Abstract: This invention relates to an improved oil-base drilling fluid composition and its use. The improved oil-base drilling fluid composition of this invention is characterized by thixotropic properties which result in a yield point of at least 4.0. The composition includes an oil-base continuous phase and a gelling composition. The gelling composition includes a latex material in combination with one or more functional monomers selected from the group consisting of amides, amines, sulfonates, monocarboxylic acids, dicarboxylic acids and combinations thereof and wherein at least one of the monomers includes a nitrogen containing material.

Abstract: On occasion, during drilling operations employing oil base drilling muds, conditions occur that cause the surface of the solid materials in the mud to be water wet, changing the rheology of the drilling mud such that it is unusable and has to be discarded. In accordance with this invention, a novel method is provided to reverse this condition so that the water wet surfaces of the solid particles become oil wet again, restoring the drilling mud to substantially its original condition or level or to such a condition that it can continue to be used in drilling operations. This is accomplished by adding to the drilling mud containing water wet particles at least one of a specific and critical group of imidazolines.The imidazolines may be added to stable oil mud drilling fluids to decrease possible water wetting of the particle surfaces therein.