After digging well and hit the oil tank, due to high pressure in the reservoir, oil flows to the outlet of the well. This extraction step, which causes the pressure inside the reservoir itself, is called the primary oil recovery. In the initial harvest of oil, the reservoir’s energy is used to produce oil. Of course, this does not mean that if oil does not come to the ground itself, there will be no initial harvest, but when we use the pump to raise oil, in We are still in the first stage of oil extraction. At this stage, there is no particular energy entering the reservoir. As production increases and pressure decreases, the speed of production decreases as well, until the pressure is reached so much that no other oil is removed. At this stage, 30 to 50 percent of the total oil can be extracted from the reservoir. In addition to reservoir pressure, there are other factors that influence the properties of the reservoir rock and their porosity, as well as the temperature of the reservoirs, in the amount of production.
For example, the total US oil reservoirs in the United States were about 109 x 400 barrels, up to 1970, about 109 x 100 barrels were extracted by primary methods. Of course, the higher the amount of free gas in the tank, the greater the amount of oil produced by this method, Because the gas volume changes in response to the pressure change is very high. For example, in Pennsylvania, due to low permeability (less than 50 mA) and low energy consumption due to low natural gas content, the amount of oil extracted by primary methods was between 5% and 25% of total oil. And that’s why in this state the second stage methods began in 1900.
When the tank was evacuated and we could not transfer oil directly from the reservoir to the well and from the well to the ground, then the use of the secondary EOR method would begin. To use this method, today the injection method Water is customary. In this method, the injection wells are injected into the reservoir and the oil is exploited from the well. In this way, we inject fluid into the system, and the injected fluid directs oil to the production well. . Instead of water, gas can be injected into the gas injection process. It should be noted that the use of these two injectable methods is different by injection of water or gas that is used to maintain and maintain the pressure of the reservoir. Because injecting water and gas to maintain reservoir pressure, the injected fluid does not cause oil to move, but prevents a rapid drop in reservoir pressure from exploitation.
In the secondary state, the time comes when, while water is injected into the reservoir, we are faced with the production of water in the well. In this case, since the water-to-oil ratio increases and production does not have economic efficiency, then we need to use another method to increase the harvest. If we stop the water injection and use other processes, such as CO2 injection. Effective methods in the second phase are one of the water flooding and the other is gas flooding or gas injection.
In the water-flooding method, high-pressure water in the wells around the well produces oil into the reservoir and generates the necessary force for extraction of oil. Generally, around each oil well there are four wells for water injection. In gas flooding, gas (such as natural gas) with high pressures enters the reservoir instead of water and flows the oil towards the outlet well. In Venezuela, about 50% of the produced natural gas is returned to the oil wells for extraction in the second phase. The injection method is similar to water injection in the form of five wells. In cases where oil viscosity is very high, water vapor is used to extract the second stage. The injection of water vapor increases the temperature and reduces viscosity. In this method of using water vapor instead of water, reducing the viscosity of the oil, the flow is easier and the production speed rises.
After extraction with the help of the second-stage methods, about 30-50% of the oil can still be left unattended in the reservoir. Here is where oil extraction is done using the third step method. One of the methods of the third stage is injection of micellar solution, which after injection, the polymeric solutions are injected into the well as buffer solutions. In the US, methods for using Mishelar solutions may include up to 50% of all third-stage methods. Miscelar solution is a mixture of water, surface active agents, oil and salt. In new methods, micellar solution, oil, salt and auxiliary surfactants have been removed. The suspensions reduce the surface tension between water and oil up to a value of about or equal to 0.000 dyne / cm.
The viscosity of the polymer solution is about 2 to 5 times the viscosity of the oil. The concentration of polymer is about 1000 ppm. Polyacresides and biopolymers are currently used as a polymer in a buffer solution. Surface active agents are usually sodium sulphonates and are chemically similar to detergents in terms of properties and structure. Alcohols are used for surfactant auxiliaries. The cost of producing Michelin solutions for the production of barrels of oil in 1975 was around $ 1.5 a dollar.
Another method of the third stage is the method of underground combustion. In this way, the oxygen in the air beneath the earth burns with hydrocarbons, and some minerals and gas are produced, the pressure of the reservoir goes up. It also reduces the viscosity and makes the oil flow easier. Another method of the third phase, which has recently been considered, is the carbon dioxide gas injection method, which is part of the convergent displacement method. Carbon dioxide gas is very cheap, it is also soluble in oil and it lowers its viscosity. In other ways, the third stage is the explosion of underground bombs, It creates stones and simplifies the flow of oil. In these processes, the third stage is the oil recovery (Tertiary Oil Recovery). It is said that the stages of oil extraction can be further subdivided, that instead of saying that the first, second or third stage, we can say Primary Recovery, Improved Oil Recovery, or IOR, and EOR or Enhanced Oil Recovery. Improved Recovery or IOR is a process used to adjust the technology used to increase harvest. Now this process can be done in the first stage of production or in the second and third stages. Technologies such as horizontal drilling, selective grinding, or insitu gelation are IOR types. Thus, in the IOR, the process of production is not changed, but the technology is moderated so that with the same process as before, more oil from the reservoir It is produced. While EOR or EOR is referred to as a process in which it attempts to minimize the percentage of saturated oil as much as possible and minimize the residual oil in the reservoir. Processes such as chemical flooding, CO2 injection and on-site combustion are the same. After the water injection operation, the process can be changed. Another way is to modify water injection operations. For this purpose, in different transitional layers, the water enters the permeable layers and is directed towards the well, so it should be done to close these layers. This is done by injecting the gel into the desired layers. Miscible Displacement refers to the recovery of oil by injecting material that is melting with oil. In the displacement, the contact surface of the oil and the injected material disappears and the displacement is carried out in a single-phase movement. If the conditions in each case for injection and injection of oil are provided, then such a process is 100% in the swept areas. Injectable gas has a lower viscosity than the reservoir oil and therefore has more mobility than this. This property of injectable gas One of the reasons is the possibility of its mixing with the reservoir oil, since the high mobility of gas relative to oil causes the gas to contact the oil at various stages and ultimately the state of the mixing between the oil reservoir and the injected gas. The problem of The high mobility of gas results from the fact that the gas tends to fingering and channeling, resulting in areas of gas reservoir It does not sweep, and this will reduce the Recovery Factor in the mixing process.