Schlumberger

Technical Paper: Flexible Cement Improves Wellbore Integrity in SAGD Wells

Society: SPE
Paper Number: 119960
Presentation Date: 2009
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Abstract

Zonal isolation and cement sheath integrity are key requirements for heavy oil development and production. Current commercial production techniques use steam to provide heat to mobilize oil and allow production. One such technique is Steam Assisted Gravity Drainage (SAGD). Maintaining cement sheath integrity prevents unwanted fluid migration, especially oil, gas, and or steam. Flexible cement systems can be designed and installed so that the cement sheath can withstand the expected stresses in the well. Installation practices are critical to providing a high quality cement sheath. Challenges that are prevalent in SAGD wells are centralization in the soft formations, assessment of the cement bond between the cement and formation, and assessment of the cement bond after steaming.

Case History—Comparison of two cement systems with flexible properties installed in seven SAGD well pairs (14 wells). Two cement systems were selected for installation and comparison in SAGD well pairs for a project in Alberta. These cement systems have flexible properties, with Young's Modulus varying from 2000 MPa to 6000 MPa. Careful planning and process control were required to deliver the system with the desired properties to the wellbore. Industry best practices were used for placement of the cement systems, including the use of centralizers, viscous fluid spacers and pipe movement.

Zonal isolation and wellbore integrity are examined with the use of cement cement evaluation logs and ultrasonic cement evaluation tools. These logs provide evidence that zonal isolation is achieved and is improved with the use of industry best practices for cement placement. The flexible cement systems are proven for zonal isolation in these SAGD wells.

More than half of the 9 to 13 trillion barrels of world oil resources in place are classified as “extra-heavy” and “oilsands and bitumen”. Current commercial methods for developing these reserves such as SAGD may place significant stresses on the cement sheath which could lead to failure. The use of best practices for placing the cement slurry, and the use of cement systems with flexible properties improves well integrity enabling efficient development of world heavy oil reserves.

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