The group of airlift methods of hydrocarbon production in oil and gas fields has long been used by domestic industry as an alternative to fountain well development. This technology in certain application conditions provides significant advantages of an economic and technical nature, but also requires the connection of additional resources. In most cases, the optimal solution is the gas-lift method of oil production, in which a gas mixture is used as an active lifting medium. This solution justifies itself due to its high performance, but also imposes additional organizational requirements in terms of security. For this reason, the method is used for the most part by large organizations with a sufficient resource base.
General characteristics of the gas-lift method of oil production
The principles of airlift, that is, the technology of raising the borehole resources of an underground field, first began to be used in the late 18th century. The emergence of the idea of this method was due to the rapid development of mining technology, but for a long time its full use was limited by the lack of sufficiently developed compressor equipment. The author of the gas-lift method of oil production is the German engineer Karl Losher, who put forward a general scheme for raising resources using the energy of air mixtures. In the future, the technique was repeatedly subjected to optimization, modernization and improvement in certain aspects of operation. The practical use of airlift on an industrial scale with the creation of a theoretical base for its technical implementation began only in the 20th century. In oil fields, the first experience with gas lift was in 1985.
Nowadays, the application of gas lift technology pays off mainly in wells with high flow rates. Also, in conditions of a high content of impurities, gas lift is the most economical solution to raising the resource to the surface. This applies primarily to oil mixtures, which contain salts, resins and paraffins, which make it difficult to lift the masses. Regarding comparison with the airlift as such, we can say that the gas-lift method of oil production is a continuation of the general technology of artificial lifting of liquids. Only if in a classical airlift an air mixture is used as an active medium, then a gas-lift uses carbon-containing substances. For this reason, one of the key operational characteristics of the technology is considered specific gas consumption. In calculating the cost of using a gas lift, the energy cost of maintaining and supplying gas mixtures is about 30% of the total cost of the projects.
The scope of the gas-lift method of oil production
A high-yield well with high bottomhole pressure is the target location for the implementation of gas lift. Such deposits are a favorable environment for the organization of airlift lift in principle. But the practice of limiting fountain methods of oil production also determines a number of conditions under which gas lift becomes the only possible method of working in a well. At least, the general characteristic of the gas-lift method of oil production as the most adapted to dynamically unbalanced hydraulic media allows it to be used in faces with low saturation pressure and in sand wells with hard-to-reach technical installation conditions. For example, a gas lift system can be used in flood conditions, in marshy areas or in the presence of flood risk. Pressure indicators, by the way, can be artificially balanced using compressor equipment - although the rise depends on the borehole gas energy indicators, it can be adjusted to current needs.
On the other hand, if a centralized supply of technical and gas materials with a high level of mechanization of the production process is not expected, then it is better to use the traditional fountain production scheme. As in the case of the airlift, the gas-lift method of oil production is a continuation of the technology of the fountain method, but in an augmented embodiment. It is the technological expansion of the producing infrastructure that does not allow the use of this method in small wells, the operation of which is designed for short periods.
Mining process
After the development of the well, the structural base of the head is formed on the surface, which subsequently acts as a platform for organizing the main work processes. In the niche of the wellbore, a closed tunnel is organized with cameras and transitional valve assemblies that perform the function of a resource movement regulator. Moving the produced fluid up the channel is the main operational process that is supported by a gasified bottomhole environment. To ensure gasification downward parallel to the channel along the insulated circuit, a chamber with an active mixture nozzle is lowered. Actually, the principle of the gas-lift method of oil production is reduced to the direction of gas into the liquid medium of the target resource, after which the lifting process should take place. It is important to note that enrichment in gas-air mixtures alone does not provide a rise in liquid. Special pumps are used for this operation. The lifting force depends on the degree of gasification, and on the power of the pump, and both factors of influence can be adjusted. For integrated control of the pressure indicators in the circuit is a compressor unit located on the surface.
The resource extraction rate can be controlled by manual mechanics or automatic systems with electronic sensors. Operating parameters are set in accordance with the capabilities of the receiving equipment. A feature of the gas-lift method of oil production is a special treatment after resource extraction. Since the liquid rises with the gas mixture, special separation is required, after which the already refined oil is sent to a special sump. Moreover, since gas lift is often used in conditions of increased sludge contamination, multi-stage coarse filtration may be required before the resource enters the temporary storage tank.
Applied Equipment
The entire technical infrastructure is formed by two groups of equipment - universal devices and devices for organizing well servicing processes and special installations that are used in the operation of a gas lift. The first group can include pumping circulation equipment, casing equipment, fixing fittings, metal pipes for pumping, etc. As a rule, the work of both the fountain and gas lift methods of oil production with insignificant structural differences is based on this equipment.
