Rheological specifications of drilling mud which contains nano zinc oxide ( 1 gr) in high temperature – high pressure viscometer are considered in this work to simulate the drilling conditions occurred in deep wells. Shear stress, shear rate, effective viscosity, plastic viscosity and gel strength are measured versus temperature (30, 40, 50, 60, 70 and 80 C) and working time (0, 1, 3, 5, 7, 10, 12 and 15 days). Also, experiments are held to investigate the effect of aging time and temperature on a prepared water based drilling mud. Rheological data of nano contained drilling mud are compared with the obtained data from simple water based drilling mud. About 63% and 64% decrease in the amount of plastic viscosity of simple and nano drilling fluid is obtained through 15 days working time, respectively. Also, aging time (15 days) effect on the amount of effective viscosity is about 56% and 57% and on gel strength is 62% and 60% for simple and nano drilling mud, respectively.

Keywords: Rheological specifications; Nano zinc oxide; Drilling mud; Gel strength; Yield point; viscosity.