In this paper, the types and uses of well tests in the disciplines of hydrology, petroleum engineering, and geothermal engineering are reviewed. Geologic and economic factors that influence the design of well tests are summarized along with the difficulties of designing tests for each category of applications. The types of data needed for hydrothermal tests are discussed in detail, and the problems commonly encountered when taking measurements under various operating conditions are reviewed.

A historical review of well-testing instruments includes information on some of the latest equipment advances in the field. The ideal instrument array for well testing would measure pressure, temperature, flow rate, enthalpy, and concentration simultaneously and at several locations. The accuracy and durability limits of commercially available equipment are evaluated against this ideal according to the properties the equipment measures. Finally, the instruments that come closest to meeting the standards of well log analysts are identified.