Effect of CO2 on the integrity of well cement examined

March 5, 2013 by Linda Morton
NETL studies effect of CO2 on the integrity of well cement
Three layers of steel (casing and tubing)and two layers of durable, long-lasting cement separate the contents from the surrounding groundwater.

Geologic carbon storage is the separation and capture of carbon dioxide (CO2) from large stationary sources, such as power plants, followed by injection into deep geologic formations. Long-term storage of CO2 pre-supposes very low or no leakage from the formation. The majority of locations that are being considered for CO2 injection are in areas that have a history of oil, natural gas, and/or coalbed methane production, and are typically penetrated by a significant number of wells from exploration and production. The ability to effectively store large quantities of CO2 may be compromised by the presence of these active or abandoned wells, which represent potential leakage paths.

Once an oil or gas well is drilled, it is typically lined with a steel casing cemented into place. The cement is placed in the annular column (the annulus) between the casing and the surrounding to support the steel casing and to prevent the flow of fluids and gases along its outside diameter. When a well is ultimately abandoned, the casing is typically plugged with cement to block of fluids. Cement is not stable in a CO2 environment and can be vulnerable when a wellbore is exposed to CO2 injected into the surrounding formation for permanent storage. The integrity of cement has important implications for the long-term fate of CO2. As a result, DOE's National Energy Technology Laboratory research has focused on the integrity of wellbore cement when contacted with injected CO2 under storage conditions. This entails simulating deep underground injection and wellbore conditions such as and pressures using common wellbore cements. Results show that temperature, pressure, cement type, cement additives, and fluid properties play a significant role in the rate of reaction and alteration.

Chemical and microstructural changes resulting from exposure to CO2 were examined using a variety of analytical techniques including scanning electron microscopy and x-ray diffraction.

Results of long-term CO2/cement experiments show that the CO2 reaction with typical wellbore cement is too slow to cause leakage in a properly constructed well in good condition, and are in excellent agreement with the examination of cement samples obtained from a well that had been exposed to CO2 for EOR (enhanced oil recovery). However, cement in old or abandoned wells that may have deteriorated could be a problem. As a result, NETL researchers are now studying situations in which gaps or fractures may be present in the cement column.

Co-sequestration, which involves injection of a mixture of CO2 and hydrogen sulfide (acid gas) is increasingly being practiced. For example, there are over 40 wells being used for acid gas injection in Alberta, Canada. In contrast to pure CO2 injection, there is little understanding of the effects of acid gas on exposed wellbore cements under geological storage conditions. Therefore, NETL researchers have initiated studies on the interaction of cement under co-sequestration conditions.

Explore further: Pulverized rocks used to strip CO2 from large emitting plants

Related Stories

Pulverized rocks used to strip CO2 from large emitting plants

December 6, 2012

Researchers in Quebec are developing a process that would see steel, coal and cement plants as well as oil and gas facilities remove most of the carbon dioxide (CO2) from their emissions through chemical reactions with various ...

Underground CO2 storage study to begin

October 25, 2007

The University of Texas has received a $38 million subcontract to conduct the first U.S. long-term study of underground carbon dioxide storage.

Carbon study could help reduce harmful emissions

February 14, 2008

Earth scientists at The University of Manchester have found that carbon dioxide has been naturally stored for more than a million years in several gas fields in the Colorado Plateau and Rocky Mountains of the United States.

Study tracks safety of underground CO2 storage

December 13, 2011

(PhysOrg.com) -- In a paper published today in the Proceedings of the National Academy of Sciences, an international team of geoscientists, including Simon Fraser University groundwater expert Dirk Kirste, ...

Recommended for you

Mineral resource exhaustion is just a myth: study

April 28, 2017

Recent articles have declared that deposits of raw mineral materials (copper, zinc, etc.) will be exhausted within a few decades. An international team including the University of Geneva (UNIGE), Switzerland, has shown that ...

El Nino and the end of the global warming hiatus

April 27, 2017

A new climate model developed by Yale scientists puts the "global warming hiatus" into a broader historical context and offers a new method for predicting global mean temperature.

Vinegar offers hope in Barrier Reef starfish battle

April 27, 2017

Coral-munching crown-of-thorns starfish can be safely killed by common household vinegar, scientists revealed Thursday in a discovery that offers hope for Australia's struggling Great Barrier Reef.

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Mar 05, 2013
Hence the requirement for Mechanical Integrity Tests (MITs) of all shut-in wellbores at appropriate intervals.
See Chap. 3. - OPERATIONAL RULES, DRILLING RULES, Sec. 16. - Temporarily Abandoned or Shut-In Wells (Forms 2 and 4)., ΒΆ(c), of the regulations of the Wyoming Oil and Gas Conservation Commission.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.