Rheological measurements of a typical delayed titanium crosslinked hydroxypropyl guar (HPG) fluid were made with crosslinking reactions occurring under controlled shear rates (40, 120, and 170/sec) and heating rates (4 and 8°F/min and preheated bath). Five different bobs were used, showing the effect of gap width and percentage of total fluid within the gap. Some bob-cup combinations allowed the gel plugs formed in low shear rate conditions to easily circulate back into the gap and influence subsequent fluid viscosity. Other combinations allowed little circulation or had minimal plugs. As a result of this study more accurate fluid rheology measurements can be made with the Fann Model 50 viscometer if a realistic thermal and shear history are used, along with a bob-sleeve combination which maximizes the fluid contained within the gap and minimizes circulation of gel plugs back into the gap. Application of the findings in this work will help reduce the large differences typically observed between laboratories testing crosslinked fluids.

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