New study measures methane emissions from natural gas production and offers insights into 2 large sources

A team of researchers from the Cockrell School of Engineering at The University of Texas at Austin and environmental testing firm URS reports that a small subset of natural gas wells are responsible for the majority of methane emissions from two major sources — liquid unloadings and pneumatic controller equipment — at natural gas production sites.

With natural gas production in the United States expected to continue to increase during the next few decades, there is a need for a better understanding of methane emissions during natural gas production. The study team believes this research, published Dec. 9 in Environmental Science & Technology, will help to provide a clearer picture of methane emissions from natural gas production sites.

The UT Austin-led field study closely examined two major sources of methane emissions — liquid unloadings and pneumatic controller equipment — at well pad sites across the United States. Researchers found that 19 percent of the pneumatic devices accounted for 95 percent of the emissions from pneumatic devices, and 20 percent of the wells with unloading emissions that vent to the atmosphere accounted for 65 percent to 83 percent of those emissions.

“To put this in perspective, over the past several decades, 10 percent of the cars on the road have been responsible for the majority of automotive exhaust pollution,” said David Allen, chemical engineering professor at the Cockrell School and principal investigator for the study. “Similarly, a small group of sources within these two categories are responsible for the vast majority of pneumatic and unloading emissions at natural gas production sites.”

Additionally, for pneumatic devices, the study confirmed regional differences in methane emissions first reported by the study team in 2013. The researchers found that methane emissions from pneumatic devices were highest in the Gulf Coast and lowest in the Rocky Mountains.

The study is the second phase of the team’s 2013 study, which included some of the first measurements for methane emissions taken directly at hydraulically fractured well sites. Both phases of the study involved a partnership between the Environmental Defense Fund, participating energy companies, an independent Scientific Advisory Panel and the UT Austin study team.

The unprecedented access to natural gas production facilities and equipment allowed researchers to acquire direct measurements of methane emissions.

Study and Findings on Pneumatic Devices

Pneumatic devices, which use gas pressure to control the opening and closing of valves, emit gas as they operate. These emissions are estimated to be among the larger sources of methane emissions from the natural gas supply chain. The Environmental Protection Agency reports that 477,606 pneumatic (gas actuated) devices are in use at natural gas production sites throughout the U.S.

“Our team’s previous work established that pneumatics are a major contributor to emissions,” Allen said. “Our goal here was to measure a more diverse population of wells to characterize the features of high-emitting pneumatic controllers.”

The research team measured emissions from 377 gas actuated (pneumatic) controllers at natural gas production sites and a small number of oil production sites throughout the U.S.

The researchers sampled all identifiable pneumatic controller devices at each well site, a more comprehensive approach than the random sampling previously conducted. The average methane emissions per pneumatic controller reported in this study are 17 percent higher than the average emissions per pneumatic controller in the 2012 EPA greenhouse gas national emission inventory (released in 2014), but the average from the study is dominated by a small subpopulation of the controllers. Specifically, 19 percent of controllers, with measured emission rates in excess of 6 standard cubic feet per hour (scf/h), accounted for 95 percent of emissions.

The high-emitting pneumatic devices are a combination of devices that are not operating as designed, are used in applications that cause them to release gas frequently or are designed to emit continuously at a high rate.

The researchers also observed regional differences in methane emission levels, with the lowest emissions per device measured in the Rocky Mountains and the highest emissions in the Gulf Coast, similar to the earlier 2013 study. At least some of the regional differences in emission rates can be attributed to the difference in controller type (continuous vent vs. intermittent vent) among regions.

Study and Findings on Liquid Unloadings

After observing variable emissions for liquid unloadings for a limited group of well types in the 2013 study, the research team made more extensive measurements and confirmed that a majority of emissions come from a small fraction of wells that vent frequently. Although it is not surprising to see some correlation between frequency of unloadings and higher annual emissions, the study’s findings indicate that wells with a high frequency of unloadings have annual emissions that are 10 or more times as great as wells that unload less frequently.

The team’s field study, which measured emissions from unloadings from wells at 107 natural gas production wells throughout the U.S., represents the most extensive measurement of emissions associated with liquid unloadings in scientific literature thus far.

A liquid unloading is one method used to clear wells of accumulated liquids to increase production. Because older wells typically produce less gas as they near the end of their life cycle, liquid unloadings happen more often in those wells than in newer wells. The team found a statistical correlation between the age of wells and the frequency of liquid unloadings. The researchers found that the key identifier for high-emitting wells is how many times the well unloads in a given year.

Because liquid unloadings can employ a variety of liquid lifting mechanisms, the study results also reflect differences in liquid unloadings emissions between wells that use two different mechanisms (wells with plunger lifts and wells without plunger lifts). Emissions for unloading events for wells without plunger lifts averaged 21,000 scf (standard cubic feet) to 35,000 scf. For wells with plunger lifts that vent to the atmosphere, emissions averaged 1,000 scf to 10,000 scf of methane per event. Although the emissions per event were higher for wells without plunger lifts, these wells had, on average, fewer events than wells with plunger lifts. Wells without plunger lifts averaged fewer than 10 unloading events per year, and wells with plunger lifts averaged more than 200 events per year.Overall, wells with plunger lifts were estimated to account for 70 percent of emissions from unloadings nationally.

