Research Briefs from Around the Institute

 
From exploring alternative energy sources to developing new technologies for the production, generation, and utilization of energy, the EMS Energy Institute is involved in almost every aspect of energy research. This section highlights the diversity of some of our ongoing projects.

Reservoir Flow Behavior in Coalbed Methane

-- Information Contributed by Shimin Liu

Coalbed methane (CBM) has become an important part of the world’s natural gas resource portfolio. Coal deposits act as self-sourced natural gas reservoirs where the three crucial elements of a petroleum system – source rock, reservoir, and trap – are located together in a single geological unit. Methane is generated during the process of coal formation, either through a biogenic or thermogenic process. The methane is then adsorbed on to the internal surface of the coal matrix or compressed in the void space within the coal.

The energy industry classifies coal as an “unconventional gas reservoir” and has worked continuously on developing methods to economically produce gas from these formations. Because flow behavior through a coalbed methane reservoir is a complex process, a comprehensive understanding of flow dynamics through coal is essential to accurately model and predict gas production.

Gas storage capacity depends on the in situ pressure and adsorbed gas content in the coal and is usually quantified by the Langmuir sorption isotherm, which is established using crushed coal samples in the laboratory. For gas transport to take place in a coal seams the gas is first desorbed or released from the internal coal surface, then the gas is disffused through the coal matrix bounded by the cleat, and finally, the gas flows through the naturally occurring fracture network, known as the cleat system.

Pressure depletion is the standard practice for coalbed methane production. As the name suggests, this process involves depressurizing the coal by pumping water out of the coal seam since most coalbed methane reservoirs are initially saturated. When the pressure in the coal seam falls below a specific level, the methane is released and moved towards the cleat system. In the cleat system, there are three stages for flow in coalbed methane reservoirs: 1) single-phase water flow during dewatering; 2) non-saturated single-phase water flow; and 3) gas and water two phase flow – gas flow starts with further reduction in reservoir pressure and gas relative permeability increases with depletion. The changes in gas/water saturation in cleats result in fluid mobility changes in the cleat system, leading to a unique feature observed during coalbed methane production, a negative gas decline rate. The gas production rate initially increases to a peak production rate as the seam dewaters and the relative permeability to gas increases. After the peak rate is reached, it is followed by a normal decline in production rate as reservoir pressure decreases with continued production.

Shimin Liu, assistant professor of energy and mineral engineering, and his graduate students have established an experimental system to characterize the sorption behavior and estimate the sorption capacity of coal seams, estimate the pressure-dependent diffusivity of the coal, and measure and estimate the apparent permeability of coal with continuous depletion. Currently, Liu is working on a project to characterize the flow behavior of Pennsylvania coals. The results will be used to analyze coalbed methane production and carbon dioxide sequestration potentials in Pennsylvania coal seams, as well as to plan gas drainage systems for safe underground coal mining.

Project Looks at Predicting Fluid Volume and Composition from Shale Reservoirs

-- Information Contributed by John Yilin Wang

Shale gas production is promising in the U.S. and especially in Pennsylvania; however, many of the extraction technologies are relatively new and there is still a lot of uncertainty regarding the environmental impacts and other risks of developing this resource.

John Yilin Wang, assistant professor of petroleum and natural gas engineering, is working with four doctoral students on an integrated approach to make accurate, long-term predictions of fluid volume and composition produced from reservoirs. The work, being done in conjunction with the Department of Energy’s National Energy and Technology Laboratory, will be used to assess the environmental impacts and risks in developing shale gas resources, especially in Marcellus shale formations.

Although samples of flowback fluids taken over a few months provide valuable information for understanding short-term effects, flowback volume and composition is affected by geology, well completion, stimulation treatments, field operations, and other physical mechanisms governing the fluids flow in the reservoirs. For this project, researchers are using integrated methods to understand and rank pertinent factors, including reservoir geology, stimulation, and fluid properties, affecting the volume and composition of produced fluids, such as gas, oil, and water. The goal is to provide a scientific understanding and assessment tools to ensure these key domestic oil and gas resources can be produced safely and in an environmentally sustainable way.

First, researchers use a statistical approach that involves data acquisition and analysis of hundreds of actual Marcellus shale gas wells. Next, researchers use numerical experiments to understand, quantify, and rank the factors affecting hydraulic fracture network propagation, proppant transport and long-term fracture conductivity, and volume and composition of flowback and produced fluids. Using these data, researchers will build a reduced-order model for quick and easy predictions of produced fluids in Marcellus plays.  

This research will inform best practice procedures for improved efficiency and increased reserves in unconventional shale gas reservoirs, such as optimized drilling, well completion, stimulation, production operations, and produced water management. In addition, economic, environmental, and risk assessment of shale gas development will help policy makers during the rapid development of shale gas resources.

 
An example of hydraulic fracture network and width at the end of a stimulation treatment from Wang’s hydraulic fracturing model.
Image contributed by John Yilin Wang

Community Powered Solar Energy Installation

-- Information Contributed by Jeffrey Brownson

One of the major challenges that Central Pennsylvania faces in regards to solar electric is the perception that the region does not have enough sun to support solar as a major energy source. However, our local solar resource data shows that there is abundant sunshine in our region for successful photovoltaic systems. An ongoing project, “Community Solar on State: A Living Laboratory Framework for Outreach, Education, and Research” is taking on the challenge of changing that perception. Jeffrey Brownson, associate professor of energy and mineral engineering and materials science and engineering, along with Susan Stewart, assistant professor of aerospace engineering and architectural engineering, and Rob Cooper, director of energy and engineering for the Office of Physical Plant, are leading the solar project, which combines research with education and outreach to bridge the University, the surrounding community, and alumni.

The project’s goal is to implement and document the integrative design process for a “solar garden” at the Penn State campus and to use the collected information to create an outreach and educational platform that will enable the greater community to move beyond a pilot photovoltaic project and enable additional solar projects as they evolve in the future.

The visibility of a large photovoltaic array at the University will serve as an important signal of a progressive approach to energy and sustainability on campus. In addition, the project is aligned with Penn State’s strategic plan for emissions and would contribute to the continued efforts to reduce our collective greenhouse gas (GHG) impact.

Although the pursuit of a solar energy installation on the Penn State University Park campus has been ongoing for several years, efforts have been decentralized and largely undocumented for the broad base of alumni and the State College area community. This project will consolidate these efforts and provide guidance on how each component can come together to see a community solar project through to fruition. Researchers plan to leverage the Penn State community, State College area residents, and Penn State alumni living in Pennsylvania to support a central photovoltaic installation, separate from their own homes, by purchasing energy through a central energy firm that will manage the installation of the photovoltaic array on the Penn State University Park campus. The Community Solar on State project would be first university and community driven project in Pennsylvania, and perhaps the nation.

Beyond establishing a photovoltaic installation on campus, the goal of this project is to document the design and installation process in order to create online videos, materials, and educational modules as an open resource for future solar project development as well as for K-12 and college learning opportunities. In addition, the photovoltaic installation will serve as a living laboratory and provide hands on experience for student researchers. Currently, researchers are planning an integrative design workshop event to occur at the end of August as the next step in the process.

Image contributed by Jeffrey Brownson