Canada has the third-largest oil reserves in the world, with 168 Bbbl situated in the oil sands of Alberta and Saskatchewan. However, more than 80% of this resource is too deep to be mined and requires an in situ recovery technique.

The oil sands consist of a mixture of sand, water, clay and highly viscous bitumen. This mix requires a complex combination of thermal and artificial lift techniques to mobilize the fluid to surface. But despite the tough environment, the valuable prize contained in the oil sands inspired an industry accustomed to technical challenges to hone its methods for extracting heavy oil.

SAGD and ESPs to the rescue

Steam-assisted gravity drainage (SAGD) emerged as the preferred in situ recovery method for these oil sands. SAGD involves the horizontal drilling of two wells, one (an injector well) above the other (a producer well), typically with 5 m (16 ft) of vertical separation. Steam is pumped into the upper injector well to heat the bitumen and reduce its viscosity. Through gravity drainage, the resultant emulsion of oil and water can be produced to surface via the lower producer well.

On paper, this process sounds simple; however, its effectiveness depends on many factors, including reservoir depth, quality and thief zones, where the required reservoir pressures and temperatures needed to mobilize and lift the bitumen to surface can be difficult to achieve. Additionally, the steam/oil ratio (SOR) has a significant impact on the efficiency and economics of the SAGD process, and optimizing the SOR is key to a successful project.

Initially, most SAGD wells were completed with gas lift systems, which provided a simple completion solution and had no temperature limitations. The downside was that gas lift required a minimum reservoir pressure, and with the drive to optimize the SOR through lower steam and reservoir pressures, the limitations of gas lift completion were soon recognized. The industry was forced to look for alternative artificial lift solutions.

One such alternative was electrical submersible pumps (ESPs). ESPs do not have the reservoir pressure limitations of gas lift and can operate over a wide range of flow rates typical of SAGD wells. The challenge was that the maximum operating temperature of the electric motor was 150 C (302 F), too low for SAGD wells.

The introduction in early 2003 of the Schlumberger REDA Hotline 550 ESP system changed the landscape because this system was the first high-temperature ESP—rated to 218 C (424 F). This increased temperature rating provided SAGD operators with the ability to install ESPs in their wells, enabling them to lower reservoir pressures, lower SOR and ultimately lower production costs. The enhanced capabilities marked the start of an ESP revolution, and today more than 700 ESPs are operating in SAGD wells in Canada.

Challenge and success

The success of the Schlumberger Hotline ESP encouraged SAGD operators to push the pump’s operating envelope, challenging ESP suppliers to develop systems that could operate at even higher operating temperatures—up to 250 C (482 F)—and with the improved reliability needed to prolong ESP run life. Starting in 2007, engineering teams in Singapore and the U.S. began working on a new high-temperature ESP system. The result was the REDA HotlineSA3 third-generation high-temperature ESP system, which features the first step-change in ESP design. A new integrated configuration of the internal motor is a complete rearrangement of the traditional ESP design. Unlike conventional ESP systems, the seal section of the integrated motor, often referred to as the protector, is split in two. The shaft sealing functions are maintained on top of the motor section within the shaft seal module (SSM), while the motor oil compensation and pressure equalization functions are moved below the motor. The SSM, motor and compensator, and sensor portal make up the integrated motor component.

The short shaft sealing sections are stacked on top of the motor to add redundancy and layers of protection, thereby enhancing motor reliability. The shorter SSM increases the tolerance to dogleg severity (DLS), which can be substantial in SAGD wells. When operating in high-DLS wellbores, the ESP components—shafts, flanges, bolts and bearings—are subjected to mechanical stresses that can be detrimental to the ESP and can ultimately reduce run life. The SSM also includes filters to prevent damage to sealing components and ceramic bearings with a high load capacity to handle abrasives. With the compensator located at the bottom of the motor configuration, the pressure equalization and abrasives are isolated from the critical components of the SSM.

To further improve the reliability of the system, all nonmetallic components were reassessed and upgraded to withstand the new well temperature rating of 250 C and internal motor temperature rating of 300 C (572 F). O-rings, motor insulation, motor oil, and radial and thrust bearings also were upgraded.

The integrated motor incorporates a prefilled plug-in concept, which reduces the potential for human error during system installation. Motor oil is prefilled at the factory or service center, eliminating the need for filling at the well site. The prefilling process uses ultrapurified motor oil that increases insulation and reliability. The plug-in pothead design has a positive pressure system and dual elastomeric seal to prevent fluids from escaping and entering the motor while the connection to the power cable is being completed.

Finally, to improve ESP performance and provide the opportunity for well optimization, a sensor portal was added to the system. The sensors measure internal motor temperature and annulus pressure and temperature.

Paradox solved

At first glance, the challenge of successfully operating an ESP in a SAGD well seemed impossible. The presence of very high temperatures, high well deviations and abrasives were all components that typically led to early ESP failure. However, by tackling the problem head on, engineers eliminated each of these problems. Moving away from conventional ESP architecture to the integrated motor configuration along with the availability of high-temperature materials proved to be the turning point in improving ESP reliability and operating range.

The result was that ESPs—which lower lift costs and improve production uptime—continue to be the preferred artificial lift method in SAGD.