Additionally, researchers found that the Rocky Mountain region, with its large number of wells with a high frequency of unloadings that vent to the atmosphere, accounts for about half of overall emissions from liquid unloadings.

The study team hopes its measurements of liquid unloadings and pneumatic devices will provide a clearer picture of methane emissions from natural gas well sites and about the relationship between well characteristics and emissions.

The study was a cooperative effort involving experts from the Environmental Defense Fund, Anadarko Petroleum Corporation, BG Group PLC, Chevron, ConocoPhillips, Encana Oil & Gas (USA) Inc., Pioneer Natural Resources Company, SWEPI LP (Shell), Statoil, Southwestern Energy and XTO Energy, a subsidiary of ExxonMobil.

The University of Texas at Austin is committed to transparency and disclosure of all potential conflicts of interest of its researchers. Lead researcher David Allen serves as chair of the Environmental Protection Agency’s Science Advisory Board and in this role is a paid Special Governmental Employee. He is also a journal editor for the American Chemical Society and has served as a consultant for multiple companies, including Eastern Research Group, ExxonMobil and the Research Triangle Institute. He has worked on other research projects funded by a variety of governmental, nonprofit and private sector sources including the National Science Foundation, the Environmental Protection Agency, the Texas Commission on Environmental Quality, the American Petroleum Institute and an air monitoring and surveillance project that was ordered by the U.S. District Court for the Southern District of Texas. Adam Pacsi and Daniel Zavala-Araiza, who were graduate students at The University of Texas at the time this work was done, have accepted positions at Chevron Energy Technology Company and the Environmental Defense Fund, respectively.

Financial support for this work was provided by the Environmental Defense Fund (EDF), Anadarko Petroleum Corporation, BG Group PLC, Chevron, ConocoPhillips, Encana Oil & Gas (USA) Inc., Pioneer Natural Resources Company, SWEPI LP (Shell), Statoil, Southwestern Energy and XTO Energy, a subsidiary of ExxonMobil.

Major funding for the EDF’s 30-month methane research series, including their portion of the University of Texas study, is provided for by the following individuals and foundations: Fiona and Stan Druckenmiller, the Heising-Simons Foundation, Bill and Susan Oberndorf, Betsy and Sam Reeves, the Robertson Foundation, TomKat Charitable Trust and the Walton Family Foundation.

Geologists dig into science around the globe, on land and at sea

University of Cincinnati geologists will be well represented among geoscientists from around the world at The Geological Society of America’s Annual Meeting and Exposition. The meeting takes place Oct. 19-22, in Vancouver, Canada, and will feature geoscientists representing more than 40 different disciplines. The meeting will feature highlights of UC’s geological research that is taking place globally, from Chile to Costa Rica, Belize, Bulgaria, Scotland, Trinidad and a new project under development in the Canary Islands.

UC faculty and graduate students are lead or supporting authors on more than two dozen Earth Sciences-related research papers and/or PowerPoint and poster exhibitions at the GSA meeting.

The presentations also cover UC’s longtime and extensive exploration and findings in the Cincinnati Arch of the Ohio Valley, world-renowned for its treasure trove of paleontology – plant and animal fossils that were preserved when a shallow sea covered the region 450 million years ago during the Paleozoic Era.

Furthermore, in an effort to diversify the field of researchers in the Earth Sciences, a UC assistant professor of science education and geology, Christopher Atchison, was awarded funding from the National Science Foundation and the Society of Exploration Geophysics to lead a research field trip in Vancouver for students with disabilities. Graduate and undergraduate student participants will conduct the research on Oct. 18 and then join events at the GSA meeting. They’ll be guided by geoscience researchers representing the United Kingdom, New Zealand, Canada and the U.S. Those guides include Atchison and Julie Hendricks, a UC special education major from Batavia, Ohio, who will be using her expertise in American Sign Language (ASL) to assist student researchers representing Deaf and Hard of Hearing communities.

The meeting will also formally introduce Arnold Miller, UC professor of geology, as the new president-elect of the national Paleontological Society Thomas Lowell, professor of geology, is a recently elected Fellow of the Geological Society of America – a recognition for producing a substantial body of research. Lowell joins colleagues Warren Huff, professor of geology, and Lewis Owen, professor and head of the Department of Geology, as GSA Fellows.

Here are highlights of the UC research to be presented at the GSA meeting Oct. 19-22:

Staying Put or Moving On? Researchers Develop Model to Identify Migrating Patterns of Different Species

Are plant and animal species what you might call lifelong residents – they never budge from the same place? That’s a relatively common belief in ecology and paleoecology – that classes of organisms tend to stay put over millions of years and either evolve or go extinct as the environment changes. UC researchers developed a series of numerical models simulating shifting habitats in fossil regions to compare whether species changed environments when factoring geological and other changes in the fossil record. They found that geologically driven changes in the quality of the fossil record did not distort the real ecological signal, and that most species maintained their particular habitat preferences through time. They did not evolve to adapt to changing environments, but rather, they migrated, following their preferred environments. That is to say, they did not stay in place geographically but by moving, they were able to track their favored habitats. Field research for the project was conducted in New York state as well as the paleontological-rich region of Cincinnati; Dayton, Ohio, Lexington, Ky.; and Indiana. Funding for the project was supported by The Paleontological Society; The Geological Society of America; The American Museum of Natural History and the UC Geology Department’s Kenneth E. Caster Memorial Fund.

