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.

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.

Volcanic rock probe helps unlock mysteries of how Earth formed

New insights gleaned from volcanic rock are helping scientists better understand how our planet evolved billions of years ago.

Studies of basalt, the material that forms from cooling lava, are being used to develop a timeline of how the planet and its atmosphere were formed.

Scientists examined liquid basalt – or magma – at record high pressures and temperatures. Their findings suggest molten magma once formed an ocean within the Earth’s mantle, comprising two layers of fluid separated by a crystalline layer.

Scientists agree that Earth formed around 4.5 billion years ago, at which time much of the planet was molten. As it cooled, Earth’s crust was formed. Researchers are keen to pin down how the planet’s core and crust took shape and how its volcanic activity developed.

The discovery by a European team of scientists involving the University of Edinburgh, using hi-tech laboratories, supports current theories of how and when our planet evolved. To recreate conditions at the Earth’s core, scientists placed basalt under pressures equivalent to almost one billion times that of Earth’s atmosphere and temperatures above 2000 Celsius.

They found that at high pressure, silicon atoms in the basalt change the way in which they form bonds, which results in a denser magma. Their discovery helps pinpoint how magma behaves deep in the Earth and is a missing piece in the puzzle of how Earth’s core formed.

The study, published in Nature, was supported by the Scottish Universities Physics Alliance and European Research Council and carried out with the DESY Photon Science facility at Hamburg, the Universite Pierre et Marie Curie in Paris, Vrije Universitat Amsterdam, and Goethe-Universitat Frankfurt.

Dr Chrystele Sanloup, of the University of Edinburgh’s School of Physics and Astronomy, who took part in the study, said: “Modern labs make it possible for scientists to recreate conditions deep in the Earth’s core, and give us valuable insight into how materials behave at such extremes. This helps us build on what we already know about how Earth formed.”

Volcanic rock probe helps unlock mysteries of how Earth formed

New insights gleaned from volcanic rock are helping scientists better understand how our planet evolved billions of years ago.

Studies of basalt, the material that forms from cooling lava, are being used to develop a timeline of how the planet and its atmosphere were formed.

Scientists examined liquid basalt – or magma – at record high pressures and temperatures. Their findings suggest molten magma once formed an ocean within the Earth’s mantle, comprising two layers of fluid separated by a crystalline layer.

Scientists agree that Earth formed around 4.5 billion years ago, at which time much of the planet was molten. As it cooled, Earth’s crust was formed. Researchers are keen to pin down how the planet’s core and crust took shape and how its volcanic activity developed.

The discovery by a European team of scientists involving the University of Edinburgh, using hi-tech laboratories, supports current theories of how and when our planet evolved. To recreate conditions at the Earth’s core, scientists placed basalt under pressures equivalent to almost one billion times that of Earth’s atmosphere and temperatures above 2000 Celsius.

They found that at high pressure, silicon atoms in the basalt change the way in which they form bonds, which results in a denser magma. Their discovery helps pinpoint how magma behaves deep in the Earth and is a missing piece in the puzzle of how Earth’s core formed.

The study, published in Nature, was supported by the Scottish Universities Physics Alliance and European Research Council and carried out with the DESY Photon Science facility at Hamburg, the Universite Pierre et Marie Curie in Paris, Vrije Universitat Amsterdam, and Goethe-Universitat Frankfurt.

Dr Chrystele Sanloup, of the University of Edinburgh’s School of Physics and Astronomy, who took part in the study, said: “Modern labs make it possible for scientists to recreate conditions deep in the Earth’s core, and give us valuable insight into how materials behave at such extremes. This helps us build on what we already know about how Earth formed.”

Drilling for hydrocarbons can impact aquatic life

This large drilling sump exhibits ponding both on the surface and perimeter. -  Joshua Thienpont
This large drilling sump exhibits ponding both on the surface and perimeter. – Joshua Thienpont

The degradation of drilling sumps associated with hydrocarbon extraction can negatively affect aquatic ecosystems, according to new research published November 6th in the open-access journal PLOS ONE by Joshua Thienpont and colleagues at Queen’s University and other institutions.

