Well Control – Causes, Indicators, and preventative actions of Kick

Well Control refers to the techniques used in oil and gas well drilling/completion/workover under control. In overbalanced operations, hydrostatic pressure should be maintained more than formation pressure in order to prevent formation fluids from influx into the wellbore; while in underbalanced operations, hydrostatic pressure remains below formation pressure as the objective is to allow formation fluids to freely flow to surface and that must be under control as well. In both cases, working wellbore pressure must be remained sufficient within a range that allows maintaining safe operation.

Well control includes measures, practices, procedures and equipment to ensure safe and environmentally protective operations. The main three well control barriers are: drilling fluids DF, pressure control equipment PCE such BOP, and well trained personnel.

Kick is the unexpected and uncontrolled influx of formation fluids into wellbore, which indicates failure of primary well control barrier that is DF. Objective of second along with third barriers is to immediately handle a kicking well and bring it under control. If appropriate precuations are not taken, the situation could deteriorate into subsurface blowout and then surface blowout.

Major potential well control problems:

• Incorrect mud weight
• Swabbing or surging
• Failure to monitor the well
• Failure to keep the well full of mud
• Mud loss circulation
• Operation in deep and HPHT wells
• Operation in wells containing trapped pressure
• Unexpected transition from normal/sub-normal zones to abnormal zones.

Hydrostatic pressure is maintained by controlling the fluid density in a well. Standpipe gauge, trip tank, and other monitoring devices are usually used to monitor pressure and flow check of fluid volume pumped into a well or displaced from a well; to ensure exact fluid density and hole full of fluids during operation particularly during tripping. For more pertinent information to swab/surge pressures, loss circulation, and operation in deep and HPHT well, read under related articles:

?Common kick indications:

• As the influxed fluids normally have lighter weight; HP decay, working string to annulus U-tube effect, decreasing in pump pressure, and increasing in return flow rate and pit volume gain are major indications of kick.
• Change in working string weight due changing in buoyancy
• Change in cutting sizes and shapes with chloride, oil, and gas show; or significant change in fluids rheological properties.
• Change in torque and sudden increase in ROP with no associated increase in WOB.

Prevention and Mitigation measures

• Maintaining well control during operation is in line with beforehand prepared plan according to the identified potential vulnerabilities, and an appropriate contingency plan for preventing underground blowout and mitigating surface blowout.
• Since drilling fluid is the first line of defense in well control, we will highlight some of the preventative action for maintaining sufficient mud density and full hole in order to operate at safe pressure window between formations pore pressure and fracture gradient.
• Before re-circulating the mud back downhole cuttings, solids, and gas should be removed; and agitators used to stir mud in the tanks to avoid settling of solids and to maintain uniformed mud properties, and always keep the fluids within the desired density range.
• Avoid fluids dilution by rain or cleaning pits. In HPHT, utilizing less susceptible fluids to influence of density change that resulted from downhole severe condition such as invert-emulsion fluids.
• Finally no operation poses more hazards than tripping. Serious well control incidents have occurred during tripping, thus, continuous filling up the hole while tripping according to the monitored and calculated displacement volume, and pumping heavy slug fluids before breaking up Kelly or power swivel.