Invention

Part 3 - Oil Drilling

The first oil wells were hand dug or drilled with impact tools (Early Chinese wells used a cylindrical cast iron bar that was repeatedly lifted and dropped) but in the 20th century, these techniques were replaced with rotary drilling, which could drill boreholes to much greater depths and in less time. In 2008 the 12,289 metre long (40,318 ft) (7.6 mile) Al Shaheen oil well in Qatar surpassed the Russian Kola Borehole that was over 12,000 metres (39,000 ft) deep.

Modern wells typically start with a hole (12 cm to 1 meter (5 in to 40 in) in diameter) with a drill bit attached to a drill string of pipes rotated by a drilling rig. The hole is then fitted with a slightly smaller steel pipe casing and the space between the casing and the hole is filled with cement. This section isolates potentially dangerous high pressure zones from the surface and from the water table.

The well is then drilled deeper with a smaller bit and fitted with a smaller casing. The completed well typically has two to five sets of sequentially smaller holes with each casing cemented in place.

With the weight of the drill string behind it, the drill bit cuts into the rock by compressive failure or by shearing slices off the rock as the bit turns. Drilling fluid (mud) is pumped down the inside of the drill pipe string, exits at the drill bit and returns to the surface in the annular space between the drill string and the casing. The drilling fluid is typically water and clay with a complex mixture of liquids, solids and chemicals that are carefully tailored for optimal safely and performance of the drilling process. The fluid has to cool the drill bit, lift rock cuttings to the surface, prevent damage to the wellbore walls and providing sufficient pressure to prevent fluids from entering the wellbore from the rock. In some cases oil wells may be drilled with air or foam as the drilling fluid.

Rock cuttings, swept by the drilling fluid up to surface, then pass through "shakers" where they are separated, allowing the fluid to be reused. The oil or gas may be pushed to the surface by the natural pressure of the reservoir. But, where necessary, especially in depleted fields, where the natural pressures have been reduced by other wells or oil reservoirs with low permeability, downhole pumps, gas lift or surface pump jacks are used to raise oil to the surface.

After drilling, the top of the wellbore is usually outfitted with a collection of valves called a Christmas tree or production tree. These valves regulate pressures, control flows, and allow access to the wellbore in case further work is needed.

Injection wells (often old production wells), may be used when reservoir pressure is depleted or high oil viscosity hinders recover. Water, steam or carbon dioxide flooding may be used to increase reservoir pressure to push hydrocarbons out of the reservoir. Often, unwanted gas is pumped back into the reservoir through an injection well for storage or to increase the pressure in the oil field. Or, it may be liquified into synthetic gasoline, diesel or jet fuel through the Fischer-Tropsch process so it can be transported with conventional rail or road tankers. Proponents claim GTL fuels burn cleaner than comparable petroleum fuels. 

The Fischer–Tropsch process was developed by Franz Fischer and Hans Tropsch at the Kaiser-Wilhelm Institute for Coal Research in Germany, in 1925. A series of chemical reactions, using metal catalysts at 150–300 °C (302–572 °F) and pressures of up to tens of atmospheres, converts carbon monoxide and hydrogen into liquid hydrocarbons. 

The drilling techniques developed by the oil industry are now commonly used to install water, gas and sewage piping in urban areas with minimal disruption of traffic.