Oil Drilling and Refinement
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Drilling

 Various methods are used to identify locations of oil wells.  This job is typically performed by geologists working for oil companies or contracted from private firms.  Many hurdles must be cleared to actually begin drilling once an oil deposit has been found, including an in-depth environmental analysis and legal permission.  Once permission has been obtained, drilling can begin.

Oil Rig

The first step in oil drilling is setting up an oil rig.  An oil rig is what is used to drill the hole necessary to pump the oil.  A schematic of an oil rig is shown below.


 Once the rig is in place, the drill bit begins to drill farther down into the earth, pumping up the displaced mud as it goes.  Along the way, cement casings are placed in the hole to prevent it from collapsing in upon itself.  To determine if an oil well has been reached, testing is done on the mud that is constantly being displaced to see if it contains any oil sands, usually an indicator that an oil well has been reached.  When this happens, extensive testing is done to determine if the oil well has been reached.  If not, drilling continues.  If the oil well has been reached, then extraction can begin.

Oil Extraction

Once the oil well is reached, the oil rig is removed and a pump is put in its place.  In some cases, if the oil is too thick to be pumped, steam will be injected into the well at a place away from the pump.  This provides the twofold effect of thinning the oil and creating a pressure difference encouring the oil up the well.  The oil that is obtained from the oil well is known as crude oil.  A schematic of a simple oil pump is shown below.   

Refinement

Crude oil in itself is not very useful, because it contains many different types of hydrocarbons mixed together.  To convert crude oil into its useful products, we employ a process known as refinement.  Different types of hydrocarbons have different physical and chemical properties that allow us to devise methods to separate them.  The first step in the refinement of crude oil into its useful products is known as fractional distillation.  Some of the products of fractional distillation can then be further modified to convert them into more useful products, such as gasoline.  This step is known as chemical processing.  Upon completion of these steps the commercial products of oil refinement can then be sold.

Fractional Distillation

Fractional distillation is a method of separation that uses the differences in boiling points between different compounds to separate them.  For hydrocarbons, boiling point increases as the length of the carbon chain increases.  A distillation column can be used to separate the different hydrocarbons based on their different boiling points.  A schematic of this is shown in the figure below.  In fractional distillation, the initial crude oil mix is heated to begin the boiling process.  As the crude oil first begins to boil, vapors start to rise into the distillation column where they pass through trays which allow the vapor to cool.  Some of the vapor in the tray cools to form a liquid, giving the tray a liquid-vapor mixture.  As vapor continues to rise through the column, it continually loses heat as more of the vapor condenses back to liquid, so that the top of the column will be cooler than the bottom of the column.  The hydrocarbon vapors with the lowest boiling points will rise to the top of the column as vapor before being condensed at the lowest temperatures.  The hydrocarbon vapors with the highest boiling points will condense at the bottom of the column at the highest temperatures.  Due to these differences in boiling points, different hydrocarbons can be collected at different stages of the column.

(How Stuff Works, 2001)

Different hydrocarbons and their boiling points and uses are described below.

  • Petroleum Gas - Used for heating, cooking, and making plastics
      -small alkanes (1 to 4 carbon atoms)
      -commonly known by the names methane, ethane, propane, butane
      -boiling range = less than 104 degrees Fahrenheit / 40 degrees Celsius
      -often liquified under pressure to create LPG (liquified petroleum gas)
  • Naphtha - intermediate that will be further processed to make gasoline
      -mix of 5 to 9 carbon atom alkanes
      -boiling range = 140 to 212 degrees Fahrenheit / 60 to 100 degrees Celsius
  • Gasoline - motor fuel
      -liquid
      -mix of alkanes and cycloalkanes (5 to 12 carbon atoms)
      -boiling range = 104 to 401 degrees Fahrenheit / 40 to 205 degrees Celsius  *
  • Kerosene - fuel for jet engines and tractors; starting materials for making other products
      -liquid
      -mix of alkanes (10 to 18 carbons) and aromatics
      -boiling range = 350 to 617 degrees Fahrenheit / 175 to 325 degrees Celsius  *
  •  Gas oil - used for diesel fuel and heating oil; starting material for making other products
      -liquid
      -alkanes containing 12 or more carbon atoms
      -boiling range = 482 to 662 degrees Fahrenheit / 250 to 350 degrees Celsius  *
  • Lubricating oil - used for motor oil, grease, other lubricants
      -liquid
      -long chain (20 to 50 carbon atoms) alkanes, cycloalkanes, aromatics
      -boiling range = 572 to 700 degrees Fahrenheit / 300 to 370 degrees Celsius  *
  •  Heavy gas or fuel oil - used for industrial fuel; starting material for other products
      -liquid
      -long chain (20 to 70 carbon atoms) alkanes, cycloalkanes, aromatics
      -boiling range = 700 to 1112 degrees Fahrenheit / 370 to 600 degrees Celsius  *
  •  Residuals - coke, asphalt, tar, waxes; starting material for other products
      -solid
      -multiple-ringed compounds with 70 or more carbon atoms
      -boiling range = greater than 1112 degrees Fahrenheit / 600 degrees Celsius


Chemical Processing

As seen above, many different products are obtained from distilling crude oil.  Depending on the market value of each of the products, it can be profitable to convert some of the products of crude oil into another product.  To do this, chemical processing techniques are used.

There are several different chemical processing techniques that can be used to convert one product to another.  To convert a large hydrocarbon into two or more smaller hydrocarbons, a process known as cracking is used.  To convert two or more smaller hydrocarbons into one or more larger hydrocarbons, a process known as unification is used.  A third process, alkylation, can also be used to rearrange the chemical structure of a hydrocarbon into a more desired structure.  These processes are described below.

Cracking

Cracking is the process of taking a large hydrocarbon and breaking into smaller hydrocarbons.  There are two main cracking methods currently used; thermal cracking and catalytic cracking.  In thermal cracking, large hydrocarbons are heated to very high temperatures until they break apart.

Several different methods of thermal cracking are used.  The first is steam thermal cracking, where high temperature steam is used to crack butane, naptha, and ethane into ethylene and benzene.  Next is visbreaking, which is where residuals from distillation are heated, cooled, and then burned to produce tar.  The third process is coking, where residuals from distillation are heated until they crack, eventually producing a pure carbon residue known as coke.

In catalytic cracking, a catalyst is used to produce new hydrocarbons.  The hydrocarbons produced depend on the catalyst used.  In fluid catalytic cracking, a very hot fluid catalyst is used to break down heavy oils into diesel oils and gasoline.  In hydrocracking, a different catalyst is used at lower temperatures to crack heavy oils into gasoline and jet feul.

Unification 

Unification is the process where smaller hydrocarbons are converted into larger hydrocarbons.  Typically this process is used to convert naphtha into aromatic compounds that can be used as an additive to gasoline or in the production of various chemicals.  This process uses platinum catalysts to transform the naphtha.

Alkylation

An alkylation reaction is one where where an alkyl group (CnH2n+1 chain) is transferred from one molecule to another.  Propylene and butylene can be mixed in this way in the presence of an acid catalyst to produce high octane hydrocarbons, which are useful additives to gasoline.

Final Treatment

Before being sold, the products obtained from fractional distillation must undergo one final purification step to remove any undesired impurities.  This purification includes passing the products through one or more of the following:

  • A column of sulfuric acid - used to remove unsaturated hydrocarbons, nitrogen compounds, oxygen compounds, and any solid residuals
  • An absortion column - typically filled with drying agents to remove water
  • Sulfur scrubbers - used to remove any sulfur containing compounds

Upon passing through this final treatment the resulting products are ready for market.

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