Presenter: Andrew Zaffos, UC geology doctoral student

Co-authors: Arnold Miller, Carlton Brett

Pioneering Study Provides a Better Understanding of What Southern Ohio and Central Kentucky Looked Like Hundreds of Millions of Years Ago

The end of the Ordovician period resulted in one of the largest mass extinction events in the Earth’s history. T.J. Malgieri, a UC master’s student in geology, led this study examining the limestone and shales of the Upper Ordovician Period – the geologic Grant Lake Formation covering southern Ohio and central Kentucky – to recreate how the shoreline looked some 445 million years ago. In this pioneering study of mud cracks and deposits in the rocks, the researchers discovered that the shoreline existed to the south and that the water became deeper toward the north. By determining these ecological parameters, the ramp study provides a better understanding of environments during a time of significant ecological change. Malgieri says the approach can be applied to other basins throughout the world to create depth indicators in paeloenvironments.

Presenter: T.J. Malgieri, UC geology master’s student

Co-authors: Carlton Brett, Cameron Schalbach, Christopher Aucoin, UC; James Thomka (UC, University of Akron); Benjamin Dattilo, Indiana University Purdue University Ft. Wayne

UC Researchers Take a Unique Approach to Monitoring Groundwater Supplies Near Ohio Fracking Sites

A collaborative research project out of UC is examining effects of fracking on groundwater in the Utica Shale region of eastern Ohio. First launched in Carroll County in 2012, the team of researchers is examining methane levels and origins of methane in private wells and springs before, during and after the onset of fracking. The team travels to the region to take water samples four times a year.

Presenter: Claire Botner, a UC geology master’s student

Co-author: Amy Townsend-Small, UC assistant professor of geology

Sawing Through Seagrass to Reveal Clues to the Past

Kelsy Feser, a UC doctoral student in geology, is working at several sites around St. Croix in the Virgin Islands to see if human developments impact marine life. The research focuses on shells of snails and clams that have piled up on the sea floor for thousands of years. Digging through layers of thick seagrass beds on the ocean floor, Feser can examine deeper shells that were abundant thousands of years ago and compare them to shallower layers that include living clams and snails. Early analysis indicates a greater population of potentially pollution-tolerant mussels in an area near a landfill on the island, compared with shells from much earlier time periods. Feser is doing this sea grass analysis around additional sites including tourist resorts, an oil refinery, a power plant and a marina. Funding for the research is provided by the Paleontological Society, the GSA, the American Museum of Natural History and the UC Geology Department.

Presenter: Kelsy Feser, UC geology doctoral student

Co-authors: Arnold Miller

Turning to the Present to Understand the Past

In order to properly interpret changes in climate, vegetation, or animal populations over time, it is necessary to establish a comparative baseline. Stella Mosher, a UC geology master’s student, is studying stable carbon, nitrogen, sulfur and strontium isotopes in modern vegetation from the Canary Islands in order to quantify modern climatic and environmental patterns. Her findings will provide a crucial foundation for future UC research on regional paleoclimatic and paleoenvironmental shifts.

Presenter: Stella Mosher, graduate student in geology

Co-authors: Brooke Crowley, assistant professor of geology; Yurena Yanes, research assistant professor of geology

A Study on the Impact of Sea Spray

Sulfur is an element of interest in both geology and archaeology, because it can reveal information about the diets of ancient cultures. This study takes a novel approach to studying how sea spray can affect the sulfur isotope values in plants on a small island, focusing on the island of Trinidad. Researchers collected leaves from different plant species to get their sulfur isotope value, exploring whether wind direction played a role in how plants were influenced by the marine water from sea spray. Vegetation was collected from the edges of the island to the deeply forested areas. The study found that sulfur isotope values deeper inland and on the calmer west coast were dramatically lower in indicating marine water than vegetation along the edges and the east coast. The findings can help indicate the foraging activities of humans and animals. Funding for the study was supported by the Geological Society of America, the UC Graduate Student Association and the UC Department of Geology.

Presenter: Janine Sparks, UC geology doctoral student

Co-authors: Brooke Crowley, UC assistant professor, geology/anthropology; William Gilhooly III, assistant professor, Earth Sciences, Indiana University-Purdue University Indianapolis

Proxy Wars – The Paleobiology Data Debate

For the past several decades, paleobiologists have built large databases containing information on fossil plants and animals of all geological ages to investigate the timing and extent of major changes in biodiversity – changes such as mass extinctions that have taken place throughout the history of life. Biodiversity researcher Arnold Miller says that in building these databases, it can be a challenge to accurately identify species in the geological record, so it has been common for researchers to instead study biodiversity trends using data compiled at broader levels of biological classification, including the genus level, under the assumption that these patterns are effective proxies for what would be observed among species if the data were available. Miller has been involved in construction of The Paleobiology Database, an extensive public online resource that contains global genus- and species-level data, now permitting a direct, novel look at the similarities and differences between patterns at these two levels. Miller’s discussion aims to set the record straight as to when researchers can effectively use a genus as a proxy for a species and also when it’s inappropriate. This research is funded by the NASA Astrobiology Program.

