Locating Deep Oil with Geological and Seismic Surveys Land-based and offshore rigs target reservoirs on land and beneath the ocean floor, but the hardest task is first finding oil 2–3 km down. Geological work samples rocks and soils, checks natural gas seeps for hydrocarbons like methane or ethane, and scans satellite temperature anomalies for hints. Seismic surveys then map subsurface layers: vibrosis trucks press vibrating plates onshore and air guns fire offshore, while geophones and hydrophones record reflections to outline likely traps. Even the best surveys only raise probability; they never guarantee oil.
Transforming a Drill String into a Rock-Cutting System Drilling begins with a cemented conductor casing 15–20 ft deep for surface stability, then a mast supports steel pipes and a roller cone bit with tungsten carbide or diamond teeth. A Kelly drive rotates the growing drill string: a hexagonal Kelly rod locks into a powered drive rod, and a bushing with cooling and lubrication lets it spin while moving vertically via pulleys. Weight from the heavy string plus hoist force applies bit pressure, while multiple high-pressure mud pumps push drilling mud to cool and lubricate the bit and lift cuttings for surface cleaning and recirculation. Unlike fast air-driven water wells that reach ~800 ft in 4–5 hours, oil wells descend 7,000–8,000 ft over about a month to meet strict integrity needs.
Casing, Cementing, and Blowout Protection Loose topsoil is opened with a larger initial hole by a standard borewell machine, a casing is set and cemented to block soil and water, and deeper drilling continues until weak or water-bearing layers demand reinforcement. Each stage runs a steel casing leaving an annulus; a float shoe, a bottom plug and cement slurry, then a top plug displace mud, fill the annulus, clean the casing, and prevent backflow while the cement sets for about 24 hours. Layer by layer—conductor, cement, surface casing, cement, intermediate casing, cement, and production casing—the wellbore is stabilized and formations are isolated. As reservoir pressure rises near target zones, a blowout preventer with annulars and pipe rams can seal the well or clamp the pipe to stop a kick from becoming a blowout.
Directional Drilling Expands Reach with Mud Motors To extend reach, a mud motor replaces the bit to steer the well without rotating the entire string, using drilling mud pressure for power. A slight 1–3 degree tilt cuts a gradual arc over roughly 1,500–3,000 ft, so the rigid string simply follows the curved path like a train on tracks. The curved section is cased and cemented just like the vertical segments, allowing one surface site to drain an area that would otherwise require many vertical wells.
Perforation and Artificial Lift Bring Crude to Surface With drilling complete, the rig is removed, production casing is cemented across the reservoir, and a perforation gun detonates multiple small charges to tunnel through casing and cement into the formation. If natural pressure suffices, oil flows; if not and depths are around 500 m, a beam pump lifts 50–500 barrels per day onshore, while submersible pumps serve deeper or offshore wells. Crude oil, often accompanied by natural gas, is collected and shipped to refineries, with large tankers transporting the oil.