Heavy duty behaviour of a cage and sleeve choke valve

The wellhead choke valves, which are commonly used to control the flow from the reservoir, are often exposed to solids as with liquids and gases due to sand production in extraction processes. There are many significant drawbacks and negative outcomes associated to the presence of solids in the flow, which may produce considerable economic damages. On one side, a massive amount of sand can produce changes in the performance of the devices, as a consequence of the different flow structure and the risk of occlusion due to the sedimentation of the solids. On the other side, the prolonged exposure to an even small amount of solids can result in removal of material from the devices (a phenomenon referred to as impact erosion), thereby causing structural weakening, leakage, and possible reduction of the flow control capacity. This work aims at investigating the behaviour of a 2 inches cage and sleeve choke valve subjected to the flow of sand-water mixtures from dilute to dense. First, a fluid dynamic characterization of the device in the absence of sand is provided by means of experimental tests performed in the Hydraulic Laboratory of Politecnico di Milano and numerical simulations. This allowed determining the valve opening curve and the flow structure within the device at different openings. Afterwards, the behaviour of the valve in presence of a small amount of sand (1‰ by volume) is numerically investigated by means of a two-phase CFD model. Algebraic erosion correlations have been applied to predict the erosion produced by the sand particles, thereby allowing the identification of the parts of the device which are most vulnerable to wear and preliminary estimation of the loss of material. At last, a different two-phase CFD model specifically developed by our research group has been employed to simulate the solid-liquid flow within the valve in presence of volume fractions of sand up to 20%. This allowed determining the effect of a massive presence of sand on the fluid dynamic characteristic of the device. Finally, a practical formula for estimating the change in the flow coefficient with respect to the single-phase case has been proposed.