Geological Storage and Utilisation of CO 2

Transcription

1 1 Geological Storage and Utilisation of CO 2 Stig Bergseth, Statoil, N-4035 Stavanger, Norway Gerd Halmø, Statoil Deutschland, Emden, Germany Olav Kaarstad, Statoil, N-4035 Stavanger, Norway ABSTRACT In the short to medium term capture and storage of carbon dioxide (CO 2 ) can play a part in sequestering already concentrated CO 2 -streams, such as from natural gas treatment or ammonia or hydrogen production plants. CO 2 -storage may provide an important route to achieve the deep reductions in greenhouse gas emissions to atmosphere to possibly limit anthropogenic climate change. This is believed to be good news for an increasing global population and the global economy into the 21 st century. Underground storage of carbon dioxide captured from natural gas as a climate change mitigation effort was decided as a pioneering project by Statoil (operator) and partners in the Sleipner North Sea licence in Another similar decision was taken by Statoil (operator) and a different set of partners in the Snøhvit licence in the Barents Sea in the autumn of The Sleipner field has been injecting CO 2 from 1996 while the Snøhvit project will start operations in At Sleipner the CO 2 is extracted from natural gas at an offshore platform and injected in a highly permeable sandstone formation, the Utsira formation 1000 meters below the seabed. Utsira is overlain by 800 meters of denser rock. The Sleipner CO 2 -injection has been keenly studied in a broadly based, multinational R&D effort, the so-called SACS (Saline Aquifer CO 2 -Storage programme). In the Snøhvit case the there will be no surface installations offshore and the CO 2 -rich natural gas will be sent to shore in a 160 kilometre long pipeline to be processed in an LNG (Liquefied Natural Gas) plant. After removal the CO 2 is sent back to the field in a separate pipeline and will be injected in a separate formation under the natural gas field itself. A near term goal of Statoil is to make more constructive use of captured carbon dioxide by focusing on its utilisation for the purpose of enhanced oil recovery. In this way a large market and a widespread CO 2 transport infrastructure may come into being aided by the carrot of market pull in combination with the stick of Kyoto mechanisms. INTRODUCTION In the years following the 1992 UN Conference on Environment and Development in Rio, it has been generally accepted that anthropogenic emissions of greenhouse gases are causing changes in the climate. The major contributor is carbon dioxide (CO 2 ), which arises mainly from use of fossil fuels. Measures, such as improved energy efficiency and use of alternative energy sources, will help reduce emissions. However, considering that about 85% of the world s commercial energy needs are met by fossil fuels, a rapid move away from oil, natural gas and coal is unlikely to be achievable without serious disruption to the global economy.

2 2 Mill. tonnes oil equivalents per year Hydro Nuclear Natural gas Oil 5000 Today Future projection (DoE/EIA) Coal Biomass Figure 1 The development of world energy use from 1860 to 2003 with forecast to Today it is starting to be recognised that emissions of CO 2 from fossil fuel combustion could be much reduced by its capture and safe storage in geological formations. Capture and storage of CO 2 can in the short to medium term play a part in sequestering already concentrated CO 2 -streams, such as from natural gas treatment or ammonia and hydrogen production plants. In the longer term underground CO 2 -storage may provide an important route to achieve the deep reductions in greenhouse gases that seems to be required to limit anthropogenic climate change. Figure 2 Sites for large and concentrated point sources of carbon dioxide (green dots) are here shown together with oil- and natural gas regions (in red) and major coal areas in black. (Courtesy of IEA Greenhouse Gas R&D Programme).

