Sustainable Energy, Environment & Particle Technology and Integrated Carbon Capture and Storage Research

Release of heavy metals into Fracking fluid and its novel in-situ treatment using functionalized proppants during shale gas extractionN Situ carbon mineralization in geologic formations

The recent development of hydraulic fracturing and horizontal drilling technologies, and the discovery of abundant reserves of shale gas have led to its use as a preferred energy source in many sectors. While natural gas has a much lower carbon density compared to other fossil energy sources such as coal, there are considerable environmental concerns associated with the generation of shale gas. Particularly the use of large quantity of water for hydraulic fracturing and their post-treatment have been suggested as one of the main challenges for the shale gas extraction. In addition to water, chemicals and proppants are co-injected into geologic formations to increase the extraction of gas and/or oil, and to keep the fractures open for more effective extraction, respectively. Some studies have also reported that the fracturing operations can lead to the leaching of heavy and radioactive metals into the fracking fluid. As a result, there is increasing concerns of the potential contamination of ground water systems and a need for more rigorous treatment for post-fracking fluid. The process of treating fracking water and disposing the heavy metals ex-situ is energy intensive and complicated by fouling of filtration membranes, and is environmentally unsustainable in the long-run. Therefore, research efforts have to be directed towards limiting the demand for water for fracking operations and reducing the heavy metal release into the ground water system. To address these environmental challenges, this study aims to investigate the leaching behaviors of heavy metals from shale, particularly when supercritical CO2 is used as an alternative (waterless) fracking fluid. Next, an in-situ immobilization scheme for any leached heavy metals will be studied via the surface functionalization of proppants using chemical and bio-functional groups with great affinity towards heavy metals. Overall, this study will not only provide a new approach towards environmentally benign shale gas extraction but also foster new fundamental insights into the design and synthesis of novel organic-inorganic hybrid materials based on proppants and their interactions with heavy metal and supercritical CO2 under various environmental conditions. This approach will bring a great paradigm shift in the energy and environmental field since this will allow long-term and sustainable production of shale gas while ensuring the water quality.

In situ heavy metal mobilization

Figure 1: Overall concept of the proposed in-situ heavy metal immobilization using functionalized proppants

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