Keywords: A B S T R A C T Available in: http://jips.ippi.ac.ir Iranian Journal of Polymer Science and Technology Vol. 26, No. 1, 3-13 April - May 2013 ISSN: 1016-3255 Online ISSN: 2008-0883 drilling fluid, polyacrylamide, mud contaminant, fluid loss, shale recovery F luid properties with constant improvement in effciency have been noticeable as important criteria in drilling operation. The main drilling fuid properties highly depend on utilization of new polymers with high effciency in drilling fuid composition. In this paper, the performance of a new polymer, called partially hydrolyzed polyacrylamide polymer (PHPA), is studied which has recently entered the drilling fuids industry in Iran. Hence viscosity property, fuid loss control and shale inhibition of this polymer have been evaluated based on an international standard method of API-13-I by considering the drilling and operational priorities of the country. Then the thermal effect, salt contaminants such as sodium chloride, calcium chloride, magnesium chloride and pH tolerance effect as major pollution indicators are also investigated in relation to polymeric fuid properties. The results obtained by the tests show that furthermore polymer PHPA increases rheological properties (apparent viscosity, plastic fuidity and yield point) and it plays important role in increases in fuid loss. This polymer has also demonstrated acceptable resistance toward sodium chloride contaminants, but its effciency decreases toward calcium and magnesium ion contaminants. The thermal tests show that polymer PHPA has high thermal stability up to 150°C. This polymer improves shale inhibition property and by encapsulation mechanism prevents dispersion of shale cuttings into the drilling fuid system as it stops any changes in fuid properties which will fnally results in wellbore stability. (*)To whom correspondence should be addressed. Eـmail: nasiriar@ripi.ir Performance of Partially-Hydrolyzed Polyacrylamide in Water Based Drilling Fluids Ali Reza Nasiri* and Majid Valizadeh Research Institute of Petroleum Industry, P.O. Box: 14665-1998, Tehran, Iran Received 10 April 2012, accepted 8 April 2013