Detailed information on the quality of the cement job is vital to ensure economical, safe and stable production from a reservoir. A crucial part of this is the ability of cement to bond to the formation. Improper removal of drilling fluid or cement placement, or debonding due to unfavorable wellbore conditions can create potential flowpaths. Loss of zonal isolation from cement sheath failure can appear at three possible locations: at the cement-formation interface, in the bulk cement or at the casing-cement interface.

This experimental study focused on the cement-formation interface. The primary objective was to quantify the effect of various rock formation types on the cement-formation bonding, and the effect of altering the rock surface with various drilling fluid films before cementing. The secondary objective was to visualize the interfaces using micro-computed X-ray tomography (p-CT) and to observe any link between the measured shear bond strength and the presence of pores, cavities or films along the cement-formation interface.

The results showed that the different rock formations exhibited different interactions with the cement. However, it was also shown that the presence of drilling fluid, and drilling fluid type, were more crucial parameters for cement-formation bonding. The drilling fluid presence reduced the bonding strength, and it was shown that by using oil- or water-based drilling fluids the cement-formation bond was affected differently.

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