A kick is an occurrence during an oil or gas drilling when the bottom hole pressure (BHP) drops below the formation pressure. As a result, formation fluid flows into the wellbore. A kick, when uncontrolled, can become a blowout that can cause huge damage to the rig equipment and well, not to mention the possibility of injury and loss of life during the eruption. A blowout can erupt into a huge explosion and cause fire. By utilizing well control techniques, kicks and blowouts can be avoided.
For proper formulation of well control procedures, understanding the common causes of kicks is necessary.
· Failure to Keep the Hole Full – During a trip, which is removing the drill string or steel from the drill hole, a displacement occurs. It is this crucial moment when an equal volume of mud is not replaced immediately, causing a loss of hydrostatic pressure and bottom hole pressure. When the bottom hole pressure drops below the formation pressure, a kick occurs.
· Lost of Circulation – Lost circulation can occur when the hydrostatic pressure is greater than the fracture pressure of the open formation. This results in the fracture of the open formation, causing a decrease in fluid level and consequently a lower hydrostatic pressure in the well bore. When this happens, a kick can occur.
· Swabbing – While tripping out of the hole, removing the drill pipe, drill collars and tubing empties out the space, which must be replaced by mud. Pulling out the metal too fast can leave the space void and decreases the bottom hole pressure, causing the formation fluid to enter the well bore.
· Abnormal Pressure – Abnormal pressures can be caused by salt formations, massive shales, faulting and uplifting, trapped formation fluids and artificially charged zones. When the formation pressure exceeds the bottom hole pressure, which is typical during abnormal pressures, it results in a kick.
· Insufficient Density of Fluid – Keeping formation pressures in check is necessary in preventing a kick from occurring. When the well is filled with insufficient density, which affects the hydrostatic pressure in the well, a kick can occur. Insufficient density fluid can be caused by excessive dilution of the mud and heavy rainfall in the pits.
Proper well control can restrain the effects of a kick when it occurs to avoid a blowout. However, well control can also be utilized to prevent the occurrence of a kick and thus, understanding the causes of a kick is necessary to make this strategy work. With the right planning and application, damage and loss can be prevented in the drilling rig.