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Synthetic based muds (SBMs) are water-in-oil emulsions in which the base oil is produced artificially. These fluids are produced to depict favorable properties of both water based muds (WBMs) and oil base muds (OBMs). SBMs are as non-reactive as OBMs in clay-shale formations, while they are as environmentally friendly as WBMs. As a result of these advantages, SBMs are one of the most commonly used drilling fluid types in today’s drilling operations, especially in ultra-deep drilling activities and offshore operations. However, their rheological properties fluctuate severely with down hole conditions. For that reason, rheological behavior of SBMs under down hole conditions should be determined precisely. Consequently, pressure losses can be estimated with higher accuracy. Extensive analysis of SBM under high pressure and high temperature conditions is under progress. The rheological model analysis of the fluid based on Fann 70 HPHT rotational viscometer readings and Chan 35 rotational viscometer surface readings. It is found out that, Yield Power Law (YPL) model describes the shear stress-shear rate relation of the fluid precisely. Effect of pressure and temperature on rheological parameters of YPL fluid is determined using constant model rheological characterization (CMRC). In addition to that Relative Dial Reading (RDR) analysis is used to characterize shear stress behavior of SBM at different temperatures, pressures and shear rates. All these effect on shear stress are shown in one simple relation. Results obtained from RDR analysis and CMRC characterization is compared. Similarities and differences between these methods are stated.
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