Zone control for improved recovery and lower costs
Managing injection or production along a well path or between laterals is known as zone control. This includes closing off or reducing undesirable inflows of water or gas to a production well, stimulating individual zones to increase output from the specific zones and achieving better clean-up of long horizontal well paths.
The main aim is to optimise drainage and production. That could be particularly relevant for wells where formation quality varies considerably, as in tight reservoirs (see chapter 3, "The challening barrels"). Opportunities to exercise zone control provide better reservoir management and thereby improve oil recovery.
The NPD mapped the use of zone control in wells during June 2017. A total of 593 active well paths with zone control were reported by the companies. These included 119 multilaterals with 301 laterals in all.
Zone control can be conducted in several ways. One involves using inflow control devices (ICDs) and autonomous ICDs (AICDs), which control and correct the pressure drop from the formation to the reservoir. An AICD is the more advanced type, and can measure which liquid is flowing in order to close off or reduce non-oil flows.
Another example is the inflow control valve (ICV), which can be controlled hydraulically or electrically from the surface. Zone control can also be exercised by manual methods – running mechanical tools from intervention vessels or drilling rigs into wells to perform operations.
Some fields have a substantial number of well paths with active zone control. Passive or autonomous ICDs are installed along all producing paths on Troll, and many have surface-managed valves for controlling laterals. On Snorre, surface-managed valves have been installed in a considerable number of injection wells as well as in producers.
A substantial increase has occurred in the application of more advanced zone control methods over the past decade. Continuing to develop this type of equipment is important for efficient and optimal production from many types of reservoir. Figure 2.20 presents the trend for well paths with zone control.
Analyses of output from oil wells on Troll reveal a clear improvement in production rates after AICDs were introduced. Where Snorre is concerned, studies show that reserves can increase substantially if zone control functions as planned.
Figure 2.20 Well paths completed with zone control (ICD is included in both manual and surface-managed methods).