What effect does fluid weight have on jar placement in the drilling string?
A1: Due to buoyancy, items in fluid weigh less than in air. For drilling fluids, the following formula can be used to determine a weight ratio that can be used to correct for the string weight. R = 1.0 – 1.0/65.49 * Mud Weight Here the mud weight must be in pounds per US gallon. So if the string weight in air was 100,000 pounds, in 12 lb/gal mud, the string weight can be determined as follows R = 1.0 – 1.0/65.49 * 12 R = 0.8168 Buoyed Weight = 100,000 * .8168 = 81,680 lb. Since, in this case, the string’s buoyed weight is approximately 80% of the string’s dry weight, the jar placement would have to be corrected for this 20,000 lb difference.
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