Kick Tolerance at the Casing Shoe

ScopeHow big a gas kick a well can take and still be shut in and circulated out without breaking down the formation under the last casing shoe. From the leak-off test, the mud weight, the shoe and well depths and a kick intensity, it gives the maximum allowable casing pressure, the tallest gas column the open hole holds, and the pit gain that equals. A 10 ppg mud under a 14 ppg shoe at 3,000 ft, drilling at 5,000 ft, takes 34 bbl at a 0.5 ppg kick with the whole influx taken around the bottom-hole assembly, and 43 bbl, set at the shoe, once a 600 ft assembly is entered so the gas above it sits in the wider drill-pipe annulus. Single-bubble method, vertical well. The operator's well-control standard governs.

Formula or tableMud gradient Gm = 0.052 x mud weight, psi/ft. Shoe limit = 0.052 x leak-off equivalent x shoe TVD - safety margin. Maximum allowable casing pressure = shoe limit - Gm x shoe TVD. Formation pressure Pf = 0.052 x (mud weight + kick intensity) x well TVD. Shoe pressure with H ft of influx in the open hole = Pf - Gm (open hole - H) - Gi H; setting it to the shoe limit gives H = (shoe limit - Pf + Gm x open hole) / (Gm - Gi), capped at the open hole. Volume at the shoe = H x drill pipe annulus, converted to shut-in conditions by Boyle's law, x the shoe pressure with that influx below it / Pf (the shoe limit when H is the limiting height, less when H was capped at the open hole). Volume at bottom = BHA length x BHA annulus + (H - BHA length) x drill pipe annulus, or H x BHA annulus when no BHA length is entered. Kick tolerance = the smaller. Largest kick with no influx = maximum allowable casing pressure / (0.052 x well TVD).

Source and editionThe single-bubble kick tolerance method as well-control manuals state it, cited by name; the steps follow the method summarized at drillingmanual.com (kick tolerance calculation), which presents the operator-manual procedure: maximum allowable casing pressure, maximum influx height, volume at the weak point and at the bottom, Boyle's law, and the smaller of the two volumes.

Free accessHydrostatics and the ideal gas law; no table is reproduced. The DrillingFormulas.com kick tolerance worked example (12.0 ppg mud, 14.7 ppg LOT at 5,500 ft, 9,500 ft, 850 ft BHA) is reproduced: 772 psi, 1,021 ft, 109.8 bbl around the BHA, 84.5 bbl kick tolerance. The tile is also checked by its own balance: with the reported height of gas in the open hole, the pressure at the shoe equals the shoe limit to round-off.

What governsEstimate. AHJ and licensed professional govern.

API field namesmud_weight_ppg, shoe_emw_ppg, shoe_tvd_ft, well_tvd_ft, kick_intensity_ppg, influx_gradient_psi_ft, annular_capacity_dp_bbl_ft, annular_capacity_bha_bbl_ft, safety_margin_psi, maasp_psi, formation_pressure_psi, max_influx_height_ft, volume_at_shoe_as_shut_in_bbl, volume_at_bottom_bbl, kick_tolerance_bbl, max_kick_intensity_ppg

• Influx gradient 0.1 psi/ft for dry gas unless enteredcommon planning value
• Kick intensity 0.5 ppg default; enteredoperator standard
• Vertical well, single bubble hole angle, gas dispersion and migration are not modelledscope of this tile
• Isothermal ideal gas Boyle's law between the shoe and bottom-hole pressurescope of this tile