Western Siberia Sees Improvement in Drilling Efficiency

Achieving significant improvements in drilling efficiency is most often the result of an integrated approach. First, the appropriate combination of hardware and software tools must be selected for the particular task to be accomplished. The second requirement is an experienced, dedicated directional-drilling team capable of seamless timely communication with the operator. This combination recently delivered excellent results on a large-scale field-development program in western Siberia.

Sibneft-Khantos operates the South Priobskoye field in the Khanty-Mansiysk autonomous region of western Siberia (Fig. 1). The Priobskoye fields straddle the Ob River and are among the most productive oil fields in a region known for prolific oil fields. Starting in 2005, the company launched an ambitious development program designed to place 200 wells on production each year while optimizing drilling processes and while saving time and money by streamlining procurement and logistics programs. A combination of Russian and foreign service/supply companies was to be used, so it was essential to establish clear procedures and workable metrics by which progress could be monitored and evaluated. Specific goals included using the best-substantiated drilling technologies to reduce drilling time, simplify well design, reduce environmental impact, and improve well quality. Historically, all drilling had been performed employing local service companies using rigs equipped with nonrotating aluminum drillpipe and locally manufactured mud turbines.

Fig. 1—Starting in 2005, the operator set a goal to place 200 wells on production each year in the South Priobskoye oil field.

The operator identified five focus areas for improvement:

Upgrading of drilling rigs and drillstring components.
Drill-bit procurement and supply-chain management.
Drilling efficiency and wellbore quality.
Improvement in drilling-fluid properties.
Improvement of cementing efficiency and quality.

Wells at South Priobskoye are pad drilled, generally following an S-shaped profile with average lateral displacement of 3,182 ft from the surface location. Typically, the casing program consists of 12 3/4-in. surface pipe, a 9 5/8-in. intermediate section, and a 7in. production interval. In addition to improving drilling efficiency, Sibneft was concerned with ensuring that all wells were landed precisely in the target formation and that borehole angle-build rates never exceeded design criteria. In addition, because of the number of wells emanating from each drilling pad, there was a risk of borehole collisions. Accordingly, procedures to prevent this were an essential part of the plan and the subsequent practice. Finally, the company was determined to minimize unnecessary borehole extensions or sidetracks.

In September 2005, responsibility for directional-drilling, measurement-while-drilling (MWD), and drilling-engineering services was turned over to Schlumberger. PowerPak greater-torque (GT) positive-displacement motors and SlimPulse MWD tools were used for the project. GT motors allow use of more aggressive bits and deliver maximum rates of penetration. They consist of three main components: a power and transmission section that can be customized to match the desired torque and rotation speed at mud-flow rates optimized for the bit being used and for thorough cuttings removal; a surface-adjustable bent housing for optimal angle-build rates; and a bearing assembly with a surface-exchangeable near-bit stabilizer (Fig. 2). The MWD tool provides real-time direction and inclination information, as well as tool-face and gamma ray measurements. Telemetry automatically switches between sliding mode and rotating mode to provide continuous steering data for trajectory control. Data are transmitted through mud-pulse telemetry to the surface sensors.

Fig. 2—The positive-displacement motor is designed for use with aggressive drill bits.

Sibneft drilled more than 80 S-shaped wells in 2005–2006 with the positive-displacement-motor/slim-MWD-tool combination. All wells landed in their target zones, and angle-build rates never exceeded design. Borehole quality and cleaning were excellent, as evidenced by significant improvement in casing installation and cementing efficiency and quality. The steerable bottomhole assembly with real-time data transmission resulted in minimal borehole extensions and no collisions, and no remedial work has been required in the wells.

Penetration rates also improved. Using Russian-manufactured polycrystalline- diamond-compact bits and improved drilling-fluid design, the tool reduced nonproductive time to 3% of total operating time. The number of wells placed on production exceeded plan by 23.7% in 2005 and 35.3% in 2006. Specific steps taken and results for drilling-rig upgrades, bit-procurement modification, and improvements in drilling -fluids and cementation procedures can be found in paper SPE 103735.

Information provided by R.M. Fecenec, Sibneft-Khantos, and Tim Day, Schlumberger