About My Ambitious Project: Introducing Carbon Sequestration into Carbonate Formation in Indonesia, the First in Asia
My project is proposing a safe and reliable geological CO2 sequestration into carbonate rocks as deep as 3 kilometres underneath the earth in Indonesia, the first in Asia. This will turn the damaging CO2 greenhouse gas into rocks and store it in the crust for years. I develop a technique of seismic monitoring and a computer program to ensure that this project is safe and reliable for humankind.
Could you save the world from climate change with your own way? I have my own way to do that. The earth’s temperature that has been rising since the past ten years would be so harmful to life on earth if we could not control the greenhouse gas emissions from entering the atmosphere. As number of industries, for instance oil and gas industries as one of the highest contributors of carbon dioxide, and transportations increase significantly to meet with the demand of increasing consumption due to increasing human population up to 8 billion in 2024, the release of carbon dioxide worsens the atmosphere and is responsible to tragic natural disasters such as cyclones and drought. Humans have to be the ones who are mostly responsible to climate change. My concern in this tragic climate change grows owing to my professor and also a best friend, Dr.rer.nat Armi Susandi, an expert in climate change mitigation and adaptation, giving lectures at class. “You have to pay each release of carbon dioxide at high cost because disasters are also highly costly,” Prof. Armi states almost in every lecture he teaches. I ask you if you think that Indonesia is not a clean country. My answer is simply yes. People do not care about this situation, and that is why as an engineer and geophysicist, I start my passion in carbon sequestration.
Indonesia has been experimenting carbon sequestration since 2012 under a team led by Dr.rer.nat Mohammad Rachmat Sule from Bandung Institute of Technology, Indonesia. He is a doctor from Karlsruhe Institute of Technology, Germany. Not only is he a brilliant lecturer but also he has broad knowledge about everything, especially in geophysics and study opportunities abroad. I became fascinated to learn the so-called carbon capture and storage (CCS) with Prof. Sule until I decided to take CCS as my bachelor thesis topic. The CCS project that he led is located in Gundih, Central Java, Indonesia. This area will be a very huge storage of carbon dioxide captured from the gas plant in the field from being released into the atmosphere. The field approximately produces as much as 800 tonnes of CO2 each day. There are recently many master and doctoral students under Prof. Sule researching Gundih. As part of the researchers, I am very ambitious that I could make a contributive innovation in this project.
Under my CCS work area there are various rock formations, mostly clastic formations that are composed of sandstone and shale, but what really interests me is the carbonate formation under Gundih. This carbonate formation is very huge and beautiful if you see it in the subsurface. Geologists and geophysicists can clearly describe this as a carbonate reef, but let us think of limestone hill that is buried as deep as 3 kilometres in the crust. This carbonate reef is as high as almost 200 metres and the areal coverage of about 40 square kilometres! 34 to 23 million years ago, during Oligocene epoch, this carbonate reef platform started to grow from remnants of calcareous sea micro-organisms and healthy reefs, and then it was deeply buried (an ancient relevance to the present Great Barrier Reef in offshore Australia). Now, I am working on to propose that this ancient wonder could be storage for carbon dioxide. I believe that this will be a tremendous hit to other countries around the world which are also on the way developing carbon sequestration. There has been only one CCS that injects CO2 into carbonate formation in Hontomin, Spain until this time being. Hence, if this project is successful, Gundih carbonate CCS will be the second after Hontomin and perhaps the first in Asia!
What is my project about?
CO2 is injected in supercritical phase deep into Gundih field. Injection of a supercritical fluid is very critical. Every step should be considered carefully. When you inject something into the earth as deep as 3 kilometres, there will be immense pressure and temperature that you must deal with. What is different about supercritical condition is that carbon dioxide will have different physical properties compared to in fluid or gas phase. Imagine that you have a bottle of gaseous CO2 at 25°C and almost vacuum (0.01 atmosphere), and then you add pressure to the bottle and heat it gradually. When the temperature reaches 31.5°C and pressure of 73 atmosphere (about 700 times of initial vacuum pressure), the gaseous phase gradually change to liquid phase. If you continue to pressurize and heat it, you will consider that you are no longer seeing obvious distinction between its gaseous and fluid phase. This is called supercritical CO2 or scCO2.
