Aqueous clay base mud for deep drilling

An aqueous clay base mud containing per m.sup.3 from about 0.5 to 40 kg of a protective colloid, the protective colloid contained in the mud being a copolymer, which has the K-value of about 110 to 200, of

• I vinyl or allylsulfonic acid or the potassium, sodium, lithium or ammonium salts thereof,
• Ii acrylic or methacrylic acid amide, -nitrile or -methyl ester and,
• Iii a N-vinyl-N-alkyl-carboxylic acid amide of the formula ##STR8## in which R.sub.4 is hydrogen, --CH.sub.3 or --C.sub.2 H.sub.5 ;
• R.sub.5 is --CH.sub.3 or --C.sub.2 H.sub.5 or R.sub.4 and R.sub.5 together represent a propylene group forming a pyrrolidone radical with the inclusion of the radical ##STR9## the monomers being present in moieties of 5 - 50% by weight I, 40 - 80% by weight II and 10 - 35% by weight III.

An aqueous clay base mud containing per m.sup.3 from about 0.5 to 40 kg of a protective colloid, the protective colloid contained in the mud being the alkaline hydrolysis product of a copolymer, which has a K-value of about 110 to 200, of

• I vinyl or allylsulfonic acid or the potassium, sodium, lithium or ammonium salts thereof,
• Ii acrylic or methacrylic acid amide, -nitrile or -methyl ester and,
• Iii a N-vinyl-N-alkyl-carboxylic acid amide of the formula ##STR10## in which R.sub.4 is hydrogen, --CH.sub.3 or --C.sub.2 H.sub.5 ;
• R.sub.5 is --CH.sub.3 or --C.sub.2 H.sub.5 or R.sub.4 and R.sub.5 taken together represent a propylene group forming a pyrrolidone radical with the inclusion of the radical ##STR11## the monomers being present in moieties of 5 - 50% by weight I, 40 - 80% by weight II and 10 - 35% by weight III.