ERE
Energy, Resources and the Environment

Early Career Scientists

The mysterious subsidence of the seafloor due to oil production – How to predict it with a simple model?

by Daniel Keszthelyi
Physics of Geological Processes group at the Department of Physics, University of Oslo

Over 40 years of oil production from the Ekofisk field caused the overlying seafloor to sink over 9 meters during the years and while there have been numerous researches on the topic; the clear understanding of what happens with the reservoir rocks during production is still missing. We created a simple model of compaction with physics-based assumption to estimate the magnitude of the subsidence.

The Ekofisk field situated some 320 km off the coast of Norway is one of the largest petroleum fields of the country. Oil is produced from carbonate rocks (chalk) lying almost 3 km below the seabed to an oil platform standing in 76 meter deep water. The depletion of oil from the carbonate rocks caused a dramatic decrease in the pore pressure in these rocks and in turn a large increase in the effective stress acting to them. This increased effective stress then led to their compaction which was much more significant than expected by previous models.

The compaction has positive effect on the oil production as it pushes out oil from the rock; however it also puts at risk the surface facilities (oil platform and pipelines) and decreases the permeability of the rock making the flow of fluids inside them more difficult.

Our new model of compaction is based on very simple assumptions and describes rock as a collection of pores where these pores are material weaknesses. Imagine a sheet of paper with a small cut made in the middle of the paper. Then if you try to tear or shear the paper slowly you can see that this cut starts to grow until the sheet of paper is torn into two pieces. Similar things happen to the rock if effective stresses are increased: the pores – like the small cut in the middle of the sheet of paper – will become nuclei of new fractures and eventually a fracture network will be created. According to linear elastic fracture mechanics the larger the pore the less stress is needed to involve it into fracturing and vice-versa the larger the stress the smaller pores can be fractured: so with increasing effective stresses considerably more fractures can be created.

The Ekofisk field: location, mechanism of compaction and predicted subsidence (by Daniel Keszthelyi)

The Ekofisk field: location, mechanism of compaction and predicted subsidence (by Daniel Keszthelyi)

Fluids originally inside the pores can flow into these new fractures and if the fluid is water or partly water it can dissolve the material of rock: in carbonates calcite. The exact mechanism is called pressure solution which vaguely speaking means that the solubility of calcite depends on the pressure and therefore it can dissolve at grain-grain contacts along the new fracture and precipitate anywhere else. According to our model this dissolution will lead to the compaction of the carbonate rock.

The speed of dissolution can be calculated from pressure solution theories and the number of fractures can be calculated by statistical means and therefore the speed of deformation (the strain rate) can be predicted knowing some parameters without using any fitting parameters. All we have to know is porosity, pore size distribution, effective stress, water saturation, temperature and how the solubility of calcite depends on pressure and temperature: all of these can be measured independently in laboratory experiments.

If we apply this model to the Ekofisk field using an estimated pressure history of the reservoir we get quite good agreement with the measured subsidence values. This means that with a very simple model with no fitting we are able to predict the subsidence of the Ekofisk field. Furthermore, with simple modifications might also help to better understand other subsidence cases related to oil, gas or water production.

This post is based on the EGU talk Compaction creep by pore failure and pressure solution applied to a carbonate reservoir by Daniel Keszthelyi, Bjørn Jamtveit and Dag Kristian Dysthe. Daniel Keszthelyi is a PhD candidate at the Physics of Geological Processes group at the Department of Physics, University of Oslo. For further information please contact daniel.keszthelyi @fys.uio.no.

Funding opportunity for Early Career Researchers to attend GSA Baltimore

The Heritage Stone Task Group in southern Europe is a Task Group within the IUGS. In March, HSTG  had a proposal accepted as Project 637 of the International Geoscience Programme (IGCP 637). With this acceptance, IGCP 637 offered $US6,000 in 2015 to support conference participation.

