“Wellbore Barriers — More than Just a Good Cement Job” will be presented by keynote speaker Glen Benge at NGWA’s Groundwater and Oil and Gas Development: Improved Management Practices for Groundwater Protection and Water Supply workshop, which is taking place March 4-5 in San Antonio, Texas.
Benge is an independent consultant specializing in wellbore isolation and well cementing. Retired from ExxonMobil where he spent more than 24 years working as a technical adviser in drilling, he has 40 years of experience associated with all aspects of well cementing and isolation, and has authored numerous papers and texts on all aspects of cementing design and application.
Benge shares his insights on wellbore integrity and gives a preview of his keynote presentation.
NGWA: How did you become interested in wellbore integrity?
Benge: My career has centered around cementing oil and gas wells, and the establishment of barriers. As a key part of well construction, I found the technology of cementing evolved from one of just needing the cement to set up and get hard to one of understanding wellbore stresses and designing systems that can withstand the downhole environment throughout the lifetime of the well. We now are concerned with the mechanical properties of the cement and how to manipulate the material to do things we did not consider in the past.
NGWA: What do you see as the primary factors affecting long-term wellbore integrity?
Benge: There are two areas I describe as the chemistry and physics of barrier placement when it comes to cementing. You must design the slurry properly, meaning the materials and additives must address the downhole environment from the potential corrosion aspect as well as the temperatures and pressures to be encountered. The physics of placing that cement properly employs fluid dynamics, wellbore preparation, use of proper downhole equipment such as centralizers, etc. Without attention to both the chemistry and physics of cementing, it is not possible to obtain a lasting wellbore seal.
NGWA: The title of your keynote presentation is “Wellbore Barriers — More than Just a Good Cement Job.” Can you give us a hint about what you mean and what the take-home message is of your presentation?
Benge: The talk will discuss the definition of a barrier, both in terms of an overall barrier and various barrier elements. With respect to cementing, many folks believe if they have paid attention to the chemistry and physics of the cement job, then they should be in good shape. The issues that come up are maintaining that barrier within its operating envelope, something that is often overlooked with hydraulic fracturing operations.
The real question comes to be one of do we depend on a single element, in this case cement, to provide a barrier for the life of the well, or should we be looking at barrier systems that contain not only cement but also some sort of mechanical barrier. If the latter is the case, then how does one evaluate and test the individual barrier elements that make up the system. If I have both cement and a packer for example and obtain a successful pressure test, I do not know if both the cement and packer passed the test, or if only the packer or the cement passed. I must understand how to evaluate barrier systems that consist of multiple elements.
For me to consider something a barrier, I have to test it in the “as installed” position to make sure it is functioning as it was designed. This becomes quite difficult when I can only test a system that may have multiple parts. If the test fails, then I know none of the parts were properly functioning. If the test passes, then I know the total system may work, but do not know anything about which part or parts are working. The only thing I know for sure is at least one of them is working.
I will talk about the definition of a barrier and barrier elements, and try to take a look at what it takes to gain wellbore integrity. Another area is wellbore integrity, which brings up questions of if there is an acceptable “leak rate” for well integrity. This is often measured as a pressure at the wellhead. If it is not zero, but some small number — 100 psi as an example — yet my system is rated to 5,000 psi, then do I have well integrity?
NGWA thanks Benge for his time in answering these questions and in being the keynote presenter at the Groundwater and Oil and Gas Development: Improved Management Practices for Groundwater Protection and Water Supply workshop.