Aqueous displacement fluid compositions for use in wellbores

A method for displacing a wellbore fluid comprising introducing a spacer fluid into a wellbore and displacing said wellbore fluid with the spacer fluid, said spacer fluid comprising a mixture of:

• a) water;
• b) a water soluble nonionic aliphatic polyoxyalkylene monool surfactant;
• and
• c) a water insoluble nonionic aliphatic polyoxyalkylene monool surfactant.

A method comprising introducing into a wellbore an aqueous spacer fluid composition mixture comprising:

• a) water;
• b) a nonionic aliphatic polyoxyalkylene monool surfactant having an HLB of more than 10.5;
• and
• c) a nonionic aliphatic polyoxyalkylene monool surfactant having an HLB of 10.5 or less.

A method for cementing casing in a wellbore, comprising:

• (a) introducing casing into a wellbore;
• (b) introducing a hollow drill string within the casing;
• (c) introducing for continuing a flow of a drilling mud through the hollow drill string and within an annulus between the casing and the drill string;
• (d) displacing and removing the drilling mud from the drill string with a composition comprising water, a water soluble non-ionic aliphatic polyoxyalkylene monool surfactant, and water insoluble non-ionic aliphatic polyoxyalkylene monool surfactant;
• and
• (e) introducing a cement into the casing and within an annulus between the wellbore and the casing.