The combination of increasing global energy demand, known reserves being depleted, and the offshore locations of new oil and gas discoveries is pushing drilling and production into deeper and deeper waters. As a result, the number of subsea wells has increased steadily over the years to more than 5,500 by the end of 2012. Unfortunately, due to their location in deep water, interventions in subsea wells have typically required drilling rigs. Thus operators have been reluctant to perform interventions on these wells. This problem has only been exacerbated as drilling rates increase and sourcing rigs becomes more and more difficult. Thus, recovery factors are much lower—typically 10% to 30% lower—than recovery rates of dry-tree, platform-based wells. Therefore, cost-effective riserless light well interventions (RLWI) are crucial if subsea operators are to realize the full potential of 50% oil recovery (or more) from their subsea fields. This becomes increasingly true as wells age without proper maintenance.
Many opportunities exist to increase recovery rates in brownfields. From milling scale and debris to cutting tubing without using explosives to setting packers and manipulating or changing downhole hardware—all these and much more can be done with RLWI. As proof of concept, several case studies of specific interventions and the resultant productivity increases will be discussed. We will also discuss how adoption and use by North Sea operators has let them increase recovery from 36–46%. For example, Statoil estimated that in 2010, the contribution of RLWI interventions was in the range of 15 billion NOK (2.5B USD).
In addition, we will show the increasing effect pro-active interventions have on recovery rates over time, for selected Norwegian fields. Finally, we will discuss how increased use has made these operations much more routine while also providing opportunities for the technology to evolve. This is a trend that will only continue as operators request additional services in increasingly challenging environments, particularly outside the North Sea.