Basic physical properties and characteristics of oil and oil products.

Density- one of the main physical parameters and quality characteristics of raw and commercial oil... The relative density of oil usually ranges from 0.83 to 0.96.

Knowing the density of oil, we can draw some conclusions about its chemical and factional composition, that is, to assume which components prevail in the mixture, which in turn affects raw material cost... The lighter the oil, the higher the content of the most valuable light fractions in it, the less effort is required for its processing, and, accordingly, the more valuable it is. A prominent representative of light oil is the American grade WTI, which is called in another way - Light Sweet, which translated from English means "light and sweet" (sweet in this case means low-sulfur). Some types of light oils, for example, the so-called "white oils", have a density of only 0.75 - 0.77.

In contrast, heavy oil contains a large amount of high molecular weight impurities, such as, resinous asphaltene substances, which makes processing quite resource-intensive. Therefore, heavy grades of oil are much cheaper than light grades. Such oils have a density close to unity.

Thus, density is an essential characteristic of every oil grades.

In addition, the density of oil needs to be known when converting its quantity from volumetric units to mass units, and vice versa, which is necessary during acceptance, accounting and shipment at refineries and during transportation. This takes into account the ambient temperature, as well as the climatic zone, season, etc. Consequently, data on the density of oil is necessary not only for calculating technological processes, but also for economic planning.

Density as a physical quantity

Density is the ratio of body weight to the volume it occupies.

The value calculated by this formula is also called absolute density... In the SI system, this value is expressed in kg / m 3.

In practice, however, most often they resort to the definition of the so-called relative density- the ratio of the absolute density of the investigated substance to the absolute density of any standard at a certain temperature.

In most cases, including in the oil industry, distilled water is used as a reference. Measurements of oil samples are usually carried out at 20 ° C, and accordingly, the obtained values ​​are referred to the density of distilled water at 20 ° C, or at 4 ° C (the absolute density of water at a given temperature is equal to unity).

It was found that the dependence of the density of most oils and petroleum products on temperature is linear (in the temperature range 0-50 ° C) and is expressed by the following formula:

Based on this dependence, you can calculate the density of oil at any temperature, knowing its density at a different temperature. In particular, a fairly common characteristic of oil is its relative density at 20 ° C relative to water at 4 ° C:

API gravity is calculated from the relative gravity measured at a standard temperature of 15.6 ° C (60 ° F) using the formula:

To calculate the relative density, knowing the density value in API degrees, you can use the inverse formula:

Correspondence table of API degrees and relative density of oil ( at a temperature of 15.6 ° C):

What determines the density of oil

The density of oils depends on many factors: primarily on the fractional and chemical composition, as well as on the content of dissolved gases, conditions of formation, etc.

In particular, the deeper the oil deposits are, the lighter it is. The fact is that the deeper the oil lies, the older it is, and the more hydrocarbons with minimal free energy, such as alkanes, accumulate in it.

Sometimes there are exceptions to this rule, which, however, are explained by secondary phenomena, for example, the migration of oil into the upper layers.

Publication date 01/09/2013 13:37

Modern requirements for quality oil are high enough. Therefore, its production constantly requires perfection so that petroleum products meet all standards and norms. The respective organizations exercise control over the production and the final product.

The standardization system, which has been developed by the state, is the standard by which all manufacturers are equal. Compliance with its terms is mandatory for everyone.

Oil and other petroleum products is a liquid mixture with a complex composition of hydrocarbon compounds and closely boiling hydrocarbons, as well as heteroatoms of oxygen, nitrogen, sulfur, some metals and acids.

One of the quality indicators is oil density... This is the amount of resting mass per unit volume. The density of oil products and its determination is a prerequisite for easier calculation of their mass quantity. This is due to the fact that accounting for oil in terms of volume is not very convenient, because this indicator can change depending on temperature changes.

