Maintaining well integrity is a critical element of good asset husbandry, ensuring sufficient barriers are in place to ensure no loss of hydrocarbon containment to the environment.
It is good practice to have at least 2 barriers between any hydrocarbon bearing formation (such as the production reservoir) and the environment. The annular cement placed when the production casing is installed is often the primary isolation barrier, with the annular wellhead seal at surface providing the back up.
However, the barriers can often be compromised. This can occur during the life of the well, with a number of potential root causes, including pressure and temperature effects or chemical reaction with the wellbore fluids. It can also occur during initial well construction when the hole conditions are particularly challenging and/or cementing operations are less than optimal.
The loss of integrity this leaves, creates the opportunity for sustained annulus pressure at surface, with a reduction in the number of barriers between hydrocarbons and the environment, and a potential risk of casing collapse.
It also potentially reduces or eliminates isolation between formations which may permit co-mingling of fluids, contamination of water bearing formations, or additional water production leading to reduced or lost production.
Where the casing is not stabilized properly during the well construction, this can cause immediate problems with subsequent drilling and completion operations. The lack of stability means that any subsequent drilling below the shoe runs the risk of hole collapse and stuck pipe.
Running completions through an un-stabilised production casing can also be problematic with similar risks that the lower completion cannot be run to depth and set correctly.
Traditionally, when the preceding issues have been identified, a ‘perf and squeeze’ job is often attempted to repair the isolation behind the casing. Although this operation is relatively simple, it faces a number of challenges and is often not successful. Unless there is a clear circulation path, the volumes of cement injected into the annulus are commonly very small and thus the likelihood of successfully sealing all the leak path channels, or providing sufficiently robust stabilisation, are low.
Perf, Wash and Cement (PWC) is a cost effective, predictable and efficient alternative method of restoring the cement isolation or casing stability.
The method has been demonstrated to be significantly quicker than repeated ‘perf and squeeze’ operations and provides a higher confidence in achieving a long-term isolation barrier.
HydraWell offers a complete service of preparatory engineering and specialist tooling provision and operation, including managing the critical interfaces with cement, wash fluid, and perforating gun providers, in order to integrate our services into an optimised operational procedure.
From our experience, we have concluded that it is critical to ensure that perforation sizes provide sufficient access to the annulus and the washing programme parameters. This includes that flowrates, pass speeds, and jetting velocities are optimised within any constraints, such as ECD and pore pressure limits posed by the wellbore configuration. In addition, fluid choice driven by existing annular contents is key to ensuring effective cleanliness of the annulus prior to commencing cementing.
As the inventors of PWC, and specialists in this specific area, we pride ourselves on having the best and most extensive track record in this sector of the industry, with our latest tooling design bringing the cost benefits of significantly reduced operations durations compared with alternative versions of the technique available. Please see details of our track record and a comparison of differing PWC techniques on our ‘About’ page.
HydraWell’s PWC methodologies are being employed by an increasing number of Operators including Shell, BP, ConocoPhillips, Chevron, Petronas and Equinor in many locations including UK, Norway, Netherlands, Canada and Malaysia.
Historically, three basic methods have been used to achieve an annular barrier. Each carries the risk of technical failure or of significant delays and increased cost beyond the forecast.
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