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Description:
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This study presents a simplified and accurate procedure for selecting the
rheological model which best fits the rheological properties of a given non -
Newtonian fluid and introduces five new approaches to correct for tool joint
losses from expansion and contraction when hydraulics is calculated . The new
approaches are enlargement and contraction (E &C ) , equivalent diameter (ED ) ,
two different (2IDs ) , enlargement and contraction plus equivalent diameter
(E &C+ED ) , and enlargement and contraction plus two different IDs (E &C+2IDs ) .
In addition to the Newtonian model , seven major non -Newtonian rheological
models (Bingham plastic , Power law , API , Herschel -Bulkley , Unified , Robertson
and Stiff , and Casson ) provide alternatives for selecting the model that most
accurately represents the shear -stress /shear -rate relationship for a given non -
Newtonian fluid .
The project assumes that the model which gives the lowest absolute average
percent error (EAAP ) between the measured and calculated shear stresses is the
best one for a given non -Newtonian fluid .
The results are of great importance in achieving correct results for pressure drop
and hydraulics calculations and the results are that the API rheological model (RP 13D ) provides , in general , the best prediction of rheological behavior for the
mud samples considered (EAAP=1 .51 ) , followed by the Herschel -Bulkley ,
Robertson and Stiff , and Unified models . Results also show that corrections with
E &C+2IDs and API hydraulics calculation give a good approximation to
measured pump pressure with 9 % of difference between measured and
calculated data . |