Presenter: Arnold Miller, UC professor of geology

A Novel New Method for Examining the Distribution of Pores in Rocks

Oil and gas companies take an interest in the porosity of sedimentary rocks because those open spaces can be filled with fuel resources. Companies involved with hydraulic fracturing (“fracking”) are also interested in porosity because it could be a source for storing wastewater as a result of fracking. In this unique study, UC researchers made pore-size measurements similar to those used in crystal size distribution (CSD) theory to determine distribution of pores as a function of their sizes, using thin sections of rock. In addition to providing accurate porosity distribution at a given depth, their approach can be extended to evaluate variation of pore spaces as a function of depth in a drill core, percent of pores in each size range, and pore types and pore geometry. The Texas Bureau of Economic Geology provided the rock samples used in the study. Funding for the study was supported by the Turkish Petroleum Corporation.

Presenter: Ugurlu Ibrahim, master’s student in geology

Co-author: Attila Kilinc, professor of geology

Researchers Turn to 3-D Technology to Examine the Formation of Cliffband Landscapes

A blend of photos and technology takes a new twist on studying cliff landscapes and how they were formed. The method called Structure-From-Motion Photogrammetry – computational photo image processing techniques – is used to study the formation of cliff landscapes in Colorado and Utah and to understand how the layered rock formations in the cliffs are affected by erosion.

Presenter: Dylan Ward, UC assistant professor of geology

Testing the Links Between Climate and Sedimentation in the Atacama Desert, Northern Chile

The Atacama Desert is used as an analog for understanding the surface of Mars. In some localities, there has been no activity for millions of years. UC researchers have been working along the flank of the Andes Mountains in northern Chile, and this particular examination focuses on the large deposits of sediment that are transported down the plateau and gather at the base. The researchers are finding that their samples are not reflecting the million-year-old relics previously found on such expeditions, but may indicate more youthful activity possibly resulting from climatic events. The research is supported by a $273,634 grant from the National Science Foundation to explore glacio-geomorphic constraints on the climate history of subtropical northern Chile.

Presenter: Jason Cesta, UC geology master’s student

Co-author: Dylan Ward, UC assistant professor of geology

Uncovering the Explosive Mysteries Surrounding the Manganese of Northeast Bulgaria

UC’s geology collections hold minerals from field expeditions around the world, including manganese from the Obrochishte mines of northeastern Bulgaria. Found in the region’s sedimentary rock, manganese can be added to metals such as steel to improve strength. It’s widely believed that these manganese formations were the result of ocean water composition at the time the sediments were deposited in the ocean. In this presentation, UC researchers present new information on why they believe the manganese formations resulted from volcanic eruptions, perhaps during the Rupelian stage of the geologic time scale, when bentonite clay minerals were formed. The presentation evolved from an advance class project last spring under the direction of Warren Huff, a UC professor of geology.

Presenter: Jason Cesta, UC geology master’s student

Co-authors: Warren Huff, UC professor of geology; Christopher Aucoin; Michael Harrell; Thomas Malgieri; Barry Maynard; Cameron Schwalbach; Ibrahim Ugurlu; Antony Winrod

Two UC researchers will chair sessions at the GSA meeting: Doctoral student Gary Motz will chair the session, “Topics in Paleoecology: Modern Analogues and Ancient Systems,” on Oct. 19. Matt Vrazo, also a doctoral student in geology, is chairing “Paleontology: Trace Fossils, Taphonomy and Exceptional Preservation” on Oct. 21, and will present, “Taphonomic and Ecological Controls on Eurypterid Lagerstäten: A Model for Preservation in the Mid-Paleozoic.”


UC’s nationally ranked Department of Geology conducts field research around the world in areas spanning paleontology, quaternary geology, geomorphology, sedimentology, stratigraphy, tectonics, environmental geology and biogeochemistry.

The Geological Society of America, founded in 1888, is a scientific society with more than 26,500 members from academia, government, and industry in more than 100 countries. Through its meetings, publications, and programs, GSA enhances the professional growth of its members and promotes the geosciences in the service of humankind.

Ancient sea-levels give new clues on ice ages

International researchers, led by the Australian National University (ANU), have developed a new way to determine sea-level changes and deep-sea temperature variability over the past 5.3 million years.

The findings will help scientists better understand the climate surrounding ice ages over the past two million years, and could help determine the relationship between carbon dioxide levels, global temperatures and sea levels.

The team from ANU, the University of Southampton (UoS) and the National Oceanography Centre (NOC) in the United Kingdom, examined oxygen isotope levels in fossils of microscopic plankton recovered from the Mediterranean Sea, dating back as far as 5.3 million years.

“This is the first step for reconstructions from the Mediterranean records,” says lead researcher Eelco Rohling from the ANU Research School of Earth Sciences.

Professor Rohling said the team focused on the flow of water through Strait of Gibraltar, which was particularly sensitive to sea-level changes.

“As continental ice sheets grew during the ice ages, flow through the Strait of Gibraltar was reduced, causing measurable changes in oxygen isotope ratios in Mediterranean waters, which became preserved in the shells of the ancient plankton,” he said.

Co-author Gavin Foster from UoS said the research for the first time found long-term trends in cooling and continental ice-volume build-up cycles over the past 5.3 Million years were not the same.

