Deep Storage

This spring, a powerful drilling tip pierced the earth in western Kentucky, grinding downward into the soil and rock. The drill bit hollowed out a narrow tube, eventually reaching a depth of 8,126 feet–about a mile and a half below the grass.

Digging a well to bring something valuable up to the surface is an old idea.

But at this test site in Hancock County, the new idea is to put something down in the ground. And leave it there.

That something is a gas very much in the news–carbon dioxide, which has been blamed for global warming. Since burning coal produces carbon dioxide, and since nearly all of Kentucky’s electricity is produced by coal-fired power plants, our state has a strong interest in research on underground storage of greenhouse gases.

The idea of burying the carbon dioxide is called carbon capture and sequestration. The concept is simple: don’t let the carbon dioxide gas from human activities into the air at all. Instead, trap it at the source (capture), then store it deep underground (sequestration).

Drill team
In 2007, the Kentucky Legislature voted to provide $1.5 million to help test the storage part of this idea.

Soon after that historic legislation, scientists began asking questions. How deep should the storage area be? What’s the best kind of rock to use? Where does that occur?

Maps and detailed knowledge from experts at the Kentucky Geological Survey offered many answers about potential storage areas.

But setting up the test required teamwork from other experts–and a lot more money. Altogether, the U.S. Department of Energy’s National Energy Technology Laboratory, the Tennessee Valley Authority, the Illinois Office of Coal Development and Marketing, and several investor-owned energy companies spent an additional $6.5 million on this project.

During 2008, Kentucky Geological Survey chief scientist Rick Bowersox and other geologists recommended an area of ancient rocks called the Knox formation, which lies below many states in the Midwest. In Kentucky’s Hancock County, the target zone is an underground sandwich of different layers of materials, including quartz sandstone and deep reservoirs of salty water.

David Williams, manager of the Kentucky Geological Survey’s western Kentucky office in Henderson, says, “These substances don’t have any other use at these locations, and have the physical properties we need to store the carbon dioxide.”

Agreements with the surface landowner and the parties who hold the rights to the underground layers were arranged and permission to dig the hole granted.

The long hollow passage–about eight inches across at the bottom-does not end in an empty chamber like a cave. Instead, it stops amid porous rocks. Tiny spaces in these rocks will allow the gas, mixed with brine already there, to spread out–but not up. Just above what Williams calls the “injection zone” at the bottom of the hollow tube is a layer of solid rock that will also help hold the gas down so it cannot seep upward. The brine is also under tremendous natural pressure at these depths, vital to keeping the added gas from coming up to the surface.

Real gone gas
By late summer, everything at the Hancock County site was ready for the next step. Carbon dioxide captured directly from flue gases at a power plant is not readily available–the technology to do that is still being developed and is not part of this test. Instead, tanker trucks brought in food grade carbon dioxide (the same kind that’s put in soft drinks) as a reasonable substitute.

Team members gathered as mighty pumps began to push the gas deep into the ground.

“We put 323 tons of pure carbon dioxide into the well over a two-day period, August 19 and 20,” Williams recalls. “Then we temporarily plugged the well. We will be monitoring water wells and springs in the area, as well as soil gases, to check that nothing is escaping. We’ll continue testing for about five years to see if anything does come to the surface, but frankly, we don’t expect to see any of this gas ever again.”

The results of this kind of research will be especially important to Kentucky’s electric co-ops, as they work to provide energy and protect the environment.

One of those cooperatives is Henderson-based Big Rivers Electric Corp., which operates four coal-fired power plants, providing electricity for distribution co-ops that serve parts of 22 western counties, including Hancock County, where the test well was drilled.

Big Rivers Vice President of Governmental Relations and Enterprise Risk Management Albert Yockey says, “Big Rivers and other energy-intensive industries are following developments in carbon capture and sequestration tests.”

Commercial demonstrations of underground storage are still far in the future. The Hancock County test and similar tests elsewhere in the state are just the beginning. Other scientists and engineers around the world are trying to find practical ways to capture carbon dioxide at power plants and industrial sites. Then the capture technology will need to be combined with the storage method into a complete and workable system.

EARLY TEST RESULTS

The rig rising over Hancock County drilled a well to inject carbon dioxide into a formation of dolomite, a rock porous enough to absorb greenhouse gas. Dianna Tickner, chair of the Western Kentucky Carbon Storage Foundation, says, “We are pleased that early results from the injection tests suggest good potential for safely storing substantial volumes of (carbon dioxide) deep underground in Kentucky’s substantial Knox dolomite formations.”