Production Logging-The Key to Optimum Well Performance

Abstract

Abstract Included in the family of production logging devices are two types of flowmeters (a continuous and a packer type), high-resolution thermometers, gradiomanometers, production fluid samplers, densimeters, water cut meters, and through-tubing calipers. The instruments enable recording of: profiles of flow rate; fluid characteristics that enable determination of the fluid composition; hole sizes; and temperatures. In addition, casing collars are recorded for depth control. Fluid samples, suitable for PVT studies, can be obtained at any depth in the fluid column. Interpretations of these data, especially when used in conjunction with through-tubing gamma ray-neutron and cement bond logs, define most production problems. In new completions, production logging services are used both to ensure optimum ultimate recovery and to explain production problems brought to light by surface performance. In older wells, the logs aid in planning remedial work for declining producers. Monitoring of secondary recovery projects is another important application of production logging services. Introduction Experience indicates that surface fluid measurements are not adequate to describe the efficiency of the down-hole production system. In many wells that appeared to be producing properly, down-hole malfunctions were found that, if uncorrected, would appreciably reduce ultimate recovery. In some instances the malfunctions, if allowed to persist, would even preclude effective application of secondary recovery techniques. Because the operation of the down-hole system has a great effect on ultimate recovery, a more diagnostic means of measurement is required. Production logging tools are designed to operate downhole under dynamic producing conditions. Thus, this family of tools provides the information necessary to evaluate the performance of the well-completion scheme. Included in the family are instruments that locate fluid entry (or injection), measure flow rates, and enable determination of fluid composition from each zone of fluid entry. The tools are built to operate through 2-in. tubing, and to perform properly at pressures up to 10,000 psi and temperatures up to 300F. Pressure control equipment allows safe entry into producing wells with surface pressures as high as 6,000 psi. and into injection wells with pressures up to 7,200 psi. Production Logging Measurements Great progress in production logging has been made recently in the development of tools to work under dynamic conditions. Combinations of these tools (a flow rate meter, fluid identification devices, and some form of depth control) provide answers to the question, "How much of what fluid is coming from where?" Flow rate measurement is not new to the industry. However, downhole determination of fluid composition has always been a problem. The new devices enable identification of the various fluids flowing, and permit computation of the fraction of total flow that each represents. With the constituent fluids thus identified, down-hole flow rate measurements are much more meaningful. The problem of fluid identification is complicated by the variety of possible mixtures of oil, gas and water. and by the effects of fluid velocities on these mixtures. Both the fluid mixture and velocity must be considered in selecting appropriate logging devices. The first consideration must be measurement of parameters that vary sufficiently for reasonable resolution between the constituent fluids of a multi-phase flow. For example, the greatest benefits of a device that measures fluid densities are realized when defining gas entry into liquids. For oil-water mixtures the specific gravities are more nearly the same and resolution is difficult. JPT P. 137ˆ