“In fact, for temperature the major step toward the ice ages of the past two million years was a cooling event at 2.7 million years ago,” he said.

“But for ice-volume, the crucial step was the development of the first intense ice age at around 2.15 million years ago. Before our results, these were thought to have occurred together at about 2.5 million years ago.”
Professor Rohling said the findings will help scientists better understand the nature of ice ages and development of coastal sediment.

“The observed decoupling of temperature and ice-volume changes provides crucial new information for our understanding of how the ice ages came about,” he said.

“However, there are wider implications. For example, a more refined sea-level record over millions of years is commercially interesting because it allows a better understanding of coastal sediment sequences that are relevant to the petroleum industry.

“Our record is also of interest to climate policy developments, because it opens the door to detailed comparisons between past atmospheric carbon dioxide concentrations, global temperatures, and sea levels, which has enormous value to long-term future climate projections.”

The findings have been published in the latest on-line edition of Nature.

Study provides crucial new information about how the ice ages came about

An international team of scientists has discovered new relationships between deep-sea temperature and ice-volume changes to provide crucial new information about how the ice ages came about.

Researchers from the University of Southampton, the National Oceanography Centre and the Australian National University developed a new method for determining sea-level and deep-sea temperature variability over the past 5.3 million years. It provides new insight into the climatic relationships that caused the development of major ice-age cycles during the past two million years.

The researchers found, for the first time, that the long-term trends in cooling and continental ice-volume cycles over the past 5.3 million years were not the same. In fact, for temperature the major step toward the ice ages that have characterised the past two to three million years was a cooling event at 2.7 million years ago, but for ice-volume the crucial step was the development of the first intense ice age at around 2.15 million years ago. Before these results, these were thought to have occurred together at about 2.5 million years ago.

The results are published in the scientific journal Nature.

Co-author Dr Gavin Foster, from Ocean and Earth Science at the University of Southampton, says: “Our work focused on the discovery of new relationships within the natural Earth system. In that sense, the observed decoupling of temperature and ice-volume changes provides crucial new information for our understanding of how the ice ages developed.

“However, there are wider implications too. For example, a more refined sea-level record over millions of years is commercially interesting because it allows a better understanding of coastal sediment sequences that are relevant to the petroleum industry. Our record is also of interest to climate policy developments, because it opens the door to detailed comparisons between past atmospheric CO2 concentrations, global temperatures, and sea levels, which has enormous value to long-term future climate projections.”

The team used records of oxygen isotope ratios (which provide a record of ancient water temperature) from microscopic plankton fossils recovered from the Mediterranean Sea, spanning the last 5.3 million years. This is a particularly useful region because the oxygen isotopic composition of the seawater is largely determined by the flow of water through the Strait of Gibraltar, which in turn is sensitive to changes in global sea level – in a way like the pinching of a hosepipe.

As continental ice sheets grew during the ice ages, flow through the Strait of Gibraltar was reduced, causing measurable increases in the oxygen isotope O-18 (8 protons and 10 neutrons) relative to O-16 (8 protons and 8 neutrons) in Mediterranean waters, which became preserved in the shells of the ancient plankton. Using long drill cores and uplifted sections of sea-floor sediments, previous work had analysed such microfossil-based oxygen isotope records from carefully dated sequences.

The current study added a numerical model for calculating water exchange through the Strait of Gibraltar as a function of sea-level change, which allowed the microfossil records to be used as a sensitive recorder of global sea-level changes. The new sea-level record was then used in combination with existing deep-sea oxygen isotope records from the open ocean, to work out deep-sea temperature changes.

Lead author, Professor Eelco Rohling of Australian National University, says: “This is the first step for reconstructions from the Mediterranean records. Our previous work has developed and refined this technique for Red Sea records, but in that location it is restricted to the last half a million years because there are no longer drill cores. In the Mediterranean, we could take it down all the way to 5.3 million years ago. There are uncertainties involved, so we included wide-ranging assessments of these, as well as pointers to the most promising avenues for improvement. This work lays the foundation for a concentrated effort toward refining and improving the new sea-level record.”

Noting the importance of the Strait of Gibraltar to the analysis, co-author Dr Mark Tamisiea from the National Oceanography Centre, Southampton adds: “Flow through the Strait will depend not only on the ocean’s volume, but also on how the land in the region moves up and down in response to the changing water levels. We use a global model of changes in the ocean and the ice sheets to estimate the deformation and gravity changes in the region, and how that will affect our estimate of global sea-level change.”

Researchers use simple scaling theory to better predict gas production in barnett shale wells

Researchers at The University of Texas at Austin have developed a simple scaling theory to estimate gas production from hydraulically fractured wells in the Barnett Shale. The method is intended to help the energy industry accurately identify low- and high-producing horizontal wells, as well as accurately predict how long it will take for gas reserves to deplete in the wells.

Using historical data from horizontal wells in the Barnett Shale formation in North Texas, Tad Patzek, professor and chair in the Department of Petroleum and Geosystems Engineering in the Cockrell School of Engineering; Michael Marder, professor of physics in the College of Natural Sciences; and Frank Male, a graduate student in physics, used a simple physics theory to model the rate at which production from the wells declines over time, known as the “decline curve.”

