With the development of unconventional oil and gas exploration, a new technology named hydraulic fracturing (also well-known as fracking) has been used intensively to assist in oil and gas production. The use of fracking generated large volumes of wastewater, which contains high concentrations of potential contaminants.
The wastewaters are termed differently according to their different usage and can be categorized as drill fluid (used to drill through mud and rocks), injection fluid (injected to cause fracture in source rock), original brine (the saline water that pre-existed in the source rock), and returned fluid (including late fracking fluid, flowback water, and produced water — with latter names generally refer to later stages of fluid returning to surface).
These wastewaters are usually hyper-saline with high levels of naturally occurring radioactive materials and heavy metals (see Fig. 1). Examples include sodium (Na), magnesium (Mg), chloride (Cl), bromide (Br), radium (Ra) and barium (Ba). These chemicals can be problematic in various ways. For instance, once mix with sulfate-rich surface water, high concentrations of Ba will precipitate and form scale inside of pipelines to hinder production efficiency.
One thing worth attention is that: although looking at it’s absolute values, Ra concentration is not high at all and is therefore considered a trace chemical in wastewater, the amount of Ra in wastewater is already up to 10,000 times higher than what was allowed in safe natural water suggested by US Environmental Protection Agency. Therefore, the relatively high levels of Ra becomes a severe environmental threat, and this work aims to investigate the potential sources of Ra226 and Ra228 (the most abundant form of Ra found in wastewater).
Here, I have looked into the chemistry report data collected by multiple sources (Department of Environmental Protection, US Geological Survey, and CUAHSI, etc.) and introduced a brief study to the sources and processes that lead to Ra contamination during fracking. This chemistry report data summarizes more than 100,000 records of features. More than 100 categories of records were included in this survey, with examples like:
Radium contamination is determined in four sources: drill fluid, injection fluid, original brine, and rock. Below, I display my understanding on how sources of Ra contamination is partitioned, and then compare two machine learning methods used to relate the sources of Ra contamination with other features.
This content was originally published here.