Leak-off test: fracture gradient at the shoe and MAASP
Fracture (leak-off) equivalent density and pressure at the shoe from a LOT or FIT, and the maximum allowable annular surface pressure (MAASP) for the current mud weight.
ρ_fr = ρ_t + P_lo / (g · H_sh)P_fr = P_lo + ρ_t · g · H_shMAASP = (ρ_fr − ρ) · g · H_shRecalculate MAASP after every change of mud weight. The Kazakhstan industrial safety rules (item 1000) also limit the pressure at the closed-in wellhead to 80 % of the casing test pressure; take the smaller of the two. The result is for the shoe; check weaker zones in the open hole separately.
Source: IWCF/IADC well control: MAASP from a leak-off test; Kazakhstan industrial safety rules for the oil and gas industries (order No. 355 of 30.12.2014), item 1000
Inputs
You can change a field's unit: the value is converted to the formula's units automatically.
Where the pressure–volume plot leaves the straight line; for a FIT, the test pressure.
Unit converter for this formulaDensity and °API · Pressure · Length · Pressure gradient and equivalent density
- 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.
- P_fr — Fracture pressure at the shoe–
- MAASP — Maximum allowable annular surface pressure–
More in Pressures and drilling fluid
Pressure of a column of drilling or kill fluid at a true vertical depth, and its gradient (equivalent density).
Kill mud weight from the shut-in drill pipe pressure, and the initial and final circulating pressures for the driller's and the wait-and-weight methods.
Equivalent density of the pore pressure and the mud weight that keeps the hydrostatic pressure above it by the margin of the Kazakhstan industrial safety rules (item 85-2), with the depth-dependent cap on the overbalance.
The density equivalent to the bottomhole (or shoe) pressure while circulating: the static mud column plus the annular friction loss above that point.
How much weighting material (barite, hematite, calcium carbonate), water or another fluid to add to bring the mud to the required density, and the final volume.
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.