Overcoming the Weak Link in Cemented Isolation
- Karen Bybee (JPT Assistant Technology Editor)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- May 2008
- Document Type
- Journal Paper
- 101 - 104
- 2008. Society of Petroleum Engineers
- 0 in the last 30 days
- 75 since 2007
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This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 110523, "Overcoming the Weak Link in Cemented Hydraulic Isolation," by N. Moroni and N. Panciera, Eni E&P; A. Zanchi, Stogit; and C.R. Johnson, SPE, S. LeRoy- Delage, SPE, H. Bulte-Loyer, SPE, S. Cantini, SPE, E. Belleggia, SPE, and R. Illuminati, SPE, Schlumberger, prepared for the 2007 SPE Annual Technical Conference and Exhibition, Anaheim, California, 11-14 November. The paper has not been peer reviewed.
The full-length paper describes a unique isolation solution based on a responsive cement system with intrinsic self-healing properties that are activated automatically upon hydrocarbon exposure. Activation occurs whenever the integrity of the cement sheath is compromised. The new sealant system rapidly forms a complete barrier by swelling and continues to reseal should further damage occur. The technical advantages of this sealant have been demonstrated through successful field tests.
New Sealant System
In recent years, the well-cementing industry has begun to concentrate on the ability of set cement to provide zonal isolation throughout the lifetime of the well. Even if the cement has been placed properly and initially provides a competent hydraulic seal, zonal isolation could be compromised as a result of changing downhole conditions over the lifetime of the well. Studies have shown that the main causes of cement-sheath damage are stresses induced by varying downhole conditions.
The loss of zonal isolation after cement has hardened can be a result of mechanical failure of the set cement itself or debonding of the casing from the cement or the cement from the formation. Several solutions have been developed and applied successfully in field applications. One current method to improve cement resistance to physical stresses involves the addition of fibrous or ribbon-like materials to increase the toughness of the cement matrix. While these methods increase the resistance of the cement matrix to physical stresses, none of these approaches can accommodate problems that occur once the cement sheath has actually failed and becomes permeable.
The objective of the self-healing cement (SHC) system is to pro-vide long-term zonal isolation with a cement-based system that incorporates self-healing additives. Hydrocarbons activate the self-healing additives whenever the integrity of the cement sheath is compromised (e.g., cracks and micro-annuli), and the cement matrix would seal the leak path through a swelling mechanism.
Application of this responsive sealant targets a wide range of wells to mitigate risks of future cement-sheath degradation through unplanned well events and operations, and to ensure long-term zonal isolation throughout the productive and abandoned periods. The versatile sealant can be strategically placed, from surface to total depth of the well in any string of the well, to provide an effective long-term seal.
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