the risk perception survey, the assessment indicates that the risk of contamination of the three scenarios evaluated is between medium-high to high.