Recovery of Heavy Oil from Unconventional Source (Oil Sands) with Design Steam Injection System
Abstract
The use of steam ranging from 100oC to 280oC in extracting and producing oil from unconventional reservoir (oil sand) was investigated. Core samples were obtained from Edo state in Nigeria. An oil sand laboratory reservoir model was used to investigate technical feasibility of the injection of steam as an enhanced oil recovery agent for tight hydrocarbon reservoirs and the effect of temperature on the petrophysical properties such as porosity and permeability of oil sand reservoir. Steam was injected into the oil sand reservoir to recover bitumen at different temperatures ranging from 100oC to 280oC. Results showed that as the temperature of the steam increased, more hydrocarbon (bitumen) was recovered due to the reduction of its viscosity and oil-water interfacial tension. The core experiment indicates that the porosity and permeability of a tight formation such as that of oil sand at ambient temperature is 0.038 and 0.007MD respectively. An increase in reservoir temperature by the injection of steam altered the petrophysical properties (porosity and permeability) of the reservoir. Samples collected and analyzed after recovery showed a decrease in porosity and an increase in the permeability of the formation. Results indicate that the viscosity of bitumen decreased with an increasing temperature. Maximum recovery of bitumen was obtained at 280oC. The injection of steam at temperature of 300oC and above, would produce more bitumen at industrial scale and could be refined and upgraded to liquid fuels to supplement the drastic reduction of the conventional oil. The results obtained from this work showed good agreement with data from existing data.
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Introduction
Oil sands are either loose sands or partially consolidated standstone containing a naturally occurring mixture of sand, clay and water, saturated with a dense and extremely viscous form of petroleum technically referred to as bitumen (or colloquially as tar due to its superficially similar appearance)(Ezra, 2011). crude bitumen is a thick, sticky form of crude oil, so heavy and viscous (thick) that will not flow unless heated or diluted with higher hydrocarbon such as light crude oil or natural gas condensate. At room temperature, it is much like cold molasses (Michael, 2009). The presence of water has long been considered to be an integral part of oil sands structure, although there is some conjuncture as to its extract nature. Early Cryotransmission election microscopy (TEM) studies provided evidence that water in natural oil sands exists as water-in-oil (w/o) emulsion (Zajic et al, 1981). On the other hand, a model of oil sands with a layer of water (approximately 10mm thick) separating bitumen from the sand surface has been proposed(Takumura, 1982). It is also necessary that the oil composition may change during thermal production of bitumen with steam, for example a common observation is that the produced oil is lighter than the original, which is believed to be a consequence of in situ upgrading processes (Montgomery et al., 2014).
Natural bitumen is oil having a viscosity greater than 10,000 centipoises under reservoir conditions and an AP1 gravity of less than 100 API (Hoffman, 2009). The unconventional formations may be as porous as other sedimentary reservoir rocks, their extremely small pore sizes and lack of permeability make them relatively resistant to hydrocarbons flow. The lack of permeability means that the oil and gas typically remain in the source rock unless natural or artificial fractures occur.
Conclusion
A technical feasibility of heavy hydrocarbon bitumen recovery in an oil sands reservoir is evaluated on the laboratory scale and from an unconventional reservoir model. The following conclusions were drawn based on preliminary findings.
The unconventional (oil sands) reservoir (sample from Edo state) is a tight formation with porosity of 0.038 and a permeability of 0.007MD.
The recovery of heavy hydrocarbon (bitumen) with the injection of steam remains challenged by factors such as low permeability and low porosity; however experimental results do indicate that the injection of steam is enhanced oil recovery method based upon encouraging increase in bitumen production obtained in the laboratory.
The increase in the production of bitumen is dependent on an increase in temperature. As the temperature of the steam injected into the reservoir increase, recovery also increases.
The softening and melting points temperature of bitumen are 1100C and 1160C respectively. The higher the temperature, the more bitumen softens, melts and turns into a pumpable slurry as the viscosity reduces.
Oil recovery method based upon encouraging increase in bitumen production obtained in the laboratory.
The increase in the production of bitumen is dependent on an increase in temperature. As the temperature of the steam injected into the reservoir increase, recovery also increases.