Droplet Size Analysis: A New Tool for Improving Qilfield Separations

Abstract

A new approach in the development of oil-water separation equipment is based on droplet size analysis. Droplet sizes are critical information in the design and evaluation of oil-water separators. This paper illustrates how good sampling technique and droplet size analyzers can be combined to make droplet measurements in actual production streams. Droplet size measurements from actual field tests will be shown. Problems associated with droplet size measurements are discussed. Current limitations and future applications of this technique will also be presented. In addition, we have examined how droplet sizes can be used in applications to evaluate separators and other production equipment such as pumps, valves, and strainers. Introduction In a typical production operation, the amount of produced water increases as the field matures. In produced water increases as the field matures. In some operations the bulk of the volume of produced fluids may be water. Although there is no direct economic incentive, recent tightening of government regulations regarding the amount of oil in discharged waters has increased interest in improving and optimizing oily water separators. Today as well as in the future, the oil industry needs to take advantage of the newest technology available to improve and optimize separation processes. Many factors affect oil-water separation processes. One of the major factors influencing performance in both hydrocyclone and traditional flotation cells/ plate separators is the size distribution of oil plate separators is the size distribution of oil droplets in water. The separation of smaller droplets is slower and more difficult. Thus, droplet sizes are critical information for the design of oil-water separation equipment. Yet, little is known about the droplet sizes in production streams because of the difficulty of making these droplet size measurements. The effects of droplet size distributions on the efficiency of hydrocyclone separators were reported by workers at Southampton University. They showed that droplet sizes directly affected oil removal efficiency. Eighty-five percent of the oil could be removed with a volumetric mean droplet size of about 35 microns, while minimal recovery was achieved with streams containing mean droplet sizes below 10 microns. However, these tests were conducted under laboratory conditions. The crude oil was injected into fresh tap water and sent through a turbine pump to create different droplet distributions at approximately room temperature, 60 degrees F. This paper outlines work being done to take droplet measurement technology out of the laboratory and into the field. Droplet size measurements and the associated problems with sampling are discussed. Actual field test results for samplers, pumps, valves, and strainers are presented. Conclusions can be drawn from these results that can help improve current separation processes. DROPLET SIZE MEASUREMENT DEVICES A number of devices are on the market for determining the size of particles in liquids. However, we know of no devices which were specifically designed to measure the liquid droplets dispersed in another liquid. Five devices using different detection and measurement techniques were evaluated for their ability to measure droplet sizes. The detection methods included image analysis, light abstraction, laser defraction, conductivity change across an orifice, and colormetric change in a centrifugal tube. Three basic conclusions were made:No direct droplet size measurements could be made; therefore, the stream must be sampled. P. 233

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