Advancements in horizontal hydraulic fracturing technologies combined with the exploration of vast unconventional shale resources have led to an energy boom that is rapidly transcending economics of the Appalachian region. Unfortunately, shale development activities are progressing at a rate that is driving new regulatory policies before the possible detrimental effects of these techniques on water resource sustainability are understood. The biological, physical, and chemical properties of the hydrofracking fluids will govern their interaction with pore structures and formation fluids. Understanding the fate and longevity of these fluids is critical to framing our understanding of the risks of these activities to potable water supplies. The objective of this research is to better characterize the biophysiochemical properties of fluids relevant to unconventional shale development, and formulate a risk-based flow and transport model for solving their spatiotemporal distribution in the subsurface. The investigators will examine the physical properties and biodegradability potential of fracking and flowback fluids, and measure the governing physical characteristics of rock cores from unconventional shale and surrounding formations in order to quantitate the constitutive relationships that describe how fluids move through media. The investigators will combine experimentally-derived properties with industry knowledge and a probabilistic fracture hydraulic conductivity to formulate a risk-based flow and transport model capable of predicting fluid movement from shale formations to groundwater aquifers.
This research will help quantify the likelihood that hydrofracking processes occurring at depth could migrate to shallower groundwater aquifers that serve industrial, commercial, or domestic water supplies within a foreseeable time frame. It should also provide insight into how long the fracking fluid compounds would persist in the subsurface environment if they were mobilized from the unconventional shale formations. By integrating experimentally-derived properties with expert knowledge and a transport modeling approach, this research will both advance our understanding of fluid properties used during energy development activities and provide a new tool for practitioners to assess migration risk under a range of hydrogeologic scenarios. The research undertaken in this project will be communicated to a broad range of stakeholders through participation in extension meetings and ongoing workshop forums on shale energy development in the Appalachian region.
Hydraulic fracturing is used to enhance the permeability of geologic units. It has been applied to the extraction of natural gas from deep shale rock formations that are found thousands of feet below the earth’s surface. A literature review revealed that little work has been done to assess the risks associated with horizontal hydraulic fracturing for natural gas extraction. Risk assessments that have been conducted have examined worst case scenarios that do not accurately represent the physical reality of deep shale gas formations and thus do not provide an accurate representation of risk. The model developed for this project is based on generating physically feasible and appropriate representations of reality. This is achieved through the use of random distributions that are based on field observations. Flow of fracking fluids and the transport of contaminants are then calculated through a numerical computer model that is applied to the generated domain. The preliminary model was able to predict flow through fractured media that reasonably approximated the flow distribution and method in which contaminants would be transported. Data on well locations and depths has been collected for New York and Pennsylvania and has been analyzed to determine spatial densities within the states. This information can be used to assess the risk of abandoned wellbores in the region contributing to upward flow of fracturing fluids. Additional data has been collected on fracture propagation lengths caused by hydraulic fracturing as well as the depth of initiation. This data will be used as an input into the model to develop an approximation of how easily water is able to flow within that region. Data on natural fractures within black shales of the New York and Pennsylvania region has also been collected and will be added to the model to represent large scale faults and joints within the system. Primary results from this study have been to determine that the numerical model that we developed is capable of handling flow and transport through fractured media and that a risk analysis based on real data is possible. The current work is on scaling the code to handle the area associated with hydraulic fracturing as well as to run the code with many realizations of the random physical parameters. Results of the preliminary study have been presented at an EPA workshop on hydraulic fracturing. Further results have been presented at the University of Vermont through classroom lectures and presentations to student clubs. Presentations to clubs have focused on hydraulic fracturing, but also on the benefits of conducting research and providing a forum for students to ask questions about what graduate level research involves. Initial results indicate that risk assessment of hydraulic fracturing for natural gas will yield useful results that will help to inform decisions made regarding hydraulic fracturing.
