With the price of crude oil at US $85/bbl and higher, financial incentives are feeding a renewed and growing interest in using EOR methods to access trapped oil in mature fields. While much of the oil has been recovered, experts estimate that more than 60% of the usable oil remains in the ground after primary and secondary recovery attempts. Hundreds of thousands of wells are sited on top of this oil but are unable to bring it up.
This “residual” oil could amount to 1 Tbbl to 4 Tbbl worldwide, with more than 380 Bbbl in the US alone. However, with growing environmental concerns and tightening regulations, many of the traditional EOR methods are no longer viable. Thus, new techniques are sought that can effectively and economically recover this oil with less impact on local environments.
One approach showing great promise is the enhancement of existing chemical or synthetic surfactant formulations with natural green, renewable, and affordable biosurfactants called rhamnolipids. American Green Agricultural and Environmental (AGAE) Technologies LLC, a biotech firm headquartered in Corvallis, Ore., has developed technologies to produce high-quality and high-purity rhamnolipids in industrial quantities for just such a purpose.
In addition to producing user-friendly and cost-effective rhamnolipids, AGAE Technologies investigates EOR surfactant formulations that are enhanced by the addition of rhamnolipids. Low concentrations of rhamnolipids can lead to a significant reduction in the interfacial surface tension (IFT) between water and oil trapped in diverse reservoir matrices. Low IFT greatly facilitates recovery of hard-to-extract oil. AGAE also works with remediation experts to develop more effective remediation products that include rhamnolipid biosurfactants.
Benefits of rhamnolipids
AGAE’s findings show that not only do the new rhamnolipid-containing formulations bring down critical IFTs to extremely low levels but also that the IFT effect can be accomplished using very low concentrations of rhamnolipids and smaller amounts of chemical surfactants. These results are significant on several levels. First, significant cost savings can be achieved for surfactant-based oil recovery since the amount of required surfactants can be reduced by very low concentrations of rhamnolipids. This means less surfactant must be purchased and transported to recovery sites.
Second, the environmental impact of recovery will be diminished by the use of rhamnolipids and less chemical surfactant product, as most chemical surfactants are toxic to the environment. Rhamnolipids, on the other hand, are earth-friendly and nontoxic. In addition, by using less chemical surfactant, there will be less post-recovery chemical surfactant needing disposal.
Third, rhamnolipids used for recovery actually can help remediate oil spillage and contamination after recovery because the presence increases the bioavailability and mobility of petroleum hydrocarbons and acceler- ates the natural endogenous microbial-based degradation, both in situ and ex situ.
How rhamnolipids work
Surfactants are detergent-like, surface-active agents that work in the boundary or interface between two immiscible substances to lower IFTs. In the case of oil and water, this interface is the thin layer between the water and the oil. Each surfactant molecule has a hydrophilic, or water-loving, head that is attracted to water molecules and a hydrophobic, or water-hating, tail that repels water and attaches itself to the crude oil molecules.
These complementary chemistries loosen the grip of the reservoir matrix on the oil and allow a temporary interaction with water to sweep the hydrocarbons toward an extraction point. Most surfactants, however, are of petroleum origin and synthetically produced and show limited effectiveness in extreme conditions.
Rhamnolipid biosurfactants, in contrast, are glycolipids produced naturally in the earth by the bacterium Pseudomonas aeruginosa, which is commonly found in contaminated soil. These exhibit higher selectivity and specific activity in extremes of pH, salinity, and temperature than most chemical surfactants. For these reasons, scientists have long been interested in using rhamnolipids as “green” replacements for chemical or synthetic surfactants.
Rhamnolipids from AGAE are produced from renewable feedstock and can be produced in virtually unlimited quantities. Due to excellent surfactant activity, rhamnolipids can be used in very low concentrations and in extreme conditions. In addition, rhamnolipids are biodegradable and nontoxic, properties that make them more environmentally compatible than most chemical surfactants.
Because of the superior ability to enhance the breakdown over time of less soluble or completely insoluble hydrocarbons in the environment, rhamnolipids have been of particular interest to scientists and engineers involved in the oil industry. In fact, rhamnolipids have been studied for more than 60 years, but only recent breakthroughs have made large-scale quantities of rhamnolipids available for commercial use.
Studies in the scientific literature have demonstrated that rhamnolipids are effective surfactants for improving oil recovery, remediation, sludge removal, tank cleaning, and pipeline flow. In all of these studies, rhamnolipids have been consistently effective at increasing the mobility and bioavailability of water-insoluble petroleum hydrocarbons. As natural surfactants produced by soil bacteria that take up and use petroleum hydrocarbons for growth, rhamnolipids seem to be tailor-made for mobilizing oil components.
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