GeoLog

Going deeper underground – why do we want to know how rocks behave?

Stephanie Zihms August 12, 2016

Photo taken at the Soapbox Science event courtesy of Sarah Caldwell (smcneem)

Imagine you find yourself standing atop a wooden box in the middle of your home town, on a rainy weekend day, with the sole aim of talking to passersby about your research work. It can be a rather daunting prospect! How do you decide what the take-home message of your work is: which single nugget of information do you want members of the public to take away after having spoken to you? Even more important still, how are you going to grab their attention in the first place? After all, they’ll be going about their business and not expecting to see you there, on top of your box, least of all talk to you about your work! But if you fancy the challenge, then read on, as Stephanie Zihms, the ECS Representative of the Earth Magnetism and Rock Physics Division, describes her experience doing just that!

Now in its 6th year Soapbox Science is spreading and I was selected to take part in the 1st Edinburgh event on July 24th on The Mound. The weather was typically Scottish but it didn’t seem to bother the crowds and it definitely did not dampen the enthusiasm of the 12 speakers.

I have done a range of different outreach events but I was particularly drawn to Soapbox Science because it specifically promotes female scientists and their work. It was great to meet the other scientists and to see the range of soapbox “performances” as well as the variety of props utilised to showcase each research topic.

Photo taken at the Soapbox Science event courtesy of Sarah Caldwell (smcneem)

The scary thing for this type of event is that you don’t know who might stop, listen & ask questions since we were standing on The Mound in Edinburgh – this also means that your material has to be accessible and engaging to a wide audience.

Here is what I did to explain my research in geomechanics: Going deeper underground – why do we want to know how rocks behave?

I opted for a big PVC banner showing different heights & depths. With help from the audience I added a picture to each line to show what it represented. I used this banner to set the scene for the type of work I do. I’m a researcher in geomechanics – I want to understand why rocks deform the way they do and what part or component of the rock controls the deformation. The rocks I work with are related to a very deep oil field that lies under 2km of ocean and 5km of rocks. It would take me ~1 hour to run this. At this depth the pressure squeezing the rocks is very high – each square meter of rock experiences the pressure of 16 African elephants per km of depth. So at 5km depths that is 80 African Elephants per square meter.

Under these high pressures the slightest change in conditions e.g. through oil production affects the rocks and changes the distribution of this pressure onto the rocks. I want to understand how different rocks respond to these changes. I do this by collecting rock samples that are easy to get to e.g. from quarries. But they have to be similar to the ones found in the oil field of interest – we call this an analogue (or think of it as a sibling).

Rock sample before it is placed into the Hoek Cell. Image Credit: Stephanie Zihms

In the lab at Heriot-Watt University I have an apparatus that lets me deform rocks under different conditions. The sample, usually a core sample (seeimage above) gets placed into a rubber sleeve before being placed into a stainless steel cell called a Hoek Cell. The space between the rubber sleeve and stainless stell cell is filled with oil that can be pressurised. That way the rock samples can be placed under different pressures that mimic the conditions at different depths. After this initial pressurisation the rock is squeezed in a press until it deforms. When the readings pass a peak value it indicates that the rock sample can’t withstand the squeeze pressure any longer and the test is stopped.

Unfortunatley we can’t see what happens to the rock during the squeezing process but we measure the sample before and after testing – we can also take a x-ray images of the entire sample. We do this with the sample before it is deformed and then again afterwards. This technique lets us see inside the rock – similar to having a x-ray in hospital to see if a bone is broken or not.

Using special computer software we can then look at different parts of the rock’s inside – I am particularly interested in the fractures that formed during the deformation and I’m working on ways to relate these observed features to the rock type, grain size and pore shape.

Why is this important? As I mentioned above I look at rocks related to an oil field – and the response of the rocks to oil production could hinder or help extraction. Oil companies are very interested in predicting the rock response to ensure it does not have a negative impact on oil production.

3D reconstruction of the rock sample using the x-ray images. Image Credit: Stephanie Zihms

Additionally this research is also relevant to other areas: for example geothermal energy. One method of generating geothermal energy is by pumping water into a rock that is hotter than the surface to increase the water temperature. When this water then reaches the surface it can be used to generate electricity. Adding water into the rock also changes the pressure conditions. Another field is Carbon Capture & Storage – If we want to store CO2 securely and long-term into the subsurface e.g. in a disused gas field – understanding how rocks respond to changes in conditions firstly by removal of gas & secondly by filling the rocks with CO2 is important.

By Stephanie Zihms, Postdoctoral researcher and ECS Representative of the Earth Magnetism and Rock Physics Division.

This post was published under the original title:Going deeper underground – My Soapbox Science Edinburgh contribution, on Stephanie Zihms’ personal blog.

