Well Revival in an Offshore Marginal Field Using Through Tubing Straddle Gas Lift Technology - A Case Study

Abstract

LG is a marginal offshore field lying in the west coast of India. Well A and B in field LG were completed using 4 ½ - in and 3 ½ - in single-string multizone completion intersecting gas and oil-bearing zones. During the initial phase of its production, the wells only produced gas, until the oil-bearing sands were perforated, and the wells produced commingled gas and oil. These wells had been flowing naturally on self-drive and recently ceased to flow after showing gradual decline in their production. The diagnosis suggested a failure of Vertical Lift Performance (VLP) indicating a need to change the production technique and possibly a need for artificial lift in the wells to bring them online. The paper discusses an innovative and cost-effective approach involving the implementation of through-tubing mechanical straddle pack-off with gas lift assistance to bring the wells back to production and increasing the overall recovery from the field. A detailed analysis of the various techniques for bringing the well online was evaluated keeping in mind the associated cost and time for each method. The considerations lead to the plan of introducing gas lift as an artificial lift method for these wells. Wells A and B were not equipped with any gas lift mandrel for introducing artificial gas lift. Workover for these wells would result in higher cost, time & risk factors for the wells. The economic viability of such a workover was not justifiable given the incremental production anticipated. After performing a detailed technical and economic analysis, the decision was made to implement a through-tubing gas lift technique using a straddle packer conveyed on slickline across the circulation Sliding Sleeve Door (SSD). The straddle pack-off was to be introduced in the existing 4 ½ - in and 3 ½ - in production tubing with internally mounted gas lift mandrels/orifice valves. Detailed modelling was performed to determine the correct orifice size for different lift parameters. The operations in candidate wells A and B were successfully conducted and the surface setup for the gas lift was installed. The mechanical pack-off was set at the desired depths without any issue, and the gas was injected through the annulus leading to instantaneous production from the well. The total operations period was minimal as compared to the workover operations, far safer and more cost-effective for the production enhancement achieved. This paper describes the job design, technique implemented, and challenges overcome during the successful activation of a theoretically dead well to 1000 BOPD production, establishing the viability of through-tubing gas lifting. Learnings from the paper will help professionals plan for such well interventions involving the use of mechanical straddle pack off for gas lift operations.