For industry the goal of improved oil recovery (IOR) is not to maximise absolute recovery but rather to increase economic recovery. Both overall field performance and individual well productivity are important.

IOR is any activity which causes the primary recovery factor (that achieved using only the natural energy of the reservoir and its aquifer) to be exceeded. In the North Sea, oil fields are produced typically through the injection of water or immiscible gas. Further improvements to recovery may be possible by inducing physico-chemical changes in the reservoir fluids (enhanced oil recovery or EOR).

In the North Sea, in addition to conventional water or gas injection, IOR techniques receiving current attention include:

• engineered depressurisation of reservoirs;

• water and gas injection (WAG);

• polymer gel placement within reservoirs for flow diversion;

• microbial techniques for flow diversion.

Improving well productivity is a key challenge. Well performance depends on a multitude of factors including:

• improved characterisation of reservoir geology;

• avoidance/remediation of formation damage upon drilling;

• effective perforation of the bore-hole wall;

• improved understanding of multiphase fluid flow processes in the near-well bore region, at the formation/borehole interface (in-flow performance) and in well-bore valves and tubulars;

• geometry of the downhole completion system;

• artificial stimulation of the reservoir;

• well-bore integrity and sand production control;

• produced water shut-off/flow diversion capability, particularly in maturing fields.

Extended reach and horizontal well technology also contribute to IOR as does the new capability to drill multiple drain holes from a single well (multilateral/ multibranch technology). Improved reservoir imaging from surface seismic, crosshole seismic tomography and sensing ahead of the drill bit, together with precise geo-steering/positioning of the drill, are likely to bring even greater benefits in the next 10 years by reducing infill drilling failures and improving access to remaining, unswept oil.

Application of best reservoir management practices and improved understanding of the static and dynamic aspects of the reservoir, impact beneficially upon recovery factors. A potentially valuable new aid will come from the wider use of 4D seismic imaging (3D plus time lapse). Options will include permanently or temporally installed sea-bottom seismic sources and/or receivers, with the option of permanently installed down-hole sensors.

However, the viability of improved recovery projects is sensitive to timing and rate of return on investment, especially when placed in the context of ageing field infrastructure. Looking ahead 10 years, with a continued emphasis on full life cycle field economics and an improving technical capability, there is the prospect of optimising the deployment of a range of technologies from an IOR toolkit, together with a capability to monitor and respond to changing reservoir performance with time. With growing confidence in IOR technology, companies will carefully assess the relative attractions of adding to their recoverable reserves base from further exploration or from IOR projects. At present, the main task is to reduce the technical risk and costs associated with innovative IOR technology; demonstration trials will be a key requirement if this technology is to find commercial application. RTD targets relevant to extending field life are listed in Sections 5.2 and 5.3.