Petroleum Composition

Most people presume petroleum to be similar to gasoline or petrol, simply a less pure form, which needs to be refined. In actuality the chemical composition of petroleum in its raw state can vary extremely. This variation is the reason why petroleum composition differs so much in colour and viscosity between crude oil fields and geographical areas.

Petroleum, or crude oil as it is now usually referred too when raw, contains several chemical compounds, the most prolific being the hydrocarbons themselves which give thepetroleum composition its combustible nature.

Although the composition of petroleum will contain many trace elements the key compounds are carbon (93% – 97%), hydrogen (10% - 14%), nitrogen (0.1% - 2%), oxygen (01.% - 1.5%) and sulphur (0.5% - 6%) with a few trace metals making up a very small percentage of the petroleum composition. The actual overall properties of each different petroleum source are defined by the percentage of the four main hydrocarbons found within petroleum as part of the petroleum composition. The percentages for these hydrocarbons can vary greatly, giving the crude oil a quite distinct compound personality depending upon geographic region. These hydrocarbons are typically present in petroleum at the following percentages: paraffins (15% - 60%), napthenes (30% - 60%), aromatics (3% to 30%), with asphaltics making up the remainder.

The composition of petroleum is defined as laid out above, and it is this composition which gives the crude oil its properties.

Raw petroleum is usually dark brown or almost black although some fields deliver a greenish or sometimes yellow petroleum. Depending upon the field and the way the petroleum composition was formed the crude oil will also differ in viscosity.At the extreme ranges petroleum can be almost solid, and required a significant investment of resources to refine into a useable state as anything other than bitumen. At the other end of the scale the petroleum composition can be a clear fluid resembling kerosene or gasoline, needing very little refining to be useable as a fuel. When discussing the composition of petroleum it is important to note that the compound of the raw petroleum tends to dictate the usage of the refined product. Petroleum is generally measured in volume, and for some composition of petroleum it is not cost effective to refine these into fuel. A lighter, less dense raw petroleum composition with a compound that contains higher percentages of hydrocarbons is much more profitable as a fuel source. Whereas other, denser petroleum composition with a less flammable level of hydrocarbons and sulphur are expensive to refine into a fuel and are therefore more suitable for plastics manufacturing and other uses.

Unfortunately the worlds reserves of light petroleum (light crude oil) are severely depleted and refineries are forced to refine and process more and more heavy crude oil and bitumen.

In some cases the refining process will need to remove carbon and add hydrogen, adding an extra, costly step to the refining process. This change in compound of the world's energy producing petroleum and the associated rise in refining costs has directly affected the price of gasoline across the world.

Petroleum Formation

Petroleum formation occurs by various hydrocarbons combining with certain minerals such as sulphur under extreme pressure. Modern day scientists have proven that most if not all petroleum fields were created by the remains of small animal and plant life being compressed on the sea bed by billions of tons of silt and sand several million years ago. When small sea plants and animals die they will sink, they will then lie on the sea bed where they will decompose and mix with sand and silt. During the decomposition process tiny bacteria will clean the remains of certain chemicals such as phosphorus, nitrogen and oxygen.

This leaves the remains consisting of mainly carbon and hydrogen. At the bottom of the ocean there is insufficient oxygen for the corpse to decompose entirely. What we are left with is the raw materials for the formation of petroleum.

The partially decomposed remains will form a large, gelatinous mass, which will then slowly become covered by multiple layers of sand, silt and mud. This burying process takes millions of years, with layers piling up one atop another. As the depth of the sediment build up increases the weight of the sand and silt pressing down on the mass will compress it into a layer which is much thinner than the original. Finally, when the depth of the buried decomposing layer reaches somewhere around 10,000 feet the natural heat of the earth and the intense pressure will combine to act upon the mass. The end result, over time, is the formation of petroleum. With petroleum formation the actual temperature applied to the original organic mass is critical in determining the overall properties of the resulting petroleum. Typically lower temperatures during petroleum formation will result in thicker, darker raw petroleum deposits, the most solid of which being a bitumen substance. If the heat applied during the formation of petroleum process fluctuates too much then gas will be produced, often separating from the petroleum, sometimes remaining mixed with the raw oil. If temperatures are too high, in the somewhere over 450 degrees Fahrenheit then the original biomass will be destroyed and no gas or petroleum is formed. As the mud and silt above the deposit become heavier and the forces placed upon the silt and mud begin to change the bottom layers of the compressing layer above the petroleum then it will turn into shale.

As the shale forms the oil will be forced out of its original area of formation. The raw petroleum then moves to a new rock formation, usually termed a reservoir rock, and lays trapped until it is accessed in some way. As we can see, the formation of naturally occurring rawpetroleum  takes millions of years, certainly far longer than can be deemed renewable, yet mankind has managed to almost complete deplete the world supply in little more than a century. It is important that people are educated and come to realise that burning such a precious fuel, which takes so long to form, at such a rate as we do now is nothing short of disastrous for the environment.