Real-time Aquifer Monitoring for Shale Oil and Gas Extraction
Extraction of hydrocarbons within shale oil and gas formations present different technical and environmental challenges when compared to extraction from conventional hydrocarbons formations. The main concern is related to the use of hydraulic fracturing processes to break apart the rock and release the hydrocarbons. One of the primary environmental issues in relation to this process is the underground water supplies which can become contaminated by chemicals used in the fracking process as well as contaminants (such as methane) released from the shale rock itself.
The most urgent environmental challenge for the European shale oil and gas industry is to be able to demonstrate and guarantee safe exploration and exploitation. Current methods for monitoring the quality of underground water generally rely on manual methods which involve taking samples at hydrological monitoring boreholes and analyzing them in an off-site laboratory. However, the process of collecting, preparing and transporting the water samples is manpower intensive and prone to errors. Moreover, analyzing the samples can take several weeks, allowing pollution to go undetected for a long time. As natural fluctuations occur in the underground water reservoirs, the low sampling frequency of the current monitoring methods makes it difficult to see small systematic changes in the occurrence of especially methane which could arise from pollution from the fracking process.
Hence, there is a clear need to develop and implement a new in-situ technology that can continuously and reliably monitor the underground water quality in real-time which could dramatically reduce the response time in the case of aquifer contamination.
In this contribution, we present the idea and results from the ShaleSafe project (funded from the European Union's Horizon 2020 research and innovation programme, grant agreement No 691527) where an instrumentation system which allows multiple sensor probes to be deployed in hydrological monitoring wells to provide automated real-time monitoring of the several contaminants is developed. These probes are employed in a network and transmit the data wirelessly to the site controller.
The pollutants of interest are mainly volatile organic compounds (VOCs) and methane dissolved in the water. The VOCs cover a broad range of the used chemicals in hydraulic fracturing including among others the biocide additives acrylamide and glutaraldehyde. The equipment developed to measure the concentrations of dissolved methane and VOCs follows the approach of extracting the dissolved gases into the gas phase prior to transduction. This is done by using a membrane characterized by hydrophobic properties and high permeability to methane and VOCs. In addition, each probe is equipped with an electrical conductivity sensor for monitoring salinity of the water which can also be affected by potential contaminants. The first prototypes of sensor probes have been produced and laboratory tests show promising results in regards to detecting potential contaminants.
The increased frequency of readings over manual methods will undoubtedly improve data quality, allowing more accurate trending to be obtained and most importantly dramatically decrease the response time in case of a possible contamination.
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Dr Maj Frederiksen (Danish Technological Institute)
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