Well control

Well control is the technique used in oil and gas operations such as drilling, well workover, and well completions to maintaining the fluid column hydrostatic pressure and formation pressure to prevent of formation fluids into the wellbore. This technique involves the estimation of formation fluid pressures, the strength of the subsurface formations and the use of casing and mud density to offset those pressures in a predictable fashion. Understanding of pressure and pressure relationships are very important in well control.

Fluid is any substance that flows; e.g. oil, water, gas, and ice are all examples of fluids. Under extreme pressure and temperature almost anything will become fluid. Fluid exerts pressure and this pressure is as a result of the density and the height of the fluid column. Most oil companies usually represent density measurement in pounds per gallon (ppg) or kilograms per cubic meter (kg/m³) and pressure measurement in pounds per square inch (psi) or bar or pascal (Pa). Pressure increases as the density of the fluid increases. To find out the amount of pressure a fluid of a known density exerts for each unit of length, the pressure gradient is used. A pressure gradient is defined as the pressure increase per unit of the depth due to its density and it is usually measured in pounds per square inch per foot or bars per meter.It is expressed mathematically as; pressure gradient = fluid density × conversion factor. The conversion factor used to convert density to pressure is 0.052 in English system and 0.0981 in Metric system.

Hydro means water, or fluid, that exerts pressure and static means not moving or at rest. Therefore, hydrostatic pressure is the total fluid pressure created by the weight of a column of fluid, acting on any given point in a well. In oil and gas operations, it is represented mathematically as; Hydrostatic pressure = pressure gradient × true vertical depth or Hydrostatic pressure = fluid density × conversion factor × true vertical depth .

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