Running Head: POLYMER FLOODING 1
POLYMER FLOODING 2
Polymer flooding is the most commonly used chemical enhanced oil recovery methods in recovery of oil at the tertiary recovery level of oil in the wells. Polymer flooding has been proven to be effective in this extraction process and thus, it has been used in most of the recoveries. This method operates under the mobolity ratio principle and this is determined by the polymer used and the mobility control agent used. These two elements must thus be selected with a lot of considerations on the preveiling conditions inside the well, with the main consideration being given to the temperatuires. The use of polymer flooding is effective in realization of more than 30 percent of oil which is at the tertiary level.
Using Polymer Flooding in Enhancement of Oil Recovery
Currently, the demand for energy has risen enormously in the years. Oil is the main source of energy which is used in all the countries around the world and it provides the highest percentage of the total energy used around the world every day. Approximately 101 million barrels of oil are used every day as a primary source of energy for different systems (Amirian, 2018). As a result of the increased demand for the use of oil, the depth of oil wells has continued to increase and depletion is also being experienced. This makes the recovery process enter into the tertiary recovery stage, also called the enhanced oil recovery stage. This stage calls for the use of chemical enhanced oil recovery methods. The most commonly used of these methods is the polymer flooding method. This is a straight forward method which has a lengthy commercial use history and whose results have been proven to be the best for the tertiary level of oil extraction. The use of this technique is from the enormous advantages that it has as a technology which makes it easy to use and also cheap compared to other extraction methods.
The method is not complex. It makes use of polymers and augmented water in order to increase the viscosity and increase the sweep efficiency of oil in the reservoir (Clarke, 2016). The extraction of oil using polymer flooding is an effective method. The primary or initial recovery process of oil accounts for an extraction of between 20 percent to 40 percent of the total oil in the reservoir whereas the secondary extraction process accounts for about 30 percent of the entire volume, leaving about 30 percent which is extracted in the tertiary level and this is the percentage which is extracted through polymer flooding method (Unsal, 2018). Being the most popularly used method for tertiary recovery, polymer flooding is a friendly method and easy to use as well as being cost effective.
Recovery Process Using Polymer Flooding
This method makes use of water and polymer as well as a surfactant as the main components. Polymers are long chain molecules composed of many repeated subunits with high molecular weight (Seright, 2010). The polymer is used in order to mix with the water in the process of extraction so as to increase the viscosity of the water used and reduce the permeability of the water as a result of mechanical entrapment in the extraction process (Seright, 2010). The mechanical entrapment occurs as a result of high mobility which is decreased by the use of the polymer. The mobility ratio is a very important factor in oil extraction and it has an impact on both vertical and aerial sweep efficiency. Actually, the process of tertiary oil recovery by use polymer flooding is dependent on the mobility ratio created by the use of the polymer and water. There are two forms of mobility which are important in polymer flooding, that is, vertical mobility and aerial mobility. The vertical and aerial mobility is expressed as M = (k/µ) water / (k/µ) oil (Clarke, 2016), where M is the mobility ratio and k/µ is the ratio of mobility of reservoir to fluid component. The polymer must thus be of the right quality and it should be compatible with the conditions in the reservoir for proper working.
The process involves the mixture of water with surfactants at first before pumping them into the reservoir. This is the initial stage of extraction. The mixture is then pumped into the reservoir in order to reduce the interfacial tension which exists between oil and water phases. This makes the surfactant an important factor in polymer flooding. By adding the surfactant and water into the reservoir, the wettability of the reservoir rock is altered and this is done to improve the oil recovery (Unsal, 2018). After that, the polymer is added into the reservoir with a mixture of water. This injection is done over a long period of time as the process is monitored. This period can take up to a year or several years depending on the size of the reservoir as well as its depth. The pumping process is done until about 30 percent to 50 percent of the reservoir’s pore volume is fully occupied to make the next extraction process easier (Sheng, 2015). The process has to involve a monitored pumping of the polymer mixture. The monitoring can be done either electronically or manually depending with the technology being used and the place of extraction. When this reservoir volume is achieved, the drive is terminated and the pumping process is commenced. The drive water is pumped into the injection well to drive the polymer slug and the oil bank in front of it toward the production wells (Shah, 2012). At the production well, recovery is done and the separation of the water mixture with the polymer as well as the oil is done. The rest of extraction process involves the purification of the oil. Due to the economical factor of the polymer flooding oil recovery process, the method is commonly used in tertiary extraction.