HSTG has decided that this funding should be used in 2015 to support attendance to our session in the GSA Baltimore conference. Amounts not exceeding $US2000 will likely be available. We have been asked by the IGCP Secretariat to give preference to supporting scientists from developing countries or who are young or women scientists. Recipients will also be expected to make a conference presentation in our session, related to natural stones, architectonic heritage and related issues.

Early Career researchers who are interested should send a message showing interest and a short cv, with a potential title for the contribution in the HSTG session, to the HSTG secretary general Barry Cooper: Barry.Cooper@unisa.edu.au

Applicatons will be received up to 30 June 2015.

Please contact Dr Lola Pereira for further information (mdp@usal.es)

ERE Division Outstanding Young Scientist Award: who would you nominate?

Every year the EGU rewards outstanding young or early career scientists with the Arne Richter Outstanding Young Scientist Award (OYSA), or one of the Division Outstanding Young Scientist Awards. These awards are granted for an outstanding research contribution in the Earth, planetary and space sciences, and are intended to identify the awardees as role models for the next generation of young scientists.

If you know an outstanding YS, who has made a significant contribution to Energy, Resources and the Environment, please consider nominating them for the ERE Division OYSA! 🙂

For more information on the awards and medals awarded by EGU, check here. Please be aware that all nominations must be submitted online by the 15th of June! Go to the EGU website for a checklist on what to do before you submit.

Award Ceremony at the EGU GA 2015. Will you be on stage next year?

Award Ceremony at the EGU GA 2015. Will you be on stage next year?

What to see at EGU?: Young Scientist events

Within a week the EGU General Assembly will kick off! This year the topic will be A Voyage Through Scales. For those that will attend for the first time, the scale of EGU itself may be impressive enough already. So how do you decide where to go? Here we hope to point you to a few interesting sessions, in case you get completely lost.

To start with, there are a number of interesting events for Young Scientists. For you! 🙂

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Ice Breaker Reception

On Sunday evening the EGU General Assembly 2015 will be kicked off with the Ice Breaker Reception, at 18.30h in Foyer E. A gathering point for young scientists provides the opportunity to meet like-minded fellows, especially if it is your first time at the General Assembly or you are coming alone.

The Young Scientist Forum

The YS Forum takes place on Tuesday at 12.15 to 13.15h in room G8. Come along and meet your young scientist representatives, find out what the EGU does for young scientists and take the chance to become more involved in the Union. This forum is a great opportunity to let us know what you would like from the EGU, find out how you can get involved in the Assembly and meet other scientists in the EGU young scientist community.

Young Scientists’ Lounge

For the Young Scientists, on the Red Level of the conference centre you can find a place to take a break, grab a free coffee or soft drink and gather your thoughts away from the buzz of the Assembly. The lounge is also a great place to catch up with colleagues you haven’t seen in a while and perhaps strike up a new collaboration. On the notice boards you can find information about cultural activities on offer in Vienna. There is also the opportunity to provide feedback via suggestion boards.

Young Scientists Lounge

Young Scientists’ Lounge

Young Scientist Reception and Medallist Reception

To bring together Young Scientists and past EGU-medallists, there will be a reception with drinks and light snacks. The reception take place on Tuesday 14 April, from 19:00 to 20:30 in room Y1.

This networking reception will provide an informal setting in which scientists can establish links with outstanding early career researchers and established scientists; offering an opportunity for young scientists to find answers to specific questions, which often cannot be found in your usual textbook. It offers a great opportunity for medallists to share their experience with researchers embarking on their academic career. To attend the reception, you need to register for the event in advance via this online form. Places at the reception are limited and will be allocated on a first come, first served basis. Your place is guaranteed only once you receive a confirmation email from the EGU Communications Officer, Laura Roberts.

Sessions for YS at the General Assembly

In addition to the above networking events, there are a number of other sessions catering the YS. A short list of these sessions with a strong YS focus can be found here. Of special interest are the two career workshops, focussing on: 1) Adding value to your research experience, and 2) Job applications and interviews. Note that you must register for the workshops in advance via the links provided!