Rig-Less Through Tubing Gas Lift Deepening Below Production Packer Deployed Using Catenary Coiled Tubing Successfully Improves Production Rates and Prevents Cross Flow in a Multi-Zone Single String Oil Producer

Abstract

Well E is an offshore deviated well, completed in 2006 as a gas lifted single string oil producer with sliding sleeve doors (SSD) to allow selective production from six producing zones. The well was observed fluctuating between two distinct flow conditions: high flow and low flow.

Pressure and temperature gradient surveys indicated no drawdown was being applied across the bottom zones of the well during the low flow condition. A multi rate test was conducted while running memory production logging paired with acoustic sensors to further understand the zonal contributions during the different flowing conditions.

Detailed well modelling was done using the acquired data and various options for improving the well vertical lift performance were considered, including workover to change out the tubing, or gas lift deepening above the packer using a gas lift straddle. A rigless coiled tubing conveyed solution was selected which could deepen the gas lifting point below the production packer. A conventional straddle would be limited to deepening the gas lift down to the first inflow point.

This led to the selection of the retrofit deep gas lift (RDGL) system which would ensure a stable drawdown could be applied across the deeper zones to eliminate crossflow while maximizing hydrocarbon recovery by allowing commingled production of all six completion zones.

The RDGL system straddles the circulation SSD above the production packer in the completion string, utilizing the existing gas lift supplied through the casing-tubing annulus. An upper and lower packer directs lift gas through a cross-flow subassembly into a coiled tubing string hung from the lower packer. This coiled tubing string is installed with a gas lift mandrel to deliver lift gas below the production packer at any depth and does not require the shallower SSDs to be closed. The injection depth is limited only by the hanging capacity of the lower packer slips and the injection gas pressure.

Reservoir fluids are produced through the production tubing and coiled tubing annulus until reaching the crossflow subassembly. This features an internal flow path which allows produced fluids to flow through the straddle and into the original completion production tubing to surface. No modifications to the Christmas tree or wellhead are required. The new gas lift injection depth achieved was 1,550 ft below the production packer, and 1,626 ft below that the deepest side pocket mandrel. 1.5″ coiled tubing was utilized as the gas injection tube and was successfully run to the designed injection depth.

Due to platform space and crane capacity limitations, vessel assisted catenary coiled tubing was required to deploy the system. The installation was successful in achieving an instantaneous gain of ~200 barrels of oil per day and the well has continued to flow in stable conditions without fluctuations since.