Surprisingly, this process of pressurization and temperature increase are naturally occurred deep in the subsurface, and this will be adopted in my project. When the CO2 is injected into deep subsurface, the pressure and temperature rise and keep the CO2 in supercritical phase. When it reaches the rock formation, in my case is carbonate formation, the injected scCO2 enters the rock pores, begins chemically interacting with the brine water in the pores and rock matrix, and finally be safely contained inside the rock pores.
Some might ask how to capture the CO2 from the field. In most oil and gas fields onshore and offshore, flaring seems to be a popular, favourable, and instant way of processing CO2. After producing barrels of oil or cubic feet of gas, CO2 contained in the hydrocarbon has not economic value or useless. Therefore, combusting the CO2 into free air will dispose the useless gas. This is called flaring. When you see a huge, violent, and bright flare comes out of the rig, it means the flaring is on the way. Flaring badly hurts the atmosphere because you know, tons of CO2 are released into atmosphere. Imagine how bad it is!!! Carbon sequestration is a way to capture CO2 contained in the hydrocarbon using chemical reactors and separators, so that flaring will be no more. And then, the captured CO2 is transported and ready to be injected into the subsurface.
What technique do I use?
The process of injection and storage of scCO2 must be monitored because you have never known the condition deep inside, especially here I deal with a very huge structure of ancient carbonate reef as a reservoir target for injection. Now, with the advancement of geophysical technologies, the process of injection could be monitored from the surface. So, this is what my project is about. I develop seismic time-lapse forward modelling technique. I do seismic ray modelling to construct the physical phenomena of seismic wave propagation through my carbonate formation. Seismic wave propagation is a natural phenomenon that occurs inside the crust. Humans can generate a seismic wave by using detonation into the earth and record how much time lag until you hear the detonation using special receivers. The principle is quite the same like ocean sonar, but the only difference is that the ocean is now the solid earth. Seismic wave propagates inside the earth because the subsurface is very heterogeneous, thus having different seismic velocities abbreviated as Vp.
Seismic velocity is telling you different rock types in your subsurface. I make a simple illustration that you could see above. If you recognize a zone of low seismic velocity in your subsurface, you might encounter low density rocks for example sandstone. However, if you recognize a zone of high seismic velocity, you might encounter high density rocks for example carbonate rocks. But earth’s crust is not that simple. It also contains zones with fluid saturation. Fluid has the characteristic of low density, therefore its Vp will be much lower than that of rocks. If you recognize that your seismic wave velocity slows down, you might encounter a zone with fluid saturation. Now, how do I incorporate this simple idea to my project? The injection of CO2 increases the saturation up to 100% saturation in the rocks, creating a CO2 plume. Over the years, the plume will develop and spread within the rocks in the formation. However, while being injected, we could not surely recognize the shape of the plume and its saturation. Therefore, time-lapse seismic modelling is a technique to monitor the CO2. The different fluid saturation in the rock formations will change the seismic velocity of the rocks. If we could record the seismic velocity change in the CO2 reservoir after continuous injection, we would be able to determine how much percentage CO2 has filled the reservoir.
I believe this technique would be very practical, but you need a good processing and computation skill. To work on this technique, I will use powerful software named NORSAR. NORSAR is a software developed by Norwegian geophysical service company that is very powerful and robust for seismic computation. I am very sure that this technique will interest more people in the field of carbon sequestration.
How sure am I that this project is safe for humankind?