New study of natural CO2 reservoirs: Carbon dioxide emissions can be safely buried underground for climate change mitigation

Suzanne Hangx July 28, 2016

The rocks in the Colorado Plateau, USA, are representative for reservoirs currently under consideration for CO2 storage in Europe. Layer Cake . Credit: Suzanne Hangx (distributed via imaggeo.egu.eu)

New research shows that natural accumulations of carbon dioxide (CO₂) that have been trapped underground for around 100,000 years have not significantly corroded the rocks above, suggesting that storing CO₂ in reservoirs deep underground is much safer and more predictable over long periods of time than previously thought, explains Suzanne Hangx a postdoctoral researcher at the University of Utrecht.

The findings, published today in the journal Nature Communications, demonstrate the viability of a process called carbon capture and storage (CCS) as a solution to reducing carbon emissions from coal and gas-fired power stations, say researchers.

About 80% of the global carbon emissions emitted by the energy sector come from the burning of fossil fuels, which releases large volumes of CO₂ into the atmosphere, contributing to climate change. With the growing global energy demand, fossil fuels are likely to continue to remain part of the energy mix. To mitigate CO₂ emissions, one possible solution is to capture the carbon dioxide produced at power stations, compress it, and pump it into reservoirs in the rock more than a kilometer underground. This process is called carbon capture and storage (CCS). The CO₂ must remain buried for at least 10,000 years to help alleviate the impacts of climate change.

The key component in the safety of geological storage of CO₂ is an impermeable rock barrier (the ‘lid’ or caprock) over the porous rock layer (the ‘container’ or reservoir) in which the CO₂ is stored in the pores – see Figure X. Although the CO₂ will be injected as a dense fluid, it is still less dense than the brines originally filling the pores in the reservoir sandstones, and will rise until trapped by the relatively impermeable caprocks. One of the main concerns is that the CO₂ will then slowly dissolve in the reservoir pore water, forming a slightly acidic, carbonated solution, which can only enter the caprock by diffusion through the pore water, a very slow process.

Some earlier studies, using computer simulations and laboratory experiments, have suggested that caprocks might be progressively corroded as these acidic, carbonated solutions diffuse upwards, creating weaker and more permeable layers of rock several meters thick and, in turn, jeopardizing the secure retention of the CO₂. Therefore, for the safe implementation of carbon capture and storage, it is important to accurately determine how long the CO₂ pumped underground will remain securely buried. This has important implications for regulating, maintaining, and insuring future CO₂ storage sites.

Schematic diagram of a storage site showing the injection of CO2 (in yellow) at a depth of more than one kilometer into a layer of porous rock (the ‘container’ or reservoir), and kept from moving upwards by a sealing layer (the ‘lid’ or caprock). Via Global CCS Institute

To understand what will happen in complex, natural systems, on much longer time-scales than can be achieved in a laboratory, a team of international researchers and industry experts traveled to the Colorado Plateau in the USA, where large natural pockets of CO₂ have been safely buried underground in sedimentary rocks for over 100,000 years. The team drilled deep below the surface into one of the natural CO₂ reservoirs in a drilling project sponsored by Shell, to recover samples of these rock layers and the fluids confined in the rock pores.

The team studied the corrosion of the rock by the acidic carbonated water, and how this has affected the ability of the caprock to act as an effective trap over long periods of time (thousands to millions of years). Their analysis studied the mineralogy and geochemistry of the caprock and included bombarding samples of the rock with neutrons at a facility in Germany to better understand any changes that may have occurred in the pore structure and permeability of the caprock.

They found that the CO₂ had very little impact on corrosion of the caprock, with corrosion limited to a layer only 7cm thick. This is considerably less than the amount of corrosion predicted in some earlier studies, which suggested that this layer might be many metres thick. The researchers also used computer simulations, calibrated with data collected from the rock samples, to show that this layer took at least 100,000 years to form, an age consistent with how long the site is known to have contained CO₂. The research demonstrates that the natural resistance of the caprock minerals to the acidic carbonated waters makes burying CO₂ underground a far more predictable and secure process than previously estimated. With careful evaluation, burying carbon dioxide underground will prove safer than emitting CO₂ directly to the atmosphere.

By Suzanne Hangx, Post Doctoral Researcher at the University of Utrecht

Reference:
Kampman, N.; Busch, A.; Bertier, P.; Snippe, J.; Hangx, S.; Pipich, V.; Di, Z.; Rother, G.; Harrington, J. F.; Evans, J. P.; Maskell, A.; Chapman, H. J.; Bickle, M. J., Observational evidence confirms modelling of the long-term integrity of CO₂-reservoir caprocks. Nat Commun 2016, 7.

