Pipe light, which is a special term in a snubbing operation, describes the condition of the well which well head pressure and buoyancy acting upward again a cross sectional area of pipe is greater than weight of the string. If the light pipe condition is happened and the string is not controlled by the snubbing unit, the string will be pushed out of the well. Pipe Light Calculation 1 After knowing the concept of the light pipe, we will apply it to determine how many feet of tubular required snubbing into the well before the weight will overcome the surface pressure plus buoyancy force. Pipe Light Calculation 0 Snubbing Unit (Hydraulic Workover) works against wellbore pressure. Image from RIGZONE.COM Basic drilling formulas for this topic Force = Cross sectional area x Pressure Cross sectional area = 0.7854 x Diameter2 Buoyancy factor = (65.5 – mud weight) ÷65.5 Note: The biggest size of tubular planned to run in hole is used to determine force acted to the tubular string. For this example, we will use the oilfield unit so the Force in lb Cross sectional area in square inch Diameter in inch Mud weight in ppg Well Information Pipe Light Calculation 2 Surface pressure = 800 psi Brine weight in hole = 9.0 ppg Tubing size = 2 -7/8”, 6.4 ppf Disregard friction for the calculation Solution Cross sectional area of tubing = 0.7854 x 2.8752 = 6.492 square inch Force of wellbore pushing = 6.492 x 800 = 5,194 lb Buoyancy factor = (65.5 – 9) ÷ 65.5 = 0.8626 Tubing must have a total weight of 5,194 lb to overcome the wellhead pressure however we need to account for buoyancy factor because this factor reduces the weight. Therefore, the total weight accounted for buoyancy factor is equal to calculated weight in the air divided by buoyancy factor. Total tubing weight accounted for buoyancy factor = 5,194 ÷0.8626 =6,021 lb. Total length of tubing = Total weight ÷ weight per ft Total length of tubing = 6,021 ÷ 6.4 = 941 ft
Posted on: Wed, 04 Sep 2013 10:56:04 +0000
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