Closer look at carbon storage plan

Wei Kuo-yen 魏國彥  / 

Fri, Jul 05, 2013 - Page 8

A major story published in the Apple Daily recently said that Taiwan Power Co (Taipower) and state-run oil refiner CPC Corp, Taiwan, are secretly planning to store carbon along the west coast of Taiwan “right under people’s noses.”

Residents of Yunlin and Changhua counties have expressed concern about these plans, citing a case of mass asphyxiation in the West African country of Cameroon.

On Aug. 21, 1986, Lake Nyos, a crater lake saturated in carbon dioxide, suddenly released a large cloud of carbon dioxide gas into the atmosphere, asphyxiating everything within a 25km circumference and causing the deaths of about 1,700 people and 3,500 livestock.

This tragedy was an example of the dangers involved in storing carbon dioxide.

Yet carbon dioxide capture and storage (CCS) is nothing new: It has been used by many petroleum companies to increase underground pressure and displace oil from underground fissures — a process known as carbon dioxide enhanced oil recovery (EOR). EOR is used to increase yields in aging oil fields and to store carbon dioxide underground, killing two birds with one stone.

CPC’s current plan is to pour carbon dioxide back into exhausted underground gas-bearing structures, or reservoirs, in Miaoli, from which natural gas has already been extracted, essentially pumping waste emissions back into the reservoirs that had originally held the gas in its natural state.

The structures already have impervious overlying strata, otherwise they would have been unable to hold the natural gas in the first place. Pouring the carbon dioxide gas into the reservoirs would be like placing bonds or old newspapers into a safe after you have removed your cash: It presents no risks whatever.

Taipower, for its part, intends to store carbon in deep salt water reservoirs from 2km to 3km underground. To ascertain the conditions in the underground strata, it is already drilling exploration wells that will later be reincarnated as monitoring wells.

The upper level in the stratigraphic sequence in this area is a cap layer, followed by an impermeable layer and then a storage layer.

When the carbon dioxide seeps into the salt water reservoir 3,000 meters down, it will set off a series of chemical reactions leading to a process of mineralization.

After this, the carbon dioxide will cease to act as a gas, a process known as “geological sequestration,” at which point the process is no longer pure storage. Furthermore, the strata intended to store the gas slants up toward the west. If the gas placed underground migrates, it will do so in this direction and leak out into the ocean floor of the Taiwan Strait.

The 1986 Lake Nyos incident, however, was caused by a completely different mechanism. Nyos is a vast volcanic lake 200m deep. The depth means that the gas exchange rate varies depending on the level. There is little oxygen at the bottom of the lake, where the concentrations of carbon dioxide are relatively high.

Also, the volcano at the lower corner of the lake gently emits heat, increasing the temperature in the lake. When the water hits a certain temperature it rises, displacing the cold water above, which then sinks, and it is when the water with high concentrations of carbon dioxide comes into contact with the surface that it releases the gas into the air.

Lake Nyos is in a basin, surrounded by mountains. The carbon dioxide, on this occasion, became quite concentrated before it spilled out and spread over the local area, asphyxiating people and animals.

In southwest Taiwan, the rocks contain both methane and carbon dioxide. Many mud volcanoes spurt out gas.

If methane is released it can spontaneously combust on reaching the surface, which is the mechanism behind the famous “fire water grotto” in Guanzihling (關仔嶺). Carbon dioxide is also released, albeit in a less spectacular fashion. Thankfully, there have been no reports of either causing a catastrophe.

Naturally, CCS requires government regulation and supervision. Industry cannot be left to do as it pleases.

In the US and Canada seven regional carbon storage associations exist, involving business, industry and academia. In the UK, the EU and Australia there are organizations specifically established for this purpose. These advanced countries are all trying to capture this greenhouse gas and store it underground to tackle global warming.

The recent revelations of Taipower and CPC’s plans show that our energy sector is applying business principles and taking a responsible and proactive approach to CCS. They also demonstrate the strengths of Taiwan’s petroleum industry and geological surveys. We should be encouraging this, not criticizing it.

Government institutions like the Environmental Protection Administration should also introduce more legislation and supervision for all aspects of the geological storage of carbon dioxide — from carbon capture through transport to storage — as well as creating comprehensive legislation for every stage of the CCS life cycle: planning, construction, operation and decommissioning.

This will clarify the legal responsibilities of government and other organizations, and the emissions allowances. Together, this will lay the foundations for the commercialization of carbon storage and establish the required technical standards. This can then be used not only in Taiwan, but also exported to form a new energy sector.

We could also find international partners to join this venture — including China, which currently has real problems with carbon dioxide emissions and smog produced by burning coal.

If this catches on, we may even be able to postpone or evade the dangers of global warming.

Wei Kuo-yen is a professor of geosciences at National Taiwan University.

Translated by Paul Cooper