Permeability-modifying drilling fluids and methods of use

A method of reducing the permeability of a subterranean formation to aqueous-based fluids during a drilling phase, the method comprising the steps of:

• providing a water-soluble relative permeability modifier that comprises a hydrophobically modified polymer, the hydrophobically modified polymer consisting of alkyl chains bound to a hydrophilic polymer,
• wherein the hydrophilic polymer consists of a polymer backbone that contains polar heteroatoms, at least one of which is not a nitrogen atom, and at least a portion of the polar heteroatoms are functionalized with the alkyl chains, wherein the hydrophilic polymer comprises at least one hydrophilic polymer selected from the group consisting of a cellulose, a chitosan, a polyetheramine, a polyhydroxyetheramine, a polylysine, a polysulfone, and a starch, and
• wherein the alkyl chains have a carbon chain length between about 4 and about 22 carbons,
• placing the water-soluble relative permeability modifier into the subterranean formation during the drilling phase, and
• allowing the water-soluble relative permeability modifier to attach onto a surface within the subterranean formation.