A New Field Procedure for Determining Potassium in Drilling Fluids
Authors: Steiger Ronald P. 
Published: December 2007

Steiger, Ronald P., Exxon Production Research Co.

A simple, reliable field procedure for measuring potassium-ion concentration-levels in drilling fluids used potassium-ion concentration-levels in drilling fluids used to stabilize water-sensitive shales has been developed. Potassium-based drilling fluids are used to drill problem shale formations in many areas. Potassium ions problem shale formations in many areas. Potassium ions in the drilling fluid exchange with sodium, calcium, and other ions on clays in the formation, cuttings, and bentonite. It is important to monitor the potassium concentration to be certain that an adequate amount of potassium is carried in the mud to successfully inhibit potassium is carried in the mud to successfully inhibit shale sloughing and cuttings dispersion. Over the past few years, several analytical methods have been proposed and used, but none has been satisfactory in field applications. They include (1) a sodium tetraphenyl boron-zephiran chloride titration method, (2) sodium cobaltinitrite and sodium perchlorate gravimetric methods, and (3) specific-ion electrode techniques. The first is lengthy, complicated, and more suited to laboratory applications. The two gravimetric methods were adapted to settling-tube and centrifuge tests. The settling-tube tests are too time consuming, while the centrifuge tests, as developed, are insufficiently accurate or reliable. The cobaltinitrite method is pH-dependent. Specific-ion electrode analysis is subject to interference from other ionic species and requires an expensive, sensitive specific-ion meter. The new test method is a centrifuge technique in which a chemical is added to a mud-filtrate sample to precipitate the potassium. The sample is then precipitate the potassium. The sample is then centrifuged in a special tube at a constant speed so the precipitate volume can be read accurately. The reading is precipitate volume can be read accurately. The reading is compared with a calibration curve to obtain the potassium concentration in the filtrate. The field procedure potassium concentration in the filtrate. The field procedure can he run by the mud engineer in just over 1 minute. (See the Appendix for the complete test procedure.) This method has given excellent results in laboratory and field tests. Table 1 shows results of 15 potassium tests on mud filtrates by both this method and the atomic absorption method. The atomic absorption method is a complex, accurate laboratory technique that requires very expensive equipment and is not adaptable to field use. In Table 1 the amount of potassium in the filtrate is reported as percent potassium chloride. The new test for potassium can determine the percent potassium chloride in the filtrate to within 0.25 percent. potassium chloride in the filtrate to within 0.25 percent. This accuracy is more than sufficient to adequately monitor and treat a potassium chloride mud system. We recommend this test be made whenever a potassium mud is used. potassium mud is used.

TABLE 1 - COMPARISON OF POTASSIUM ANALYSES OF MUD FlLTRATES

Percent KC1 by Weight Mud- Filtrate New Field Atomic Absorption Sample No. Method* Method 1A 1.75 1.77 2A 1.50 1.70 3A 1.50 1.67 4A 1.25 1.27 5A 1.25 1.25 6A 1.25 1.15 1B 3.10 3.09 2B 3.10 3.17 3B 3.30 3.26 4B 3.24 2.99 5B 2.95 2.96 6B 3.05 2.93 7B 2.65 2.60 8B 3.05 2.66 9B 2.85 2.65

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