They describe their new model of the decline curve in the paper “Gas production in the Barnett Shale obeys a simple scaling theory,” published this week in the Proceedings of the National Academy of Sciences. To test their theory, the researchers analyzed 10 years of gas production data from the Barnett Shale licensed to the university by IHS CERA, a provider of global market and economic information.

On average, they found that gas production in individual wells begins declining after about five years of production. They also found that wells generally produce less gas than predicted under previous, theoretical models and that production can be increased if hydrofractures connected better to the natural fractures in the rock.

The team’s estimates were an instrumental part of the comprehensive assessment of Barnett Shale reserves funded by the Alfred P. Sloan Foundation and issued earlier this year by the Bureau of Economic Geology at UT Austin.

Until now, estimates of shale gas production have primarily relied on models established for conventional oil and gas wells, which behave differently from the horizontal wells in gas-rich shales.

The researchers estimate the ultimate gas recovery from a sample of 8,294 horizontal wells in the Barnett Shale will be between 10 trillion and 20 trillion standard cubic feet (scf) during the lifetime of the wells. The study’s well sample is made up of about half of the 15,000 existing wells in the Barnett Shale, the geological formation outside Fort Worth that offers the longest production history for hydrofractured horizontal wells in the world.

“With our model at hand, you can better predict how much gas volume is left and how long it will take until that volume will be depleted,” Patzek said. “We are able to match historical production and predict future production of thousands of horizontal gas wells using this scaling theory.”

“The contributions of shale gas to the U.S. economy are so enormous that even small corrections to production estimates are of great practical significance,” Patzek said.

The researchers were surprised by how all of the wells they analyzed adhere to that simple scaling curve.

“By analyzing the basic physics underlying gas recovery from hydrofractured wells, we calculated a single curve that should describe how much gas comes out over time, and we showed that production from thousands of wells follows this curve,” Marder said.

Patzek adds: “We are able to predict when the decline will begin. Once decline sets in, gas production goes down rapidly.”

The decline of a well happens because of a process called pressure diffusion that causes pressure around a well to drop and gas production to decrease. The time at which gas pressure drops below its initial value everywhere in the rock between hydrofractures is called its interference time. On average, it takes five years for interference to occur, at which point wells produce gas at a far lower rate because the amount of gas coming out over time is proportional to the amount of gas remaining.

Using two parameters – a well’s interference time and the original gas in place – the researchers were able to determine the universal decline curve and extrapolate total gas production over time.

The researchers found that the scaling theory accurately predicted the behavior of approximately 2,000 wells in which production had begun to decrease exponentially within the past 10 years. The remaining wells were too young for the model to predict when decreases would set in, but the model enabled the researchers to estimate upper and lower production limits for well lifetime and the amount of gas that will be produced by the wells.

“For 2,057 of the horizontal wells in the Barnett Shale, interference is far enough advanced for us to verify that wells behave as predicted by the scaling form,” Patzek said. “The production forecasts will become more accurate as more production data becomes available.”

As a byproduct of their analysis, the researchers found that most horizontal wells for which predictions are possible underperform their theoretical production limits. The researchers have reached a tentative conclusion that many wells are on track to produce only about 10 percent of their potential.

The researchers conclude that well production could be greatly improved if the hydrofractures connected better to natural fractures in the surrounding rock. The process of hydraulic fracturing creates a network of cracks, like veins, in rocks that was previously impermeable, allowing gas to move. If there are high porosity and permeability within those connected cracks and hydrofractures, then a well is high producing. By contrast, if the connection with hydrofractures is weak, then a well is low producing.

“If this finding spurs research to understand why wells underperform, it may lead to improved production methods and eventually increase gas extraction from wells,” Marder said.

Work is underway on how to improve performance of hydrofractures in horizontal wells, Patzek added.

Gas injection probably triggered small earthquakes near Snyder, Texas

A new study correlates a series of small earthquakes near Snyder, Texas between 2006 and 2011 with the underground injection of large volumes of gas, primarily carbon dioxide (CO2) – a finding that is relevant to the process of capturing and storing CO2 underground.

Although the study suggests that underground injection of gas triggered the Snyder earthquakes, it also points out that similar rates of injections have not triggered comparable quakes in other fields, bolstering the idea that underground gas injection does not cause significant seismic events in many geologic settings.

No injuries or severe damage were reported from the quakes identified in the study.

The study represents the first time underground gas injection has been correlated with earthquakes greater than magnitude 3.

The results, from Wei Gan and Cliff Frohlich at The University of Texas at Austin’s Institute for Geophysics, appear this week in an online edition of the journal Proceedings of the National Academy of Sciences.

The study focused on an area of northwest Texas with three large oil and gas fields – the Cogdell field, the Salt Creek field and the Scurry Area Canyon Reef Operators Committee unit (SACROC) – which have all produced petroleum since the 1950s.

Operators began injecting CO2 in the SACROC field in 1971 to boost petroleum production, a process known as CO2 Enhanced Oil Recovery (CO2 EOR). Operators began CO2 EOR in the Cogdell field in 2001, with a significant increase starting in 2004. Because CO2 has been injected at large volumes for many years, the Department of Energy has funded research in this region to explore the potential impacts of carbon capture and storage (CCS), a proposed technique for reducing greenhouse gas emissions by capturing CO2 and injecting it deep underground for long-term storage.

