An enhancement wet co-precipitation method was developed for synthesized cobalt ferrite nanoparticles. XRD, FTIR, TGA and FE-SEM techniques were applied as NPs characterizing route in this research. In the second part of this work, effecting of adding this synthetic NPs on the (rheological, filtration, thermal stability, lubricity and shale inhibition properties of drilling fluids were studied. Rheological and filtration properties of NSDF (prepared by adding deferent concentrations of cobalt ferrite NPs to fresh water bentonite fluid) appeared improved rheological properties and minimum filtrate results compared with blank FWBF.ICP-MS and FE-SEM testing also, were applied to study the effect of NPs on filtrations properties and decreasing filter volume amount. On the other hand, rheological and filtration properties of NSDF also were studied at 40 and 70 °C. Results approved that nano smart drilling fluid pre has good thermal stability compared with conventual rheological improver and filtration controller CMC-HV polymer mud. Compared with traditional drilling fluid lubricant(graphite), better ability of decreasing coefficient of fraction showed with adding different concentrations of the NPs to (6%wt, FWBF). Hence, ability of using of cobalt ferrite as lubricant in drilling fluids. Shale inhibition ability. which consider as one of the more important challenges in drilling fluid of cobalt ferrite NPs was investigated by three different steps. firstly, influence of adding different concentrations of the NPs to 4% bentonite KCl mud was investigated. liner swelling meter results appeared decreasing in shale plug length with all concentration of NPs, which means ability of this NPs to decreasing the shale swelling. Nano -KCl polymer mud then compared with PHPA/KCl polymer mud with concentration of PHPA at (0.3%wt). Results appeared slightly decrease in shale plug length with (0.05 and 0.1%wt) of NPs and increase with (0.2%wt) of NPs. Compaction between KCl-polymer mud and direct addition of adding (0.1%wt) of NPs to 4%wt of FWBF was studied as the third steps. Result appeared ability of using direct addition of NPs on FWBF as shale inhibitors compared with traditional KCl-polymer mud. Previous testing and results approved that ability of cobalt ferrite NPs to enhancing drilling fluids properties, hence, minimize drilling fluid challenges.
