EOR, also known as tertiary recovery, is the implementation of various techniques for increasing the amount of oil that can be extracted from an oil field. Typically 30 to 60 percent of the reservoir’s original oil can be extracted with EOR, compared with only 20 to 40 percent using primary and secondary recovery.
What are the EOR techniques?
- Water Flood / Polymer Flood
- Gas Injection
- Chemical Injection
- Thermal Recovery
GLE has extensive experience designing and installing water floods, polymer floods, and gas injection for enhanced oil recovery.
GLE has an extensive history designing and installing water flood facilities. Water flood is generally implemented in mature operating areas where water production rates can exceed 90 percent water by volume. Water is recovered from the owner’s production and re-injected into the formation. This re-injected water serves to replace the voidage caused by previous production and to return reservoir pressures to their previous level. This in turn drives increased oil recovery.
Produced water is separated from oil production in a series of equipment which may include large, low pressure separator vessels, heater-treaters and production tanks. Design and selection of the separation systems relies on an understanding of the characteristics of the field production, and the interaction between the produced water and oil emulsion. GLE has successfully designed these systems for a both heavy oil and lighter, more conventional production.
Polymer flooding is an enhancement of a water flood system whereby the viscosity of the produced water is significantly increased via mixing with a water-soluble polymer product, typically in powder form. The viscous, non-Newtonian water mixture is able to more effectively sweep the formation, and yield higher oil recoveries.
Polymer flooding largely follows the same process as basic water flooding, however it involves an additional step – polymer mix-down – which occurs prior to pressurization. Prior to mix-down it is extremely important to have very clean water from a standpoint of both oil and solids content, especially solids in the form of iron sulfides or iron oxides. The mix-down is then a two-stage process which results in a consistency polymer-water mixture. In the first stage, specially designed “slicer” units ensure that polymer is mixed with the water into an extremely viscous slurry. The second stage of mix-down involves ‘aging’ the polymer (allowing sufficient time and agitation for it to properly hydrate) before further blending to the desired injection viscosity.
Polymer flooding involves an additional set of challenges which GLE is equipped to deal with through the specialized equipment necessary and experience/expertise of our personnel.
High Viscosity Design
The process of polymer mix-down involves handling of extremely viscous fluids and slurries. Rotating equipment and piping design must consider the challenges of moving highly viscous non-Newtonian product. This is critical to equipment lifespan and system operability.
Iron and Iron Oxides Formation
Produced water often contains ionic iron. When the water is exposed to oxygen (as is possible during mix-down) iron oxides may form. These iron oxides can build up in piping and cause injection plugging. Process designs must ensure that oxygen ingress does not occur during the mix-down process. Iron content in produced water also impacts the solubility of the polymer powder. In cases of high iron content, steps may be required to remove these impurities. Several technologies are available for this purpose.
Increased viscosity in the water polymer mixture is caused by the length of the polymer molecular chains. As such this process is very sensitive to polymer breakdown via mechanical shearing. Care must be taken to select the right pumps, mixers, and pressure control devices for this service.
After a sustained period of polymer injection, polymer will begin to return with production. It is imperative to investigate the design of existing facilities and ensure that polymer received in oil processing equipment will not cause problems. Heat exchangers as well as heated tanks and vessels are particularly at risk, as polymer has a tendency to coat high temperature surfaces, leading to premature failure. Early identification of at risk equipment is critical to project success.
Gas injection, also known as miscible flooding, introduced miscible gases into the reservoir to enhance oil recovery. The gas maintains reservoir pressure and improves oil displacement because the interfacial tension between oil and water is reduced, thus improving displacement efficiency. Gases used include CO2, Nitrogen, and Liquefied Natural Gas (LNG). CO2 is the most commonly used because it reduces the oil viscosity and is less expensive than LNG.
A slug of gas, typically CO2 is injected into the reservoir, followed by water. This process is repeated multiple times to increase the amount of oil recovery. Oil recovery is increased due to the injected CO2 and oil mixing and then being pushed by water. WAG oil recovery is typically higher than that of basic water injection.