TNK-BP Dual Completion: Unlocking Hidden Potential
Studies by the Tyumen Petroleum Research Centre (TNNC) show that TNK-BP is failing to take full advantage of the major benefits that could be gained by applying dual completion (DC) technology at its oil fields. Each of the Company’s target subsidiaries (TS) has encountered its own specific difficulties when it comes to deploying dual completions, as well as more general issues shared by all.
Dual completion has been recommended in project documentation for 35 fields across the Company, including 13 key fields. These assets are concentrated primarily in the Orenburg Region, although some of the blocks are operated by Varyoganneftegaz and TNK-Uvat. Overall, plans have been made for dual completions in over 900 wells.
As of January 1, 2012, 248 DC assemblies had been installed across TNK-BP, mainly at the Samotlor field, where the focus is on injection wells. The largest number of dual production (DP) units has been installed in the Orenburg Region.
Falling Behind Schedule
A study of the actual deployment of DC solutions at 25 major fields within TNNC’s sphere of responsibility has identified eight fields at which the pace of work needs to be stepped up.
This is greatly complicated, however, by the complex decision making procedure for applying DC technology, which involves a whole chain of geological, technological and economic issues (Fig. 1). A negative result at any link in this chain means that dual completion cannot be used. Further complicating the picture, each TNK-BP region has its own specific difficulties to contend with when applying DC technology.
Analysis of the potential for boosting production through DC technology indicates that it could be applicable in the Orenburg Region, at Samotlor, in various fields operated by Varyoganneftegaz and at TNK-Uvat’s Ust-Teguss field. Fields operated by TNK-Nyagan require further trial production work to evaluate the potential scale and applicability of DC assemblies. At the Verkhnechonskoye field, the potential for DC is constrained by the use of complex equipment to drill horizontal wells with limited anticipated flow-rate increments. Meanwhile, at Rospan International, DC would not be appropriate given the limited understanding of the fields and their later commissioning dates.
Implementation Issues
TNK-BP’s largest asset is the Samotlor field, which consists of 11 development targets with over 1,200 commingled wells. The main reason for using DC at Samotlor is to reduce the planned number of lowrate wells and to isolate productive formations in commingled wells. This is essential to make development more efficient and to optimize reserves depletion. At the same time, due to the long history of commingled production at Samotlor, deploying DC assemblies is no easy matter. The constraints include a complex distribution of residual reserves, the large number of wells with integrity failures in production strings and sidetracks, and the presence of gas caps in some formations. The overall number of candidate wells for DC at Samotlor is around 300 wells, with potential to produce an estimated 9 mln t of additional reserves.
In the Orenburg Region, TNK-BP operates over 70 stacked reservoirs, with reserves varying from 1 to 50 mln t of oil. In many key fields there is potential for accelerating the rate of reserves depletion in low-productivity formations. The Garshinskoye field, for instance, could produce from as many as eight individual formations, where recompletions are currently planned or drilling of marginal wells is required. The main aims of applying dual completions in that region are therefore to speed up the recompletion programme, to reduce the number of planned low-rate wells, and to isolate formations in commingled wells, which number approximately 600. Experience to date has highlighted a number of technical issues hindering the widespread application of dual completion technology: first, a lack of reliable equipment for fields with a high gas content in the oil; second, the considerable depth of most of the accumulations rules out the use of sucker rod pumps, while deployment of electrical submersible pumps (ESP) in ESP + ESP assemblies is limited by the small diameters of the production strings in existing wells (168 mm or less). Excluding wells already identified as problematic, the potential well stock for dual completions at key fields alone in the Orenburg Region could be around 1,400, with an estimated residual reserves potential of 23 mln t.
Varyoganneftegaz is developing seven stacked reservoirs with over 200 commingled wells. Formations of the Verkhne-Kolik-Yoganskoe field containing around one third of its current recoverable reserves are being tapped using a high ratio of commingled wells, though a large part of the reserves remains untouched. DC are an essential tool for Varyoganneftegaz to speed up its recompletion programme, to reduce drilling of marginal wells, and to isolate productive formations in commingled wells. As in the case of Samotlor, the residual reserves in Varyoganneftgaz’s fields have a complex distribution and the wells have been in operation for a considerable period of time. Further problems have been encountered in operating DC units after hydrofracking. Varyoganneftegaz, as a whole, has the potential to deploy DC in over 350 wells to produce an additional 11 mln t of recoverable reserves of oil.
In the Uvat project DC technologies are well suited to the Ust-Teguss field, where they could reduce the total well stock and accelerate depletion rates. The field is already using DC equipment in an ESP + ESP assembly. Research has revealed that the main issues here are the high cost of DC, the need to drill large-diameter wells (245 mm) and the risk of failing to confirm geological predictions, which could reduce the effectiveness of DC or result in a decision not to deploy them. At the same time, the use of DC at Ust-Teguss field will eliminate the need to drill a second grid and reduce well numbers, bringing up to 17 mln t of recoverable reserves on stream with 115 fewer wells.
Shared Goals and Good Potential
Studies have shown that the motivation for applying DC solutions is virtually identical across TNK-BP’s TS: to drill fewer marginal wells, to speed up field developments, and to isolate productive formations in commingled wells for separate control of depletion rates. Any differences between the various TNK-BP regions are merely a matter of the relative importance of the above objectives. Across the Company as a whole there are over 3,000 candidate wells for DC jobs, with a potential production increment of several tens mln t of oil.
Continued development and deployment of DC technologies will therefore help to unlock the potential for incremental production, boost output and expedite field developments, while also enabling cost-effective production of reserves that would otherwise be marginal or subcommercial.
Published with thanks to TNK-BP and Innovator Magazine
