Asphaltene deposition

In part II of the present report the nature and molecular characteristics of asphaltene and wax deposits from petroleum crudes are discussed. The field experiences with asphaltene and wax deposition and their related problems are discussed in part III. In order to predict the phenomena of asphaltene deposition one has to consider the use of the molecular thermodynamics of fluid phase equilibria and the theory of colloidal suspensions. In part IV of this report predictive approaches of the behavior of reservoir fluids and asphaltene depositions are reviewed from a fundamental point of view. This includes correlation and prediction of the effects of temperature, pressure, composition and flow characteristics of the miscible gas and crude on (i) Onset of asphaltene deposition (ii) Mechanism of asphaltene flocculation. The in situ precipitation and flocculation of asphaltene is expected to be quite different from the controlled laboratory experiments. This is primarily due to the multiphase flow through the reservoir porous media, streaming potential effects in pipes and conduits, and the interactions of the precipitates and the other in situ material presnet. In part V of the present report the conclusions are stated and the requirements for the development of successful predictive models for the asphaltene deposition and flocculation are discussed. 

Asphaltene deposition during oil production and processing is a very serious problem in many areas throughout the world. In certain oil fields (12,13,14) there have been wells that, especially at the start of production, would completely cease flowing in a matter of a few days after an initial production rate of up to 3,000 BPD. The economic implications of this problem are tremendous considering the fact that a problem well workover cost could get as high as a quarter of a million... 

Even for reservoirs in which asphaltene deposition was not reported previously during the primary and secondary recovery, it was reported that asphaltene deposits were found in the production tubing during carbon dioxide injection enhanced oil recovery projects (18). 

The downtime, cleaning, and maintenance costs are a sizable factor in the economics of producing a field prone to asphaltene deposition. Considering the trend of the oil industry towards deeper reservoirs, heavier and as a result asphaltic crudes, and the increased utilization of miscible gas injection techniques for recovering oil, the role of asphaltene deposition in the economic development of asphaltene containing oil discoveries will be important and crucial. 

Catalyst bed plugging can arise in a variety of ways, but the overall effect of bed plugging is always the same expensive shutdowns and possibly complete renewal of the expensive catalyst. Thus, the deposition of rust, coke, or metal salts (e.g., sodium chloride) from heavier and dirtier feedstock may all contribute to the plugging of a catalyst bed. Vanadium and nickel may also be deposited onto the surface of the catalyst as well as into the pore system. Asphaltene deposition from residua and heavy oils is also a potential means of bed plugging— coagulation of the asphaltenes becomes appreciable at temperatures above 420°C (790°F) with the formation of hard, coke-like materials on the catalyst. 

Reactor deposit analyses do not reflect compositions consistent with asphaltene deposition the V, Ni, and S values are high., and the LOI value is low. The current authors doubt that the increased readiness of the effluent to precipitate asphaltenes is of relevance at reactor conditions. 

In contrast, asphaltene deposition seems to be a major contributor to vacuum tower fouling in the H-Oil unit. 

Previous work in our laboratory (1) implied that higher recovery efficiency may be achieved through the injection of an extracted resinous component, deasphaltened crude oil slug, prior to the injection of the alkaline phase. Results indicated that improvements in tertiary recovery efficiency did occur. The injection of this extracted resinous crude component aided in recovery by preventing asphaltene deposition, thereby increasing permeability of oil to rock, by forming an oil bank, and again, in-situ emulsification was observed to aid in enhanced recovery. 

Results of our experimentation QJ suggests that the occurrence of permeability reductions during enhanced oil recovery may be avoided and the formation of a continuous oil bank may be initiated and maintained by using a slug of an extracted resinous fraction. These results support the work of Lichaa and Herrera (10,11), where they found that severe permeability reductions due to asphaltene deposition, could be avoided by the injection of a mixture of highly resinous Boscon Crude (29% wt. resin) with a Boscon refined oil. Cooke ( recommended a similar process where a bank of highly acidic crude oil would be injected prior to the injection of the alkaline water for cases where the crude oil acid concentration is low. 

The deasphaltened crude oil slug, extracted resinous component, may have improved tertiary recovery by preventing asphaltene deposition, thereby increasing permeability of oil to rock, by forming an oil bank, or again, in-situ emulsification may have enhanced oil recovery. 

Lichaa, P. M., "Asphaltene Deposition Problem in Venezuelan Crudes—Usage of Asphaltenes in Emulsion Stability". Paper presented at the Canada—Venezuela Oil Sands Symposium 77. Edmonton, Alberta, Canada, May 27 - June 4, 1977. 

Lichaa, P. M. Herrera, L., "Electrical and Other Effects Related to the Formation and Prevention of Asphaltene Deposition Problem in Venezuelan Crudes", SPE/AIME No. 5304. 1975. 

The role of asphaltene deposition in miscible flooding processes is also examined. Experimental data together with coupled equation of state models and Flory-Huggins polymer solution theory have been used to illustrate the effect of various parameters such as solvent type, solvent/oll ratio and pressure on the amount of asphaltene precipitation during addition of solvents to heavy oil. 

Asphaltene Deposits - Hassi Messahoud Field, Algeria,". Pet. Tech., pp. 387-391, April, 1965. 

Lichaa, P. M., "Asphaltene Deposition Problem in Venezuela Crudes - Usage... 

FIGURE 7.7. Asphaltenic deposits found in the heat exchangers. 

In conclusion to this chapter, we would like to point out that the term precipitation, whether used for wax or for asphaltene, is synonymous with thermodynamic equilibrium. Wax and asphaltene deposition, which are more complex, include kinetics and require detailed knowledge of the deposition process and the associated transport phenomena. The topic of deposition is in a very early stage of development and, therefore, is not covered. 

In addition, askarels, unlike oils, do not form asphaltene deposits. This is why manufacturers insist that maintenance on PCB-immersed equipment is unnecessary, so much so that international recommendations do not even provide for any aging tests. 

The formation of the asphaltenes deposit is one of the most studied phenomena in the production and processing of crude oil. Researches are looking increasingly for the improvement about the chemical structure of molecules present in the asphaltene fraction and, consequently understand its behavior in oil. 

The cost associated with the asphaltene deposition during production and refining operations is in the order of billions of dollars a year. For this reason, the prevention or minimization of precipitation of asphaltenes is an important goal for many oil companies (Rogel et al, 2010). 

Almehaideb, R.A. Zekri, A.Y., (2001). Possible Use of Bacteria/Steam to treat Asphaltene Deposition in Carbonate Rocks. European Formation Damage Conference, SPE 11851, 1-11... 

C. Ijogbemeye Oseghale and F. O. Ebhodaghe, (2001). Asphaltene Deposition and Remediation in Crude Oil Production Solubility Technique. Journal of Engineerind and Applied Scinces 6 (4) 258-261,2011... 

Asphaltene Deposition of Viscous Asphaltic Crude Oil-in-Water Emulsions for Pipeline Transportation. Petroleum Science and Technology, 19,425- 435. 

Fig. 3-5. Asphaltene deposit recovered from well (Courtesy BJ Services)...

The purpose of the preflush is to remove organic or inorganic scale from the wellbore tubulars prior to injection of the acid stage. An aromatic solvent, such as xylene, can be used to remove hydrocarbon deposits. For asphaltene deposits, specifically, terpene-based solvent solutions can be quite effective. Circulation of 5%-7.5% HCl downhole is adequate to remove rust and other inorganic scale for rust removal in particular, non-add (nearneutral) removal solutions exist and may be preferable at temperatures of MOT (60°C) and higher. 

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