№2 February 2012Table of contents Issue Archive
№ 1 (January 2011)
The majority of TNK-BP fields contain multiple stratified oil reservoirs. In many cases the fluid properties, geological parameters and reservoir pressure conditions are such that each reservoir has to be developed separately, as dictated by legislation. This means additional drilling grids or producing zones consecutively over time using same wellbore. First option implies heavy CAPEX commitments, while the other means significant production delay with drastic negative impact on NPV.
By Eduard Muslimov, Head of Well Operation Optimization Section, TNK-BP Pavel Zhelonin, Director, Oil Production Department, TNK-Uvat
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 5/8-inch production casing in Ust-Tegusskoye green field of TNK-Uvat in Western Siberia. Baker Hughes and Schlumberger had been selected as lead contractors for dual completions design and equipment. Each contractor had been assigned one well to demonstrate their technology. Specialized wellhead equipment had been provided by Cameron. The biggest challenge was technical complexity, numerous items of specialized equipment and multidisciplinary nature of the project involving geology, reservoir, drilling, workover, production domains and science. The scope of work required management of various specialized contractors, mobilization of a special 100-ton workover rig, extensive use of Western expertise. The field is accessible by road only in the winter period, which makes logistics and high service quality extremely important with no room for mistakes.
The design and preparation works had started in the first quarter of 2009, well locations had been selected based on hydrodynamic models performed by Tyumen Oil Scientific Center (TNNC), well construction and completions basis of designs had been developed, equipment purchased and delivered (see Fig. 1 for generic schematic of dual completion design). Wells had been drilled in the second quarter of 2010. The execution of the first dual completion with Baker Hughes had been performed in June and put in production a month later.
Results and Lessons Learned
The pilot project had been successfully completed without any service quality or HSE accidents. Initial production was as follows: lower layer (J4) Q fluid = 806 BFPD, Qoil – 782 BOPD, water cut – 3 percent; upper layer (J2) Q fluid = 151 BFPD, Qoil – 142 BOPD, water cut – 6 percent. The well is stably producing at present.
Post job economic evaluation of first pilot well shows that the dual option NPV is similar to the option with drilling two standard wells (casing size 6 5/8 inches or 7 inches) in this particular case. Within the scale up phase it is expected that the value from dual completion will be much higher in comparison with additional drilling grid. This will be achieved with progression on the learning curve, higher scope of work to obtain per job cost reduction, using the standard for TNK-BP production casing sizes, reduced geological uncertainty (in the first pilot well additional sidetrack had to be drilled), reduction in equipment costs by elimination of unneeded technical complexity where possible. Additional value will be gained with accelerated production and reduced ecological footprint.
Implementation phase had demonstrated that the value of project management should not be underestimated when dealing with technically complex projects involving many contractors. There should be contingency plan to account for the geological uncertainty to be able to have the most optimum pumping equipment for the actual inflow. The learning curve should be continued with contractors as well as TNK-BP functions to build the local expertise in Russia. The second completion in 9 5/8-inch production casing (with Schlumberger design) will be performed in the first quarter of 2011 after fracturing of reservoirs to test the technology in more hostile operating environment for ESPs. Further work will be focused on cost efficiency and adapting the technology to the standard production casing sizes in TNK-BP (casing size 6 5/8 inches or 7 inches) to maximize the project value. Dual concentric ESP pilot tests in 7-inch production casing with Western and Russian contractors are additionally planned. Consideration in design should be given to possible complications related to scale and produced solids.
TNK-BP team jointly with contractors had demonstrated high level of professionalism and validated the technology in remote Western Siberian conditions. Once the technology is fully tested and optimum cost / benefit solution is found, it will be scaled up in other TNK-BP fields.