Hydrocarbons are a primary source of energy as combustible fuel. Although hydrocarbon exploration and extraction are profitable enterprises, hydrocarbons contribute to the formation of greenhouse gases and are therefore a major stressor to the environment.

During the process of exploring for hydrocarbons, drilling sumps are used to permanently store the waste associated with drilling. In the Mackenzie Delta region of Canada’s western Arctic, more than 150 drilling sumps were constructed for this purpose. Although the areas surrounding the sumps were believed to be frozen by the surrounding permafrost, recent findings suggest that these areas may actually be thawing. In this study, the authors examine the environmental effects of this type of drilling sump containment loss in the Mackenzie Delta.

Because drilling fluids are saline, they tested whether leakage to surface waters was occurring by measuring changes in conductivity, as saline is more conductive than pure water. They also hypothesized that if saline-rich wastes from drilling sumps were impacting lakes, there should be changes in the types of life forms present. Zooplankton, for example, are a key component of aquatic ecosystems and various species survive differently in saline versus fresh water.

Through an analysis of lake sediments, they found changes in the community composition of zooplankton due to sump degradation. These results suggest that climate change and permafrost thaw can have deleterious consequences to aquatic life through the degradation and leaking of drilling sumps.

Thienpont elaborates, “The leaching of wastes from drilling sumps represents a newly identified example of one of the cumulative impacts of recent climate change impacting the sensitive freshwater ecosystems of the Arctic.”

Drilling for hydrocarbons can impact aquatic life

This large drilling sump exhibits ponding both on the surface and perimeter. -  Joshua Thienpont
This large drilling sump exhibits ponding both on the surface and perimeter. – Joshua Thienpont

The degradation of drilling sumps associated with hydrocarbon extraction can negatively affect aquatic ecosystems, according to new research published November 6th in the open-access journal PLOS ONE by Joshua Thienpont and colleagues at Queen’s University and other institutions.

Hydrocarbons are a primary source of energy as combustible fuel. Although hydrocarbon exploration and extraction are profitable enterprises, hydrocarbons contribute to the formation of greenhouse gases and are therefore a major stressor to the environment.

During the process of exploring for hydrocarbons, drilling sumps are used to permanently store the waste associated with drilling. In the Mackenzie Delta region of Canada’s western Arctic, more than 150 drilling sumps were constructed for this purpose. Although the areas surrounding the sumps were believed to be frozen by the surrounding permafrost, recent findings suggest that these areas may actually be thawing. In this study, the authors examine the environmental effects of this type of drilling sump containment loss in the Mackenzie Delta.

Because drilling fluids are saline, they tested whether leakage to surface waters was occurring by measuring changes in conductivity, as saline is more conductive than pure water. They also hypothesized that if saline-rich wastes from drilling sumps were impacting lakes, there should be changes in the types of life forms present. Zooplankton, for example, are a key component of aquatic ecosystems and various species survive differently in saline versus fresh water.

Through an analysis of lake sediments, they found changes in the community composition of zooplankton due to sump degradation. These results suggest that climate change and permafrost thaw can have deleterious consequences to aquatic life through the degradation and leaking of drilling sumps.

Thienpont elaborates, “The leaching of wastes from drilling sumps represents a newly identified example of one of the cumulative impacts of recent climate change impacting the sensitive freshwater ecosystems of the Arctic.”

X-rays reveal inner structure of the Earth’s ancient magma ocean

This shows thin slices of basalt with a diameter of just a fraction of a millimeter were subjected to high pressure in a diamond anvil cell. This sample has been molten and subsequently probed with X-rays three times. -  Chrystèle Sanloup, University of Edinburgh
This shows thin slices of basalt with a diameter of just a fraction of a millimeter were subjected to high pressure in a diamond anvil cell. This sample has been molten and subsequently probed with X-rays three times. – Chrystèle Sanloup, University of Edinburgh

Using the world’s most brilliant X-ray source, scientists have for the first time peered into molten magma at conditions of the deep Earth mantle. The analysis at DESY’s light source PETRA III revealed that molten basalt changes its structure when exposed to pressure of up to 60 gigapascals (GPa), corresponding to a depth of about 1400 kilometres below the surface. At such extreme conditions, the magma changes into a stiffer and denser form, the team around first author Chrystèle Sanloup from the University of Edinburgh reports in the scientific journal Nature. The findings support the concept that the early Earth’s mantle harboured two magma oceans, separated by a crystalline layer. Today, these presumed oceans have crystallized, but molten magma still exists in local patches and maybe thin layers in the mantle.

