A Study on the Hydraulic Isolation Property of Cement-casing and Cement-formation Interfaces by Oleophilic Cement Slurry
When cementing with oil-based drilling fluid in shale gas wells,oil in casing and wellbore is easy to reduce the interface isolation performance and form channeling circulation channels,which will have a negative impact on subsequent production.Although the pre-fluid can effectively improve the interface wetting reversal,the oil film retention and adhesion will still occur due to the limitation of flushing efficiency.To this end,we add oil-wetting surfactants to cement slurry,and form oil-wetting cement slurry,giving cement oil-wetting ability.Contact angle,shear bonding strength and interfacial hydraulic isolation tests were used to evaluate the oil-wetting ability and interfacial isolation effect of the cement.It is found that the contact angle of non-polar solvent on the surface of oil-wetting cement is much lower than that on the surface of conventional cement,and the non-polar solvent has good oil-wetting performance.After oil-wet cement cementing with casing and shale core containing white oil and oil-base drilling fluid,the resistance to fluid cross-flow pressure of the cement-casing interface and cement-formation interface were increases by 5 times and 4 times,and the shear bonding strength increases by 205%and 122%,respectively.The addition of oil-wetting surfactant has no negative effect on the hydration degree of cement,mechanical properties of cement and basic engineering performance of cement stone.The results show that the addition of the oil-wetting surfactant can effectively improve the cement ring and oil-bearing interface,and has the potential to improve the cement sheath,casing and formation interface bonding and isolation performance under oil-based drilling fluid condition.
shale gaswell cementinginterface isolationoil base drilling fluidsurfactant