Geology rears its ugly head in subsea engineering mishap

Oil IT Journal editor gets out and about—at SMi’s Production Optimization masterclass and GE Oil & Gas’ Smart Center. Researching a piece on subsea production, he stumbles upon the ‘Tordis incident,’ a fascinating tale of high tech engineering, ‘faulty’ geology and perceived CO2 injection risk. Reminiscing on his formative years as a seismic interpreter in the North Sea, he concludes that it’s the things we take for granted that are likely to surprise—especially when geology is involved.

In my early days as a seismic interpreter I was stuck on a completely intractable problem. A horizon—I think it was the top Palaeocene—refused to tie across to the next well—and after a few hours cussing and checking, I called in my boss. He cussed and checked some more and then, to my relief, agreed with me that ‘we had a problem.’ The problem was that we had a certain idea of the marker as a single volcanic event—and the seismic just refused to cooperate with this accepted view of the geology.

My boss was something of a renaissance man and got on the phone to call in some support. Over the next few weeks, well cuttings were retrieved and analyzed by company petrographers and palynolygists (do these still exist?). After a couple of months, it was determined that the volcanic marker found in the well was a different event. In fact, contrary to our world view, there were two volcanic events in the Palaeocene. The seismics (and me) was ‘right.’

Of course, if I had been wrong, I would probably not be telling you this story, but I am not relating this just in a spirit of self-aggrandizement, but also because it is a great example of what we might call today a ‘holistic’ workflow. Although the silo boundaries crossed were all inside the ‘geo’ domain, there was integration and great organization in action. I was impressed by the company that I was working for—rather unusual for a twenty-something year old.

Events this month made me remember this formative event. While attending the SMi/TNO ‘Masterclass’ on Production Monitoring (a report will appear in next month’s Oil IT Journal) we were set an exercise that involved the design of a retrofitted monitoring system to a subsea development that was experiencing slugging problems (big bubbles of gas collecting in the gathering system and blasting dangerously large liquid slugs up the riser.)

Not having an engineering background made this a tricky problem involving musings as to how much data you might expect to monitor on a subsea well and how much control over it you might expect to have. I imagined that there would be some measure of pressure, maybe temperature, maybe flow and choke position. Although my problem solving colleague knew a bit more than I did about production monitoring, in the end our answer was more buzzword bingo than real-world solution.

Fortuitously, the next day I travelled west to Bristol to visit GE Oil and Gas’ Vetco Grey unit that manufactures subsea control systems for the ‘digital oilfield.’ (A report from Nailsea will appear in a future edition of Oil IT Journal.) There I learned that a modern subsea control system streams thousands of data points per day to the topside and perhaps on to the shore. Interestingly, currently, most operators use only a very small subset of the information. I sensed a great story in development for a future issue on the potential to use much more of this data.

It seemed like a good place to start was the fact that in our July 2009 issue, we reported on the ‘monster’ contract for subsea computers that Statoil (the company dropped the ‘Hydro’ tag last month) awarded to GE for the Tordis Vigdis Controls Modification (TVCM) revamp. As I am sure many of you know, Tordis is a groundbreaking subsea development in that it uses a novel system of subsea separation of water from the oil. The world’s first full-scale commercial subsea separation, boosting and injection system was installed by FMC Technologies in 2007. The Tordis improved oil recovery (IOR) project was a state-of-the art development that relied on high end hardware like multi phase meters and control systems and communications. Tordis IOR was estimated to increase recovery from 49% to 55%, around 35 million bbls of extra oil.

And yet there was a problem on Tordis. In May 2008 it emerged that the produced water, rather than being injected into the Tertiary Utsira formation, was leaking to the seabed. Sonar imagery showed a magnificent pockmark where the water reached the seabed. Statoil launched an internal investigation into the incident to conclude that the Utsira reservoir was absent in the Tordis area. A report from the Norwegian Petroleum Directorate (NPD), ‘Faulty Geology Halts Project’ was published last month confirming the new interpretation.

In the meanwhile unfortunately, with Copenhagen approaching, Greenpeace seized on the Tordis incident to warn of the potential danger of CO2 sequestration. Statoil has an ongoing carbon capture and storage (CCS) project on Sleipner East, some 300km south of Tordis.

NPD noted however that the ‘the Tordis leak cannot be used as a general argument against storage in the Utsira since this formation is not actually present in the area.’ Statoil confirmed that ‘no leakage of CO2 is ongoing or is to be expected from the Sleipner CO2 injection project.’

I think this is a great story about the hard realities of oil and gas production and the obligatory nature of cross silo integration. Who would have thought that a flagship subsea engineering project would come unstuck because of a mis-picked Tertiary horizon. While it is easy with hindsight to find fault, it is often the case that it is the things we take for granted, like the nature of the top Palaeocene or the existence of the Utsira reservoir that are most likely to surprise.

On the positive side, the Tordis incident demonstrates the merit of openness from the operator and an apparently good, if robust, relationship with the regulator.

Have a great holiday break!

More on the Tordis incident on The NPD report is available at links/0912_2.

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