A New Coiled Tubing Application to Enhance Operating Envelope for Deepwater Production

Abstract

The objectives of this study were to investigate the effects of coiled tubing size, flow path, gas lift and water cut on the onset of severe slugging and overall operating envelope. The coiled tubing was investigated as a technique for delaying the onset of slugging, which involved the use of larger diameter coiled tubing strings to decrease the flowing area in the annulus, or routing the flow up within coiled tubing instead of annulus to flow directly in coiled tubing. The operating envelope considering slugging and other system constraints was also investigated with the use of coiled tubing. The minimum nonslugging rate was reduced by using larger coiled tubing size with normal flow through annulus. A very low non-slugging rate was achieved with small diameter coiled tubing when producing through the coiled tubing, but a very narrow operation window was left when other system constraints were considered. The minimum non-slugging rate increased rapidly as the coiled tubing size increased when flowing within coiled tubing. Gas lift was effective in reducing the minimum non-slugging rate when it was increased from 0 to 4 mmscfd, but not very effective in one of the risers when it was further increased from 4 to 8 mmscfd. Increase of water cut appeared not to have a significant effect on the minimum non slugging rate. The study explored a new way of coiled tubing application in production design. It provides a guidance of how to effectively use coiled tubing as a technique to reduce the minimum non slugging rate, especially the flow through either annular or within coiled tubing. The field life can be extensively extended with a proper selection coiled tubing size, flow path and gas lift. A workflow of coiled tubing size selection and operating window determination considering different system constraints was also demonstrated.