Wellbores

Wellbores are drilled passages created to access subsurface resources or to carry out subsurface operations. They range from shallow groundwater boreholes to deep, engineered wells used for hydrocarbon production, geothermal energy, or carbon dioxide sequestration. The term refers to the hole itself before surface equipment is installed, with open-hole sections used for evaluation and later sections lined with steel casings cemented in place to isolate formations and provide structural support.

During drilling, a rotating drill string cuts the rock while circulating drilling fluid (mud) to remove cuttings, control pressure, and stabilize the borehole. Once the target interval is reached, casing is run and cemented to seal the formation boundaries. Production tubing is installed inside the casing, and a wellhead provides access for production, injection, or monitoring. Subsurface logging tools may be run to characterize rock properties and fluids along the borehole.

Wellbores serve multiple applications: oil and gas wells, water wells, geothermal wells, and injection or disposal wells. In oil and gas, multiple casings and completion schemes are used to optimize flow and ensure safety. Geothermal wells extract heat or inject fluids; CO2 sequestration wells aim to isolate stored gas in suitable formations.

Integrity and safety are maintained through proper cementing, casing design, and abandonment procedures, as well as blowout prevention and managed-pressure drilling where appropriate. Environmental considerations include protecting aquifers, avoiding leaks, and monitoring for subsidence or contamination, under regulatory oversight and well-abandonment requirements.