This injection of supercritical CO2 project into carbonate rock formation is safe and sustainable only if many factors are considered. The main concern of all injection projects is the integrity of reservoir to be capable to store the injected CO2 for a long time. In rock physics, we know that rocks have certain failure threshold. Imagine that you give a gradually increasing stress to a rock, you will see that up to certain point of the stress magnitude you give, the rock will stay strong. If you exceed the stress limit, the rock will break apart or swell. In the lab, we determine the stress limit of a certain rock sample using triaxial compression test. Stress in rocks occurs in three kinds: vertical stress, maximum horizontal stress, and minimum horizontal stress. The reservoir rocks do also have stress limit due to high pressure and high temperature at depth. The carbonate reef rock in my project is also surely stressed due to its being compacted by the overburden sandstone and shale formation as thick as nearly 3 kilometres from above!!!
If we apply a handmade stress in the lab, in the case of CO2 injection we apply an injection pressure to the rock. Soon after the fluid enters and fills the rock pores, the rock will be pressurized or stressed. Therefore, we should know the stress limit of the reservoir rock so that we know the limit of injection pressure that we must apply to avoid the rock failure. Why is the reservoir rock failure a very damaging problem? The consequence will be so damaging. There are two possible consequences, either creating an earthquake or upward penetration of CO2 to underground water storage. The most feared consequence is the second one, since CO2 is very toxic. However, I am sure that the second consequence is nearly impossible because the reservoir is 3 kilometres deep. That is why I decide that the carbonate is very potential to be a sustainable storage.
Here, I am developing a computer program that could monitor the injection pressure.
This program will tell you how close your injection pressure to the stress limit of the reservoir rock so that you should not exceed the injection pressure above the limit. The code is assembled based on principle of geomechanics. The computer program will compare the value of calculated stress limit of the reservoir rock and the value of injection pressure, and then it will tell you whether the injection pressure exceeds the limit or stay below the limit. If it exceeds the stress limit, the program will then inform you to reduce the injection pressure. In this way, we could ensure that the injection is safe.
How do I know that my carbonate formation is a perfect storage place?
Carbonate rocks are naturally formed in a unique way. Tectonic and sedimentary processes are two main ingredients that influence the deposition and growth of a carbonate platform, therefore there will be variety of kinds of carbonate platform around the world. However, one common thing that controls all those varieties is the sedimentary environment, marine environment. Due to seasonal rising-up and falling-down of sea level that ranges at interval of years or even hundreds of years, the growth of carbonate reefs follows the changes. When sea level rises, the ancient reefs become highly fertile and robustly grow up. In contrast, during the period of falling sea level, the topmost part of the reef will gradually decease and become eroded. This weathering process creates pores inside the calcareous reef and becomes porosity. Some become karstified. Inside the rocks, the calcium carbonate (CaCO3) is crystallized. During the crystallization, dissolution also occurs. This process significantly makes pores within the grains. Some become vuggy porosity and others become fenestral, moldic, and many other types of porosities. This is why carbonate porosity is different from clastic porosity, for instance sandstone.
Years after supercritical CO2 injection, the CO2 will be trapped inside the carbonate vuggy pores. It interacts safely with the reservoir brine water and the rock matrix. Researchers at CarbFix project that target CO2 injection into basaltic rocks in Hellisheidi, Iceland, successfully showed that CO2 is mineralized together with the rocks to form mineralized calcium carbonate. It really turns out that turning CO2 into rocks is very possible as well as in Gundih.
Conclusion
The pressure of climate change that makes countable consequences on humankind has transformed the way we live. The continuing practice of environmentally unfriendly production of fossil energy that contributes tremendous emission of greenhouse gases into the atmosphere makes me fear a lot. Before the earth becomes uncontrollably warming up, I believe that this project could re-open eyes of humankind to remember a very famous line said by Neil Armstrong, “One small step for man, one giant leap for mankind.” If I could prove that CO2 could be injected into carbonate rocks in the crust in the far future, I believed that this innovation will transform the technology of carbon sequestration.
Yohanes Nuwara, a zero-carbon warrior
Acknowledgment: Dr.rer.nat Mohammad Rachmat Sule
