A colorimetric test procedure has been developed to measure polyglycol concentrations in drilling fluid filtrates up to 10 volume % polyglycol. The procedure is based on visual color matching using a "color wheel" and is reliable to 0.5 volume %. A self-contained rig site test kit has also been developed based on the procedure and documentation on it's use on 2 wells is presented.
Successfully reaching the production targets in some of our most challenging drilling areas has traditionally required the use of invert emulsion drilling fluids. Use of these fluids, however, typically results in high localized organic loading in the immediate vicinity of any wastes discharged due to the high concentration of organics in these systems and the adherence of the fluid to the discharged materials. The environmental impact of these discharges has been reduced over the years as the base fluid has been upgraded from crude oils to diesel oil, later to lower toxicity mineral oils and more recently to synthetics, although the problem of the high localized organic loading of the environment remains. High performance water-based systems are a popular alternative and those based on polyglycol technology have received the most attention and use. These polyglycol systems are now offered by most service companies through out the most active drilling areas of the world and have proven track records in hundreds if not thousands of wells.
Use of these systems, however, has always been hampered by the lack of a reliable technique for monitoring and ensuring an adequate level of polyglycol to successfully do the job. Most applications end up relying on material balance alone to maintain adequate concentrations but this approach ignores potential losses through leak off and/or adsorption on solids removed by solids control equipment. A direct measurement of the actual polyglycol concentration was needed.
In order to develop a useful method, the specifications listed in Table 1 were set. Initially several potential methods (see Table 2) were evaluated.
Applications, in the detergent industry, of colorimetric procedures to measure the concentration of nonionic surfactants have been known for many years. We applied a similar approach to measure polyglycol concentrations in filtrates using a set of standard color solutions which are compared to the color of the test filtrate. To eliminate the need for a spectrometer we decided to use a set of standard colors for comparison.
A sample tube size of 8 cm3 (see Figure 1) was selected to give enough volume for unaided visual discrimination of differences in color saturation and optical density, without requiring a lot of the expensive and environmentally undesirable organic solvent. The solvent to color reagent ratio of 1 to 1 (wt/wt) provided good sensitivity at the 0.5% level
Filtrate sample size was optimized around the sample vial size and solvent to color reagent ratio. One cm3 of filtrate was found to exhaust the color reagent and yield solvent phase colors too intense to distinguish one concentration from another. Volumes less than 100 L produced undetectable colors in the 0.5 to 2.0 % range but did extend the range at the upper end.
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