Experimental study of shear and hydraulic bonding strength between casing and cement under complex temperature and pressure conditions

The cement sheath plays a vital role in preventing gas channelling. It is important to understand the interfacial bonding between the casing and cement sheath when the downhole temperature and pressure change. This paper demonstrates the results of an experimental study to investigate the effect of high temperature and high pressure and their variations on the cement sheath interfacial bonding strength (CSIBS). An experimental device was developed that is used to test the shear and hydraulic bonding strength with the method of uniaxial compression and gas channelling. The results show that both temperature and pressure have a significant influence on the CSIBS. As the curing temperature increases with a constant curing time or as the curing time increases with a constant curing temperature, the CSIBS first increases and then converges to a stable value. The casing roughness has a crucial effect on the shear bonding strength but little effect on the hydraulic bonding strength. Though the CSIBS decreases obviously with the decrease in temperature, it undergoes little change when the temperature first increases and then recovers to the initial value. When the internal casing pressure decreases to a certain value or first increases to a certain value followed by recovery to the initial state, the hydraulic bonding strength tends to be 0 MPa, which means that the interface undergoes debonding between the casing and cement.