3 3 WHAT SHOULD WE LOOK FOR IN UNDERGROUND CO 2 - STORAGE? Underground CO 2 -storage of any kind must take place in sedimentary rocks. Only they are porous enough to have storage capacity of interest. Figure 3 gives a global overview of the World s sedimentary basins. These are also the only places where coal, oil and natural gas are to be found. Figure 3 Sedimentary basins of the world. Onshore basins are shown in green. Offshore basins are in lavender (Source: Slumberger). The suitability of saline aquifers and oil and natural gas fields for CO 2 storage within these basins will vary widely. In order to achieve large storage capacities underground, CO 2 should be stored above supercritical pressure (supercritical point at 31 o C, 74 bar) and therefore deeper than 800 meters below the surface. At these pressures CO 2 is very compressible and will typically have a density of 600 to 800 kilograms per cubic meter. This means that CO 2 will be buoyant and tend to move upwards less strongly than natural gas, but more strongly than oil. Underground storage of CO 2 is conceptually easiest when done in oil and natural gas fields where long-term storage has already been proven for by the containment of these hydrocarbons. To store CO 2 in a saline aquifer means that we do not have the same assurance as in oil and natural gas reservoirs that there is a closure or other mechanism capable of preventing the upward migration of CO 2. On the other hand these aquifers are structures that for the same reasons will not have been penetrated by oil and gas wells in the past. An underground storage site for CO 2 need to have a reasonably good porosity and a less porous roof preventing upward mobility. Also it needs to have a reasonable size in order to prevent pressure build up. A closure, which prevents CO 2 from spreading under the roof, may at first sight be seen as required. The experience from and modeling of the Sleipner injection, which does not rely on horizontal closure, indicates that the spreading distances will be limited. The injected CO 2 will over time dissolved into the brine, become heavier than the fresh brine and tend to sink to the bottom of the aquifer. The possibility also exists to dissolve the CO 2 in brine before or as part of the injection process. In this case the injected fluid would be heavier than the surrounding brine and tend to settle to the bottom of the aquifer. Some aquifers will contain rock, especially silicates rich in calcium, magnesium and iron that will tend to react with the injected CO 2 to form carbonates giving storage a very high degree of permanence. There may also be problems connected to such chemical reactions, as they may tend to lower the injectivity of the wells. National regulations for underground injection will be important for insuring safe and reliable CO 2 - storage. Industry will be able to give valuable input, such as the Manual of Best Practice that has been produced as part of the Sleipner/SACS project.

4 4 In order to make the concept of CO 2 -storage in aquifers more real and show how different circumstances may be even for seemingly similar schemes, I will below describe briefly the existing Sleipner CO 2 -storage scheme (presented in more detail in another WGC 2003 paper) and the future Snøhvit CO 2 -injection. THE SLEIPNER CO 2 INJECTION The first decision to apply underground storage of carbon dioxide (CO 2 ) captured from natural gas - as a climate change mitigation effort - was taken by Statoil (operator) and partners in the Sleipner North Sea licence. Around 1990 the Statoil operated Sleipner West offshore gas-condensate field were being planned. A small technical team proposed offshore removal of carbon dioxide from the natural gas which contains about 9% CO 2 too much to be sold without treatment. The CO 2 to be removed amounts to one million tons per year, or nearly 3% of the Norwegian CO 2 emissions at that time. The technical team therefore was influenced by the discussions taking place in the Norwegian Parliament about climate change and a possible national carbon tax (introduced in 1991). They therefore proposed that the removed CO 2 should be injected for permanent storage into a deep saline aquifer underlying the Sleipner installations. After some discussion with the field partners, this became the approved solution. When the field came on stream in October 1996, the field concept contained not only a massive offshore CO 2 -removal plant a world first -, but also the world s first CO 2 -storage in a saline aquifer (the Utsira formation) 1000 meters below the sea bottom. Figure 4 The Sleipner CO2-injecton as seen in an artist s impression. The carbon dioxide captured from high-pressure natural gas is being injected back into a geological formation called Utsira. THE FUTURE SNØHVIT CO 2 INJECTION In the fall of 2001 operator Statoil and license partners in the Snøhvit (name means Snow White ) natural gas field in the Barents Sea off North Cape in Northern Norway made an investment decision to develop the field. The field, which will come on stream in 2006, consists of a fully sub sea offshore development, a 160 kilometer multiphase pipeline to shore, a liquefaction plant for making LNG for shipment to USA and Continental Europe and last but not least a 160 kilometer CO 2 -pipeline back to the field to store 0,7 million tons/yr of CO 2 captured from the natural gas during the processing to LNG.

