Chemical Enhanced Oil Recovery

The recovery of crude oil from the oil reservoir involves three steps of recovery.  They are known as primary, secondary and tertiary recovery methods. The conventional oil recovery methods involved only the first two steps.  Through these steps only forty percent of the oil reserve could be recovered. The tertiary or enhanced oil recovery method is a comparatively recent technique to be introduced in the oil industry.  The main advantage of this new method of oil recovery is that the oil companies can obtain more than sixty percent of the oil inside the well by way of tertiary oil recovery method.  This technique is commonly known as EOR method of oil recovery. 

The three major categories of EOR technique of oil recovery are thermal recovery, gas injection and chemical injection.  Thermal recovery and gas injection are the commonly used techniques in enhanced oil recovery.  Compared to these two methods chemical injection is expensive and is commonly used.  In the United States of America only less than one percent of the oil companies employ chemical injection method for enhanced oil recovery.

Chemical injection method adopted in enhanced oil recovery is also known as oil flooding method.  Chemical injection is a process in which special chemical solutions will be used to inject into the oil well to bring more oil to the surface by reducing the viscosity of the oil trapped inside the oil reservoir rock. These chemicals are used mainly to improve oil recovery, clean blocked perforations and to reduce inhibit corrosion and there by upgrade the quality of crude oil and allow its free flow from the well to the surface. Chemicals can be injected to the oil well continuously without interruption through injections wells so as to attain optimum recovery.  Chemicals can be administered to the production wells also though not continuously.   

The chemicals used for chemical injection are mainly polymers such as polyacrylamide or polysaccharide.  The intention of injecting these chemical substances in to the oil well through injection wells is to improve the sweeping efficiency of oil.  The chemical solutions are injected continuously in to the oil well through injection wells.  These chemical substances improve the mobility of crud oil that is remaining in the oil reservoir after the primary and secondary stages of oil recovery. 

Apart from polymers chemical substances which have the characteristics of a soap or detergent are also used for chemical injection.  Unlike polymers, the function of these chemicals is to reduce the surface tension between oil and water within the oil reservoir.  This process will in turn enhance the free flow of oil there by making it easier to bring the oil to the surface by mechanical methods like using pumps. 

Chemical injection method involved in enhanced oil recovery is also known as chemical flooding for the reason that in this method chemicals are injected to the oil reservoir through injection wells continuously without any interruption.  The general procedure in injection of chemicals involves primary injection of low saline water followed by the chemical solution and finally by plain water.  The primary injection of low saline water is known as preflush and the injection of plain water at the final stage is known as mobility buffer.  The entire process is known as chemical flooding or chemical injection.