First In A Series of Technical Updates From Winterhawk Well Abandonment Ltd.
Since 2015 Winterhawk Well Abandonment Ltd. has been researching, developing and testing multiple technologies to reduce the cost and increase the effectiveness of oil and gas well decommissioning. One of the business units is Winterhawk Casing Expansion, which has developed its proprietary Casing Expansion Technology, or CET.
Expanded casing in a shop test using Winterhawk’s proprietary (patent pending) CET assembly
Multi-Finger Casing Caliper log image of downhole test expansions conducted in 2020 using the CET
One of the industry’s more common but challenging aspects of wellbore decommissioning is sealing gas leaks in the production casing annulus. These are caused by multiple factors, including no cement (cementing production casing to surface was not a requirement for many years), poor primary cementing practices, cement deterioration, or the challenge of achieving a secure and permanent cement seal across formations with higher porosity, permeability, water or natural gas.
In Canada this is commonly called a Surface Casing Vent Flow (SCVF), gas which flows from the surface casing vent. In other jurisdictions subsurface gas leakage in the annulus is referred as Surface Casing Pressure (SCP). Routine testing of the existence of SCVFs is a regulatory requirement in Canada.
Often the leak paths to surface are caused by small cracks or gaps, often called a “microannulus.” These can be caused by a breakdown of the seal between the cement and the casing, the cement and the formation, the development of cracks within the cement itself, or a combination thereof.
The traditional method of sealing SCVFs involves re-cementing the production casing annulus, a so-called “cement squeeze.” This involves puncturing the production casing by a variety of methods (most commonly perorating, but more aggressive methods have been developed) to allow cement to be pumped into the annulus at the desired interval from inside the casing, squeezing cement into the source formation, above the source, and/or the leak paths above the depth of the intervention.
However, cement squeezes are expensive with a low success rate, even after years of progress and refinement. Industry experience has shown that cement squeezes have no greater than a 50% success rate or less. This means that if you have to do one, in a single well or the next well you will likely have to do two or more.
The main advancements in cement squeezes have been bigger holes in the casing to accept more cement, or injecting different compounds for sealing such as bismuth or resins.
One of the challenges is that tiny gas flow paths are not easy to find, and even harder to squeeze cement into.
Winterhawk believed another method of achieving the same outcome was a physical cement squeeze, in which the casing would be expanded from the inside causing a reduction in the cross-sectional area of the annulus on the outside. This would result in “squeezing” the cracks shut by compressing the cement.
The ideal device would be a powerful, reliable, retrievable assembly that could expand the casing in a controlled fashion without materially damaging the pipe or impairing the utility of the wellbore and the integrity of the casing. The expansions would not prevent the continued normal use or re-entry of the wellbore, and the integrity would be maintained by not perforating or puncturing the casing.
Development of the CET was based upon the principle that using casing expansion to seal SCVFs could be done at a materially lower cost than traditional methods with a significantly reduced environmental footprint.
Field trials on the CET using a sturdy elastomer expansion element began in the summer of 2018 under a multi-well test program sponsored by a major operator. However, the original tool did not have sufficient power to achieve and sustain what Winterhawk calls permanent “ductility,” where the casing was expanded to the point that it remained plastically deformed. The CET was redesigned with twice the power in late 2018.
However, what followed in late 2018 and 2019 was a series of industry downturns that were not materially reversed until 2021. Operator interest in investigating new ways of solving problems not directly related to sustaining the future of the company declined sharply.
In the spring of 2020 Winterhawk secured a test well for the new CET design. The well had steady SCVF from multiple sources and was deemed an excellent candidate for field testing.
The only way to fully understand the behavior of a new downhole tool assembly is to test it in a well. The operational issues identified were resolved over multiple visits to that wellbore. Multiple modifications were made to the tool during this period. Winterhawk conducted extensive shop testing and third-party engineering on the behavior of cement during compression and steel during expansion, as well as the properties of an elastomer that would provide enough force to expand cemented casing in a wellbore yet reliably contract for multiple expansions in a single run and ensure predictable removal from the wellbore when required.
Of particular importance was the ability to perform multiple expansions during one trip in the hole.
In late 2020 an operator had a unique problem in an old wellbore (drilled in 1951) that contained a stubborn SCVF. Multiple unsuccessful attempts at remedial cementing had been conducted. But until the leak was sealed, a reclamation certificate was not achievable. Casing expansion was considered a viable alternative.
The CET was employed and the casing expanded six times in one run. The leak—as evidenced by bubbles in the fluid in the production casing annulus—stopped immediately. The well was monitored for several months. Gas migration tests were conducted in spring 2021 to determine if there was any leakage around the surface casing. No more flow, pressure or gas migration was detected.
Multi-Finger Casing Caliper log of casing post-expansion; all annular gas flow stopped immediately and permanently
The well was “cut and capped” in October 2021. Winterhawk retained the wellhead and casing stubs so the production casing could be analysed to determine how much the properties of casing had changed in the past 60 years. There are a large number of legacy wells in Canada with casing with different properties than the pipe used today.
A familiar sight in the 21st century oil industry, except this cutoff wellhead and surface casing stub was the first where the vent flow was sealed using Winterhawk’s proprietary Casing Expansion Technology
For the first time in history, a SCVF was sealed and a well fully decommissioned using a completely new method solving this old and growing problem.
More technical information on the various applications of casing expansion as a producing wellbore remedial solution with multiple applications will be featured in future articles.
For further information contact www.winterhawkwellabandonment.ca.