“Silicate liquids like basaltic magma play a key role at all stages of deep Earth evolution, ranging from core and crust formation billions of years ago to volcanic activity today,” Sanloup emphasised. To investigate the behaviour of magma in the deep mantle, the researchers squeezed small pieces of basalt within a diamond anvil cell and applied up to roughly 600,000 times the standard atmospheric pressure. “But to investigate basaltic magma as it still exists in local patches within the Earth’s mantle, we first had to melt the samples,” explained co-author Zuzana Konôpková from DESY, who supported the experiments at the Extreme Conditions Beamline (ECB), P02 at PETRA III.

The team used two strong infrared lasers that each concentrated a power of up to 40 Watts onto an area just 20 micrometres (millionths of a metre) across – that is about 2000 times the power density at the surface of the sun. A clever alignment of the laser optics allowed the team to shoot the heating lasers right through the diamond anvils. With this unique setup, the basalt samples could be heated up to 3,000 degrees Celsius in just a few seconds, until they were completely molten. To avoid overheating of the diamond anvil cell which would have skewed the X-ray measurements, the heating laser was only switched on for a few seconds before and during the X-ray diffraction patterns were taken. Such short data collection times, crucial for this kind of melting experiments, are only possible thanks to the high X-ray brightness at the ECB. “For the first time, we could study structural changes in molten magma over such a wide range of pressure,” said Konôpková.

The powerful X-rays show that the so-called coordination number of silicon, the most abundant chemical element in magmas, in the melt increases from 4 to 6 under high pressure, meaning that the silicon ions rearrange into a configuration where each has six nearest oxygen neighbours instead of the usual four at ambient conditions. As a result, the basalt density increases from about 2.7 grams per cubic centimetre (g/ccm) at low pressure to almost 5 g/ccm at 60 GPa. “An important question was how this coordination number change happens in the molten state, and how that affects the physical and chemical properties,” explained Sanloup. “The results show that the coordination number changes from 4 to 6 gradually from 10 GPa to 35 GPa in magmas, and once completed, magmas are much stiffer, that is much less compressible.” In contrast, in mantle silicate crystals, the coordination number change occurs abruptly at 25 GPa, which defines the boundary between the upper and lower mantle.

This behaviour allows for the peculiar possibility of layered magma oceans in the early Earth’s interior. “At low pressure, magmas are much more compressible than their crystalline counterparts, while they are almost as stiff above 35 GPa,” explained Sanloup. “This implies that early in the history of the Earth, when it started crystallising, magmas may have been negatively buoyant at the bottom of both, upper and lower mantle, resulting in the existence of two magma oceans, separated by a crystalline layer, as has been proposed earlier by other scientists.”

At the high pressure of the lower Earth mantle, the magma becomes so dense that rocks do not sink into it anymore but float on top. This way a crystallised boundary between an upper and a basal magma ocean could have formed within the young Earth. The existence of two separate magma oceans had been postulated to reconcile geochronological estimates for the duration of the magma ocean era with cooling models for molten magma. While the geochronological estimates yield a duration of a few ten million years for the magma ocean era, cooling models show that a single magma ocean would have cooled much quicker, within just one million years. A crystalline layer would have isolated the lower magma ocean thermally and significantly delayed its cooling down. Today, there are still remnants of the basal magma ocean in the form of melt pockets detected atop the Earth’s core by seismology.