The density of oil is measured in kilograms per cubic meter. You can easily determine the mass by knowing the indicators of volume and density. The mass, in contrast to the volume, does not depend on the temperature of the product.

Usually, an indicator such as the relative oil density... It is defined as the ratio of the mass of oil to the mass of pure water, which is taken in the same volume, having a temperature of + 4 °. This temperature level was not chosen by chance. In this case, water has the highest density, which is 1000 kilograms per cubic meter. In order to determine the relative density of oil, its temperature must be + 20 °. In this case, it can be from 0.7 to 1.07 kilograms per cubic meter.

There are other physical properties of oil.

Specific gravity is the weight that one unit of volume has. In other words, it is the force with which one unit of the volume of this substance is attracted to the earth. That is, it is density times the acceleration of gravity.

Another concept is relative specific gravity. The value of this indicator is equal to the numerical value that the relative density has. We use it to calculate this indicator.

Specific gravity and oil density can change their values ​​when the temperature changes. Therefore, in order to calculate the density found at one temperature for the same indicator with other temperature data, it is necessary to take into account the corrections for density changes depending on temperature changes.

The density of oil, calculated in practice, is considered additive. This is due to the fact that this indicator can be obtained as an average for several oil products.

Each region of oil production is characterized by its own physical properties of this product. So, for example, the density of oil in the Tyumen region on average ranges from 825 to 900 kilograms per cubic meter.

The study of the physical properties of this product is necessary not only for its rational use for economic purposes and for sale on the world market. Sometimes this is very important in eliminating environmental disasters resulting from the release of oil products into the environment, and allows you to avoid many mistakes.

So, during the liquidation of the accident, attempts are made to eliminate the oil slick by means of arson, without taking into account that the physical characteristics of this product could have changed as a result of interaction with the environment. Therefore, these circumstances should be taken into account in cases of cleaning water surfaces. This is a very important factor that should not be ignored.

0.899, with a staining degree of 7.5 mzh and an acidity of 0.640% bO ,.

Traditionally, Venezuela was the main supplier of boiler fuels for the United States, which led to the shallow refining of oil at most of the refineries (the output of fuel oil is over 50% for oil). The proportion of destructive processes (thermal and catalytic cracking) as of January 1, 1980 was 10.6%, and the total of secondary processes was 34.7%.

Oil Specific gravity at 15 ° С Pour point, С Autoignition temperature, С

Let us assume that the set X describes the quality of oil (specific gravity), and the set Y describes the quality of oil products. The elements of the sets Xi Y are quantified as follows

Oil yield,% Specific gravity. Sulfur content without purification,% Height of non-smoking flame, mm

In terms of pour point, naturally occurring oils are extremely diverse. So, for example, the Grozny paraffinic oil with a specific gravity of 0.838 solidifies already at the time when the Grozny

As you know, evaporation is a process of vaporization that occurs only from the surface of a liquid under any temperature conditions. During the evaporation of oils and oil products, as in the case of other complex mixtures, of course, the lightest parts of them evaporate first. In this case, however, depending on the conditions in which evaporation occurs, more or less significant amounts of heavier components are also entrained, even if their boiling point was much different from the temperature conditions of evaporation. To illustrate this phenomenon, the following experiment (Mabury) oil with a specific gravity of 0.815 is interesting, which gave 42% of the residue above 300 ° during distillation, was left in a flat cup with a strong air stream after a month, its specific gravity rose to 0.862, while the remainder left only 33.3 % thus, under the indicated conditions, 8.7% of the fractions distilled above 300 ° evaporated without any heating.

For research from a depth of 1400 m, Satskhenis oil was taken from well # 4, the specific gravity of which at a temperature of 10 ° C is 0.792.

