State Water Resources Research Institute Program


Project ID: 2011PA159B
Title: Development of a Subsurface Reactive Transport Model for Predicting Potential Water Quality Problems in Marcellus Shale
Project Type: Research
Start Date: 3/01/2011
End Date: 2/29/2012
Congressional District: 5
Focus Categories: Water Quality, Models, Hydrogeochemistry
Keywords: Marcellus shale, reactive transport model, geochemistry, water quality, contamination
Principal Investigators: Li, Li; Brantley, Susan
Federal Funds: $ 18,000
Non-Federal Matching Funds: $ 36,000
Abstract: The development of Marcellus Shale for the production of natural gases is a great economic opportunity for the state of Pennsylvania. At the same time, however, potential environmental problems, including the contamination of surface and subsurface water, could arise from such development. Modern technologies used in the development of tight shale include, for example, advanced drilling and hydraulic fracturing, to enhance formation permeability. These often involve extensive use of gaseous mixtures (such as CO2, N2, methanol) as components of foamed fracturing fluids to energize or stimulate the invaded tight gas formation. High concentration of gases, especially CO2, can lead to acidification of water if leaked from the fracturing wells and therefore change pH, a master variable that can trigger various reactions and result in the deterioration of water quality. These reactions include, for example, mineral dissolution and precipitation, sorption / desorption, and ion exchange. In addition, opening of subsurface for gas production can expose the subsurface to O2, which can lead to the oxidation of sulfide minerals (e.g., pyrite) that is abundant in Marcellus Shale and results in acid-generating reactions that have caused problems along I-99. Because the reactions usually occur simultaneously with flow and transport processes, it is important to develop a model that couples these processes, with the ultimate goal of predicting and managing potential water quality problems related to the development of Marcellus Shale.

Here we propose to develop a reactive transport model to advance our understanding on potential water quality issues associated with Marcellus Shale development. We will base our model on existing generic reactive transport code CrunchFlow (Steefel and Maher, 2009). CrunchFlow has been used widely to understand flow, transport, and reaction processes involved in chemical weathering, environmental remediation, and geological carbon sequestration. In addition, we have soil and aqueous geochemistry data collected by Dr. Ryan Mathur's students in Juniata College at Huntingdon, PA, as part of research within the Shale Hills Critical Zone Observatory (CZO). We will use these data to validate our model, to set up the mineralogy and aqueous geochemistry of the site, and to identify the most important suite of reactions that can control the groundwater quality at Marcellus Shale. Some of the metals that are common at the site, such as copper, zinc, iron, can be used as metal fingerprints for water quality deterioration.

The outcomes of the proposal will include a generic reactive transport model that couple flow, transport, and multiple reaction processes. The outcome will also include a database for the Marcellus Shale mineralogy and a suite of reactions, including their thermodynamic and kinetic data, that control the weathering of the Marcellus Shale rocks and that determine the water quality. The model can be used to understand and quantify the impact of Marcellus Shale development on groundwater quality under various development conditions. It can also help predict and manage the water quality problems. If time allows we will also play with various "what if" scenarios to understand the possibility of leakage of drilling or fracturing fluids into natural or stimulated fractures, and the impacts of leakage on aqueous geochemistry. It will also help us identify the development conditions under which largest / least impacts on water quality will occur. We expect that the sulfide oxidation reactions in the Marcellus Shale are similar to acid generating reactions that have caused problems along I-99. Therefore, this work would also set us up for future investigation of environmental problems along I-99.

Progress/Completion Report, 2011, PDF

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