This will be done by developing new correlations for refractive index and colloidal instability index (CII) in terms of crude oil density. Petroleum fluid or crude oil can be divided into two, which are hydrocarbons and non-hydrocarbons, but non-hydrocarbons contribute only a small portion of the mixture. In the oil field, asphalt is known to block surface facilities, flow lines, and subsurface formations.
Additionally, they alter the wetting properties of mineral surfaces within the reservoir, disrupting oil recovery productivity. Asphaltene deposition is one of the endless problems that happen in the industry that can cause major operational obstacles. Almost all oil and gas companies these days face further challenges for both environment and ultra-environment in the exploration, development and production phases.
If this were to happen, it would adversely affect the production and ultimately the economics of the project. In this way, later it is basic to include asphalt declaration capability in the configuration phase itself and have a reliable asphalt framework prediction.
Problem Statement
Despite much study that has been done to solve this problem, there are still disadvantages in understanding the mechanism (Andersen and Speight, 1999). There are several properties that must be considered to know asphaltene stability in crude oil. Therefore, this paper focuses on the study of refractive index (RI) and colloidal instability index (CII) in which both RI and CII are used as an indicator for asphaltene stability in order to improve current available research.
Moreover, the production of liquid in these areas is under great pressure and temperature and regularly causes the deposition of organic solids such as hydrates, asphaltenes and waxes. In addition, expectations of incipient asphaltene flocculation dictated by liquid phase laboratory studies do not significantly infer that deposition of the asphaltene will occur under flow conditions. According to research by Chamkalani (2012), a new correlation of refractive index has been obtained based on correlation by Fan et al. 2002), showing the better accuracy.
On the other hand, another screening criterion to consider is colloidal instability index (CII). In this research work, efforts will be made to develop the asphaltene deposition prediction correlation that can be simulated with appropriate computer software and then validated and compared with available literature data or previous research.
Objectives
The estimation of ∆RI and colloidal instability index (CII) at 20°C and pressure at ambient (1 atm). Measure CII and RI as a function of density (ρ) of the crude oil sample not the thermodynamic model at specific temperature and pressure. Data analysis will be done instead of conducting any experiment to obtain data to develop correlation.
Measure only ΔRI and CII as screening criteria to assess asphaltene stability in the crude oil sample.
Relevancy and Feasibility of the Project
LITERATURE REVIEW
- Flow Assurance
- Fluid compositional characterization
- Phase Behaviour of Asphaltene
- Onset Point
- Flocculation Onset Point
- Asphaltene Onset Point
- Colloidal Instability Index (CII)
- Refractive Index (RI)
- Research Methodology
Buriro (2012) expressed that by subjecting the crude oil to SARA analysis, the colloidal instability index can be identified. The step involves saturating the crude oil with pentane, heptane and hexane, which are n-alkanes. The addition of n-alkanes would disrupt the thermodynamic colloidal equilibrium structure of the asphaltene-resin bond and this would cause the asphaltene to begin to agglomerate together and form precipitants.
It should be noted that the delicate balance between the heaviest and lightest fractions of petroleum affects the solubility of asphaltenes. The volume fraction of light components in crude oil increases as the pressure decreases. In general, an increase in temperature affects the aggregation of asphaltenes by decreasing the solvation force of liquids.
In addition, the amount and type of solvent added to crude oil plays an important role in estimating the amount of deposited asphaltene (Khanifar et al., 2011). In both the petroleum and refining industries, asphaltene phase behavior is a very important thing to understand given the ability of asphaltene to phase aggregate and phase with changes in fluid composition, pressure, and temperature. The term is characterized as the potential of colloidal particles to aggregate or flocculate under any conditions, including changes in composition, temperature, and pressure.
If the value of CII is above 0.9, the crude oil is considered unstable and asphaltene deposition may occur. Whereas if the value of CII is less than 0.7 then the crude oil is said to be stable. 2003) state that by using the refractive index of crude oil, the presence of asphaltene and the stability of crude oil can be easily determined.
When precipitant for example n-heptane is added to the crude oil, a point will be reached when the asphaltene precipitation will be produced, and due to the non-flammable nature of the asphaltene, the refractive index of the crude oil will gradually decrease after the addition of the precipitant (Karthighaibalan, 2014). Therefore, the deviation from linearity observed can be said to be the onset of the asphaltene precipitation. Nevertheless, experiments will not be performed due to the limited time accessible and also due to the unavailability of such equipment to use.
For this study, the relationship between density of the crude oil and RI is carried out. Accumulating literature data and running the simulation of the process and comparing it with current research results.
RESULT AND DISCUSSION
Refractive Index (RI)
Correlation between Refractive Index and SARA Fraction
RI values obtained from experiment are compared with RI calculated by Fan et al.
RI vs Saturate
RI vs Aromatic
RI vs Resin
Based on Figures 4.2 to Figures 4.5, the graph shows that the RI from the experimental data gives the same trend line as the RI obtained from Fan et al.
RI vs Asphaltene
Correlation between Density and Refractive Index
This section shows the relationship between RI and CII values with crude oil density as a parameter. Since the density data of Dulang, Tapis, Dubai and Miri samples are not available, the density value of these samples has to be calculated by correlation. The density of Dulang, Tapis, Miri and Dubai samples is determined and shown in Table 4.7.
The relationship between RI from experimental data and density is plotted in Figure 4.6 so that a new correlation can develop. Using the new correlation, a new set of RI is calculated and the results are compared with experimental RI and RI obtained from Fan et al.
RI vs Density
Correlation between Density and Asphaltene Onset Precipitation (P RI )
Since the RI from the new correlation is already obtained, the calculation for the new ∆RI can be done. From the new set of ∆RI, the data will then be compared with the ∆RI that was obtained by Fan et al. The index of refraction in the rainfall onset data is taken from the previous study of Karthighaibalan (2014).
Karthighaibalan presented the measurement of PRI by plotting a graph of RI against crude oil volume percentage. PRI is recognized by a linear line, where deviation from linearity indicates asphaltene excretion. To develop a correlation linking the two parameters, a plot of PRI versus density should be plotted.
Then the PRI values are used to measure ∆RI by using RI from the new correlation, RI calculated from experimental data, and also RI obtained from Fan et al.
PRI vs Density
RI vs PRI
Correlation between Density and Colloidal Instability Index
RI Comparison
For this section, the same procedure is used to determine the correlation between density and RI. After a new correlation has been determined, a new set of CII is obtained using the new correlation. The new correlation using crude oil density as a parameter is applicable at a standard pressure and temperature of 20°C.
CII vs Density
It is clear from Figure 4.12 that the CII obtained from the proposed correlation is almost the same as the experimental data.
CONCLUSIONS AND RECOMMENDATIONS
Conclusion
In summary, a background study on asphaltene deposition and an intensive review of previous and literature has been performed with the specific end goal of highlighting the need to perform correlations to predict asphaltene deposition. This study would greatly benefit the general public as the deposition of liquid solid hydrocarbons including wax, hydrate and asphaltene to interrupt the production flow system is currently at a peak. Numerous studies are being conducted to reduce the rate of asphaltene deposition and many correlations have emerged.
For this study, a data analysis methodology will be taken due to the time constraint and the inaccessibility of the supplies to conduct the experiment. With the schedule of the undertaking outlined, ideally this project will be executed and completed smoothly and on time.
Crude oil polar chemical composition derived by FT− ICR mass spectrometry accounts for asphaltene inhibitor specificity.
APPENDIX