The Mid-Continent field, taken as a whole, seems to still be considered the most significant oil field in the world. It includes Ok.t1ahoma, Kansas, North, Central and West Texas, North Louisiana and Mexico. The productive horizons stretch from the Ordovician layers to the Miocene. Mid-continental oils are heavier and contain more sulfur compounds and asphalt substances than Pennsylvanian oils. Their specific gravity varies in the range of 0.810-0.930, the sulfur content is on average about 0.5%. However, oils from West Texas and Arkansas typically have a sulfur content of 1.0 to 1.5%. Most of the oils are paraffinic, so they can easily be used as raw materials for the production of lubricating oils, but since there are paraffinic and naphthenic oils among the oils of this field, the oils of the entire field as a whole can be characterized as mixed base oils.

Typically, the specific gravity of oil is less than 1, that is, oil is lighter than water. The specific gravity of the majority of oils overwhelming it is in the range of 0.750-1,000. However, there are oils, the specific gravity of which is slightly more than 1. Such oils are some Mexican oils with beats. weighing 1,060 and our Gurian oil (Transcaucasia) with beats. weighing 1.038. Oils with a specific gravity of more than 0.900 are called heavy oils.

It is extremely interesting to change the specific weight of oils in the same well in connection with its depth. So, in the Baku region within the same area (Binagada) there is light oil beats. weight 0.790 and heavy oil beats. weight 0.930. In Galicia, next to the oil oud. weight 0.750 there are oil beats. weight 0.950. In Japan, next to oil oud. weight 0.805 there are oils with a specific gravity of 0.988, i.e., close to 1, etc.

Platzeritra Canyon in Southern California, 30 kl1 north of Los Angeles, in the Santa Clara Valley, produced unusually light crude oil, specific gravity 0.740-0.780, from cross-bedded micaceous crystalline shales. One of the wells laid here was producing from 7 to 9 kg per day. It must be thought that oil got into the crystalline shales from the adjacent Tertiary sediments (at a distance of 200-400 m), namely

This table shows that an increase in the specific gravity of oil fractions of various oils boiling within the same range, as a rule, corresponds to an increase in the amount of aromatic hydrocarbons. There are exceptions to this general rule, which depend on the structure of one or another. hydrocarbons that make up this fraction. For example, from the data in the table it follows that with an equal content of naphthenes in the fractions of the Surakhan and Dossor oils and a lower content of aromatics in the fraction of the Surakhan oil, the specific gravity of the latter is higher than that of the Dossor fraction. This is because the aromatic and naphthenic hydrocarbons of the Dossor oil fractions contain longer paraffinic side chains than the corresponding hydrocarbons of the Surakhan oil. Further,

Roughly it can be assumed that each pressure atmosphere when gas dissolves in oil, its specific gravity decreases by 0.0001-0.0002, and the volume increases by 0.1-0.15%. Curves in Fig. 103 (Show how the viscosity of oil changes as a function of the amount of gas dissolved in lei.

In practice, this relationship can be established with the PVT bomb. A typical dependence of density (specific gravity) on temperature and pressure, obtained experimentally for oil with specific gravity Yh = 0.852 zj M and with a gas factor Г = 100 is shown in Fig. 4.

The temperature at the exit from the light cracking furnace is 475-480 °, at the exit from the deep cracking furnace 515-530 °. Below is an approximate installation mode when operating on the no-lugudron of the Tuymazin Devonian oil with a specific gravity of 0.980, which is 33-35% for oil.

Structures 1a and Pa as containing a cyclobutap ring are unlikely and therefore unacceptable, as for the rest of the structures, their presence in the molecules of petroleum resins and asphaltenes is quite possible. As can be seen from the above structures, Hillman and Barnett do not include purely aromatic condensed systems in their schemes, while, as our studies have shown, such structures play a rather large role already in the high-molecular hydrocarbon fraction of oils. The specific gravity of condensed aromatic nuclei, especially bicyclic ones, increases significantly in resins and asphaltenes. Guided by the correct

The appearance in the post-salt deposits of heavy

Specific gravity oil is the ratio of weight to volume

where g is gravitational acceleration, σ is oil density. Specific gravity is not a reference value, as it changes with g at different points on the Earth. Therefore, it is better to consider the oil density, i.e. properties of matter, determined by mass m (physical characteristics of matter) and volume V.