Mobility Control Agent
The mobility ratio is the main factor in polymer flooding method of oil extraction. As a result, the mobility control agent becomes an important factor to be considered and its choice must be made in such a way that it complies to different characteristics which are considered best. There are characteristics which are used for an ideal mobility control agent and thus, the chosen agent must be closest possible to these characteristics in order to fulfil the need of the process. The agent must be cost effective. This is because the whole process is known to be cost effective and thus, this has to be achieved from the material being used. The agent must also have a high infectivity and resistance to mechanical and microbial degradation (Sheng, 2015). The mobility agent is subjected to different conditions inside the reservoir and if it is not resistant to degradation, then the quality of the oil as well as the entire process will be ruined.
The agent must also be able to sustain high temperatures. At the base of the reservoir, the temperatures are very high, up to about 200 degrees and this agent is used for up to ten years (Seright, 2010) and this may result into vaporization of the mobility agent if not well chosen and thus, the temperatures must be a consideration before choosing the mobility agent. The agent should also be effective when mixed with reservoir brines and have low retention properties in porous rock to avoid contamination of the oil (Clarke, 2016). These characteristics must be considered in choosing the agent to ensure that the process is effective.
Choosing the Polymer
When choosing the polymer to use on a reservoir, different factors must be considered to ensure that polymer flooding process occurs in the right manner and that the mobility is taken care of. The reservoir permeability and the viscosity of the oil must be given a major consideration. These are the factors which determine the behavior of the polymer and the ability of the polymer to drive the slug and to sink below the level of the oil, driving it upwards for extraction. The polymer retention is also a factor consideration in making the choice. This encompasses possible mechanisms responsible for the reduction of mean velocity of polymer molecules during their flow through porous media (Amirian, 2018). The other crucial factor to consider in making the choice of the polymer is cloud point that the polymer has. This determines the thermal stability of the polymer when it is subjected to high salt brine and when subjected to high temperatures (Unsal, 2018). If this is not taken care of when choosing the polymers, then it will become completely hard to achieve the set purpose as precipitation will most likely take place after the injection and thus, the process will be completely ineffective.
With the increased demand in energy and with oil being the main primary source of this energy, then polymer flooding has become an important method in oil extraction among all the chemical enhanced oil recovery methods. The method is used at the tertiary recovery or enhanced oil recovery life time of the reservoir to extract more than 30 percent of the oil which is left out by the primary and secondary recovery levels. The process involves the use of a polymer and a mobility control agent which make the process possible. The main technology behind polymer flooding is the nobility ratio which is at the core of the calculation for the type of polymer to use and the type of mobility control agent to apply. The use of polymer flooding is as a result of its ease of application and its cost effectiveness. When selecting the mobility control agent and the polymer to use, it is important to consider the conditions of the oil reservoirs, mainly the temperatures in order to make sure that that are compatible.
Amirian, E., Dejam, M., & Chen, Z. (2018). Performance forecasting for polymer flooding in heavy oil reservoirs. Fuel, 216, 83-100.
Clarke, A., Howe, A. M., Mitchell, J., Staniland, J., & Hawkes, L. A. (2016). How viscoelastic-polymer flooding enhances displacement efficiency. SPE Journal, 21(03), 675-687.
Seright, R. (2010). Potential for polymer flooding reservoirs with viscous oils. SPE Reservoir Evaluation & Engineering, 13(04), 730-740.
Shah, D. O. (Ed.). (2012). Improved oil recovery by surfactant and polymer flooding. Elsevier.
Sheng, J. J., Leonhardt, B., & Azri, N. (2015). Status of polymer-flooding technology. Journal of Canadian Petroleum Technology, 54(02), 116-126.
Unsal, E., Ten Berge, A. B. G. M., & Wever, D. A. Z. (2018). Low salinity polymer flooding: Lower polymer retention and improved injectivity. Journal of Petroleum Science and Engineering, 163, 671-682.