The mechanical properties of weakly consolidated shallow formation are low strength and low Young's modulus while the Portland cement is high strength and high Young's modulus. The cement sheath can easily undergo brittle failure under this condition, which is severely threatening the cementing isolation quality of oil and gas wells. Bridging the huge difference in the mechanical properties of the two materials is a challenge even for the elastic cement slurry system. Waterborne epoxy resin was applied as a strengthening fluid for the weakly consolidated shallow formation in deep-water to improve the cementing quality. An artificial core was utilized to evaluate the reinforcing effect. The result shows that the blended formation fluid can increase the compressive strength of the curing product with a dosage of less than 40 %. The control group indicated that the inorganic salt in the formation water is beneficial for the reinforcement of the formation. The evaluation experiment indicated that the strengthening fluid can significantly increase the cement-formation interface strength.
The isolation integrity of oil and gas wells is essential for isolating formation fluids (Mangadlao et al.,2015; Liu H. et al.,2016). Accidents caused by cement sheath failure are often severe threaten the marine ecology (Liu, Z.et al., 2015) and are costly to resolve, especially in the ocean (Pan et al., 2015; WU et al., 2018).
The principal components of weakly consolidated shallow formations in deep water are unformed rock silt and sand. In addition, the weakly consolidated shallow formation in deep water can extend hundreds of meters below the mud line (Eoff, 2000; Lavasani, 2011; Skogdalen, 2012). In 2010, the wellhead device of Husky Energy's LH29-1-3 well sunk approximately 2.5 meters, nearly causing the well to scrape. (Liu, 2015). The mechanical properties of weakly consolidated shallow formation are low strength and low Young's modulus while the Portland cement is high strength and high Young's modulus (Ribeiro, D,2019; Zhang et al., 2019; DU et al., 2018). The cement sheath is prone to brittle failure under these conditions, posing a danger to the cementing isolation quality of oil and gas wells. Bridging the huge difference in the mechanical properties of the two materials is a challenge even for the elastic cement slurry system (LIU et al., 2016; Diarra, R., 2017; Pang, X,2017; WANG et al., 2019). Therefore, we propose a novel strengthening fluid that reinforces the weakly consolidated formation to eliminate or reduce the sudden change in mechanical properties between the formation and cement sheath. The strengthening fluid is water-borne epoxy resin-based and can penetrate the weakly consolidated shallow formation and reinforce it. In this way, the cement sheath and formation can consolidate as an entirety. Due to the pore of shallow formation being full of seawater (LIU et al., 2016; Tian et al.), it is inevitable to blend seawater during the penetration of the strengthening fluid into the formation. Furthermore, alkaline filtrate will also loss when cement slurry sets (DU et al., 2019; CAO et al., 2021). Those fluids may influence the curing of strengthening fluid.
