Abstract: A hydrocarbon-based or ester-based drilling fluid or mud is described wherein the drilling fluid contains cesium phosphate. The hydrocarbon-based or ester-based drilling fluid or mud can have, for example, an external phase that contains hydrocarbon fluid and an internal phase that contains cesium phosphate. The hydrocarbon-based drilling fluid or mud can further contain at least one emulsifier or surfactant, and optionally other ingredients. The present invention can permit hydrocarbon-based drilling fluids to be essentially solids-free and may be used without corrosion and/or formation damage problems, for example, due to the use of the cesium phosphate in an internal phase of the hydrocarbon-based or ester-based drilling fluid. The present invention also relates to hydrocarbon-based or ester-based fluids for completion, workover, suspension and packer operations which contain cesium phosphate.

Abstract: Loss circulation fluids contain aqueous based compositions having at least one alkali metal formate and at least one thermally activated self-crosslinkable gel forming material, wherein the composition is easily transported to a loss circulation zone and yet has ability to close off the loss circulation zone once thermally activated to reduce the loss of circulation fluids into flow passages of a subterranean formation. In addition, packer fluids contain aqueous based compositions which contain at least one alkali metal formate and at least one thermally activated self-crosslinkable gel forming material, wherein the packer fluid forms a thermal insulating fully hydrated gel once thermally activated.

Abstract: A drilling fluid or mud is described wherein the drilling fluid contains at least one alkali metal formate or monovalent carboxylic acid salt. The drilling fluid preferably further contains at least one emulsifier or surfactant and at least one hydrocarbon-based fluid. The drilling fluids of the present invention can contain other conventional ingredients. The present invention permits drilling fluids to be essentially solids free due to the use of the alkali metal formate.