InterAct has provided major input to the recent Oil & Gas UK Well Abandonment Study
According to a report issued in March by Oil & Gas UK, there are 4635 exploration, appraisal or development wells in the UK sector of the North Sea. Of these, it is thought that 2749 (roughly 60%) could be decommissioned using existing technology and, crucially, without resorting to a drilling rig. That leaves 1886 wells that are likely to cost a good deal more to decommission – unless the industry can come up with new rigless ways of dealing with at least some of them.
Phil Chandler, senior petroleum engineer with Acteon company InterAct Activity Management Ltd, was instrumental in the preparation of the report on behalf of the well abandonment work group at Oil & Gas UK. He says, “The study has put the spotlight firmly on rigless decommissioning technology. For platform wells, it is the areas of well control and long-string tubular recovery where there needs to be some fresh thinking. Additionally, the lack of accommodation, platform cranes and deck space often poses considerable challenges to rigless well decommissioning in the southern North Sea. There also needs to be greater focus on planning and logistics to tackle the large stock of wells in this sector.
“Rigless subsea well abandonment has received considerable attention in recent years, and there has been lots of interest in new-generation well intervention vessels. A DP2 classification, the ability to run a subsea lubricator for wireline operations, and mud and cement pumping are essential. Better vessels will possess DP3 classification; a pipe handling tower, with active heave compensation, capable of running or pulling complete work or completion strings; a pipe-picking machine; mud and brine tanks; cement storage; aqueous fluid processing facilities; slickline, electric-line and coiled-tubing capabilities; and, not least, lots of deck space. However, I believe that, in the near term, limited well control capability will probably remain the major shortcoming of these vessels. Pulling a tubing hanger through a riser and blowout preventer will require a very stiff riser and a heavy blowout preventer, and therefore result in costs similar to those of a drillship. The important conclusion is that, given the existing technology, rigless abandonment will be restricted to those subsea wells where control can be achieved downhole before pulling the completion.”
Chandler feels there are many other areas where technical advances could lead to significant benefits when decommissioning both platform and subsea wells. He cites, for example, the ability to deal with leak paths caused by deeply set control lines and cables; better plugging technology; more advanced cutting tools for use at extended depths; logging tools to provide better information about annular conditions; methods for determining the location and the extent of leaks in compromised completions; improved remedial cementing technology; and ways of centralising completions and tubing in high-angle wells.
Chandler believes the findings of the report will act as a spur to investment in new technology and innovative services but stresses that it is not just simply about new technology. He says, “We have to think about how we can use existing technology in smarter ways. Acteon companies have been working in this area for several years and have undertaken scores of rigless abandonment projects in the North Sea and the Gulf of Mexico. Critical to their success has been the effort put in before going offshore to understand the way particular wells were constructed and their status at the time production ceased. Within Acteon, we have undertaken over 1300 such well reviews. They are a vital insight into the well and indispensable when it comes to engineering and planning the abandonment exercise.”
UK North Sea Well Abandonment Study, March 2009, issued by Oil & Gas UK