Arrangement for and method of restricting the inflow of formation water to a well

[0001] The present application is the U.S. national stage application of International Application PCT/NO02/00158, filed Apr. 26, 2002, which international application was published on Nov. 14, 2002 as International Publication WO 02/090714. The International Application claims priority of Norwegian Patent Application 200012261, filed May 8, 2001.

[0002] This invention regards an arrangement for and a method of automatically controlling the inflow of formation water to a petroleum well by means of buoyancy elements.

[0003] Oil and gas production will in most cases have to be stopped when the water production from a well becomes excessive. The time of water breakthrough will vary from one zone to the next, and will also depend on the measured depth of the zone due to flow pressure drop. If a zone that mainly has an inflow of water is choked, the production from zones producing mainly oil may be increased. As a result, systems have been produced in recent years which comprise valves and adjustable nozzles controlled from the surface. These are technically complex systems that require a great amount of downhole equipment, and which have so far shown poor reliability. Also, the potential for using more than 4–5 valves in each well is limited. In addition, the flow area of the production tubing is small, limiting the production.

[0004] As a simple alternative to this, a nozzle or ducting system has been developed in which the production is restricted regardless of whether the inflow consists of oil or water. Examples of this are seen in U.S. Pat. Nos. 6,112,815 and 5,435,393. The arrangements according to these documents may counter frictional effects caused by the flow of fluid flowing through the production tubing, but will not regulate the pressure drop across the system on the basis of the water cut in the wellstream. According to these patents, the produced fluids flow through a fixed flow restriction such as a capillary tube or nozzle, before flowing into the tubing. These capillary tube devices have typically been arranged around the production tubing as a helical thread where the fluid flows in the grooves of the thread.

[0005] U.S. Pat. No. 5,333,684 discusses a tool for drawing gas out of a well without simultaneously producing water. The tool is equipped with spherical, stacked controlled buoyancy elements, where the density of the buoyancy elements is lower than that of water. Upon outflow of water from the well, the elements ascend and close an opening, preventing water from flowing out of the well.

[0006] According to the invention, there is provided a restriction arrangement and a method defined in the claims.

[0007] The inflow of formation water from a well to a production tubing may be reduced by the hydrocarbon production in the well, e.g. within a 12 m long length of piping, flowing into one or more chambers connected to the production tubing. From the chamber, the oil flows on into the production tubing via a number of through nozzles in the tubing wall. A number of balls are disposed in the chamber. The balls have approximately the same density as the formation water. On production of oil, the balls will have a low mobility, as they have a density that is significantly higher than that of the oil; thus they will sink. The density of the oil is typically less than 900 kg/m3, while the water will have a density of approximately 1000 kg/m3. On partial production of water, these balls will have neutral buoyancy in the water and close nozzles through which there is a flow of formation water. Alternatively, the balls may aggregate and reduce the flow through the chamber.

[0008] Optionally, oil and formation water may flow through bypass nozzles that can not be closed by balls. These bypass nozzles will reduce the control effect, so that the production is not stopped completely, even at a high water cut. If the well zone in question produces only water, only nozzles that are not closed by balls will produce well fluid.

[0009] Arrangements according to the invention may be positioned at relatively short intervals along the production tubing, whereby the fluid production in zones experiencing inflow of water is reduced. The arrangements operate independently of each other and with immediate response. Thus is achieved greater selectivity and better control than when using surface controlled systems.

[0013] When compared with prior art, the flow pressure drops in the production tubing are considerably smaller, in as much as greater production tubing dimensions may be used. The reliability is improved, the installation work is reduced, and the costs are lower due to simpler technology with a total absence of cables, cable connections and moving high-precision mechanics and hydraulics.

[0014] For a clearer understanding of the invention, it will be described in the form of embodiments illustrated in the appended drawings, in which:

[0015] FIG. 1 shows a case where an oil stream 1 passes through a filter 2 and then into a flow chamber 3. A number of balls 4 are located at the lower side of this chamber due to the balls being heavier than the oil. The oil further flows through a filter 5 and into a space 6, in order to flow on through openings 7 and into the production tubing 8, then to follow the flow of oil up through the well.

[0016] FIG. 2 shows the same construction as FIG. 1, the difference being that here, water is flowing. The balls are now packed vertically, since the balls have neutral buoyancy. Thus is formed an aggregate 14 of balls causing a pressure drop in the flow.

[0017] FIG. 3 shows an annular sand filter 30, a bypass nozzle with a hole 31 in a production tubing 38, as well as an annular chamber 33 with balls 34, in which the balls 34 have approximately the same density as the formation water. One of these balls is shown sealing one of the nozzles 32. In addition, there is shown a plug 39 made from a drillable or acid/base soluble material, with a borehole extending almost through the plug. When the tip of this plug is removed during a well intervention, e.g. by means of a drill bit run on coiled tubing at a later stage in the lifetime of the well, the produced fluids will flow more easily into the well.