When the exploration operation confirms the presence of producing layers in the field, steps are taken towards the stage of development or production. Production is the recovery of useful hydrocarbons from the reservoir to the surface, and while exploration consists of both geophysical and geological surveys, oil and gas extraction is a production process that includes drilling, construction and maintenance of wells, removing water, sulphur and wax from extracted oil, and many other integrated operations.
Generally, there are 3 widely known ways for oil production depending on the reservoir pressure and its maintenance techniques.
Open flow production. In this method, the force that pushes the oil to the bottom of the well and often lifts it to the surface with high pressure is mainly the gas dissolved inside the oil, as well as accumulated under high pressure in the arch of the anticline folding. In some cases, the water accumulated at high levels on the wings of the anticline fold lifts the oil to the surface by compressing it under high pressure. This means the gas that comes out with the oil is the force that moves the oil. Gas pressure in new oil fields can be very high. At the top of the well, oil sometimes leaves at a 50-100 (and more) atmospheric pressures. In the old days, they were calling it a “blowout”. The more petroleum gas left in the reservoir, the longer the open flow will blow out of the well.
Artificial lift (compression). After the blow-out, the pressure in the oil reservoir decreases, and the pressure of natural gas or reservoir water can no longer lift the oil to the surface. Thus, the blowout stops. If the open flow period is considered the early years of the well, the period after the blow-out is considered to be the mature period. The most convenient method of operation of the oil well in this period is the artificial lift. Compressed air or petroleum gas is injected under high pressure through a pipe or two pipes lowered from the compressor unit to the well. At this time, the compressed air lifts the oil. Extraction of oil with compressed air is called airlift, and extraction with compressed gas is called gaslift. Oil extraction by the compressor method was widespread in the Soviet Union.
Deep well oil pumping. Over time, as the well operates, the pressure of the oil reservoir decreases, and the level of oil in the well decreases so much that it is not convenient to extract oil by the compressor method, because to extract a very small amount of oil requires a large amount of compressed air or gas. A lot of energy is used to get compressed air. Therefore, in such cases, instead of operating the well by the compressor method, they switch to the deep well oil pumping. This is when the well becomes a mature one. Deep well pumps are attached to the ends of pipes called pump mains and are lowered into the bottom of the well. To move the piston of the pump (this is called a plunger) up and down, it is connected to the rods, and the upper end of the rods is connected to the pumpjack. When the electric motor moves the pumpjack, the rods inside the pump tubes move upwards. The valve at the top of the plunger closes and the plunger lifts the oil inside the pump tubes. Depth pumps are more suitable for the operation of wells with low oil levels.
In addition, there are repeated methods of oil extraction. At present, a number of advanced methods (hydraulic fracturing, acid treatment, etc.) are widely used to intensify oil production.