Abstract: A method of separating oil, water and sand in a production fluid. The production fluid is fed through a downhole liquid/liquid hydrocyclone (9). An oil enriched stream from the hydrocyclone (9) is pumped to the surface, while an oil depleted stream is fed to a downhole solid/liquid hydrocyclone (12). Here, the bulk of the solids is separated from the water, so that water which is substantially free of solids can be transported to a downhole disposal site (14).

Abstract: A method and apparatus for subjecting a fluid to a controlled pressure drop. Fluid is supplied under pressure with a tangential velocity component to an annular passageway (17). The fluid swirls around the axis of the passageway while flowing axially along the passageway to an outlet (6). A cross section of at least a part of the passageway (17) is adjustable to enable the flow rate to be adjusted for a given pressure loss or the pressure loss to be adjusted for a given flow rate. The outlet (6) includes a second annular passageway (22) surrounding the first annular passageway so that the first annular passageway leads to, and the second annular passageway leads from, a chamber (21) common to the passageways. The second annular passageway is of increasing outer diameter and cross sectional area in the direction of flow from the chamber to the outlet.