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I spent this week in Aberdeen with a group of operators and contractors who are pro-actively addressing well integrity challenges across their existing assets. The group’s well stock, conditions, technologies, geology and countless other elements separated them, but as time went on we managed to find one piece of common ground…

I’m sure you’ve heard this before, but according to Norsok D10 well integrity is the application of technical, operational and organizational solutions to reduce risk of uncontrolled release of formation fluids throughout the life cycle of a well. Wireline, slickline, coiled tubing and other innovative solutions can help you check out what is going on in your well – but let’s jump back a step, as whether you’re dealing with a shallow platform in the Southern North Sea or a deepwater subsea asset West of Shetland, the first piece of information I was given was universal…

“The well’s life and integrity starts when the pen hits the paper and the well is designed”

• What’s the completion design?
• What’s are the tubing grades and design?
• What was the assessment of the reservoir fluids?
• What’s the strategy for cement?

…and so on.

Not being an engineer, I won’t pretend to fully understand the implications of the above – but from the inception phase it is imperative to develop a constant and consistent well surveillance plan for the future to ensure monitored and managed integrity from the get go and offer visibility for future crews who will have to work on it. Throughout the week I learnt that this was sometimes the case, sometimes it was not, and sometimes the current operator was the Xth person to own the well and all the documentation was lost. It reminded me of my first car! Perhaps it’s because I’m writing this at the end of 2016, after two years of sub $50 oil, but whether for production efficiency, structural assurance, or barrier verification, the end goal for the majority of operators also remained the same as my first car… How can I get more performance out of it and can I make it live past its life expectancy?

I owned my first car for almost ten years. It was a twenty-year-old classic Mini with a lot of miles on the clock. Ahead of passing my driving test I had managed to locate a modified engine which had been bored out to 1440cc, along with a performance manifold, induction system and straight through exhaust. It went like a rocket, but the car was ultimately a great engine in a light old rusty frame. The issues I was had with my old Mini ‘Bertie’ was similar to the relationship that the Aberdeen group had with their wells. Somehow rust bonded us and Bertie got me in the conversation.

The discussions of our group focused on both old and new wells. One person talked of a young three-year-old well that had three corroded joints. There was a change in the internal diameter profile at each joint as the well was constructed with alternate grades of joint, resulting in varied levels of corrosion at different depths. Another member of the group said they had realised a 10% metal loss in just a few months – his ESP had over heated resulting in tubing leaks and fluid circulating without getting to the surface. The general consensus of how to best deal with corrosion was through a robust scheduled monitoring programme to provide an appropriate understanding of the completion integrity status. Then one member asked the big question “what is good integrity?”. A great question… At what point is the level of corrosion “good” and at what point is it “bad”? If it is in line with regulations, does that make it good? The discussion circled but no real consensus was met – it’s dependent on the well, here are too many variables to universally apply “good” to everything, or anything.

Getting Bertie through the MOT was always a problem. He was full of rust and I was constantly welding and replacing panels to keep him certified as safe for another year of motoring. I always went to the annual Mini owners club meet and we talked about rust, as you do. My sils, door skins and floor pan were in bad shape – but somehow the car was deemed safe and road legal. I once met a guy with a 1975 Austin 1275 GT with a 1.8 Honda Civic engine replacing the original motor. This car was dangerous. Not solely due to the engine, but because to avoid corrosion issues he had cut out huge parts of the floor pan, replaced them with plastic and then painted and covered them with metal fillings – when the MOT inspector used a magnet to test the floor it appeared there was a significant and safe width of metal. There was none! The result was a false positive, but nevertheless this dangerous car was certified as safe and was on the road.

So, like this car, how do you ensure the logging data accurately represents the integrity of the well? This was a question debated in Aberdeen and to the credit of the group, they painted the best picture they had of their respective assets. Ultimately the group erred on the side of caution – using multiple logs, cameras, history and behaviour to best understand what was going on downhole. This was rigorous, they picked holes in their own findings, questioned their data and never seemed to take anything as red. This was commendable and it became clear that “good” integrity was never “good enough” – or at least never a point of giving the well a ‘thumbs up’ and not worrying about it anymore. For example, some used a traffic light system to rank the integrity of their stock – but said even a green (and therefore ‘good’) well could bypass Amber and head straight to Red due to variable changes, like reservoir conditions.

It was clear, the group in Aberdeen are not complacent and constantly and consistently monitor, question and work over their assets to ensure they are in the best possible condition. In doing so they are ensuring the productivity of our fields and industry for future generations.

More to come next month…

Tommy Angell is the Founding Director of Offshore Network, along with his business partners James Taylor And Dean Murphy. Tommy holds a Bachelors and Masters Degree from The University of North Carolina at Chapel Hill (USA) and The University of Essex (UK). He has also Served as a guest lecturer at the Hult International Business School.

Optis™ E-Line HD camera control from surface allows the best close-up shots, even as completion equipment is operated.

Introduction

The North Sea is a mature basin, and as with all mature basins the lack of drilling activity over the past 18 months has placed a greater demand on old assets to maintain or increase production levels beyond their initial design life. This inevitably raises many questions about well integrity and asset life extension.

By NORSOK D-010’s definition well Integrity is the “application of technical, operational and organizational solutions to reduce risk of uncontrolled release of formation fluids throughout the life cycle of a well.” In order to assure integrity, comply with regulations and increase recovery volumes North Sea operators conduct regular well intervention campaigns to improve, or at least maintain, the productive life of fields in the region.

