String weight in mud and hook load
String weight in air and in mud (buoyancy factor) for one or two pipe sections, and the hook load including the travelling block and top drive.
k_b = 1 − ρ / ρ_sW_air = g · (q_1 · L_1 + q_2 · L_2)W = k_b · W_air; W_h = W + W_tbρ_s = 7850 kg/m³The buoyancy factor holds when the same fluid is inside and outside the pipe; with different fluids (cementing, pills) work with the pressures on the pipe ends. In deviated wells friction makes the hook load higher when pulling and lower when running in. Steel density 7850 kg/m³ (65.5 ppg).
Source: Archimedes' principle; API RP 7G (drill string buoyancy factor)
Inputs
You can change a field's unit: the value is converted to the formula's units automatically.
Drill pipe or tubing, with tool joints (couplings), from tables.
Drill collars or heavy-weight pipe; 0 for a single section.
0 if the weight indicator reads the load without them.
Unit converter for this formulaDensity and °API · Weight per length · Length · Force and load
- kg/m³850
- g/cm³0.85
- t/m³0.85
- rel. (water 4 °C)0.850024
- lb/ft³53.0638
- lb/gal (ppg)7.09359
- SG (60/60 °F)0.850837
- °API34.8068
°API and SG refer to the density at 60 °F (15.6 °C) relative to water at 60 °F, relative density to water at 4 °C. The oil's thermal expansion between the measurement temperatures is not included. °API = 141.5 / SG − 131.5.
- W_air — String weight in air–
- k_b — Buoyancy factor–
- W_h — Hook load–
More in Drill string and volumes
Internal volume per metre and for the whole string, metal (open-end) and closed-end displacement — for the trip sheet: hole fill when pulling and returns when running in.
Volume per metre and over an interval of the annulus between the hole (or casing) and the pipe.
Fast-line and dead-line tension, derrick load and the rope breaking strength needed to lift the string on n lines, allowing for the efficiency of the block and tackle.
Results are engineering estimates from standard formulas; for design decisions check them against the codes, project documents and specialists' calculations. The formulas carried over from the original set are unchanged, and their errors are described in the notes.