Abstract: The addition of magnesium oxide to a drilling fluid additive comprising bentonite and ferrochrome lignosulfonate, the drilling fluid additive having a pH of about 9.5 to 12, increases the usefulness of such a drilling fluid additive and increases considerably the yield point of the drilling fluid containing this drilling fluid additive.

Abstract: Gelled acidic compositions suitable for matrix acidizing or fracture-acidizing of subterranean formations are provided comprising water, a water-dispersible polyalkoxylated cellulose ether, or acrylamide-derived cationic polymeric viscosifier, an acid, and a water-soluble iodine-containing redox couple system comprising a polyvalent nonmetal-containing compound and a reducing agent.

Abstract: Sodium carboxymethylcellulose and sodium carboxymethyl starch incorporated together in drilling mud, especially sea water mud, yield better flow properties with low fluid loss in drilling mud. The control of flow properties and thixotropy at low water loss values in salty drilling muds are better when the mixture is used than for either of the materials used separately.

Abstract: A low viscosity sodium carboxymethyl cellulose polymer, e.g. which has a degree of substitution (D.S.) of, say, 0.9 or higher and a Brookfield viscosity of 400 to 3100 centipoise as a 2 percent solution in distilled water at 25.degree.C, when added to a non-dispersed sea water drilling fluid followed by addition of a sodium carboxymethyl cellulose (sodium CMC) which has a D.S. of, say, 0.9 or higher and Brookfield viscosity of greater than about 10,000 centipoise as a 2 percent solution in distilled water at 25.degree.C yields a low water loss drilling fluid which has a lower viscosity and lower gel strength than when the same materials are added in reverse order or when only one or the other is added step-wise by itself to the drilling fluid.