Abstract
Abstract Shear history simulation has been a useful laboratory tool to determine the effect of tubing/casing shear on the rheology of fracturing fluids. High shear rates experienced in the wellbore can significantly impair the viscosity development of metallic crosslinked fluids. The effect of shear history on the performance of metallic crosslinked fluids has been demonstrated in past studies and led to the development of many of the delayed crosslinking fluids used today. Recently, more fracturing treatments are being performed at higher wellbore shear rates and more treatments are being conducted with delayed-crosslinking borate fluids. The borate-crosslinked fluids are generally thought to be more tolerant to shear history with the crosslinking able to "re-heal" following exposure to high shear rates. Therefore, shear history simulation is rarely, if ever, conducted during rheological evaluation of borate-crosslinked fluids. This paper examines the effect of shear history on the viscosity development of a borate-crosslinked fracturing fluid. The testing was initiated due to a series of "screen-outs" experienced with a common, delayed-crosslinking borate fluid. Testing indicated that the fluid formulation used in these treatments was not stable after exposure to the high shear experienced in the wellbore. The fluid exhibited characteristics of shear-induced phase separation resulting in significant viscosity degradation and excessive "rehealing" time. To address this problem, the fluid composition was carefully optimized to eliminate the shear-induced phase separation and accelerate viscosity development after the shear history simulation. The recommended fluid changes were implemented and resulted in successful treatments with no screen-out issues. This paper details the testing used to observe the shear-induced phase separation and recommendations for optimizing borate crosslinked fluids used in high shear environments.
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