“Unconventional Drilling/Hydraulic Fracturing and Natural Radioactivity” Webinar

Webinar Date: June 5, 2014 Hosted by: U.S. Department of Energy ( U.S. DOE) as part of the National Analytical Management Program (NAMP) Presentation by: Dr. Michael K. Schultz and Mr. Andy Nelson , University of Iowa

Mr. Nelson is currently studying radioactive elements in unconventional oil and gas (UOG) production Introduction

1 . Recently, there has been an increased demand for global energy and natural gas i s one option for meeting that demand. This webinar will discuss radioactivity in unconventional oil and gas wastes, with a specific focus on the Marcellus shale formation.

The following are examples of ways in which radiochemistry is relevant and of concern in UOG production and well development: Relevance of Radiochemistry in UOG Production

- UOG production uses up to 55,000 m 3 of water per well and recycling fluids for reuse in hydraulic fracturing can result in elevated concentrations of radioactive elements in the recycled fluid.

- The chemicals that are added to hydraulic fracturing fluid prior to downhole injection may interact with naturally occurring radioactive materials (NORM).

- Horizontally drilled wells have larger volumes of bit cuttings

, which are generated during the well drilling stage of well development

. Bit cuttings may be enriched in organics and NORM. In some instances, landfills have refused to accept drilling cuttings because the measured radioactivity is too high.

- Operators who tran sport their wastes via trucks or barge s may have concerns about spills of wastes containing high NORM concentrations. Another concern is the potential that
radon will buildup in closed trucks or other closed transportation vehicles.

- Gamma ray spectroscopy is a good method to use to measure radium 226 and radium
228

. Measuring Radioactivity

- Since radium does not emit alpha rays, alpha ray spectroscopy would not be a valid
measurement method.

- Radon emanation is another good method of quantifying radium 226 in UOG wastewater. In radon emanation, radium 226 is stored for 30 days and the radon 222 gas that is emitted out of solution is measured. The Rad7 is one type of portable machine that uses
the radon emanation measurement method.

1 Mr. Nelson referred to unconventional oil and gas (UOG) wells as any wells that are drilled horizo ntally and are hydraulically fractured.- Barium sulfate precipitat ion may not work well for measuring radium in UOG
wastewater because the barium out

- competes the radium for sulfate ions. For similar reasons, using manganese dioxide and the Rad Disk method may not work well for measuring radium in UOG wastewater samples. In general, wet chemistry methods are not good for quantifying radium in UOG wastewater.

- Radium 226 is a decay product of uranium 238. Radium 226 and Other Radioactive Isotopes

- Radium 226 may have increased solubility in environments with high ionic brine strength. Radium 226 also has increased solubility in environments with low sulfate concentrations. UOG formations may have low sulfate concentrations because of the presence of naturally

- occurring sulfate reducing bacteria.

- Radon 222 can sorb to organics and become concentrated in UOG brine. Extensive research on the presence of radon 222 in UOG waste has not been conducted. Lead 210
can sorb to minerals and thus also accumulat e in UOG brine.

- Uranium 235 is the primary source of radiation in the Marcellus shale formation. Radiochemistry in the Marcellus Shale

- In general, radioactive elements in natural gas formations exist as a result of ancient
marine formations. These formations typically contain large amounts of organic matter, which typically correlates to large amounts of radioactivity. These formations also typically contain large amounts of dissolved salts.

- Studies have shown that uranium concentrations are low in flowback. Uranium 234 is more enriched than uranium 238 in flowback because of alpha recoil enrichment.

- Thorium 230 and thorium 232 have very low (or zero) concentrations in flowback, likely because they are insoluble. Researchers have seen the presence o f thorium 228 in samples, likely as a result of the decay of radium 228. Researchers have used thorium 230 in experiments as a tracer in order to subtract from the concentration of thorium 228.

- Uranium 238, uranium 234, and the thorium decay series likely are extracted from the formation in the drilling cuttings.

- At the beginning of the flowback period, it is likely that only radium 226 and/or radium 228 are present in flowback. However, over time, radium 226 and/or radium 228 decay products will form. War ner et al. (2013) published a study noting that radium decay products can have very different properties than radium. It is important to know what isotopes exist in a waste stream when determining how to treat it. The same treatment
cannot be used to remov e radium and radium decay products from a waste stream. For example, lead 210 can be difficult to detect using gamma ray methods, but can be very harmful if left untreated. In other words, operators should not only be concerned with radioactive isotopes in their waste streams, but also with the decay products of those radioactive isotopes.