Abstract
Public concerns related to the fast-growing shale oil and gas industry have increased during recent years. The major concern regarding shale gas production is the potential of fracturing fluids being injected into the well or produced fluids flowing out of the well to contaminate drinking water resources such as surface water and groundwater. Fracturing fluids contain high total dissolved solids (TDS); thus, changes in TDS concentrations in groundwater might indicate influences of fracturing fluids. An increase of methane concentrations in groundwater could also potentially be due to hydraulic fracturing activities. To understand the possible contamination of groundwater by fracturing activities, real-time groundwater monitoring is being implemented in the Denver-Julesburg basin of northeast Colorado. A strategy of monitoring of surrogate parameters was chosen instead of measuring potential contaminants directly, an approach that is not cost effective or operationally practical. Contaminant surrogates of TDS and dissolved methane were proposed in this study, and were tested for correlation and data distribution with laboratory experiments. Correlations between TDS and electrical conductivity (EC), and between methane contamination and oxidation–reduction potential (ORP) were strong at low concentrations of contaminants (1 mg/L TDS and 0.3 mg/L CH4). Dissolved oxygen (DO) was only an effective surrogate at higher methane concentrations (≥2.5 mg/L). The results indicated that EC and ORP are effective surrogates for detecting concentration changes of TDS and methane, respectively, and that a strategy of monitoring for easy to measure parameters can be effective detecting real-time, anomalous behavior relative to a predetermined baseline.
Highlights
Natural gas has rapidly developed in recent years as an emerging and renewable clean energy source that can replace coal
Based on the well-known relationship of total dissolved solids (TDS) to electrical conductivity (EC) and a study by Atekwana et al (2004), which showed a strong correlation between TDS and EC in an aquifer contaminated with hydrocarbons, this study proposed EC as a surrogate for elevated TDS that would be expected if produced fluids contaminate low-TDS fresh water
In the first continuous flow test of the TDS surrogate experiment (Fig. 2a), where Produced water (PW) 1 was used as a contaminating source of TDS, the mean EC of the background test conducted prior to the experiment was 81.8 lS/ cm with a standard deviation of 0.39 at water temperature of 22.5 ± 0.13 °C
Summary
Natural gas has rapidly developed in recent years as an emerging and renewable clean energy source that can replace coal. Background tests were conducted for 3 days prior to each experiment to stabilize the sensors under the same condition as described above, with the exception of contaminants such as PW and methane. Water quality parameters, such as ORP, EC and pH, collected at the background tests were compared with the results from the experiments. Distributions of ORP data at steady state and background conditions were significantly different, but the DO distribution with an average of 5.93 mg/L and standard deviation of 0.09 and the range of 5.55–6.30 mg/L, was not statistically different than background (average 6.05 mg/L, standard deviation of 0.03, range of 5.93–6.17 mg/L).
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call