Experts meeting for two days in an event organized by the IEE and RCGI discussed economic viability, regulations, and CCS technologies

A variety of technologies for storing carbon were presented during the workshop on Technologies for Capturing, Storing, and Utilizing CO2 in Different Formations, which was held on November 16 and 17 in USP’s Energy and Environment Institute (IEE/USP). The event was organized by the IEE and by the FAPESP Shell Research Centre for Gas Innovation (RCGI) and had speakers from the IEE, USP’s Polytechnic School, UNICAMP, USP’s Physics Institute, and Portugal’s Fernando Pessoa University (UFP). On the first day, ten speakers made presentations. The second day was occupied by a minicourse given by UFP Professor Cristina Rodrigues.

The event opened with a quick presentation of the RCGI’s 15 new projects for CO2 abatement, by Professor Kazuo Nishimoto, who focused on Project 34, regarding the construction of salt caves – to which, in some way, all of the others related – and by Felipe Rugegre, who presented an overview of Projects 30 to 45.

Then, Professor Edmilson Moutinho spoke about Policies and Economic Perspectives of Carbon Capture, Storage and Utilization (CCUS). He emphasized that, despite the large number of publications covering the subject in recent years, doubts continue regarding the classification and identification of technologies, applications, assessing the potential for capturing, cost assessment and other core subjects. According to him, the risks are very important to the decision-making process. “Investors could favor an option with higher costs, if they feel that it implies lower risks.”

Moutinho listed several reasons for supporting CCS initiatives in Brazil, including enormous short and medium-term pressures coming from pre-salt. “Avoiding burning is a strategic need for sustainable pre-salt. As for reinjections, we must remember that today’s reinjections will become the production growth of CO2 tomorrow.” Among the difficulties, he mentions that the Brazilian government will still need a lot of time to commit to CCS, and that it will take years to convince the treasury to sponsor demonstration projects. “Actually, we are mired in the historic debate that opposes petroleum and cleaner natural gas against the utilization of more renewable energy sources, and that debate goes back to the decade of the 1990s.”

Professor Gabriel Costa Lima, of UNICAMP, called attention to the discrepancy between the minimum and maximum costs for capturing, storing, and recompressing CO2. “Capture and storage are distinct activities with distinctive costs. Back in 2004, CCS still presented a significant 30% risk to investors. The differences between the minimum and maximum values of each stage of the process were enormous, which was one more reason for the insecure feeling of those who wanted to become involved in the enterprise. Today, this should have changed a little. But what does not, and will not, change is the fact that the final decision always involves economics. If it is economically viable to do CCS, then it will work. If not, it won’t work,” he said.

Shale and salt caves – The perspectives for storing carbon in non-conventional onshore petroleum reservoirs and in sedimentary offshore basins were among the subjects dealt with during the event. This subject is the object of RCGI’s Project 36, which will study these possibilities in Southeast Brazil. “The objective is to assess the geological viability of implementing technologies for storing carbon in these reservoirs and to develop a multi-scaled model for storing CO2 in the shale of the Bacia do Paraná, combined with the simultaneous stimulation of non-conventional gas,” summarized Professor Colombo Tassinari, coordinator of the Project and an IEE researcher. “But everything will be done with models, because we cannot legally do tests in loco, on a real reservoir.”

Another possibility for storage are deepwater salt caves. In his presentation, Engineer Pedro Maia da Costa remembered that various liquids and substances are injected in geological deposits all over the world. “The technology for salt caves has already been developed and applied to the underground storage of petroleum, natural gas, and compressed air. The largest inventory of U.S. petroleum and natural gas is in a salt cave with a ceiling higher than the Eiffel Tower. Also, there are manuals of best practices for building and monitoring those caves.”

According to him, in the case of CO2, with regard to the stability of the cave, the big question would be the increased pressure after the cave is abandoned. “This is because, with the passage of time, the salt cave deforms and its volume is reduced. A cave filled with CO2 and in a supercritical state will gradually close down, reducing its volume until the interior pressure equals the external stress in the salt bed.”

Maia further stated that it is not just any type of rock that can be used for storage and that construction is slow and costly. “But, considering the reality of the pre-salt region, the construction of caves would be viable. The coast of the State of Espírito Santo is a perfect place for storing carbon in salt caves.”

Coal – Geologist Cristina Rodrigues, Professor at Fernando Pessoa University, who was invited to the event, spoke about storing CO2 between layers of coal. According to her, the injection of CO2 could improve the production of methane from coal. She began by showing the differences between conventional (deepwater saline aquifers and depleted oil and gas reservoirs) and non-conventional (layers of coal and shale gas) reservoirs and stated that the circulation and storage performance varies between them. This is because the performance of the reservoir depends on static and dynamic components.

“In conventional reservoirs, the fluids are dispersed homogeneously in the pore structures, depending on their concentrations. And those fluids circulate in a specific direction, which depends on the pressure gradient and its viscosity,” she explained. “However, in the non-conventional reservoirs, the fluids are heterogeneously dispersed in the pore structures. The molecules of the fluids attach to the walls of the pores, due to a high level of affinity with the organic structure of the reservoir. In these cases, the flow of the fluid depends on the pressure gradient of the different components present in its mixture and on its interactions with the organic structure of the reservoir, as well as the effects of the organic property of pore shrinkage and swelling.”

Cristina demonstrated how the injection of CO2 in coal can also be used to recover methane from a coal layer. “This is done in three phases: first, CO2 is captured from a gas source, then it is compressed and injected into the coal for methane recovery or storage.” In one of the previous lectures, regarding the utilization of CO2 to improve the recovery of petroleum in oil wells, physicist James de Almeida raised a similar possibility. “CO2 is the best candidate for reinjection in oil wells, in order to recover trapped oil. It would necessary to know if the CO2 could remain there, in storage.”

As Cristina sees it, coal is the most efficient form of keeping CO2 stored for a significant geological time. “The best solution, in terms of security, is coal. The bond between CO2 and the organic structure is excellent. It is the adsorption process that causes CO2 to stick to the coal structure, physically attached to it, as long as sufficient pressure is maintained.”