The unit of density with the CGS system is g / cm 3, in SI - kg / m 3.

The density of oil ranges from 0.76 to 0.96 g / cm 3 (T = 20 °) and depends on the ratio of these components. The density of ancient oils is always less than the density of oil from young fields.

An increase in the molecular weight of a hydrocarbon results in an increase in its viscosity. The highest viscosity is possessed by naphthenic carbons, lower - aromatic and paraffinic, non-hard. With increasing pressure, the viscosity increases slightly, and an increase in temperature leads to a significant change in viscosity (it decreases). As the viscosity increases, the compressibility of the oil decreases.

Viscosity– or internal friction - the ability of a liquid to resist the movement of its particles relative to each other. The unit of measure for viscosity is poise (centipoise). For the same oil, the viscosity is different depending on the temperature. Under equal measurement conditions, the viscosity of naphthenic and aromatic oils is higher than that of methane oils.

The specific electrical resistance (p) of oils reaches 10 16 Ohm, the dielectric constant is 2. The speed of seismic waves (V P) is less than in water and varies from 1300 to 1400 m / s. With an increase in density by 0.01 g / cm, the ultrasound speed increases by 7 m / s. Hydrocarbon gases in oil cause changes in physical properties. With an increase in gas (Vp), it decreases by more than 150 m / s.

Natural gases in oil fields mainly consist of methane, more volatile hydrocarbons and small amounts of nitrogen. Dry gases contain 90-99% methane. Almost all gases are stable under normal conditions (0.1 MPa, 20 s), and only pentane easily comes to a liquid state. The relative density of methane in air is 0.554. For dry air, the density is 0.00128 for methane 0.000677. The propagation speed of ultrasound at a temperature of zero degrees and a pressure of 0.1 MPa in dry air is 332 m / s, in methane - 500 m / s, in nitrogen - 338 m / s, in carbon dioxide - 261 m / s, in oxygen - 316 m / s.

Solubility of gases in oil. Any gas has the ability to dissolve in a liquid, and the amount of dissolved gas depends on the composition of the liquid and gas, on pressure, temperature and other soluble substances present in the liquid.

Oil and gas are substances of very similar composition, so their mutual solubility is high. This leads to the fact that, being in natural conditions, gases lose heavy components (ethane, propane, butane, petane), which are almost completely dissolved in oil. However, there is a process of the opposite nature.

If a natural reservoir contains a lot of dry methane gas and little oil, complete dissolution of oil in gas can occur, and in this case gas will be enriched in heavy components.

Produced water in oil and gas fields, according to their chemical composition, they are divided into two types: chlorine-calcium and alkaline.

The density of distilled water at 4 ° C is taken as 1. Above and below this temperature, the density of water is less. Since formation waters contain various salts, their density is usually higher than 1.

The specific electrical resistance (ρ), depending on the concentration of salts, varies within a wide range from 10 "to 10 mm. The dielectric constant ε 0 is 81. With increasing temperature of the solutions, p decreases. For distilled water, ρ = 2 * 10 5 Ohm.

The velocity for distilled water at I = 20 ° is 1480 m / s. With an increase in pressure and mineralization, Vp increases.

Vladimir Khomutko

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How to determine the absolute and relative density of oil and oil products?

- one of the most important characteristics of oil and oil products, therefore, the accuracy of its determination is so important.

There are two indicators of this parameter - absolute and relative.

The absolute density of oil and oil products is the amount of mass per unit volume. It is measured in grams, kilograms and tons per cubic centimeter or meter (g / cm3, kg / m3). The determination of this indicator is carried out at 20 degrees Celsius.

Relative density is the ratio of the density of light oil products, or the density of oil and dark oil fractions, to the value of this parameter for distilled water at specific temperatures of both fluids. This indicator has no unit of measurement. In our country, it is determined at 20 degrees, and distilled water at 4.

