Since 1983, the Gas Research Institute (GRI) has funded research to improve the knowledge and understanding of the viscous properties of fracturing fluids. One of the GRI research projects was the development and testing of the GRI Rheology Unit, which is a mobile rheology laboratory that can be taken to the field to measure the viscous properties of the actual fluids being pumped during the treatment.1 2 

The GRI Rheology Unit consists of a van containing two Fann Model 50 viscometers and a complete wet chemistry laboratory. In typical field operations before the treatment begins, the Rheology Unit is used to check the fracturing fluids for contaminants and to verify the fracturing fluid, mixed with the chemicals to be used during the treatment, meet the design specifications. During the treatment, the Rheology Unit is used to sample and test the fluids being pumped to ensure fracture fluid quality.

Field research with the GRI Rheology Unit has found that laboratory measured fracturing fluid properties are often not reproduced under field conditions.1 2  During the majority of treatments monitored with the GRI Rheology Unit, fluid problems were diagnosed by testing the gel using the Fann Model 50 viscometers. One of the most common fluid problems experienced in field operations is the scheduling and addition of the chemical breakers used to degrade the fracturing fluid after the treatment. Typical problems associated with the breakers were either (1) the wrong breaker type was being used or (2) the wrong amount of breaker was added for the given conditions.

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