Severe slugging mitigation by utilizing the active use of choke control valve

Abstract

One of the common flow assurance issues in offshore production facilities is riser-based severe slugging. Severe slugging is a cyclic process that occurs in the late life of reservoirs when there is not enough energy available in the system to push the liquid out of the riser. A novel technique is proposed in this study to mitigate this issue. Unlike the conventional choking techniques, where additional backpressure is applied on the riser to mitigate severe slugging, the proposed technique involves utilizing the active use of either the choke control valve located downstream of the riser in a pipeline-riser system or the separator gas control valve. This new technique can be utilized in brownfields where pipeline pressure measurement installed for feedback control loops is not feasible. The main advantage of the new technique is that it can use the available measurements and equipment (gas control valve and pressure sensors) available in a regular topside facility. In this study, an algorithm is developed that can determine the required valve operation sequence (amplitude and frequency) of the choke control valve based on the natural slugging frequency. The objective is the mitigation of the severe slugging, which minimizes imposing the additional backpressure on the pipeline-riser system. Proof of concept of the proposed technique demonstrated on a large-scale facility using the transient simulations. The results of the transient simulations using OLGA show that the active use of the choke control valve does affect the severe slugging characteristics. The results show that the valve sequence can either mitigate severe slugging or make it worse depending on the selection of the valve operation sequence. Therefore, determining the correct valve sequence is very critical. To investigate further, another case study has been presented, where the results from the algorithm developed in-house for the choke control valve operation sequence were tested using OLGA simulations. These simulation results show that the proposed technique is successful in providing a unique combination of choke control valve opening frequency and amplitude, which will mitigate the severe slugging without increasing the additional backpressure on the system.