Microbial Enhanced Oil Recovery by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9789811654657
Publisher: Springer Singapore

2.1 Properties of Crude Oil

Petroleum is a naturally occurring, complex organic mixture, comprising numerous components which can be mainly classified into the following types: alkanes (paraffins), cycloalkanes (naphthenes), aromatics, and more complex asphaltenes and resins. Crude oil is usually categorized into bitumens, heavy oils, medium oil and light oils based on American Petroleum Institute (API) gravity (Santos et al. 2014). Heavy crude oils are well-defined as liquid petroleum possessing 10–22.3° API gravity or >100 mPas viscosity in normal reservoir environments. Medium crude oil possesses API gravity of 22.3–31.1° and 33.4–100 mPas viscosity; light oil has an API gravity of >31° and viscosity <33.4 mPas (Zhang et al. 2020a). The sequential degradation usually occurs following the trend of hydrocarbon susceptibility to bacterial degradation from light to heavy chain contents. The degradation rates of aliphatic hydrocarbons were established to be higher than aromatic hydrocarbons, which can be expressed in this order: aliphatic (linear > branched) > light aromatic (mono aromatics) > cycloalkane > heavy aromatic (substituted or poly aromatics) > asphaltenes and resins (Sharma and Pandey 2020; Van Hamme et al. 2003).

MEOR technology was implemented mostly in the light conventional oil reserves largely in the USA, Russia and China from 1980 to 2010 (Belyaev et al. 2004; Youssef et al. 2009). But relatively less MEOR work has been done in heavy crude oil (density of 920–1000 kg/m3) reservoirs. The difference between heavy crude oil and traditional conventional oil are mainly high density, more complex composition possessing increased asphaltenes, resins, sulfur, nitrogen, and metal-containing compounds as well as low gas content and low hydrogen/carbon ratio. Heavy oil reservoirs can store about seven times more than conventional oil reservoirs (Leon and Kumar 2005). The largest heavy oil reservoir is located at the Orinoco oil belt of Venezuela. There are a number of heavy oil fields in Oman, where crude oil recovery is complex and expensive because of its high viscosity (Leon and Kumar 2005). The viscosity reduction of heavy oil facilitates improving oil retrieval from a reservoir due to improving the flow behaviour and minimizing the pressure drop (Santos et al. 2014). Different physical methods like heating and dilution are employed for this purpose (Santos et al. 2014).

The reduction in viscosity is also achieved majorly by two microbial mechanisms: either bioconversion of heavy into light oil fractions or by the production of microbial metabolites (e.g., biosurfactants) that modify the physical attributes of the oil, such as lowering its IFT. Several microbial isolates and produced enzymes contribute to the degradation of saturate and aromatic aerobically or anaerobically (Mbadinga et al. 2011; Nie et al. 2014; Rojo 2009; Widdel and Rabus 2001). Indigenous microflora can improve the fluidity of heavy crude oil by altering its high viscosity and subsequently forming lighter oil components (Pineda-Flores and Mesta-Howard 2001). Oil viscosity can also be reduced by produced CO2 gas (a byproduct of microbial metabolic activity), which creates pressure within the reservoir and push the crude oil upwards by fractional degradation of the large molecular components of crude oil. The produced biomass gathers between the oil and the well-rock surface and displaces

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