Production logging instruments' responses in multiphase flow wells are frequently confusing due to the effects of various parameters. An important parameter is the type of flow regime encountered during the survey Special knowledge of the flow pattern is necessary if a meaningful analysis of the data is to be made. Some of the parameters affecting the flow regime are flow rate of each phase, pipe diameter, and wellbore deviation angle.

Wells often produce a concurrent flow consisting of two or three phases. Due to different fluid properties between phases, more than one flow regime might be encountered in a survey depth interval. The cause of this transition from one flow regime to another is due in part to an increase in fluid velocity. This increase may be caused by additional fluid entering the well from perforations or from expansion due to pressure changes as the fluid moves upward through the well.

The sensitivities and operating ranges of selected production logging instruments were studied by subjecting them to different parameters that directly affect the flow regime and the instruments' responses. The logging instruments selected for testing were divided into two categories: Row rate and fluid composition.

Examples are presented that demonstrate how a slight deviation angle or an increase in flow velocity alters water fallback, holdup, and the instrument's response. Typical applications of production logging instruments are described with emphasis placed on the effects of two-phase flow. After characteristics of particular flow regimes have been developed, guidelines for instrument selection, data acquisition methods, and log quality control are given.

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