Compressor-Lift Petroleum Production

a method of raising petroleum from a formation to the surface by using the energy of compressed natural gas or air injected into the well by a compressor. An installation that lifts petroleum by this method is called a gas lift (or an air lift, if air is used).

The principle of gassing a column of liquid to lift it to the surface was first used in Hungary in the 18th century for pumping water out of flooded shafts with an air lift. Compressor airlift oil recovery was used on a small scale in the 1860’s in the oil fields of Pennsylvania (USA). The first large-scale industrial use of compressor-lift petroleum production was proposed by V. G. Shukhov and took place in 1894 in the Baku oil fields.

The principal gas-lift or air lift systems are of the continuous-flow and intermittent-flow types. Under continuous gas lifting, the flow of fluid from the formation and its movement up the ascent column and discharge at the surface are continuous. In this case, the operation of the gas lift is based on the decrease in the density of the column of mixture. To ensure the flow of oil from the formation, a certain pressure must be maintained at the bottom of the hole. In the absence of gas, the fluid column that equalizes the pressure does not reach the wellhead; gassing of the fluid column raises the level to the wellhead and creates a continuous production flow from the formation to the surface, if the required bottom-hole pressure is maintained.

Compressor-lift petroleum production is accomplished by two types of continuous gas lift systems: annular gas lifting and central gas lifting. Gas enters the ascent column (tubing string) through the gas-lift valve.

In an intermittent gas lift the production process consists of a period in which the fluid builds up in the ascent column (inflow from the formation) and a period in which the accumulated fluid is brought to the surface by the compressed gas injected into the lower part of the ascent column. The accumulation time and the flow time constitute the operating cycle of the well. Two gas-lift systems are used: intermittent gas lifting with a conventional ascent column (in which the accumulation of the fluid column and its lifting to the surface and ejection occur alternately) and intermittent gas lifting with a displacement chamber. The displacement chamber, whose diameter is greater than the diameter of the ascent column, makes possible exploitation of wells under low reservoir pressure, when the accumulated fluid column in the ascent column is not very high. The installation that services the groups of wells operates in a closed cycle. The gas-liquid mixture coming from the wells to the surface is separated in traps into liquid and gas. The part of the gas that is required for feeding into the well is sent to the intake of the compressors, and the excess gas (the gas admitted together with the petroleum from the formation) is sent for refining and consumption. The gas supplied to the compressor is compressed and fed into the wells for lifting the liquid to the surface. Thus, the gas circulates in a closed system. If the possibility exists in the oil field of extracting compressed gas from nearby oil or gas wells, the lifting is performed by supplying high-pressure gas from the wells. After completion of the fluid-lifting operation, the exhaust gas is mixed with extracted (formation) gas and sent for refining and consumption. This is called the compressorless exploitation method.

In the USSR compressor-lift petroleum production is used on a large scale at oil and gas fields in the Azerbaijan SSR; the compressorless method is used at fields in Krasnodar Krai and on the Mangyshlak Peninsula and Sakhalin Island.

The principal advantages of compressor-lift petroleum production, in comparison with other mechanized petroleum production methods, are the absence of moving parts in the well equipment, high efficency of the process with a high gas-oil ratio, and simplicity of control and automation of the production process.