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Fluid properties with constant improvement in efficiency have been noticeable as important criteria in drilling operation. The main drilling fluid properties highly depend on utilization of new polymers with high efficiency in drilling fluid composition. In this paper, the performance of a new polymer, called partially hydrolyzed polyacrylamide polymer (PHPA), is studied which has recently entered the drilling fluids industry in Iran. Hence viscosity property, fluid 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 thecountry. 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 fluid properties. The results obtained by the tests show that furthermore polymer PHPA increases rheological properties (apparent viscosity, plastic fluidity and yield point) and it plays important role in increases in fluid loss. This polymer has also demonstrated acceptable resistance toward sodium chloride contaminants, but its efficiency 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 fluid system as it stops any changes in fluid properties which will finally results inwellbore stability.

Water soluble amphoteric graft copolymers of polysaccharide were synthesized via grafting of cationic monomer onto the sodium carboxymethylcellulose ()CMC)( and then used as a shale stabilizer in the water-based drilling fluids. Accordingly, five types of CMC-graft copolymers with different ratios of acrylamide AM)( and diallyldimethylammonium chloride DADMAC)( were synthesized. Grafting of monomer()s)( onto the CMC was verified by FT-IR spectroscopy. Results showed that grafting percentage is strongly affected by the monomer type as well as the weight ratio of monomers. Synthesized CMC-graft copolymers were used in the formulation of water-based drilling fluid. Drilling fluid was then subjected to the rheological, fluid loss and shale recovery tests. It was found that ability of CMC in the shale stability enhances by grafting of cationic monomer onto CMC. Fluid loss is also controlled in the acceptable region in the presence of CMC-graft copolymers. Among graft copolymers, CMC-grafted with pure cationic monomer exhibited higher efficiency in the fluid loss control and more important in the shale stability.