5 5 Figure 5 This figure shows the offshore injection of CO 2 that will start in This CO 2 is captured onshore at an LNG plant and will be transported in a 160 kilometre long pipeline to the injection site. UNDERGROUND STORAGE AS A CLIMATE CHANGE MITIGATION TOOL In numerous climate change scenarios the use of underground storage of CO 2 is shown to be something that will be taken into use sometime between 2020 and We think it is useful to at least modify this line of thought for a couple of reasons. The first is the driver inherent in the already concentrated CO2-sources (fig. 2) and a second and even more important driver will be the use of CO 2 for enhanced oil recovery spreading out to other continents from North America. The power of the examples already there in combination with such drivers may drive the whole field faster than imagined by people outside the oil- and natural gas industry. Figure 6 illustrates this by showing how Statoil are achieving CO 2 -reductions. Figure 6 Emissions of CO2 from Statoil operated facilities would have been 1/3 higher by 2010 in a business as usual situation where no attention was paid to greenhouse gas emissions. A sizable portion of this reduction is due to the CO2-injection schemes at Sleipner and Snøhvit.

6 6 UTILISING CO 2 FOR ENHANCED OIL RECOVERY Carbon dioxide (CO 2 ) has been injected into geological formations by the oil industry for about fifty years. The purpose of this injection effort has not been climate change mitigation, but to displace/dissolve oil for increased oil production. Currently, about 40 million tons/yr of CO 2 is being injected into geological formations for the purpose of improving oil recovery from mature fields. Most of this injected CO 2 remains in an oil reservoir, but the majority of the floods cannot be considered sequestration/storage projects because the CO 2 source is another geological formation. Some CO 2 is, however, from industrial plants such as natural gas refineries as well as ammonia- and gasification plants. Over one hundred oil reservoirs have over the last fifty years (mainly the last two decades) had CO 2 injected. Of these about 70 are still in operation, mostly in the Permian Basin in southern USA. With global climate change as a forceful additional driver it seems likely that the utilisation of CO 2 for getting more oil out of aging oil fields will become more widespread in the future. Figure 7 Illustration of the utilisation of carbon dioxide for enhanced oil recovery (Courtesy of IEA Greenhouse Gas R&D Programme). CONCLUSIONS There are several drivers that now seem to make the large-scale use of geological storage of carbon dioxide more likely than appreciated up to now. The topics of CO 2 capture, -storage and utilisation have in little over a decade moved from a curiosity to something being seriously considered by energy companies and governments all over the industrialised world. The drivers are the possibly extended use of CO2 for increasing the recovery of oil from mature oil fields, global climate change as an increasingly important issue and also the recognition that there are numerous large and already concentrated point sources of carbon dioxide ready to be injected into a suitable reservoir. REFERENCES 1. Baklid, A, Korbøl, R. and Owren, G., Sleipner vest CO 2 Disposal CO 2 Injection into a shallow Underground Aquifer, SPE 36600, Denver, Colorado, USA, Gale, J.J., Christensen, N.P. Cutler, A. and Torp, T.A. Demonstrating the Potential for Geological Storage of CO 2 : The Sleipner and GESTCO projects. Environ. Geoscience, 8, 3, September 2001

7 7 3. Arts, R., Brevik, I., Eiken, O., Sollie, R., Causse, E. and van der Meer, B., Geophysical Methods of Monitoring Marine Aquifer CO 2 Storage Sleipner Experiences. In: Proceedings of the 5th International Conference on Greenhouse Gas Reduction Technologies, CSIRO, Collingwood, Australia, 2001, Edited, Williams, D., Durie., B., McMullan, M., Paulson, C. and Smith A. 4. Arts R., Eiken, O.,Chadwick., Zweigel, P., van der Meer, L., and Zinszner, B., Monitoring of CO 2 Injected at Sleipner Using Time Lpse Seismic Data. In: Proceedings of the 6th International Conference on Greenhouse Gas Reduction Technologies, Elsevier Science, London, UK, 2003, Edited by Gale, J.J. and Kaya, Y.