A well-executed cement operation is fundamental for successful zonal isolation. One method used to confirm the success of a cementing operation is cement bond-log (CBL) analysis. Various factors contribute to good bond strength at the casing-cement interface; a better shear bond helpsminimize the risk of communication between different zones and also maximize production by avoiding undesirable fluid diversion during well intervention. To enhance shear-bond strength, a thin layer of coating material can be applied on the external surface of casing before running itin the well. Variouscoating techniquesare available, such as spraying, dipping, or simply brushing. Polymer emulsions, thermosetting polymers, and inorganic-based coatings can be applied. This paper studies the effect of various coating materials on shear-bond strength.
A coated casing sample was concentrically placed inside another largercylinder and cured after filling the annular space with cement slurry. Once cured, the shear-bond strength was experimentally measured using a hydraulic press. The results obtained with various coating materials are compared to those from an uncoated control sample.
The shear-bond setup was prepared with neat standard cement slurry and cured for 3and 7days for testing. Three different types of casing coating wereevaluated for enhancing shear-bond strength—inorganic-based, aqueous polymer emulsion, and thermosetting resin. All three coatings providedenhanced shear-bond strength compared to the control sample. The inorganic-based coating almost doubled the shear-bond strength. The aqueous polymer emulsion coating increased shear bonding by approximately 30%. Finally, the thermosetting resin coating resulted in a much smaller increase in shear bonding compared to the other treatments; however, it was observed to provide better resiliency while applying loads during testing.
A thin layer of coating onthe entire length of a casing column does not significantly increase costs. On the contrary, significant value is providedthrough better shear-bond strength and potential corrosion resistance. Therefore, this practice can eliminate the necessity of remedial treatments later. Additionally, applying the inorganic-based coating on the outer surface of casing pipe provides additional bond-strength between the cement and casing, minimizing the risk of inner debonding.
The coating application process is operationally simple and can be readily implemented, and it provides a low-cost, dependable barrier. In addition to providing better bonding, coating can also inhibit corrosion and increase the life of the tubular.