RESERVOIR FLUID DISTRIBUTION AND THEORY OF HYDROCARBON FLUID BEHAVIOUR
Reservoir rocks usually contain saline water and hydrocarbons. The origins of the hydrocarbons (Liquid and Gas) are believed to be organic material such as plant and microscopic animal remains. The liquid is known as CRUDE OIL. These hydrocarbons contain atoms of carbon and hydrogen and their characteristics depend on the composition.
The simplest hydrocarbon is methane (CH4) containing a central atom of carbon surrounded by four hydrogen atoms. Others are Ethane(C2H6), Propane(C3H6), etc.
This alkane group of hydrocarbons are known as PARAFFINS. Any crude oil
composed primarily of these compounds is paraffinic hydrocarbons.
At atmospheric conditions, the paraffins from C1 to C4 are gaseous while the higher order paraffins up to paraffins up to C20 are liquids and those with larger molecules are viscous liquids or solid. Under increasing temperature and pressure, even the light paraffins can turn to liquid
Within reservoir rocks, the hydrocarbons may exist as a liquid with the lighter gaseous components in solution or as crude oil with free gas co-existing. As the number of carbon atoms increase, the structural alternatives become more abundant and the fluid becomes more complex in nature. For C5+ hydrocarbons, the molecular structure can take the form or a ring structure. E.g. Cyclohexane
If the hydrocarbon molecule does not have its full compliment of hydrocarbon atom, it is UNSATURATED. Unsaturated Cyclohydrocarbons such as benzene are very important with distinct smells – The aromatics.
Hydrocarbons can also include inorganic elements associated mainly with crude oil.
These include sulphur, nitrogen, oxygen, vanadium, sodium, and potassium.
Overall, gases comprise of the. lighter smaller chains molecules while crude oil composition can be PARAFFINIC or ALSPHALTIC(e.g. Naphtenes). The crude oil composition has a large bearing upon the production characteristics and the type of problems that can be encountered in a production system.
