Technique Improves Well Integrity by Mitigating Casing-to-Cement Debonding

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 220564, “Improvement in Well Integrity by Mitigating Casing-to-Cement Debonding Using Advanced Technique,” by Mohammed Alibrahim, SPE, and Mahdy Jezany, SPE, Saudi Aramco, and Ahmed Sadeed, SPE, ENPRO, et al. The paper has not been peer reviewed. _ This paper addresses the deployment of an external protective coating with a rough surface profile in wells identified as susceptible to common well-cementing issues. The authors present the associated challenges and highlight the benefits and robustness of the solution in effectively enhancing well integrity. Their study’s outcomes indicated that the implementation of this technique not only provides corrosion protection but also enhances the casing/cement bond. Thus, the risk of fluid migration is lowered. Introduction The authors focus on investigating the effect of casing-surface modification to enhance the casing/cement bond. The primary objective is to use flint-reinforced epoxy coating in well construction, with the dual goal of corrosion prevention and enhancement of well integrity. The resulting irregular surface of the coated pipe creates a robust environment for the cement to build a strong bond with the casing. Initially, a series of laboratory experiments was conducted using various coated and uncoated pipes to identify the optimal casing surface profile. Methods and Materials The coating consists of a three-layer system: two layers of a proprietary epoxy resin reinforced with a layer of embedded flint quartz. The resin in the coating provides corrosion resistance, while the flint quartz reinforces the resin to provide abrasion resistance. This coating system constitutes a thick heavy-duty adhesive, engineered to deliver strength, toughness, and corrosion protection for surfaces subject to elevated pressure or temperature within severe chemical and physical environments. Considering the extremes seen in some downhole environments, the coating system also was qualified to withstand temperatures up to 400°F. These features prolong the life of the casing within corrosive and erosive environments. Laboratory Experiments. A single 4½-in. bare carbon steel pipe 40 ft long was used. The pipe was cut into four pieces of 25 cm. Of the four pieces, one sample was prepared by blasting with a grit size of approximately 1.8 mm. The blasted sample later was coated with a flint coating per standard coating procedure and labeled C-1. The second sample was 4½-in. conventional smooth-finish coated pipe labeled C-2. A blasted and noncoated sample also was prepared to observe the effect of blasted surfaces on shear-bond strength. Shot blasting was performed with a shot size of approximately 1.5 mm. The blasted/noncoated sample was labeled NC-1. The last sample was bare pipe and labeled B-1. To study the coating interface with either casing or cement, the internal diameter of the 7-in. external casing was grooved. The grooves provided extra reinforcement for cement to bond with the casing. Thus, the expected failure would be in either the cement sheath, the cement/coating interface, or the coating/casing interface (adhesion) around the 4½-in. pipe.