X-rays reveal inner structure of the Earth’s ancient magma ocean

This shows thin slices of basalt with a diameter of just a fraction of a millimeter were subjected to high pressure in a diamond anvil cell. This sample has been molten and subsequently probed with X-rays three times. -  Chrystèle Sanloup, University of Edinburgh
This shows thin slices of basalt with a diameter of just a fraction of a millimeter were subjected to high pressure in a diamond anvil cell. This sample has been molten and subsequently probed with X-rays three times. – Chrystèle Sanloup, University of Edinburgh

Using the world’s most brilliant X-ray source, scientists have for the first time peered into molten magma at conditions of the deep Earth mantle. The analysis at DESY’s light source PETRA III revealed that molten basalt changes its structure when exposed to pressure of up to 60 gigapascals (GPa), corresponding to a depth of about 1400 kilometres below the surface. At such extreme conditions, the magma changes into a stiffer and denser form, the team around first author Chrystèle Sanloup from the University of Edinburgh reports in the scientific journal Nature. The findings support the concept that the early Earth’s mantle harboured two magma oceans, separated by a crystalline layer. Today, these presumed oceans have crystallized, but molten magma still exists in local patches and maybe thin layers in the mantle.

“Silicate liquids like basaltic magma play a key role at all stages of deep Earth evolution, ranging from core and crust formation billions of years ago to volcanic activity today,” Sanloup emphasised. To investigate the behaviour of magma in the deep mantle, the researchers squeezed small pieces of basalt within a diamond anvil cell and applied up to roughly 600,000 times the standard atmospheric pressure. “But to investigate basaltic magma as it still exists in local patches within the Earth’s mantle, we first had to melt the samples,” explained co-author Zuzana Konôpková from DESY, who supported the experiments at the Extreme Conditions Beamline (ECB), P02 at PETRA III.

The team used two strong infrared lasers that each concentrated a power of up to 40 Watts onto an area just 20 micrometres (millionths of a metre) across – that is about 2000 times the power density at the surface of the sun. A clever alignment of the laser optics allowed the team to shoot the heating lasers right through the diamond anvils. With this unique setup, the basalt samples could be heated up to 3,000 degrees Celsius in just a few seconds, until they were completely molten. To avoid overheating of the diamond anvil cell which would have skewed the X-ray measurements, the heating laser was only switched on for a few seconds before and during the X-ray diffraction patterns were taken. Such short data collection times, crucial for this kind of melting experiments, are only possible thanks to the high X-ray brightness at the ECB. “For the first time, we could study structural changes in molten magma over such a wide range of pressure,” said Konôpková.

The powerful X-rays show that the so-called coordination number of silicon, the most abundant chemical element in magmas, in the melt increases from 4 to 6 under high pressure, meaning that the silicon ions rearrange into a configuration where each has six nearest oxygen neighbours instead of the usual four at ambient conditions. As a result, the basalt density increases from about 2.7 grams per cubic centimetre (g/ccm) at low pressure to almost 5 g/ccm at 60 GPa. “An important question was how this coordination number change happens in the molten state, and how that affects the physical and chemical properties,” explained Sanloup. “The results show that the coordination number changes from 4 to 6 gradually from 10 GPa to 35 GPa in magmas, and once completed, magmas are much stiffer, that is much less compressible.” In contrast, in mantle silicate crystals, the coordination number change occurs abruptly at 25 GPa, which defines the boundary between the upper and lower mantle.

This behaviour allows for the peculiar possibility of layered magma oceans in the early Earth’s interior. “At low pressure, magmas are much more compressible than their crystalline counterparts, while they are almost as stiff above 35 GPa,” explained Sanloup. “This implies that early in the history of the Earth, when it started crystallising, magmas may have been negatively buoyant at the bottom of both, upper and lower mantle, resulting in the existence of two magma oceans, separated by a crystalline layer, as has been proposed earlier by other scientists.”

At the high pressure of the lower Earth mantle, the magma becomes so dense that rocks do not sink into it anymore but float on top. This way a crystallised boundary between an upper and a basal magma ocean could have formed within the young Earth. The existence of two separate magma oceans had been postulated to reconcile geochronological estimates for the duration of the magma ocean era with cooling models for molten magma. While the geochronological estimates yield a duration of a few ten million years for the magma ocean era, cooling models show that a single magma ocean would have cooled much quicker, within just one million years. A crystalline layer would have isolated the lower magma ocean thermally and significantly delayed its cooling down. Today, there are still remnants of the basal magma ocean in the form of melt pockets detected atop the Earth’s core by seismology.

