It is as simple as that, unfortunately, to say that oil drilling is mostly luck of the draw.  If oil is struck, it is normally in high pressure and gushes out of the bored hole to be collected.  If not, you are faced with the painful task of starting over.  There is very little exact science in the art of finding and drilling up oil; the brunt of the chemical aspects lies in the next important step: refining and distilling the oil.

Basics of Hydrocarbons in Petroleum

Before diving into the specifics of refining oil, it is crucial to understand the simple organic chemistry of the alkane and alkene families: the families that make up most of the mined petroleum.  Since petroleum comes almost exclusively from decomposed prehistoric organisms, it is made up of simple linear carbon-chain based molecules.  The most simple of all carbon molecules is referred to as methane, and has a single carbon atom with four covalently bonded hydrogen atoms bound to it.   Because carbon has four sites where bonding can occur, the possibilities for carbon chains seem limitless.  Carbon chains can go from a single carbon (methane) to over 25 carbons in a single strand.  It is common for unused bonding sites to be taken up by hydrogen atoms, and that is normally what happens.  The quintessential alkane petroleum molecule has a structure that looks like this,its formulae being CH₃(CH₂)_nCH₃.  It is also fairly common for carbons to form a double bond with each other, where two sites are occupied by a single carbon molecule.  These molecules are called alkenes and have one double bonded carbon pair in its linear chain of carbon and hydrogen molecules.  Two other less prominent molecules in petroleum include cycloalkanes and aromatics.  Cycloalkanes are alkanes that have been reshaped into a ring of carbons rather than a linear strand.  Aromatics consist of a special cyclic molecule called benzene (C₆H₆) with a single hydrogen removed and replace by a strand of carbons attached at that particular point.  The size of the carbon molecule is very important while processing and refining the petroleum, because different sized molecules are used for many different purposes. 

For our purposes in transportation, we will be most concerned with the range of carbon strand lengths used for gasoline, kerosene, and diesel (common fuels for an array of vehicles).  These particular petroleum parts are useful because of their state at room temperature.  Being liquids, they are the most easily harnessed for domestic fueling needs.  To harness these chemicals and separate them out from the other carbon molecules that can be used from cooking fires to asphalt, the process known as fractional distillation was developed to separate out these parts to be used in their own respective ways. Fractional distillation is performed by an apparatus known as, not surprisingly, a fractional distillation column.  It is illustrated simply here.  Basically, it consists of a column of a certain height that has a series of openings in the side at different heights that connect to collection chambers.  Crude petroleum is piped from a source through a boiler that superheats the petroleum to about 600°C.  This causes the oil to boil.  This hot oil is then pumped into the fractional distillation column.  Very small molecules from C₁ – C₄, because of their light weight, become gaseous at low temperatures.  Upon entering the distillation column, they float quickly to the top of the chamber and exit through the highest hole.  Molecules from C₅-C₁₂ float upwards as well, but not as high, and they exit through a lower hole.  These molecules are called naphtha.  Some naphtha is invariably gasoline, while others can be sent through a device called a reformer that reforms naphtha into gasoline (in order to produce more of gasoline, a major product).  Molecules from C₁₁-C₁₈ are similar in consistency to the naphtha, but their heavier weight causes them to flow through a lower hole than the naphtha.  Kerosene is a fuel from this range that flows through a particular hole, and Diesel fuel (range C₁₂₊) flows through a slightly lower hole due to its tendency to consist of heavier molecules.

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