Downhole fluids and methods of use thereof

A method for introducing a spacer into a subterranean formation, the method comprising:

• providing a spacer comprising:
• a clay, wherein the clay comprises a smectite clay;
• a hydroxylated polymer, wherein the a hydroxylated polymer comprises microfibrillated cellulose (MFC);
• a cation;
• the clay, the hydroxylated polymer, and the cation together in an amount sufficient to render the downhole fluid thermally stable at a temperature of 400° F.;
• and
• at least one additional downhole fluid component-;
• and
• pumping the spacer into the interior of a casing or a wellbore annulus in a wellbore in the subterranean formation to displace fluid remaining in the wellbore.