Crude oil contents

The temperature sensitivity of emulsion viscosity may be described as a percentage change in viscosity per unit temperature change. The temperature-adjusting factor varies for different emulsions, depending on the base crude-oil content, brine content, surfactant, and other variables and generally ranges from about 1.8 to 3.6 cP/ C. (The variation in the viscosity of water with temperature is approximately 2.2 cP/ C.)... 

The viscosity of an oil-in-water emulsion is sharply dependent on water content. Viscosity adjustment factors for water content may be obtained from a correlation such as that shown in Figure 3. In this figure, the adjustment factor is defined as 1.0 at the base level of 30% water. The actual correlation to be used is dependent on the base crude-oil content and other factors. 

Droplet growth rates and viscosity decline rates both are exponential processes, following a straight line on a semi-log plot (log x or log vs. time), where is the mean droplet diameter. Emulsion failure is also associated with a certain minimum viscosity, depending on water content, crude-oil content, temperature, etc. Viscosity and mean droplet size may be projected to estimate the time remaining before emulsion failure. The ultimate droplet size and viscosity should be determined experimentally for the same formulation in a pilot-plant pipe loop. 

In the late 1970s, the aim of PDV (7) was to transport the extraheavy erude oil to refineries located at least 200 km away, where it would be converted into fighter fractions. At that time, oil prices had reached unprecedented high levels and the whole scheme was considered feasible. On a first approach, laboratory and pilot plant tests were conducted (52—55), aimed at testing the feasibility of transporting a sufficiently stable emulsion, wifli a typical crude oil content of about 65%. It has to be noted fliat with very few exceptions (56—58) no attention was paid to the physicochemical formulation. This is understandable since little information was available at that time of flie effect of the many variables involved in the formulation, mixing, and rheology of emulsions. 

Sulfur is the heteroatom most frequently found in crude oils (see Table 1.5). Sulfur concentrations can range from 0.1 to more than 8 weight percent moreover, this content is correlated with the gravity of the crude oil and, therefore, its quality (light or heavy). 

The Reid vapor pressure is generally barely different from the true vapor pressure at 37.8°C if the light gas content —methane, ethane, propane, and butane— of the sample is small, which is usually the case with petroleum products. The differences are greater for those products containing large quantities of dissolved gases such as the crude oils shown in Table 4.13. 

For the refiner, the main problem is to meet the specifications for kinematic viscosity and sulfur content. Dilution by light streams such as home-heating oil and LCO, and selection of feedstocks coming from low-sulfur crude oils give him a measure of flexibility that will nevertheless lead gradually to future restrictions, most notably the new more severe antipollution rules imposing lower limits on sulfur and nitrogen contents. 

Sulfitr and nitrogen contents in 550°C uacaum residues according to crude oil origin. Source Total. 

The measurement of the vapor pressure and flash point of crude oils enables the light hydrocarbon content to be estimated. 

These reactions can explain the absence of olefins in crude oil, their presence being detected only in the crudes of low sulfur content. The sulfur content in crude from Bradford which is the one of the rare crudes containing olefins is about 0.4%. 

Free sulfur is rarely present in crude oils, but it can be found in suspension or dissolved in the liquid. The crude from Goldsmith (Texas, USA.) is richest in free sulfur (1% by weight for a total sulfur content of 2.17%). It could be produced by compounds in the reservoir rock by sulfate reduction (reaction 8.2). 

Water, Sediment, and Salt Contents in Crude Oils... 

The water content of crude oils is determined by a standardized method whose procedure is to cause the water to form an azeotrope with an aromatic (generally industrial xylene). Brought to ambient temperature, this azeotrope separates into two phases water and xylene. The volume of water is then measured and compared with the total volume of treated crude. 

The water content of crude oils at the wellhead is usually small as shown in Table 8.12 it generally increases during transport and storage and can attain 3%. 

Crude oil name Country of origin Water content in volume %... 

The water and sediment contents of crude oils is measured according to the standard methods NF M 07-020, ASTM D 96 and D 1796, which determine the volume of water and sediments separated from the crude by centrifuging in the presence of a solvent (toluene) and of a demulsifylng agent Table 8.13 gives the bottom sediment and water content of a few crude oils. 

Crude oil name Water and sediment contents (BS W) In volume %... 

Table 8.13 Bottom sediments and water content of some crude oils. i 1 i ...

The measurement of chlorides is standardized (NF M 07-023, ASTM 3230) the result of two measurements is expressed in mg of NaCl/kg of crude. Table 8.14 gives the contents of some crude oils these values come from measurements taken in a refinery and thereby include the salts brought in by contamination. 

A knock out vessel may on the other hand be followed by a variety of dehydrating systems depending upon the space available and the characteristics of the mixture. On land a continuous dehydration tank such as a wash tank may be employed. In this type of vessel crude oil enters the tank via an inlet spreader and water droplets fall out of the oil as it rises to the top of the tank. Such devices can reduce the water content to less than 2%. 

Crude oil is recovered from the reservoir mixed with a variety of substances gases, water, and dirt (minerals) (4). Thus, refining actually commences with the production of fluids from the weU or reservoir and is followed by pretreatment operations that are appHed to the cmde oil either at the refinery or prior to transportation. Pipeline operators, for iastance, are iasistent upon the quahty of the fluids put iato the pipelines therefore, any cmde oil to be shipped by pipeline or, for that matter, by any other form of transportation must meet rigid specifications ia regard to water and salt content. In some iastances, sulfur content, nitrogen content, and viscosity may also be specified. 

The output from oil fields, after secondary and tertiary processing [7], is considered wet oil. It consists of oil field brine, crude oil and natural gases containing a high COj content and in certain circumstances it may also contain small amounts of H2S. Wet oil can also contain solid particles from the bedrock. 

Wax Manufacture A waxy distillate cut from crude or the wax byproduct from lube oil dewaxing is first deoiled. Resulting low oil content wax is hydrofmed for color improvement and fractionated into appropriate melting point grades. 

---