Production Logging refers to a family of tools and the associated techniques used to evaluate the downhole performance of producing or injecting wells under dynamic conditions.
A knowledge of actual downhole fluid movement under normal producing conditions is of considerable value in ensuring maximum efficient recovery under both primary and secondary reservoir conditions. In particular, production problems identified from surface measurements are best explained by this knowledge, while an intelligent remedial program presupposes a knowledge of downhole flow conditions. Production Logging Tools are designed to operate under normal downhole producing conditions to measure actual fluid movement – basically, "how much of what from where"? Production Logging Tools include the Continuous and Inflatable Packer Flowmeters, Therrnorneter, Gradiornanorneter, Caliper, Densimeter and Water cut Meter as well as the well known Cement Bond Log, Neutron Log and Gamma Ray Log. All have been adequately described in the literature but a brief description of the first group is included here for the sake of completeness.
A number of field examples are presented to illustrate some of the applications of Production Logging Tools and techniques under Canadian producing conditions.
Over the past four or five years a group of specialized well surveys have evolved which have acquired the collective name of Production Logs. The classification is indistinct, with the application of a survey being more definitive than the specific tool characteristics. All, however, aredirected to the solution of one basic problem: "How can this existing well or reservoir be made to produce more profit? "
The applications of Production Logs to this problem are many and varied. They range from the identification of mechanical problems of varying complexity to the determination of specific productivity of multiple zones in a well.
In general, it has been observed that many wells do not perform downhole in a manner predicta.ble from surface observations. Worse, some wells or reservoirs seem to perform in actual defiance of Common engineering etiquette. A more complete understanding of a well's behavior can usually be gained from knowledge of actual flow conditions downhole. Certainly, any remedial program designed to alter downhole flow patterns must be based on an appreciation of these existing patterns. Production Logging-tools and techniques are designed to identify and evaluate these downhole flow patterns.
It is essential to the success of any Production Logging program that the operation be adequately planned to gather the necessary data and select the tools to be run in some logical sequence and with appropriate techniques. For example, wells producing at low flow rates require different tools and techniques than wells producing at high flow rates. The phenomena called "hold-up" or "slippage" velocity in diphasic flow must be consideredand included in the plan. Pumping wells may require an indirect approach. Pressures to be encountered must be known and, of course, the nature and dimensions of the mechanical assemblies downhole and at the well head must be known.