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Horizontal wells with one or more branches have been used to maximize reservoir contact by Statoil and other oil companies for more than a decade. Frictional pressure drop and variation in permeability and mobility will naturally lead to non-uniform inflow profile along a well. Eventually, this will result in gas and/or water breakthrough, which may reduce the well performance and recovery significantly. The breakthrough typically occurs in the heal region of the well and in regions with high reservoir permeability. Inflow Control devices (ICDs) are flow resistance elements installed along the producing zone of a well to counteract the non-uniform inflow, hence improving the well performance. The technology is regarded as standard technology by the industry and classified as passive inflow control, since the geometry of the devices is fixed or preset prior to installation. Passive inflow control is applied to delay the unwanted gas/water breakthrough. However, once occurred, conventional inflow control will not reduce or stop the breakthrough. Statoil's new autonomous inflow control device (AICD) is an active flow resistance element distributed along the well, similar to conventional passive ICDs. Statoil's AICD will, in addition to delay the breakthrough, reduce the proportions of the breakthrough. The AICD will impose a relatively strong choking for low-viscous fluids and only minor choking for viscous oil. This is due to autonomous changes in the flow area internally in the AICD. With this technology the well performance and production can be higher after a breakthrough compared to conventional inflow control. Statoil's AICD technology is piloted in two wells at two different fields in the North Sea. Each well is completed with 1-4 AICDs per screen joint, typically 200-400 per well. The AICD operates without need for human interventions and electric or hydraulic power. Well tests have shown that Statoil's AICD technology reduces the inflow of gas into the well from a reservoir containing light oil. Due to the restriction of the gas inflow, the drawdown can be kept high after breakthrough to allow significant oil production from the remaining oil zones in the well. Likewise, in a pilot well in a reservoir containing heavy oil, well tests have shown that Statoil's AICD technology reduces the inflow of gas into the well and preliminary evaluations indicate that even water inflow is reduced. Thus the drawdown can be kept high allowing high production from the remaining oil zones.

Troll is a large subsea development offshore Norway. Oil is produced to Troll B and Troll C platforms from 120 long horizontal subsea wells completed in a thin oil column. Oil production is optimized within the gas handling capacity at the platforms and the challenge is to drill and complete the wells in a way that gas does not have an easy access into the well. Troll has focused on developing and implementing inflow control devices that limits gas coning. An autonomous inflow control device, the RCP valve, has been developed by Statoil and implemented at the Troll field. The purpose of the RCP valve is to restrict gas compared to oil. The valve adjusts the choking of the fluids depending on which phase (oil or gas) being produced. Currently three wells have been completed with RCP valves. Reservoir simulations as well as production experience show a significant increase in oil production. It is observed that a well completed with RCP valves has a significantly lower gas oil ratio development compared to other Troll wells.

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