The oldest ice core

<IMG SRC="/Images/571096301.jpg" WIDTH="350" HEIGHT="278" BORDER="0" ALT="This shows Antarctic locations (in bright blue) where 1.5 million years old ice could exist. The figure is modified from Van Liefferinge and Pattyn (Climate of the Past, 2013). – Van Liefferinge and Pattyn”>
This shows Antarctic locations (in bright blue) where 1.5 million years old ice could exist. The figure is modified from Van Liefferinge and Pattyn (Climate of the Past, 2013). – Van Liefferinge and Pattyn

How far into the past can ice-core records go? Scientists have now identified regions in Antarctica they say could store information about Earth’s climate and greenhouse gases extending as far back as 1.5 million years, almost twice as old as the oldest ice core drilled to date. The results are published today in Climate of the Past, an open access journal of the European Geosciences Union (EGU).

By studying the past climate, scientists can understand better how temperature responds to changes in greenhouse-gas concentrations in the atmosphere. This, in turn, allows them to make better predictions about how climate will change in the future.

“Ice cores contain little air bubbles and, thus, represent the only direct archive of the composition of the past atmosphere,” says Hubertus Fischer, an experimental climate physics professor at the University of Bern in Switzerland and lead author of the study. A 3.2-km-long ice core drilled almost a decade ago at Dome Concordia (Dome C) in Antarctica revealed 800,000 years of climate history, showing that greenhouse gases and temperature have mostly moved in lockstep. Now, an international team of scientists wants to know what happened before that.

At the root of their quest is a climate transition that marine-sediment studies reveal happened some 1.2 million years to 900,000 years ago. “The Mid Pleistocene Transition is a most important and enigmatic time interval in the more recent climate history of our planet,” says Fischer. The Earth’s climate naturally varies between times of warming and periods of extreme cooling (ice ages) over thousands of years. Before the transition, the period of variation was about 41 thousand years while afterwards it became 100 thousand years. “The reason for this change is not known.”

Climate scientists suspect greenhouse gases played a role in forcing this transition, but they need to drill into the ice to confirm their suspicions. “The information on greenhouse-gas concentrations at that time can only be gained from an Antarctic ice core covering the last 1.5 million years. Such an ice core does not exist yet, but ice of that age should be in principle hidden in the Antarctic ice sheet.”

As snow falls and settles on the surface of an ice sheet, it is compacted by the weight of new snow falling on top of it and is transformed into solid glacier ice over thousands of years. The weight of the upper layers of the ice sheet causes the deep ice to spread, causing the annual ice layers to become thinner and thinner with depth. This produces very old ice at depths close to the bedrock.

However, drilling deeper to collect a longer ice core does not necessarily mean finding a core that extends further into the past. “If the ice thickness is too high the old ice at the bottom is getting so warm by geothermal heating that it is melted away,” Fischer explains. “This is what happens at Dome C and limits its age to 800,000 years.”

To complicate matters further, horizontal movements of the ice above the bedrock can disturb the bottommost ice, causing its annual layers to mix up.

“To constrain the possible locations where such 1.5 million-year old – and in terms of its layering undisturbed – ice could be found in Antarctica, we compiled the available data on climate and ice conditions in the Antarctic and used a simple ice and heat flow model to locate larger areas where such old ice may exist,” explains co-author Eric Wolff of the British Antarctic Survey, now at the University of Cambridge.

The team concluded that 1.5 million-year old ice should still exist at the bottom of East Antarctica in regions close to the major Domes, the highest points on the ice sheet, and near the South Pole, as described in the new Climate of the Past study. These results confirm those of another study, also recently published in Climate of the Past.

Crucially, they also found that an ice core extending that far into the past should be between 2.4 and 3-km long, shorter than the 800,000-year-old core drilled in the previous expedition.

The next step is to survey the identified drill sites to measure the ice thickness and temperature at the bottom of the ice sheet before selecting a final drill location.

“A deep drilling project in Antarctica could commence within the next 3-5 years,” Fischer states. “This time would also be needed to plan the drilling logistically and create the funding for such an exciting large-scale international research project, which would cost around 50 million Euros.”