This indicator can be determined by the following methods:

• determination by hydrometer and densimeter;
• pycnometric method;
• calculation method.

Measurement of the density of petroleum products using a hydrometer and densimeter

Hydrometers measure both the density of oil and oil products and their temperature, while densimeters measure only the density of oil products. This method is regulated by GOST 3900 - 85 and consists in the fact that a calibrated hydrometer is immersed in the test product, and then readings are made on the scale of the device under the current research conditions. After that, the result obtained is brought to a normal indicator at 20 degrees (there is a special table for this).

These measuring instruments have the following limits (g / cm³):

• aviation gasolines - from 0.65 to 0.71;
• motor gasolines - from 0.71 to 0.77;
• kerosene - from 0.77 to 0.83;
• diesel fuel and oils (industrial) - from 0.83 to 0.89;
• dark oils and petroleum products - from 0.89 to 0.95.

The research process is as follows:

The essence of the method is that a sample of the test product is poured into a pycnometer, which is a graduated vessel, then it is heated (or cooled) to 20 ° and weighing is carried out on a special balance, the error of which is not more than 0.0002 grams. The result obtained is a relative indicator.

This calculation is based on the dependence of this parameter on the temperature of the oil product.

Sequence of calculations:

• from the passport of the investigated product, take the indicator of its density at 20 °;
• measure the average temperature of the test product;
• calculate the difference between the result obtained and 20 °, rounding it to the nearest integer;
• in a special table, a correction for one degree of deviation is found, which corresponds to the passport value of the parameter at plus 20 °;
• the resulting defining correction is multiplied by the temperature difference;
• the result obtained is added to the passport if the temperature of the study is below 20 °, or subtracted from it if T> 20.

0,650…0,659 – 0,000962; 0,660…0,669 – 0,000949; 0,670…0,679 – 0,000936;

0,680…0,689 – 0,000925; 0,6900…0,6999 – 0,000910; 0,7000…0,7099 – 0,000897;

0,7100…0,7199 – 0,000884; 0,7200…0,7299 – 0,000870;0,7300…0,7399 – 0,000857;

0,7400…0,7499 – 0,000844; 0,7500…0,7599 – 0,000831; 0,7600…0,7699 – 0,000818;

0,7700…0,7799 – 0,000805; 0,7800…0,7899 – 0,000792; 0,7900…0,7999 – 0,000778;

0,8000…0,8099 – 0,000765; 0,8100…0,8199 – 0,000752; 0,8200…0,8299 – 0,000738;

0,8300…0,8399 – 0,000725; 0,8400…0,8499 – 0,000712; 0,8500…0,8599 – 0,000699;

0,8600…0,8699 – 0,000686; 0,8700…0,8799 – 0,000673; 0,8800…0,8899 – 0,000660;

0,8900…0,8999 – 0,000647; 0,9000…0,9099 – 0,000633; 0,9100…0,9199 – 0,000620;

0,9200…0,9299 – 0,000607; 0,9300…0,9399 – 0,000594; 0,9400…0,9499 – 0,000581;

0,9500…0,9599 – 0,000567; 0,9600…0,9699 – 0,000554; 0,9700…0,9799 – 0,000541;

0,9800…0,9899 – 0,000528; 0,9900…1,000 – 0,000515.

For a better understanding of this technique, consider an example.

Suppose that the passport value is 0.7960 g / cm³, and the test product is heated to plus 25 °. The difference is 25 - 20 = 5 °. In the above values, we find the quantitative value of the correction. For the range 0.7900 to 0.7999, it is 0.000778. We multiply it by the difference and we get 0.000778 x 5 = 0.00389 g / cm³. We round to four decimal places, we get 0.0039. Since 25 is more than 20, the resulting value must be subtracted from the passport value. The desired result will be 0.7960 - 0.0039 = 0.7921 g / cm³.