IWCF Level 1 cheat sheet
IWCF Level 1 · Keep the key ideas within reach.
Well Control Awareness: Fundamentals, Primary Barriers and Kick Indicators
Well control is the management of the pressure balance between the wellbore fluids and the formation fluids; the objective is to keep formation fluids out of the wellbore at all times, both during drilling and during trips, casing, cementing and completion operations.
Formation pore pressure is the pressure of the fluids trapped in the pore spaces; it is normally equal to hydrostatic pressure of a continuous column of formation water to surface, and any value above that is described as abnormal or overpressured.
Hydrostatic pressure formula: Ph = 0.052 x MW (ppg) x TVD (ft), or Ph = MW (kg/m3) x TVD (m) x 0.00981 in metric units; the constant 0.052 converts ppg and feet to psi, and only true vertical depth is used, never measured depth.
Formation fracture pressure is the pressure at which the rock begins to take fluid and part; the safe window for wellbore pressure lies between pore pressure (lower limit) and fracture pressure (upper limit), with a margin for kick tolerance and trip margin.
Overbalance means hydrostatic pressure exceeds pore pressure; underbalance means pore pressure exceeds hydrostatic pressure, which is the condition that allows an influx to enter the wellbore.
Primary well control is the hydrostatic pressure of the fluid column, normally maintained with the correct mud weight; secondary well control is the blowout preventer equipment plus the well control procedures used when primary control is lost.
A kick is an unintended influx of formation fluid into the wellbore; a blowout is an uncontrolled flow of formation fluid at surface or into another formation; an underground blowout is flow from a high-pressure zone into a lower-pressure zone downhole.
Kick warning signs while drilling: increase in pit volume, flow rate increase with pumps off, gain in trip tank volume, mud density or viscosity change, gas, oil or saltwater shows, and a flowing well with the pumps stopped.
Kick warning signs while tripping: incorrect fill volume on the trip sheet (short fill is the classic indicator), wet string, flow from the annulus with pumps off, and a string that does not take the expected overpull or drag behaviour.