Spotting pill to free stuck pipe
Volume of a spotting fluid (oil, water or acid) that covers the stuck zone in the annulus with a reserve inside the pipe, the displacement volume, and the drop in bottomhole pressure caused by the lighter pill.
V_a = π/4 · (D² − d_o²) · h · (1 + k)V_i = π/4 · d_i² · h_i; V = V_a + V_iV_d = π/4 · d_i² · (H − h_i)ΔP = (ρ − ρ_p) · g · hBefore spotting, make sure the composite column still exceeds the formation pressure: the drop ΔP must be smaller than the current overbalance (Kazakhstan industrial safety rules, item 1011); otherwise weight up the mud above the pill. In a deviated hole use the vertical height of the pill for ΔP. Tool joints and couplings are ignored.
Source: Industrial safety rules for hazardous production facilities of the oil and gas industries of Kazakhstan (order of the Minister for Investment and Development No. 355 of 30.12.2014), item 1011; volumes by volume balance, pressure by the hydrostatic equation
Inputs
You can change a field's unit: the value is converted to the formula's units automatically.
Bit size, caliper average or casing ID.
Bit or end of string: the pill rises in the annulus from here.
The stuck zone plus a margin above it.
Reserve for moving the pill in stages.
Oil 0.80–0.90 g/cm³, water 1.0, 12–15 % hydrochloric acid about 1.06–1.07.
Unit converter for this formulaLength · Density and °API · Liquid volume · Pressure · Fraction and percent
- m1
- cm100
- mm1,000
- km0.001
- ft3.28084
- in39.3701
- 1/32 in1,259.84
- 1/64 in2,519.69
- mile0.000621371
- V_a — In the annulus–
- V_i — Inside the pipe (reserve)–
- V_d — Displacement volume–
- ΔP — Drop in bottomhole pressure–
More in Tubing and stuck pipe
Length of the free pipe above the stuck point from the stretch measured for an increase in pull — an estimate of where tubing or drill pipe is stuck.
Stretch of a freely hanging string from an axial pull, from its own weight in fluid and from a temperature change, and the thermal force in a string fixed at both ends (e.g. on a packer).
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.