Abstract
Surface-Controlled Subsurface Safety Valves (SCSSVs) are designed to automatically shut-in a well below the earth's surface in the event of damage to the wellhead or other key components of a completion string. Flow rates in highly productive gas wells can produce stresses that exceed the design limits of a typical subsurface safety valve during closure in blowout conditions. High-rate uncontrolled flow conditions can act to prevent a SCSSV from closing or can subject the valve to stresses that the valve cannot withstand. Flow tests conducted to verify valve performance under certain flow conditions are often not capable of predicting valve performance when the valves are subjected to flow conditions different from the test conditions. Because the net force on the flapper is a function of the flow parameters, a valve that tests successfully at one set of conditions is not guaranteed to perform successfully in a different set of conditions.
This paper will discuss the use of Finite Element Analysis (FEA) combined with Computational Fluid Dynamics (CFD) to economically and effectively determine 1) if a SCSSV will close under various flow conditions, and 2) whether it will withstand the associated forces generated during the closure. If this method is used, the flow tests could then be used to verify the accuracy and confirm results of the FEA and CFD analyses. After the FEA/CFD models are validated through flow testing, the performance of the valve in response to changes within the flow parameters or safety valve configuration can then be predicted using FEA/CFD models. Actual testing can be performed only to confirm the results of FEA/CFD or may be avoided completely.
