Today, more than 66% of Russia’s oil and 92% of natural gas are produced in Western Siberia. Since the first discoveries in the 1960s, this region has become the heartland of Russia’s oil and gas industry. Within the last decade, the Western Siberian giant mature fields were joined by newer discoveries that have been brought onstream. The new developments are better equipped to deploy modern drilling and production technologies that allow improving drilling efficiency, increasing production and shortening time to market. The Salym Group of oil fields is one of those newcomers.

With the Mercury EM telemetry system, drillers can transmit surveys during connections, saving valuable rig time. (Image courtesy of Halliburton Sperry Drilling)

With the Mercury EM telemetry system, drillers can transmit surveys during connections, saving valuable rig time. (Image courtesy of Halliburton Sperry Drilling)

The Salym Group of oil fields is in Khanty-Mansi Autonomous Okrug, 75 miles (120 km) southwest of Surgut and 19 miles (30 km) west of Salym village. The group includes three fields – West Salym, Upper Salym, and Vadelyp. Development drilling in these fields started in the early 2000s. Since 2004, Salym Petroleum Development NV (SPD) holds licenses for the development of all three Salym oil fields with the license area totaling 827 sq miles (2,141.4 sq km). This company is a joint venture established on a 50-50 basis by Shell Salym Development BV and OAO NK Evikhon (now a subsidiary of Sibir Energy plc).

Combining best practices
According to Simon Durkin, SPD CEO, “As a joint venture, SPD seeks to adopt all valuable and advanced features from the Russian oil production experience and combine them with the best practices of the shareholders and other leading oil companies.”

This statement is verified by the recent joint success of electromagnetic (EM) telemetry transmission method introduction in West Salym field by SPD and Halliburton Sperry Drilling.

Positive displacement mud motors and standard MWD services normally are used for directional drilling and well placement in West Salym. Until 2009, mud pulse telemetry has been the only communication method used for transmitting downhole data to the surface while drilling. In 2009, SPD decided to try EM telemetry to realize time savings and improve drilling performance.

Focus on optimization
Since the first well drilled in West Salym in 2004, drilling optimization has been the focus of the SPD drilling team. They have adopted the approach called “drilling the limit,” which is used in Shell well engineering units globally. The three pillars of this approach are as follows:
• Drill the economic limit: a commitment to economically achieve maximum quality, efficiency, and best performance;
• Continuous improvement: a review of operations and rectification of deficiencies, collection, and application of best practices; and
• Team work: maintaining a close working contact with all contractors.

Sperry has been providing directional drilling and formation evaluation services to SPD since 2006. In the spirit of the drilling-the-limit approach, SPD and Sperry have open communication and regularly review performance data from the previous wells to find solutions for optimizing the drilling process and cutting the time/depth curve. During this time, the penetration rate nearly tripled. In 2004, the first well was drilled within 33 days, whereas the average drilling time today is down to 9.7 days. In Western Siberia, the average drilling time for similar wells under similar geotechnical conditions is 15 to 18 days. In 2009, SPD and Sperry set a record by drilling a well within 4.54 days.

Saving time through EM
In 2009, Sperry offered SPD to deploy EM telemetry on four wells in West Salym to further enhance drilling performance. Sperry’s EM MWD/LWD telemetry system establishes a two-way communication link between the surface and the downhole tool using low-frequency EM wave propagation. The system encodes data into EM waves with frequencies in the 2- to 15-Hz range. The signal is transmitted from the downhole tool through the drillpipe and earth, and is detected at the surface as a very low-voltage potential between the wellhead and a remote electrode.

Unlike negative and positive pulse systems, an EM system can transmit data without a continuous fluid column. This feature allows pump-off telemetry, which translates into direct time savings. Conventionally, directional surveys are transmitted after a connection; the drill crew adds new drillpipe, turns the pumps on, and then waits three to five minutes for the MWD survey to be pulsed to the surface before drilling ahead. This adds “invisible” nonproductive time (NPT) to the drilling operation. The EM signal can transmit the directional survey while the drill crew is adding new pipe, so when the pumps come on, the survey already has been received and the crew can begin drilling, saving three to five minutes per connection.

After deployment of the EM telemetry system in West Salym, SPD was able to save six to nine hours of invisible NPT per well by eliminating survey time.

Additional benefits, challenges
West Salym geology is characterized by very soft formations, particularly at shallow depths. An average well is 9,383 ft (2,860 m) measured depth (MD), and some wells extend beyond 9,843 ft (3,000 m). EM telemetry functions reliably even without a fluid column. By using the technology, SPD had the option of reducing flow in unconsolidated areas in the top hole sections, which helped to avoid the creation of small washouts and improved kickoff from vertical.

Another upside of using EM was the ability to bypass rig limitations. The rigs used in West Salym have a standpipe pressure limit of 210 bar, which sometimes necessitates a reduction of flow rate in deeper wells. EM telemetry allows drilling with lower standpipe pressure than traditional mud pulse, enabling dependable drilling performance even in the deeper sections.

The question stands, based on SPD’s positive experience, can other operators in Western Siberia apply EM telemetry in their fields? The answer to this depends on a number of variables. Firstly, not all formations are suitable for transmitting EM waves. Before application, a signal strength model must be run by specialists. The model will predict with high level of accuracy the success of EM telemetry application in a specific field depending on formation type and a specific well profile. The formations in West Salym were suitable for the application of this technology.

Secondly, the strength of the EM signal diminishes with well depth. This challenge is easier to address than the natural limitations of formation type. In areas of high signal attenuation or at deep depths, Sperry uses a repeater to increase signal strength. For instance, in West Salym, the company drilled up to 9,514 ft (2,900 m) MD with strong clear signal. In the company’s next generation EM telemetry system, coming out in early 2011, several repeaters will be used to remove the depth limitation altogether.

It is important to note that the close collaboration between SPD and Sperry was the foundation of the EM telemetry application success. Joint efforts to drill the limit and eliminate every second of NPT have paid off. With proper planning, similar benefits can be achieved by other operators in Western Siberia.