It is worth mentioning that well intervention as a subject is more inclined towards OPEX engineering work on live wells, including activities such as logging, slickline, coiled tubing, structural maintenance and other workovers to name a few. Well integrity begins at the design phase of the asset, from selecting a completion design, tubing grades and sizes, detailed assessment of reservoir fluids, testing & commissioning and complete well surveillance throughout the lifecycle of a well. Hence, well intervention and integrity activities are multidisciplinary and require excellent communication, working standards, design, engineering and a live status of the well’s behavior.

As the fields are maturing there is a natural decline following the production plateau, requiring additional applications such as Improved Oil Recovery (IOR) and Enhanced Oil Recovery (EOR) to maintain the profitability of the reservoir. It is anticipated with aging wellstock on rise issues such as declining structural integrity of wells will increase. Thus requiring preventative maintenance activities will increase such as diagnostic logging, tubing retrieval and well platform remediation will be unavoidable and necessary.

All of this demonstrates that there is a slow but steady growth towards an increase in well intervention and remediation activities. Whatever the objective is, be it production enhancement, structural assurance or both, integrity and intervention have a common goal – extending the asset’s production life.

Targeting the Highest Priority Wells

Currently, 70% of global Oil & Gas recovery comes from mature fields, but as production decreases on average by 7% year on year, there is significant pressure placed on our mature assets. Significant advances in the technology used for extending production life have greatly contributed to the vast amount of stock outliving its intended design life. A good example being advanced diagnostics that help operators identify wells that are prone to corrosion, fatigue, and abnormal movements. In the long run, regular preventive maintenance serves to be the best option for keeping old assets online and profitable. Structural Integrity and Good Practices

Two main types of well platform construction can be considered for simplicity; the well can be built on the conductors (i.e. the conductor is the structural pile in the well) or built on the surface casing support, (i.e. the surface casing is the structural pile in the well) where the conductor acts only as a marine protector.

Both types are prone to corrosion with each having advantages and disadvantages. For instance, oxygen is more prevalent in casing supported wells because the D-annulus is more exposed. Other sources of corrosion include having a low-pressure seal, having a barrier to atmosphere and seawater acting on the outside of the conductor, but it is noted that casing support wells are less prone to seawater corrosion as conductors act as protection Also, drill fluids (seawater) exist in the seabed and do improve hydraulics, however, the conductor’s joints are below sea-level, and the tidal range in D-annulus gets constantly corroded due to wet and dry cycles, which is a catalyst for corrosion. The installation of debris caps in conductor supported wells seems to be harmless but creates additional corrosion problems due to condensation loops resulting in wet and dry cycles, which in turn results in accelerated corrosion just below the wellhead.

Offshore well structures and related problems, including corrosion, raise issues on how to assess and quantify structural integrity. A process to rank issues based on severity, risk, and opportunity is critical. To effectively execute this process there are four key steps to help you develop a proactive preventative programme to aid the life extension of your assets:

• The first step is to calculate the well weight by using predictive modeling. Modeling, however, will be as reliable and accurate as well input data. Alternatively, you may have to take a direct measurement if the data is unreliable.
• Once well loads are confirmed by using either of the options (or preferably both!) a health check should be conducted to check how much actual steel is in the asset and how much will be transmitted to the load. A good practice is to record the movement of strings. If movement and behavior is ‘as per design’ it is a good indicator of well’s health.
• Next is to quantify using the remaining wall thickness to assess the total metal loss and strength capability of the structure. This can be quantified by using pulsed eddy current (PEC), C-PEC (for flexible access) and PCE. Also, multiple historical surveys can be utilised to assess the corrosion rate effectively.
• Finally, you can assess the well’s overall condition, casing support, and re-assess the well model with operational loads. External sources such as environmental factors (wave and current loads for example) can be quantified as distributed axial loads in the dynamic model.

Once the stress conditions have been corrected you have all the most important information to select the most appropriate and efficient remediation methods for low severity and medium severity assets, for example:

• Medium severity assets will need essential stabilization work. A conductor guide reinstatement and conductor/surface casing retro-fit centralisers could be used to increase the fatigue life and reduce VME stress. Further, either mechanical or grout up approaches could be used. For instance, you could either transfer the load of the well and then use conductors with a mechanical clamping mechanism or use grout to transfer the load from the well to the conductor.

Regardless of selecting the appropriate action across your assets, the main takeaway is that best practice is to investigate your wells early, identify and repair critical wells, implement preventive measures to save from developing issues, schedule monitoring, and generic studies. This offers a cost effective approach to life extension and pays off in the long term, as even though you may have to shut in wells for longer during routine inspections, you will identify remedial works and opportunities that you may or will have to address later on and outside of the inspection window. If you work outside of this window you will inherit additional cost and risk dealing with a significantly more challenging project which could have been avoided if the identified symptom was rectified during the inspection.

Conclusion

Preventative and maintenance workovers are more cost-effective in the long run than replacing a failed barrier. It is interesting to note that the oil & gas industry still has differing standards and opinions on barrier definitions, technical interpretations and so forth, but evolving nevertheless. Due to the nature of well integrity being diverse and multidisciplinary, there is a huge demand for entrepreneurship in developing shared management systems to keep the status of well stocks up-to-date. From the operator’s point of view, well integrity is somewhat process-oriented since there are hundreds of active wells and multiple teams working together. This can be leveraged for additional efficiencies. It is necessary to develop an effective relationship between data and inspection to offer a robust, proactive and cost effective integrity programme that supports asset life extension and reduces expensive and complex critical works and rig based activity, which could have been avoided.

Offshore Network have put together an original report which looks at case study on a riserless light well intervention (RLWI) campaign carried out by well services company Sapura Energy Australia.