The alternative is dual completion technology. Its advantages include drilling cost reduction, production acceleration, independent control and optimal drawdown on each layer, elimination of undesirable fluids’ mixing, ability to continue production if one of the pumps fails, elimination of well shutdown to test separate zones, reduced environmental footprint and full compliance with legal requirements.
The main requirements to allow simultaneous production from several reservoirs in one wellbore in Russian Federation are defined in Resolution No. 71 “On Approval of Subsurface Protection Rules” of the Federal Mining and Industrial Control, dated June 6, 2003. “Simultaneous production from several exploitation objects in one wellbore is allowed with presence of replaceable downhole equipment which enables separate production measurement, testing of each reservoir separately and conducting safe wells’ workover considering the difference in reservoir pressures and fluid properties,” states the resolution. Overall such requirements are applicable to 33 TNK-BP fields and there is potential to accelerate above 800 million barrels of oil with potential well stock being above 4,000.
There is a range of dual completion and dual monitoring technologies which can be applied to meet the legal requirement with a certain degree of accuracy. Selection of the right technology is critical to get optimal value from the investments. Dual completion and monitoring technologies applied in Russia can be classified as follows:
1. Single string completions (dual monitoring systems without layers’ separation (1.1); dual monitoring / control systems with layers separation and one artificial lift (1.2); dual monitoring / control systems with layers separation and two artificial lifts (1.3)).
2. Dual string completions – 100-percent independent dual completion systems (parallel design (2.1); concentric designs (2.2)).
Technologies in category 1 have a number of disadvantages with main ones being interference between reservoirs, mixing the produced fluids, complicated procedures to test each zone, deferred production and lower accuracy of production allocation. Technologies in category 2 are ideal dual technologies, which allow independent production from each reservoir. At the same time they are associated with technical complexity and cost, which demands fit for purpose application and reliability. The option 2.1 (with two sucker rod pumps) had been successfully applied for several years in the fields of Tatneft. However, operational conditions of TNK-BP are very different (98 percent of wells are on artificial lift and 90 percent of them are produced with ESPs at depth below 2,000 meters). These conditions had steered TNK-BP experts to test the alternative technology with dual concentric ESP-ESP design (option 2.2) for the first time in Russia.
The project objectives included:
to select the optimal design of ESP-ESP dual completion for given geological conditions;
to evaluate viability of the selected dual completion option and identify areas for improvement in design and execution phases;
to perform production testing of technology and outlines the further action plan to move to scale up.
Project Planning and Execution
Technology leading contractors had been challenged with this task. Based on the designs review it had been decided to drill two special wells with 9