The other day, I received an email from a representative of an international oil company, which is wholly owned by the government and reports to the Department of Energy. The email contained this statement:
“Recently, Gerrit van Tonder, a professor at the University of the Free State argues that “aid cement and steel casings in the Karoo would inevitably deteriorate and fail over time, resulting in the upward migration of fracking fluids to ground water zones. Is this true?”
This is my reply to the question.
RE: Question – “would the cement and steel casings in the Karoo inevitably deteriorate and fail over time, resulting in the upward migration of fracking fluids to ground water zones?”
The answer to the question depends on what is meant by “over time.” Nevertheless, the short answer is “Yes,” sometime in the future the casing/cement in the wellbore may undergo mechanical and/or chemical failure. But functional failure from damaged casing and cement is highly unlikely in the near future; where functional failure is the inability of the structure to perform as intended.
It is understood that the purpose of the cemented casing is to:
• “Prevent contamination of fresh water well zones.
• Prevent unstable upper formations from caving-in and sticking the drill string or forming large caverns.
• Provides a strong upper foundation to use high-density drilling fluid to continue drilling deeper.
• Isolates different zones that may have different pressures or fluids – known as zonal isolation, in the drilled formations from one another.
• Seals off high pressure zones from the surface, avoiding potential for a blowout.
• Prevents fluid loss into or contamination of production zones.
• Provides a smooth internal bore for installing production equipment.”
The well’s susceptibility to functional failure relates to the experience level, standards, regulations and oversight used to design, build, operate and plug the well. For this discussion, active life and plugging are essential to the wells performance over time. The industry has developed proven casing, cementing, drilling, completion and plugging requirements and regulations.
Active Life: The life expectancy of a well is dependent on the protection that the borehole can receive from primary cementing operations. This provides zonal isolation and preserves structural integrity over the life of the well.
End of Life: When a well reaches the end of its useful life, cement plugs are placed in the borehole to prevent migration of fluids between the different formations. Dry wells are plugged in such a way as to confine oil, gas, and water in the strata in which they are found and prevent them from escaping into other strata. Cement is required to be circulated through tubing or drill pipe across producing formations. There are highly specific plugging requirements to protect usable quality water from pollution and to isolate each productive horizon.
The caveat to ensuring a long-term, environmentally safe well after abandonment is dependent on the experience level of the contractors, adherence to best management practices, sophistication of the regulatory agencies and degree of oversight. These vary state-by-state.
In particular, the State of Texas has one of the most mature and sophisticated regulatory agencies in the U.S. Texas’ Railroad Commission (RRC), which has oversight responsibility, was established in 1891 to regulate the rail industry. Over its 118 year, the RRC has expanded to encompass many different industries, particularly the oil, natural gas, and coal mining industries. In its regulatory role, the RRC has environmental and safety responsibilities related to oil and gas production. An overarching agency goal is to encourage the responsible development of natural resources while protecting the environment.
The answer to the question lies in the fact that modern shale gas development is technologically driven and must be treated as such. There is a significant knowledge base to ensure development, production, and abandonment are done right. Sixty plus years of experience tells us, shale gas can be safely managed and controlled. Done right it is a very low risk proposition, now and for the future.
The problem may be due to the regional nature of the business whereby proven methods and regulations are not always used by local contractors and adopted by state agencies.
It is interesting to note that The Pantheon in Rome, Italy was built about 126 AD. Besides its age, the unusual aspect of this structure is its concrete dome. “Almost two thousand years after it was built, the Pantheon’s dome is still the world’s largest unreinforced concrete dome. The height to the oculus and the diameter of the interior circle are the same, 43.3 meters (142 ft).” As import, is the fact that this dome has few cracks.
My qualifications include serving as a Sr. Vice President – Engineering and Sales at a concrete company for over 10 years and reorganization by the U.S. Federal Court system as expert in concrete and related construction projects.
By. Dr. Barry Stevens