New Technologies Maximize Production in Viscous-Oil North Slope Field
Oil quality and drilling-pad constraints for a viscous-oil field defined a development scheme that consisted of a waterflood line drive with horizontal producers and water-injection (WINJ) wells side by side.
Oil quality and drilling-pad constraints for a viscous-oil field defined a development scheme that consisted of a waterflood line drive with horizontal producers and water-injection (WINJ) wells side by side. Different well designs for producer wells were implemented: a single horizontal trajectory undulating between the two sand bodies in counterphase with the related water injectors, a fishbone design with the main borehole in the lower sand and multiple branches in the upper sand, and a multilateral (ML) counterphase design with extended-reach undulating dual laterals. As a result of the ML campaign, well productivity doubled.
The field is located on the North Slope of Alaska in the Beaufort Sea in water depth less than 20 ft. The reservoir consists of four zones hydraulically communicating, named OA1, OA2, OA3, and OA4. The differentiation is mainly sedimentological; OA1 and OA3 are associated with a more-proximal depositional system, while OA2 and OA4 are characterized by a predominance of thin laminated silty sandstones because of a more-distal depositional system.
The crude quality and drill-pad constraints (one offshore, one onshore) drove a development concept that consisted of a waterflood line drive with alternating horizontal producers and WINJ wells with a 1,200-ft spacing. The lateral sections are 6,000–10,000 ft long through the reservoir with undulating counterphase trajectories across the two main sand bodies. Challenging very-extended-reach wells with a stepout ratio higher than 6 have been achieved (Fig. 1 above).
The undulating counterphase well trajectories were selected for producers and injectors to guarantee optimal pressure support and avoid early water breakthrough. The original design was based on predrilling assumptions; however, the reservoir was revealed to be more homogeneous than expected, with good petrophysical properties. These conditions led to the evaluation of ML concepts, with an expected low impact on water-cut trends and water breakthrough.
With the goal of increasing reservoir contact, the ML concept consisting of undulating counterphase dual laterals was tested in August 2013. The producer was modified to an undulating counterphase dual lateral throughout the two main sands. The injector maintained the original well concept in counterphase with the original producer mainbore. As a result, well production doubled with respect to the average before the intervention.
In parallel, key development wells were identified for data acquisition and appraisal activities that have resulted in derisking stepout opportunities as well as assessing the potential of challenging resources, such as the peripheral areas.
The Nikaitchuq development can be considered in four distinctive periods—natural depletion, WINJ, electrical-submersible-pump (ESP) optimization, and the ML campaign (Fig. 2).
Fig. 2 clearly reveals different incremental-oil-production ramp ups for the three main development phases. A positive effect in the incremental-production trend is achieved with a reduction in well number and time. An evident production step change is seen with the ML-campaign start up.
Summarizing the entire ML campaign, a doubled oil-production rate was achieved with respect to the average value before the intervention.
A parallel action was conducted in terms of possible upside identification for future development. The resources of the west and northwest areas have been unlocked thanks to the contribution of a dedicated seismic revision. The drilling feasibility brings with it the possibility of benefit in the development phase. The same approach of nurturing opportunities will be implemented for the eastern area.
A pilot well was drilled in the north sand, and an integrated reservoir study is evaluating optimal development of the updip reservoir level.
An intense campaign of reservoir monitoring was established to maximize recovery. The downhole equipment for the injectors consists of inflow-control devices coupled with distributed-temperature surveys to monitor the injection profile. As a result, the sweep efficiency will be improved. Key producers are equipped with downhole water and oil tracers that identify low- and high-oil-production areas and water-production sections. A tracer acquisition is acquired at each well shut-in. Finally, a detailed campaign of voidage replacement for each production area is established on a weekly basis.
An additional intrawell-tracer campaign will be executed for a better comprehension of reservoir communication. Concerning enhanced oil recovery, a dedicated study is evaluating a collection of processes that will help sustain and improve production in the near future (i.e., low-salinity waterflood, polymer/surfactant flooding).
The ML concept consisting of undulating counterphase dual laterals was tested in August 2013. This initial test was followed by a limited campaign. As a result, well production doubled with respect to the average before the intervention. Similar productivity improvements were also observed in the new producers. At the time, production was sustained by 20 producers and 15 injectors. Since then, eight additional laterals were added to existing producers and four new dual-lateral producers and three injection wells were drilled and completed. The fieldwide step change was evident with an overall production increase of approximately 82% in May 2014 with respect to the campaign startup.
Because of these results, the ML campaign was extended to all the producers and is now standard practice for the remaining development wells in this field.
A detailed reservoir-monitoring process has been established since the well-completion design, and it is now standard practice on the field. Tracer and distributed-temperature-survey information is acquired to monitor the water front and maximize the sweep efficiency.
Finally, the west- and northwest-area resources have been unlocked and are now in development. A pilot well in the north sand has been drilled, and new opportunities in the reservoir periphery have been identified and will be evaluated closely in the near future.
This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 171896, “The Use of New Technologies To Maximize Oil Production in a Viscous-Oil Field in Arctic Environment: The Nikaitchuq Experience,” by S. Raniolo, SPE, S. Mancini, and S. Vimercati, Eni E&P; and P. Gentil, D. Simeone, SPE, and A. Buchanan, Eni Petroleum, prepared for the 2014 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 10–13 November. The paper has not been peer reviewed.