Disclosed is a method of preventing fluids in the ground from rising around an oil well pipe by filling the space around the pipe with an oil well completion fluid comprising water, about 50 to about 65% by weight, based on total fluid weight, of dipotassium phosphate, and at least about 10 ppm hexavalent chromium. The fluid can be prepared by neutralizing wet process phosphoric acid with potassium hydroxide to a pH of less than 12 and filtering off any solids. Also disclosed is an oil well employing the completion fluid.