Artificial lift technology application in heavy oil production has been a far-reaching development in the industry over past decades guided by persistent efforts to improve the ultimate recovery of this "difficult" hydrocarbon. Heavy oil discovery in a marginal field, Cuu Long Basin, Offshore Vietnam is relatively aberrant and pose challenges to full field development. A series of systematic technical studies has been purposely planned from the first discovery of heavy oil in the wildcat well to the modeling study and facility design to accommodate the viscous fluid over the field life. Apart from the thermal method, pumping technology makes remarkable advance by enlarging the drawdown created over the conventional gas lift in several heavy oil projects. After due consideration, the Electrical Submersible Pump (ESP) was finally decided as the key driver to reinforce well production performance. Moreover, the gas lift has been brought in as a backup in case of pump failure which is not only to prolong well life, save workover expenditure but also boost production if operating in hybrid mode. This paper presents sequential events from the conceptual study to pilot test hybrid ESP/Gas lift system and ultimately the inflow/outflow curves analysis. A proper system analysis of the inflow/outflow curves is indispensable to model the outflow curve above the pump where the aid of gas lift complicated the upward flow and to generate the lift curves used in reservoir simulation. The pilot test of this electro-gas system to Well A has shown about 30% liquid production increment with lesser pump energy consumed and flexibility in control operating point. The early results promise further extension to the remaining ESP wells to enhance field production.
The first subsea multiphase boosting system was installed in 1994 and it is today a proven technology with a global track record. In addition to bringing increased production and recovery, multiphase boosting may also reduce flow assurance issues, reduce project CAPEX and OPEX, improve operability and safety as well as reduce the greenhouse gas emissions when compared to gas lift, the default lifting solution. A review of the evaluation process and drivers during subsea artificial lift evaluations over the last three decades indicates that in general only a few of the actual upsides of subsea multiphase boosting have been considered, suggesting that there is a need for a more complete overview of the advantages and an approach to uncovering and quantifying the actual value. This paper discusses the different aspects of subsea multiphase boosting through a comprehensive list of tangible benefits that may support the field development decision process towards identifying the potentially significant and hidden value of subsea multiphase boosting. Referencing experience from more than 30 installations it also provides a historical summary of the various aspects of subsea boosting and which drivers were and were not considered during the decision making process.
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.
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