Production logging denotes that area of well logging concerned with two general goals: (1) problem well diagnosis, and (2) reservoir surveillance. The purpose of logging is to track fluid movement within or behind pipe or to monitor the movement of reservoir fluid contacts. The logs have been, traditionally, tools of the workover or subsurface engineer and the reservoir engineer. However, with the increasing hazards of drilling, the logs are becoming of vital importance to the drilling engineer. In many areas of the world, a suite of production logs are obtained before a particular well is even perforated for production. This is especially important for wells drilled within or near producing fields. Successful completions through strata with unequal pressures are difficult.

Because of the increasing importance of production logs, a survey of the subject is appropriate. In this paper, we review how the various logging tools work, what they measure, and how these measurements are related to flow. By example logs, we wish to illustrate three important points. First, production logs should be run in suites of complementing devices. Seldom does one log alone give satisfactory answers to a particular problem. Second, the subtle features, rather than the obvious anomalies, of a particular log often contain the desired information. Finally, production logging evolution has only recently turned in a direction of attempting to deal with multiphase flow of gases and liquids at low rates. As a result, the technology in this area is still insufficient.

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