What Is Heavy Crude Oil?

Heavy crude oil refers to crude oil with a relative density between 0.90 and 1.00 g / cm3. It is generally dark in color, rich in gum and asphaltene, and contains less gasoline than light crude oil and medium crude oil. When the relative density of crude oil is greater than 1.00 g / cm3, it is "extra heavy crude oil". ^{[1] The} content of light ends in heavy crude oil is low, contains no wax or contains little wax, and the content of gum and asphalt is high, generally between 20% and 50% (mass fraction).

According to research, the formation of heavy crude oil is mainly affected by the tectonic uplift in the later period of the basin, which caused the early formation of paleo-reservoirs to rise and approach the surface, which caused the plugging conditions of the ancient reservoirs to suffer varying degrees of damage, resulting in A large amount of light components are lost, and because of surface water oxidation and biodegradation, naphthenes in the reservoir are oxidized to naphthenic acid, aromatic hydrocarbons are oxidized to phenol and aromatic acid; alkane is oxidized to fatty alcohol, fatty ketone, fatty acid, etc. In addition, the content of colloidal and asphaltenes in petroleum will be increased, and the degradation of petroleum by microorganisms will cause some of the hydrocarbons to disappear. The degradation of hydrocarbons will proceed in the following order: n-paraffin, isoparaffin, isoprenoid Alkenes, oligocyclic cycloalkanes, polycyclic aromatic hydrocarbons. Generally speaking, steroids and terpenoids are relatively stable. The combined effect of light component loss, biodegradation and oxidation is the formation of heavy crude oil with high density and high viscosity. The heavy crude oil has a low content of light fractions, contains no wax or contains little wax, and has a high content of gum and asphalt. Generally between 20% and 50% (mass fraction), strong post-transportation transformation can transform crude oil into natural asphalt. ^[2]

There are two methods of extracting heavy crude oil: the vertical steam extraction method and the horizontal cold extraction method.

1. Shaft steam mining method

At first, the heavy-duty crude oil was produced by the cold-shaft method, and the output of a single well was only 200-400 barrels / well · day. Due to low production and high drilling density, it is not economically feasible. So instead, the steam is injected into the vertical shaft alternately, and the heavy oil is heated to reduce the viscosity, so that it flows into the well, and then is pumped out. The recovery rate of this mining method is still low (the output of a single well is only 900-1200 barrels / well · day), which has been rarely used at present. ^[3]

1.Early processing technology

The processing mechanism of heavy crude oil is basically the same as that of oil sands asphalt. Decarbonization or hydrogenation can be used to complete the process of lightening heavy oil and removing various impurities. Constrained by technical and economic conditions, Venezuela's early heavy crude oil upgrading process was mainly based on aquaconversion and coking processes, with less hydrogenation processes, and even exported directly as diluted crude oil. The first batch (600,000 barrels) of heavy crude oil exported from Venezuela to the US Gulf of Mexico in 2001 was made with Mesa crude oil (API = 30) as a diluent, and Zuata heavy crude oil (API = 18) was adjusted to API = 16 Of diluted crude oil. ^[3]

2.Hydrothermal conversion technology

Intevel cooperated with several American companies in the late 1980s to develop and study heavy crude oil processing technology, called hydrothermal conversion process. The development concept of this process is to apply the principle of steam conversion to hydrogen production to the visbreaking process. The hydrothermal conversion test was performed on a 1-barrel / day pilot plant. Table 1 shows the comparison of hydrothermal conversion test results with conventional visbreaking data. ^[3]

3.Oil-soluble double catalyst system

In order to solve the problem of the unstable nature of the residual oil at high conversion rates, an oil-soluble dual catalyst system was developed that can convert water to hydrogen under conventional visbreaking conditions. When a condensation reaction that can generate asphaltenes occurs, The hydrogen transfer mechanism can inhibit the condensation reaction of aromatics, and thus produce a reduced viscosity residue with stable properties. The catalyst system includes two non-precious metal catalyst components: one is a catalyst that promotes hydrolysis to hydrogen and oxygen radicals; the other is a catalyst that promotes the hydrogenation of aromatic radicals to reduce the condensation reaction. The overall effect is to generate small molecules of aromatics, hydrogen radicals and carbon dioxide, effectively stopping the aromatic condensation reaction. ^[3]