This latest study was funded by the U.S. Geological Survey and the National Natural Science Foundation of China.

Using a high-resolution temporary network of seismometers, Gan and Frohlich identified 93 earthquakes in the Cogdell area from March 2009 to December 2010, three of which were greater than magnitude 3. An even larger earthquake, with magnitude 4.4, occurred in Cogdell in September 2011. Using data on injections and extractions of fluids and gases, they concluded that the earthquakes were correlated with the increase in CO2 EOR in Cogdell.

“What’s interesting is we have an example in Cogdell field, but there are other fields nearby that have experienced similar CO2 flooding without triggering earthquakes,” said Frohlich, associate director of the Institute for Geophysics, a research unit in the Jackson School of Geosciences. “So the question is: Why does it happen in one area and not others?”

In a paper published last year in the Proceedings of the National Academy of Sciences, Stanford University earthquake researchers Mark Zoback and Steven Gorelick argued “there is a high probability that earthquakes will be triggered by injection of large volumes of CO2″ during CCS.

“The fact that the different fields responded differently to CO2 injection and that no other gas injection sites in the world have been linked to earthquakes with magnitudes as large as 3 suggest that despite Zoback and Gorelick’s concerns, it is possible that in many locations large-volume CO2 injection may not induce earthquakes,” said Frohlich.

Frohlich suggests one possible explanation for the different response to gas injection in the three fields might be that there are geological faults in the Cogdell area that are primed and ready to move when pressures from large volumes of gas reduce friction on these faults. The other two fields might not have such faults.

Frohlich suggests an important next step in understanding seismic risks for proposed CCS projects would be to create geological models of Cogdell and other nearby fields to better understand why they respond differently to gas injection.

Gan and Frohlich analyzed seismic data collected between March 2009 and December 2010 by the EarthScope USArray Program, a National Science Foundation-funded network of broadband seismometers deployed from the Canadian border to the Gulf of Mexico. Because of the high density of instruments, they were able to detect earthquakes down to magnitude 1.5, too weak for people to feel at the surface and many of which were not detected by the U.S. Geological Survey’s more limited seismic network.

Using the USArray data, the researchers identified and located 93 well-recorded earthquakes. Most occurred in several northeast-southwest trending linear clusters, which might indicate the presence of previously unidentified faults. Three of the quakes identified in the USArray data were greater than magnitude 3. According to U.S. Geological Survey observations for the same area from 2006 to 2011, 18 earthquakes greater than magnitude 3 occurred in the study area.

Gan and Frohlich also evaluated data on injections and extractions of oil, water and gas in the study area collected by the Texas Railroad Commission, the state agency that regulates oil and gas operations. Since 1990, rates of liquid injection and extraction, as well as gas produced, remained fairly constant in all three oil and gas fields. The only significant change was a substantial increase in injection rates of gas, primarily CO2, in the Cogdell field starting in 2004.

Previous work by Frohlich and others has shown that underground injection of liquids can induce earthquakes.

Terahertz time-domain spectroscopy for oil and gas detection

This image shows R0% (vitrinite reflectance) dependence of α (absorption coefficients) of kerogen of different maturities at selected frequencies. -  ©Science China Press
This image shows R0% (vitrinite reflectance) dependence of α (absorption coefficients) of kerogen of different maturities at selected frequencies. – ©Science China Press

A greater understanding of the evolutionary stage of kerogen for hydrocarbon generation would play a role in easing the world’s current energy problem. Professor ZHAO Kun and his group from the Key Laboratory of Oil and Gas Terahertz Spectrum and Photoelectric Detection (CPCIF, China University of Petroleum, Beijing) set out to tackle this problem. After five years of innovative research, they have developed terahertz time-domain spectroscopy (THz-TDS) as an effective method to detect the generation of oil and gas from kerogen. Their work, entitled “Applying terahertz time-domain spectroscopy to probe the evolution of kerogen in close pyrolysis systems”, was published in Science China Physics, Mechanics & Astronomy, 2013, Vol. 56(8).

The evolution stages of kerogen and hydrocarbon generation are critical aspects of oil-gas exploration and source rock evaluation. In sedimentary rock, about 95% of the organic matter is kerogen, the key intermediate in the formation of oil and gas. The specific kerogen type and maturity level will determine the characteristics of the hydrocarbons that will be generated. Previous research has led to two primary observations: (i) kerogen serves as a significant energy source as recoverable shale oil and coal where reserves far exceed the remaining petroleum reserves; and (ii) kerogen possesses a significant sorption capacity for organic compounds. Kerogen is primarily composed of alicyclics, aromatics, and other functional groups. Therefore, the ability to generate oil and gas from kerogen is determined primarily by its specific composition and structure. However, each generation technique has advantages and disadvantages within the specific parameters of the kerogen. Thus, there is a need for new methods to characterize the numerous stages and mechanisms of hydrocarbon generation from kerogen.

