Constant rate injection of a fluid into a well for microfrac and step rate testing is accomplished through the use of an injection system. The system provides accurate flow rate control (within 2% of the desired rate) during injection, which results in superior quality of data such as the fracture extension pressure, etc. for formation analysis. The injection system eliminates discontinuities in flow rate which may be present when using an engine-driven pump with a manual transmission. The inherent flow rate fluctuations present in the positive displacement pump flow rate are also minimized by the injection system. The system permits use of a large fracturing pump for low flow rate injections, thereby increasing the rangeability of the service equipment, which results in lowering the costs.

Laboratory test data and numerically generated results of a computer model are presented in this paper, along with case histories of two jobs.

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