The research was conducted by an international consortium led by Cambridge University together with universities in Aachen (Germany) and Utrecht (Netherlands), the Jülich Centre for Neutron Science (Germany), Oak Ridge National Laboratory (USA), the British Geological Survey (UK) and Shell Global Solutions International (Netherlands). The Cambridge research into the CO₂ reservoirs in Utah was funded by the Natural Environment Research Council (CRIUS consortium of Cambridge, Manchester and Leeds universities and the British Geological Survey) and the UK Department of Energy and Climate Change.

Geosciences Column: The World’s soils are under threat

Laura Roberts-Artal July 22, 2016

Tillage in vineyards with heavy machinery is inducing soil degradation. Utiel, Eastern Spain . Credit: Artemi Cerdá (distributed via imaggeo.egu.eu)

An increasing global population means that we are more dependant than ever on soils.

Soils are crucial to securing our future supplies of water, food, as well as aiding adaptation to climate change and sustaining the planet’s biosphere; yet with the decrease in human labour dedicated to working the land, never have we been more out of touch with the vital importance of this natural resource.

Now, the first-ever comprehensive State of the World’s Soil Resources Report (SWRS), compiled by the Intergovernmental Technical Panel on Soils (ITPS), aims to shine a light on this essential non-renewable resource. The report outlines the current state of soils, globally, and what the major threats facing it are. These and other key findings of the report are summarised in a recent paper of the EGU’s open access Soil Journal.

The current outlook

Overall, the report deemed that the world’s soils are in fair to very poor condition, with regional variations. The future doesn’t look bright: current projections indicate that the present situation will worsen unless governments, organisations and individuals come together to take concerted action.

Many of the drivers which contribute to soil changes are associated with population growth and the need to provide resources for the industrialisation and food security of growing societies. Climate change presents a significant challenge too, with factors such as increasing temperatures resulting in higher evaporation rates from soils and therefore affecting groundwater recharge rates, coming into play.

The three main threats to soils

Soil condition is threatened by a number of factors including compaction (which reduces large pore spaces between soil grains and restricts the flow of air and water into and through the soil), acidification, contamination, sealing (which results from the covering of soil through building of houses, roads and other urban development), waterlogging, salinization and losses of soil organic carbon (SOC).

Global assessment of the four main threats to soil by FAO regions. Taken from Montanarella, L., et al. 2016.

Chief among the threats to soils is erosion, where topsoil is removed from the land surface by wind, water and tillage. Increasing rates of soil erosion affect water quality, particularly in developed regions, while crop yields suffer the most in developing regions. Estimating the rates of soil erosion is difficult (especially when it comes to wind driven erosion), but scientists do know that topsoil is being lost much faster than it is being generate. This means soil should be considered a non-renewable resource. When it comes to agricultural practices in particular, soils should be managed in such a way that soil erosion rates are reduced to near zero-values, ensuring long-term sustainability.

Eutrophication in lake Slotsø, Kolding, Denmark. Credit: Alevtina Evgrafova (distributed via imaggeo.egu.eu)

Soils contain nutrients, such as nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulphur (S), crucial for growing crops and pastures for raising cattle. While nutrient balance in soils has a natural variability, farming practices accelerate changes in soil nutrient content. Over-use of soils rapidly depletes the land-cover of nutrients and result in lower food production yields. This imbalance is often remedied by the addition of nutrients; in particular N and P. Excessive use of these practices, however, can lead to negative environmental effects, such as eutrophication (which increases the frequency and severity of algal blooms) and contamination of water resources. The findings of the report advocate for the overall reduction of use of fertilisers, with the exception of tropical and semi-tropical soils in regions where food security is a problem.

Carbon (C) is a fundamental building block of life on Earth and the carbon cycle balances the amount of C which ultimately enters the atmosphere, helping to stabilise the planets temperature. Soils play a significant role in helping to preserve this balance. Soil organic carbon (SOC) acts as a sink for atmospheric C, but converting forest land to crop land saw a decrease of 25-30% in SOC stocks for temperate regions, with higher losses recorded for the tropics. Future climate change will further affect SOC stocks through increased temperatures and fluctuating rainfall, ultimately contributing to risks of soil erosion and desertification and reducing their ability to regulate carbon dioxide emissions. It is vitally important that governments work towards stabilising, or better still, improving existing SOC stocks as a means of combating global warming.

Preserving a valuable resource

The case is clear: soils are a vital part of life on Earth. It is estimated that worsening soil condition will affect those already most vulnerable, in areas affected by water scarcity, civil strife and food insecurity.

