Spacer fluids and methods for cementing a casing in a wellbore

A method for cementing a casing in a wellbore, the method comprising displacing at least a portion of a drilling fluid positioned in the wellbore with a spacer fluid comprising:

• an aqueous fluid;
• a weighting agent;
• and
• a clay stabilizer consisting of one or more polyethylene polyamines having a first structure H2NCH2CH2(NHCH2CH2)xNH2, where x is an integer greater than or equal to 3, wherein:
• the one or more polyethylene polyamines comprises hexaethyleneheptamine;
• the amount of the clay stabilizer is from 0.1 wt. % to 10 wt. % relative to the total weight of the spacer fluid;
• the average molecular weight of the polyethylene polyamines in the spacer fluid having the first structure is from 200 g/mol to 400 g/mol;
• and
• all of the polyethylene polyamines in the spacer fluid having the first structure are encompassed in the clay stabilizer.