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History

The early pioneers in oil production began to recognize around 1900 a need for measuring the performance of individual wells to assess their efficiency and condition. The technology at that time was little more than allowing the test well to produce into a tank for a protracted period (typically 24 hours, or longer), and manually measuring the total (gross) and oil (net) by means of graduated stick or tape level. Of course, this method, while still in use, is crude, and is subject to inconsistencies in oil cut grind-out and sampling technique.

There was little change to this method for production testing until about 1960, when vertical separators were introduced. These systems are most effective in measuring production from oil wells having high GOR'S. It consists of a large number of mechanical devices including floats, orifice meters, valves, positive displacement meters, and chart recorders. The reliability of these separators is poor, allowing replacement of open-top tanks only with the advent of 1980's air pollution control rules.

Throughout the 1990's, and to the present, there have been many variations in well testing and equipment. There are systems, like the open top tank, that accumulate and pump the entire testing sample. These systems have the capability for higher accuracy on low net oil wells, but they suffer from long test times, large physical size, a basic inability to measure gas, high capital and operating cost, and incompatibility with environmental requirements. Moreover, the production sample is not collected under normal flowing conditions.

There are testing units that use sealed vessels for test fluid separation and accumulation. They test production wells under typical flowing conditions, are able to handle gas, and are environmentally sealed. Units that operate under steady state flowing condition suffer from poor flow rate tumdown, and are not accurate on low gross or net oil wells. Pressurized vessel testers that accumulate volumes oil and dump periodically minimize the criticality of the turndown effect. But, these systems suffer from long test times and error potential on low oil rate wells because of purging volume requirements.

Also on the market are units that attempt to measure both oil and water, or all three phases, on the entire bulk fluid stream. There are many technologies employed for this measurement, such as density, conductivity/capacitance, high radio frequency energy absorption, and others. As you can imagine, the imprecision in the detection of any component characteristic, in a background with many of variables changing is high. These full flow stream measuring systems are quite inaccurate on low oil producing wells, since even slight fluid characteristic errors are allocated over the entire fluid volume. Many of the more sophisticated testers are also quite costly in both initial capital expense and long term operation.