Effect of Composite Interface Enhancer on the Cementation Strength of Shale Formation–Cement Ring Interface

The cement strength between the cement and the formation is a key factor in determining the cementation sealing capacity. In the shale formation, due to the organic matter content, the cementing quality between the formation and the cement ring is poor, which affects the quality of cementing. It is easy to cause problems such as annulus pressure. To improve the quality of cementing, this paper investigates the effect of amino silane coupling agents, vinyl silane coupling agents and aluminium–zirconate coupling agents on the interface cementation of rock and cement under different conditions. Meanwhile, the effects of different coupling agent compounding on improving the cementation interface cement strength under different temperature and concentration conditions were investigated. This led to the development of a composite interface enhancer. The composite interface enhancer can improve the bond strength between cement and rock by 189.22%. A preflush fluid system was developed to effectively improve the cementation strength of mud shale formations, and its performance was evaluated. The density of the preflush fluid system is 1.15 g·cm−3, and it has good rheology, settlement stability, and filtration loss. In addition, it improves the cementing interface cementing strength between the cement and shale formation.