During the past five years, the Gas Research Institute has developed a comprehensive fracture fluid evaluation laboratory that is portable and is used in the field to monitor actual fracture fluid systems. Although many components of the GRI Rheology Unit are available elsewhere, no other organization offers a system that can be used in the field to fully characterize a fracture fluid before and during an actual fracture treatment.

One of the objectives of the GRI research effort is to run 3-D fracture models in real time to improve our understanding and control of hydraulic fracture treatments. The 3-D fracture models are used to history match the values of excess pressure vs. time in order to determine fracture size and shape. We have found that unless one can fully characterize the fracture fluid viscosity vs. time, temperature and shear rate, then the fracture shape computed using a 3-D fracture model will be non-unique.

To more fully explain this concept, one must understand the mechanisms that affect the excess pressure in a fracture during the treatment. The excess pressure is dominated by friction pressure as the fluid flows down the fracture. The friction pressure is affected by both the viscous properties of the gel and the shape of the fracture. We can only determine the shape if we know the viscous properties of the gel beforehand. Therefore, to improve our use of 3-D models in this research, we have determined that we must go to the field and accurately measure the viscous properties of the fracture fluid.

In the early stages of the program, most of our efforts involved surface quality control and real time monitoring of fluid parameters during the pumping operation. Although the importance of quality control and pre- and post-job materials inventory cannot be overemphasized, we have found that a more intense effort is required to quantify the viscous properties of the actual fluid on site.

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