The oldest ice core

<IMG SRC="/Images/571096301.jpg" WIDTH="350" HEIGHT="278" BORDER="0" ALT="This shows Antarctic locations (in bright blue) where 1.5 million years old ice could exist. The figure is modified from Van Liefferinge and Pattyn (Climate of the Past, 2013). – Van Liefferinge and Pattyn”>
This shows Antarctic locations (in bright blue) where 1.5 million years old ice could exist. The figure is modified from Van Liefferinge and Pattyn (Climate of the Past, 2013). – Van Liefferinge and Pattyn

How far into the past can ice-core records go? Scientists have now identified regions in Antarctica they say could store information about Earth’s climate and greenhouse gases extending as far back as 1.5 million years, almost twice as old as the oldest ice core drilled to date. The results are published today in Climate of the Past, an open access journal of the European Geosciences Union (EGU).

By studying the past climate, scientists can understand better how temperature responds to changes in greenhouse-gas concentrations in the atmosphere. This, in turn, allows them to make better predictions about how climate will change in the future.

“Ice cores contain little air bubbles and, thus, represent the only direct archive of the composition of the past atmosphere,” says Hubertus Fischer, an experimental climate physics professor at the University of Bern in Switzerland and lead author of the study. A 3.2-km-long ice core drilled almost a decade ago at Dome Concordia (Dome C) in Antarctica revealed 800,000 years of climate history, showing that greenhouse gases and temperature have mostly moved in lockstep. Now, an international team of scientists wants to know what happened before that.

At the root of their quest is a climate transition that marine-sediment studies reveal happened some 1.2 million years to 900,000 years ago. “The Mid Pleistocene Transition is a most important and enigmatic time interval in the more recent climate history of our planet,” says Fischer. The Earth’s climate naturally varies between times of warming and periods of extreme cooling (ice ages) over thousands of years. Before the transition, the period of variation was about 41 thousand years while afterwards it became 100 thousand years. “The reason for this change is not known.”

Climate scientists suspect greenhouse gases played a role in forcing this transition, but they need to drill into the ice to confirm their suspicions. “The information on greenhouse-gas concentrations at that time can only be gained from an Antarctic ice core covering the last 1.5 million years. Such an ice core does not exist yet, but ice of that age should be in principle hidden in the Antarctic ice sheet.”

As snow falls and settles on the surface of an ice sheet, it is compacted by the weight of new snow falling on top of it and is transformed into solid glacier ice over thousands of years. The weight of the upper layers of the ice sheet causes the deep ice to spread, causing the annual ice layers to become thinner and thinner with depth. This produces very old ice at depths close to the bedrock.

However, drilling deeper to collect a longer ice core does not necessarily mean finding a core that extends further into the past. “If the ice thickness is too high the old ice at the bottom is getting so warm by geothermal heating that it is melted away,” Fischer explains. “This is what happens at Dome C and limits its age to 800,000 years.”

To complicate matters further, horizontal movements of the ice above the bedrock can disturb the bottommost ice, causing its annual layers to mix up.

“To constrain the possible locations where such 1.5 million-year old – and in terms of its layering undisturbed – ice could be found in Antarctica, we compiled the available data on climate and ice conditions in the Antarctic and used a simple ice and heat flow model to locate larger areas where such old ice may exist,” explains co-author Eric Wolff of the British Antarctic Survey, now at the University of Cambridge.

The team concluded that 1.5 million-year old ice should still exist at the bottom of East Antarctica in regions close to the major Domes, the highest points on the ice sheet, and near the South Pole, as described in the new Climate of the Past study. These results confirm those of another study, also recently published in Climate of the Past.

Crucially, they also found that an ice core extending that far into the past should be between 2.4 and 3-km long, shorter than the 800,000-year-old core drilled in the previous expedition.

The next step is to survey the identified drill sites to measure the ice thickness and temperature at the bottom of the ice sheet before selecting a final drill location.

“A deep drilling project in Antarctica could commence within the next 3-5 years,” Fischer states. “This time would also be needed to plan the drilling logistically and create the funding for such an exciting large-scale international research project, which would cost around 50 million Euros.”