“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 is

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 m3 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 transport their wastes via trucks or barges 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 horizontally and are 

hydraulically fractured.
- Barium sulfate precipitation 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 accumulate 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 of 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. Warner 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 remove 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.