Bed planting in northern Ethiopia. Credit: Elise Monsieurs (distributed via imaggeo.egu.eu)

Initiatives such as the 2015 International Year of Soil and the production of the SWRS report are fundamental to raise awareness of the challenges facing soil resources, but more needs to be done:

Sustainable soil management practices, which minimise soil degradation and replenish soil productivity in regions where it has been lost, must be adopted to ensure a healthy, global, supply of food.
Individual nations should make a dedicated effort to establish appropriate SOC-improving strategies, thus aiding adaptation to climate change.
Manging the use of fertilisers, in particular N and P, should be improved.
There is a dearth of current data, with many of the studies referenced in the SWRS report dating from the 1980s and 1990s. For accurate future projections and the development and evaluation of tools to tackle the major threats facing soils, more up-to-date knowledge about the state of soil condition is required.

Soils, globally, are under threat and their future is uncertain. The authors of report argue that “the global community is presently ill-prepared and ill-equipped to mount an appropriate response” to the problem. However, adoption and implementation of the report findings might (by policy-makers and individuals alike) just turn the tide and ensure soils remain “humanity’s silent ally”.

By Laura Roberts Artal, EGU Communications Officer

References

Montanarella, L., Pennock, D. J., McKenzie, N., Badraoui, M., Chude, V., Baptista, I., Mamo, T., Yemefack, M., Singh Aulakh, M., Yagi, K., Young Hong, S., Vijarnsorn, P., Zhang, G.-L., Arrouays, D., Black, H., Krasilnikov, P., Sobocká, J., Alegre, J., Henriquez, C. R., de Lourdes Mendonça-Santos, M., Taboada, M., Espinosa-Victoria, D., AlShankiti, A., AlaviPanah, S. K., Elsheikh, E. A. E. M., Hempel, J., Camps Arbestain, M., Nachtergaele, F., and Vargas, R.: World’s soils are under threat, SOIL, 2, 79-82, doi:10.5194/soil-2-79-2016, 2016.

Status of the World’s Soil Resources, 2015, Food and Agricultire Organization (FAO) of the United Nations.

Soils are endangered, but degradation can be rolled back, 2015, FAO News Article.

Imaggeo on Mondays: Why is groundwater so important?

Laura Roberts-Artal July 4, 2016

Why is groundwater so important? . Credit: Anna Menció (distributed via imaggeo.egu.eu)

Groundwater is an often underestimated natural resource, but it is vital to the functioning of both natural and urban environments. Indeed, it is a large source of drinking water for communities world-wide, as well as being heavily used for irrigation of crops and crucial for many industrial processes. The water locked in the pores and cracks within the Earth’s soils and rocks, also plays an important role in the recharge of water in lakes, rivers and wetlands, as Anna Menció explains in today’s Imaggeo On Monday’s post.

The Pletera salt marsh area (NE Spain) is located in the north of the mouth of the Ter River, in a region mainly dominated by agriculture and tourism activities. Some of the coastal lagoons and wetlands in this area have been affected by the incomplete construction of an urban development. These wetlands and lagoons are the focus of a Life⁺ project, which aims to restore this protected area, and to recover its ecological functionality.

The Pletera coastal lagoons are periodically flooded by both, freshwater from streams and seawater, during storm events. However, the surface water inputs alone are insufficient to maintain them as permanent lagoons.

This picture is of Fra Ramon lagoon, one of the natural lagoons in the area. The preliminary results of a recent study showed that the recharge of Fra Ramon is dependent on groundwater inputs. In most of the sampling campaigns, freshwater from the aquifer may account for >50% of the lagoon water.

The ecological quality of these lagoons is also affected by nitrogen inputs, mainly produced during flooding events. Although in this area nitrate pollution is also detected in groundwater, with concentrations up to 100 mg NO₃^–/L, natural attenuation processes in the aquifer occur. Effects of these processes are particularly detected close to the lagoons area, where low nitrate concentrations in groundwater are observed, with values below the detection limit. Considering that groundwater may present lower nitrogen concentrations than surface inputs observed during flooding events, these results reinforce the importance of groundwater dynamics in these systems, not only to maintain the permanent lagoons during dry periods, but also to preserve their quality.

By Anna Menció, researcher at the Department of Environmental Sciences of the University of Girona.

Acknowledgments: the study of the Pletera coastal lagoons is founded by LIFE 13 NAT/ES/001001, MINECO CGL-2014-57215-C4-2R, and UdG MPCUdG2016/061 projects.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Energy, Resources and the Environment

New study of natural CO2 reservoirs: Carbon dioxide emissions can be safely buried underground for climate change mitigation

Geosciences Column: The World’s soils are under threat

Imaggeo on Mondays: Why is groundwater so important?

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