Patent ID: 7576039

Claim:
A drilling fluid additive comprising sulfonated asphalt and water soluble and anionic polymer component in an amount of from 0.1 to 20 wt. % with respect to the total weight of the additive wherein the anionic polymer component comprises a polycondensation product of a lignosulfonate, sulfonated phenol, ketone, naphthalene, acetone and an amino plasticizer resin and a further water soluble polymer comprising: a) at least one monoethylenically unsaturated monomer having acid groups in acidic, partially or completely neutralized form selected from the group consisting of acrylic acid, methacrylic acid, 2-ethylacrylic acid, 2-propylacrylic acid, vinylacetic acid, crotonic and isocrotonic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, vinylsulfonic acid, methallylsulfonic acid, 2-acrylamido-2-methylpropylsulfonic acid, 4-vinylphenylsulfonic acid, vinylphosphonic acid, (semi) esters or amides of said carboxylic acids, mixtures thereof or anhydrides thereof.