Increasing Oil Recovery by Preventing Early Water and Gas Breakthrough in a West Brae Horizontal Well: A Case History

Abstract

Abstract Inflow control devices, which prevent early water breakthrough by passively controlling the inflow profile of a well, have had a long and successful history in the Norwegian Sector of the North Sea and in Saudi Arabia. This paper will document the first application of inflow control devices in the UK sector of the North Sea. This application took place on a 4,288 ft horizontal sidetrack of a well in the West Brae field. The completion was designed for a homogeneous permeability but the as-drilled permeability, as shown by logging-while-drilling data, had very high permeability regions in the heel of the horizontal, and lower permeability in the toe. If conventional completion methods (i.e. stand-alone screens, gravel packs, or expandable screens) were used, the result would likely have been early water breakthrough and well abandonment. The authors will highlight the inflow control device selection process, integrated completion and reservoir analysis, well completion operations summary, and production results and predictions. The successful application of inflow control devices on this well illustrates that long horizontal wells can be completed, the problem of early water and gas breakthrough can be prevented, and oil recovery can be increased by using inflow control devices. Introduction The West Brae 16/7a-W8z well was a sidetrack of an existing well. The existing well, W1z, was chosen as a sidetrack candidate because of its increasing water cut. The sidetrack was a 6.5 in. open hole completed with 4.5 in. sand control screens. The planned well length was 4,500 ft (1,372 m). The combination of a 4,500 ft well length, 4.5 in. diameter base pipe in the screens, and the high permeability of the reservoir, put the well at risk of early water and gas breakthrough. Inflow control devices were used to prevent this problem and subsequent reduction of ultimate recovery. This was the first application of the system in the UK sector of the North Sea. The as-completed well had a 4,288 ft (1,307 m) horizontal section. The completion was designed for a zone with homogeneous permeability. However, the as-drilled permeability, as shown by the logging while drilling (LWD) data, had very high permeability regions in the heel of the horizontal and lower permeability in the toe. If conventional completion methods (i.e. stand-alone screens, gravel packs, or expandable screens) were used, a possible result could have been sand influx, early water breakthrough and reduced recovery. Aerial maps and reservoir models of the West Brae field are shown in Figures 1–5. Inflow Control Devices The key to increasing the Net Present Value of a reservoir is to increase recoverable reserves while denying sand influx, delaying unwanted water or gas production, reducing well counts, and ensuring completion longevity. Horizontal wells can increase reservoir hydrocarbon recovery but also pose unique reservoir drainage challenges. Without proactively managing inflow, destructive erosion of the sandface or early gas or water breakthrough is likely because frictional pressure drop causes the flow to be unevenly distributed and greatest at the heel of the horizontal section. Uneven drawdown dislodges sand grains, which follow the path of least resistance to create localized problems that can disable the well, or at least precipitate a costly intervention. Consequences can be serious and include limited horizontal length and significantly shorter productive well life, both of which leave reserves in the ground. Inflow control devices (Figure 6) were developed to create a uniform production profile along the entire horizontal section of a well and to virtually eliminate annular flow.[1,2,3] This greatly reduces the risk of "hot spotting," which is the primary cause of plugging and erosion in sand control screens. By eliminating the annular flow, sand dislodged from the formation will not be transported and redistributed down the annulus. This reduces the requirement for gravel packing and increases screen life.[4,]]