ABSTRACT
The rheological behavior of crosslinked hydroxypropyl guar systems is important in both the engineering design of fracturing treatments and the laboratory evaluation of potential fracturing fluid systems. A great deal of information is available in the literature from a number of workers, but there is still much to be learned about the nature of these systems.
Results obtained in this study provide insight into the effects of shear history, residence time, and chemical composition on the crosslinking reaction. Experiments are conducted in both tube and slot flow rheometers and a Rheometrics Pressure Rheometer (concentric cylinder geometry). Mixing of the crosslinker and hydroxypropyl guar solution is accomplished with a special mixing head which provides for continuous mixing. Using this mixing device, measurements are made on fluids which have not experienced any dead time (luring the mixing and measurement process.
Both steady and dynamic (oscillatory) shear tests are presented. The steady shear data provides insight into the nature of the reaction in laminar flow. An abrupt change in the reaction mechanism appears to occur below 100 s-h The fluid which exists in the slot or pipe in steady shear tests changes from a viscous fluid to a gel. Dynamic tests yield information on the effects of shear on the gel structure. Long term shear at elevated rates appear to irreversibly damage the systems ability to crosslink. The fluids which result from these tests either fail to crosslink or they do not form the same network structure present in systems which have not been subjected to high shear.
The results of a fracturing treatment are influenced by fluid performance. A better understanding of the rheology and the crosslinking process in commonly used fracturing fluids will improve our ability to optimize fracturing treatments.
