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The below mentioned article provides notes on microbial enhanced oil recovery (MEOR).
Microbial Enhanced Oil Recovery is the use of microorganisms to retrieve additional oil from existing wells, thereby enhancing the petroleum production of an oil reservoir.
In this technique, selected natural microorganisms are introduced into oil wells to produce harmless by-products, such as slippery natural substances or gases, all of which help propel oil out of the well. Because these processes help to mobilise the oil and facilitate oil flow, they allow a greater amount to be recovered from the well.
MEOR is used in the third phase of oil recovery from a well, known as tertiary oil recovery.
Recovering oil usually requires two to three stages, which are briefly described as follows:
i. Primary Recovery:
12% to 15% of the oil in the well is recovered without the need to introduce other substances into the well.
ii. Secondary Recovery:
The oil well is flooded with water or other substances to drive out an additional 15% to 20% more oil from the well.
iii. Tertiary Recovery:
This stage may be accomplished through several different methods, including MEOR, to additionally recover up to 11% more oil from the well.
The microorganisms used in MEOR can be applied to a single oil well or to an entire oil reservoir. They need certain conditions to survive, so nutrients and oxygen are often introduced into the well at the same time. MEOR also requires that water be present.
Microorganisms grow between the oil and the well’s rock surface to enhance oil recovery by the following methods:
Reduction of oil viscosity:
Oil is a thick fluid that is quite viscous, meaning that it does not flow easily. Microorganisms help break down the molecular structure of crude oil, making it more fluid and easier to recover from the well.
Production of carbon dioxide gas:
As a by-product of metabolism, microorganisms produce carbon dioxide gas. Over time, this gas accumulates and displaces the oil in the well, driving it up and out of the ground.
Production of biomass:
When microorganisms metabolise the nutrients they need for survival, they produce organic biomass as a by-product. This biomass accumulates between the oil and the rock surface of the well, physically displacing the oil and making it easier to recover from the well.
Selective plugging:
Some microorganisms secrete slimy substances called exopolysaccharides to protect themselves from drying out or falling prey to other organisms. This substance helps bacteria plug the pores found in the rocks of the well so that oil may move past rock surfaces more easily. Blocking rock pores to facilitate the movement of oil is known as selective plugging.
Production of biosurfactants:
Microorganisms produce slippery substances called surfactants as they breakdown oil. Because they are naturally produced by biological microorganisms, they are referred to as biosurfactants. Biosurfactants act like slippery detergents, helping the oil move more freely away from rocks and crevices so that it may travel more easily out of the well.
MEOR is a direct application of biotechnology. It uses biological materials, such as bacteria, microorganisms, and their products of metabolism to facilitate the movement of oil out of a well, thereby enhancing oil recovery.
Other applications of biotechnology in MEOR include genetic engineering techniques and recombinant DNA technology, which are used to develop strains of bacteria with improved oil recovery traits. By inserting genes from one type of bacteria into another, scientists may combine two desirable genetic traits into one microorganism.
For example, the temperature within an oil well is often too high for most microorganisms to survive. By inserting a gene that codes for a bacteria’s ability to aid oil recovery into the genome of an existing bacteria that can survive under high temperatures, scientists may produce microorganisms that can both survive the heat of an oil well and also help retrieve oil.
On their own, each bacterium lacks a trait necessary for oil recovery operations, but when combined through genetic engineering, the bacteria become integral to MEOR.
The environmental conditions in an oil well make it very difficult for bacteria: to survive, and those that do often have a decreased ability to carry out the chemical processes needed to enhance oil recovery. Researchers are working to create strains of bacteria that are better able to survive such harsh conditions but still retain the ability to carry out the chemistry needed for MEOR.
Genetic engineering is being used to develop microorganisms that can not only live in the high temperatures of an oil well, but can also subsist on inexpensive nutrients, remain chemically active, and produce substantial amounts of biosurfactants. Some researchers are developing bacteria that can be grown on inexpensive agricultural waste material, which is abundant in supply and is environmentally friendly.
As MEOR reduces or eliminates the need to use harsh chemicals during oil drilling, it is an environmentally compatible method of carrying out tertiary oil recovery. MEOR will become increasingly economically feasible as genetic engineering develops more effective microbial bacteria that may subsist on inexpensive and abundant nutrients.
Methods for developing and growing MEOR bacteria are improving, thereby lowering production costs and making it a more attractive alternative to traditional chemical methods of tertiary oil recovery.