Vitrinite reflectance (R0%), defined as the proportion of normal incident light reflected by a polished planar surface of vitrinite (found in kerogen), is commonly used to characterize the maturity stage of kerogen. Those stages are defined as: the immature (IM) stage, where it generally cannot produce oil and gas (R0%<0.5); the early mature (EM) stage, or heavy oil zone (0.5<R0%<0.7); the middle mature (MM) stage, which is a primary zone of crude oil generation, also referred to as the oil window (0.7<R0%<1.2); the late mature (LM) stage, or zone of light oil and natural gas (1.2<R0%2.0).

To meet the challenges of applying optical characterization in oil and gas exploration, we applied THz-TDS as a nondestructive, contact-free tool for identifying the transformational paths and hydrocarbon generation ability of kerogen. Specifically, the absorption coefficients at different temperatures and pressures indicated the maturity regime of the kerogen, which were in good agreement with the results of programmed pyrolysis experiments.

By comparing the kerogen THz curves under different R0% and the maturity stages of the hydrocarbons, we can conclude that a relationship exists between the kerogen THz optical constants and the maturity stage. The THz optical constant curves at a given frequency can be divided into several sections denoted by the IM, EM, MM, LM, and OM stages. The kerogens cannot generate any significant amount of oil or gas when in the IM stage (R0%<0.5). Therefore, the functional groups and characteristics do not alter, which results in little observed change of the THz optical constants. In the primary oil generation zone (0.7<R0%<1.2), methyl, methylene, aromatic hydrocarbon, oxygen, and nitrogen functional groups separate from the kerogen, and oil and gas begin to be generated. The residual kerogen forms macromolecules with aromatic components. From the changes in the molecular structures and features relative to those of the initial kerogen, the values of the first peak of the THz absorption coefficient curve (see Figure) and the real parts of the relative dielectric permittivity curves characterize the oil-generating stage of kerogen. At a more mature stage (R0%<1.2), alkyls in aromatic groups separate from the kerogen and begin to generate hydrocarbons in the primary gas zone (see Figure).

This study was a collaborative effect involving many university and company researchers. It was supported by a grant from the National Key Scientific Instruments and Equipment Development, a 973 grant from the Department of Science and Technology of China, and a grant from the Beijing National Science Foundation. Being nondestructive and contactless, this method has shown great promise to improve kerogen analysis. The technique needs to be applied in more instances that involve reservoir rocks and further research will determine whether it can be established as a key tool in petroleum exploration and impact the oil and gas industry.

University Lands $21.2M Software Grant

The University of Utah has been awarded a software gift valued at $21.2 million from Landmark, a product service line of Halliburton’s Drilling and Evaluation Division. The three-year, renewable donation provides advanced software, including maintenance and support, to students and researchers in the College of Engineering and the College of Mines and Earth Sciences, especially those that focus on studying energy development. The software is used to help find oil and gas resources more efficiently.

“Utah has attracted a host of talent and continues to build a reputation for important work toward more efficient, clean and renewable energy technologies,” says Paul Tikalsky, chair and professor of civil and environmental engineering at the university. “This valuable grant will provide additional tools to train our students, as well as enhance the work of interdisciplinary researchers in this area of increasing social, technical and economic importance.”

The grant allows the colleges to install on multiple computers several Landmark software programs widely used in the petroleum industry. Landmark’s GeoProbe software, for example, allows users to slice virtually into the ground and examine rock layers, formations, stresses and fractures without drilling a single hole. Users can select and manipulate detailed images of the underground terrain in various ways, and can then use the resulting observations to select drilling locations and minimize the number of wells required to reach petroleum reserves. Users can also take advantage of the software to improve petroleum reservoir prediction, allowing them to model underground reservoirs of oil-bearing rock and more precisely predict the volume of oil or gas available in various rock layers.

According to William Keach, who is in charge of the Energy and Geoscience Institute (EGI) visualization facility at the university, using this type of data can dramatically increase drilling success rates – going from three successful wells out of every 10 drilled to seven successful wells out of 10.

In the university’s Department of Geology and Geophysics, the Landmark software will give every student in a new class on seismic interpretation access to 3-D visualization, opening up new ways for students to learn to interpret and model data. Students will learn cutting-edge skills and gain valuable experience while working with partners in the global energy industry.

“Cultivating new talent will be vital if we are to continue taking petroleum-related geoscience in exciting new directions,” says Paul Koeller, vice president, Landmark. “That’s why we’re providing the University of Utah with the technologies its students and researchers need to change the way the oil and gas industry discovers and optimizes new assets.”

The Energy and Geoscience Institute, a research organization within the university’s Department of Civil and Environmental Engineering, will employ the software in many of its worldwide energy exploration projects. A recent example is research being conducted on underground storage of carbon dioxide gas, a promising technique to reduce the deleterious effects of carbon dioxide emissions, one of the so-called greenhouse gases contributing to climate change. With the software, researchers can examine layers of rock to pinpoint the most resilient location for injecting the carbon. The U.S. Department of Energy recently awarded EGI a grant of $88 million to further this work, which is led by Brian McPherson, a Utah Science, Technology and Research (USTAR) professor of civil and environmental engineering at the university.

“The university is grateful to Landmark not only for renewing, but significantly increasing, its grant for the next three years,” said Raymond Levey, director of EGI and research professor in civil engineering at the university. “Our students and researchers will have access to tools and technology not otherwise available to them, to continue vital work at the university and preparing students to find creative solutions to global energy challenges.”