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Introduction to Enhanced Oil Recovery Techniques
During primary oil production, the oil from a reservoir is forced up to the surface by the pressure underneath it. When this pressure falls, a secondary production method normally consisting of water flooding is used. Once production from the secondary phase decreases, enhanced oil recovery technology is used to extract some of the remaining oil from the reservoir.
This is another article on oil production and in particular enhanced oil recovery methods that are currently being applied to mature oil wells throughout the world. We begin with a brief overview of current techniques and then examine micellar polymer flooding and microbial EOR techniques.
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Overview of Enhanced Oil Recovery
Enhanced Oil Recovery (EOR) has been used for many years as a means for increasing crude oil production extraction rates, when the primary and secondary production methods have been exhausted.
The process we are going to examine are Micellar Polymer Flooding along with Microbial EOR, both of which reduce the oils viscosity through the use of surfactants (a wetting substance injected into a viscous liquid, lowering its surface tension).
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Enhanced Oil Recovery Using Micellar Polymer Flooding
Micellar polymer is injected into the oil reservoir to reduce the viscous and tacky crude oil's surface tension, thus releasing the oil globules from their grip on the reservoir rock.
There are can be up to five stages in micellar polymer flooding:
This first stage consists of injecting a solution of fresh water into the reservoir, flushing out the reservoir brine. This brine contains sodium, calcium and magnesium ions and, being contaminates, if not removed would impede the action of the micellar surfactant.
2. Micellar Polymer Injection
Micellar is prepared in the form of a slug that can contain numerous chemicals such as the polymer surfactant, sub-surfactant, brine, alcohol and a hydrocarbon in the form of oil. The slug is injected into the reservoir through a specially drilled injection well, spreading slowly through the rock.
3. Surfactant Mobility Enhancement
This is achieved by the injection of a viscosifier; solution of fresh water and polymer which effectively spreads the surfactant mixture through the reservoir rock to achieve maximum coverage.
4. Water Buffer
Fresh water is injected again, but this time it remains in the reservoir, preventing contamination of the slug chemicals from any surviving reservoir brine ions, by acting as a buffer between them.
5. Drive Water
In this the final stage, pressurized water is pumped down the injection well into the reservoir rock. Here it gathers up the now less viscous crude oil, and sweeping it off the rock, forces it towards the production wellhead from where it flows up the production well to the platform.
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Biochemical Enhanced Oil Recovery Process
Cultivation of the Microbes
The microbes can be cultured on the surface in containers until fully established before being injected into the reservoir or, injected into the reservoir to grow in-situ. Either way, they are supplied with nutrients such as sugars and nitrates to promote and maintain fermentation and maturity.
However the in-situ method can be less successful than the surface culture as the immature microbes have to deal with the harsh environment of the reservoir as well as trying to produce the surfactants, so when these are injected a rich mix of nutrients are injected along with them.
The Microbe Process
The process consists of introducing microbes into the crude oil reservoir which ferment in the hydrocarbon.
The microbes secrete a matter which fills the smaller pores and fractures in the sedimentary reservoir rock, making its surface smoother and aiding the oils flow towards the wellhead.
They produce a biosurfactant, which as we know releases the oils surface tension, whilst decreasing its viscosity. The microbes also emit CO2 which increases the pressure within the reservoir adding to the oils increased extraction.