As for the special technical elements for the implementation of oil recovery on gas energy, these include the following:
- Compressor. Installation to maintain optimal pressure by forcing compressed air. Mainly used industrial high-power units that can adjust the parameters of the working value in a wide range.
- Gas lift chamber. We can say the core of the infrastructure for gas lift oil production, in which the main processes of flow direction, distribution and supply of gas-air mixtures take place. This is a metal structure with pipes and branch channels, the operation of which is regulated by shutoff valves.
- Valves In this system, the valve performs not only the function of a liquid circulation blocker, but acts as a regulator of flows. Gas lift valves are used at different levels of the barrel, which allows you to more accurately control the intensity of production. The main structural feature of such valves can be called the presence of sensitive elements, which with high accuracy record pressure indicators and change their state depending on the strength of the impact on the control site.
Gas lift
In this case, the concept of a lift reflects the integrated infrastructure of a gas lift submerged in a well. Its circuit diagram contains two channels - for injecting gas and for raising the target liquid resource. Both channels are organized with the help of metal pipes, but they do not need to be joined together in parallel. Moreover, sometimes the angular direction of the gas supply pipe is provided, which is caused by the specifics of connecting the pump unit. The configuration of the placement of pipes depends on the conditions under which the gas-lift method of oil production is organized. The photo below illustrates the modern technology of using a combined injection column and raising the resource in one circuit with a diameter of 90 to 140 mm. In this case, regardless of the configuration of the direction of the channels, both from the upper part at the head and in the lower region of the shoe, a rigid fixation of the structure is possible. Technological holes (perforations) for the release of sand and other foreign particles can also be provided in the pipes.
Gas lift operation without compressor
In principle, gas supply and regulation of pressure indicators need not be carried out with the support of compressor equipment. If gas and oil fields are located within the same operating site, the downhole gas lift can be organized with its own energy support without a compressor. But even in this case, the technologies of oil and gas lift oil production will diverge, since the exclusion of regulation by compressed air from the side does not exclude the control of pressure indicators from natural gas. Moreover, in such conditions, downhole drying and preliminary cleaning of the resource is possible, which reduces the cost of the process.
Gas lift process controls
First of all, it is worth emphasizing that gas lift requires the use of a wide range of measuring devices that allow you to keep important performance indicators under control. These include pressure, temperature, humidity and gas flow. Direct control of oil production in the gas-lift method is carried out using the aforementioned valves and valves with actuating systems operating from surface generators. More advanced plants operate under the control of automatic controls, without the participation of operators, regulating the parameters of gasification and the speed of raising resources.
Technology benefits
With regard to technical implementation, the method is quite time-consuming and expensive, but it has a number of positive properties justifying its use:
- High performance.
- Wide possibilities of structural adjustment to external operating conditions and well parameters.
- Reliability and safety of the mining process.
- Operational flexibility. This property reflects both the advantages and disadvantages of the gas-lift method of oil production, which are manifested in different aspects of its application. For example, from the point of view of a qualified operator, the control process itself is quite simple and practically does not require physical effort. But, maintenance staff is dealing with complex equipment that requires large labor and financial costs for maintenance.
- Most critical equipment is placed on the surface.
- The versatility of the method.
Technology disadvantages
Nevertheless, this method cannot be called optimally suitable for all deposits, if we take into account the totality of operational factors, as well as environmental and economic aspects. The negative aspects of using the gas-lift method of oil production include:
- High energy costs. We are talking about injecting gas in industrial volumes, and about the cost of fuel for generators that provide the functions of pumping equipment with compressors.
- Investments may not correspond to the value of the extracted oil and gas materials - especially taking into account the costs of additional processes of technological cleaning and separation.
- With the exploitation of large deposits, production volumes decrease, while the level of organizational and technical support should remain the same.
Conclusion
The experience of oil and gas producing companies shows that about half of the costs of field development and exploitation projects account for the organization of technical infrastructure with support for additional work processes. It would seem that industry development trends should move progress towards the structural optimization of such events, but the gas lift method proves the opposite. As suggested by the author of the gas-lift method of oil production Karl Losher, the connection of auxiliary energy sources during the rise reduces the energy costs of the work operation, but not the organization of the event as a whole. In any case, the equipment for the lift column does not so much benefit in the form of connecting a gasification channel, but opens up wider possibilities in controlling the parameters of the production process. And this advantage lies precisely in the prospect of developing a gas lift as a way that can expand the possibilities of combining several development layers into one high-capacity production facility.