Asphaltenes extracted from seven different crude oils
representing
different geological formations from around the globe were analyzed
using the Raman spectroscopic technique. Each spectrum is fitted with
four main peaks using the Gaussian function. On the basis of D1 and
G bands of the Raman spectrum, asphaltene indicated an ordered structure
with the presence of boundary defected edges. The average aromatic
sheet size of the asphaltene molecules is estimated within the range
of 1.52–1.88 nm, which represents approximately seven to eight
aromatic fused rings. This estimation is based on the integrated intensity
of D1 and G bands, as proposed by Tunistra and Koenig. The results
here are in perfect agreement with so many other used techniques and
indicate the potential applicability of Raman measurements to determine
the average aromatic ring size and its boundary.
Carbonate rock reservoirs comprise approximately 60% of the world's oil and gas reserves. Complex flow mechanisms and strong adsorption of crude oil on carbonate formation surfaces can reduce hydrocarbon recovery of an oil-wet carbonate reservoir to as low as 10%. Low salinity waterflooding (LSW) has been confirmed as a promising technique to improve the oil recovery factor. However, the principal mechanism underpinning this recovery method is not fully understood, which poses a challenge toward designing the optimal salinity and ionic composition of any injection solution. In general, it is believed that there is more than one mechanism involved in LSW of carbonates; even though wettability alteration toward a more desirable state for oil to be recovered could be the main cause during LSW, how this alteration happens is still the subject of debate. This paper reviews different working conditions of LSW, previous studies, and field observations, alongside the proposed interfacial mechanisms which affect the colloidal interactions at oil-rock-brine interfaces. This paper provides a comprehensive review of studies on LSW in carbonate formation and further analyzes the latest achievements of LSW application in carbonates, which helps to better understand the challenges involved in these complicated multicomponent systems and potentially benefits the oil production industry.
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