ESPs Take On Heavy Oil
Date: 08/22/2008
Where oil sands are too deep to be economically extracted using traditional surface-mining techniques, operators often deploy steam-assisted gravity drainage (SAGD) technology. The SAGD method utilizes a pair of parallel horizontal wells. The production well is typically drilled a few meters above the base of the heavy-oil sand and the injection well is drilled about 5 m above the producer. Steam injected through the upper wellbore creates a high-temperature region above the producer and reduces the viscosity of the heavy oil and bitumen, which may have gravities as low as 8 to 9 API. The oil, bitumen, and condensed steam flow downward into the producer well. The fluids are then pumped to surface facilities.
According to Suncor Energy completions engineer Fernando Gaviria, high-temperature ESPs are critical to the company's SAGD efforts in its Firebag field in northern Alberta, Canada. At a recent SPE-sponsored technical conference, Gaviria took time to explain to colleagues some of the difficulties encountered in producing the heavy oil and bitumen, including environments that are challenging to ESPs.
ESPs installed in the SAGD Firebag wells are subject to extreme temperature, temporary steam flashing, temperature cycling, high production rates, and high water cut. Wellbore geometry and dogleg severity at the setting depth can increase stress, fatigue, and vibration in the system. At Firebag, several ESP-equipped strings had to pass through doglegs of up to 15° over an interval of 30 m [98 ft] before the ESPs were installed for operation in intervals with doglegs of up to 12° over 30 m.
Despite these demands, most of the ESPs have achieved satisfactory run-lives. Suncor installed the first Firebag ESP system in June 2005 after extensive engineering research, design, and testing aimed at increasing survivability in wells facing potential bottomhole producing temperatures of up to 209 degC [408 degF]. Key components of the high-temperature system used at Firebag—motor, power cables, pump, and advanced protector—are built to withstand temperatures up to 218 degC [424 degF].
Subsequent to the presentation, coauthor Olegario Rivas, an artificial lift specialist at NExT Network of Excellence in Training, credited the longevity of the REDA Hotline high-temperature ESPs installed at Firebag to an advanced motor protector design. "The Hotline model utilizes a metal bellows expansion chamber, whereas most ESPs use an elastomer bag, which is just not as robust as the bellows," Rivas said.
Suncor has installed 21 of these ESP systems and plans to install 100 to 120 more in the Firebag field by 2012.
Reference
Gaviria F, Santos R, Rivas O, and Luy Y: "Pushing the Boundaries of Artificial Lift Applications: SAGD ESP Installations in Canada," paper SPE 110103 presented at the SPE Annual Technical Conference and Exhibition, Anaheim, California, USA, November 11-14, 2007.
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