Crude Oil And Natural Gas
Oil and natural gas were formed hundred years ago from the prehistoric plant and animals. It is believed that hydrocarbon formed by the thermal maturation of organic matter buried deep in earth.
Over the millions of years under extreme pressure and high temperature these organic matter converted to hydrocarbons consisting of oil and gas. Hydrocarbons are present in the variety of forms: koregen, asphalt, crude oil, natural gas, condensates, and coal in solid form.
Oil and gas production includes exploration, drilling, extraction, stabilization. The underground traps of oil and gas are called reservoir. Various types of traps are structural traps, stratigraphic traps and combination traps. Most reservoir contain water also along with oil and gas.
Reserves are classified as proven, probable and possible reserves. Earlier finding of oil and gas was matter of luck and hit and miss process. Tools used for oil and gas exploration are based and dependent on gravity change, magnetic field change, time, change and electrical resistance. However it has become now more challenging and complex.
With advent of three dimensional seismic technology which is based on the sound waves, identify the subsurface formation by reflection of sound, there has been much improvement in identification of oil and gas traps and reservoirs.
Seismic technology significantly improves the method of estimating the oil and gas deposits. Next step after exploration is the drilling of exploratory well. Drilling may be vertical drilling or horizontal drilling.
Drilling may be performed on-shore or off-shore. Horizontal drilling and hydro-fracturing has resulted in economical and more productive drilling of shale gas which was not economical with conventional vertical drilling.
Composition of Oil
Petroleum (Crude oil) consists of mainly carbon (83-87%) and hydrogen (12-14%) having complex hydrocarbon mixture like paraffins, naphthenes, aromatic hydrocarbons, gaseous hydrocarbons (from CH4 to C4H10).
Besides crude oil also contains small amount of non hydrocarbons (sulphur compounds, nitrogen compounds, oxygen compounds) and minerals heavier crudes contains higher sulphur. Depending on predominance of hydrocarbons, petroleum is classified as paraffin base, intermediate base or naphthenic base.
Crude oil properties can vary widely depending on where the oil is found and under what conditions it was formed. Its different physical properties are used to design the right kind of refineries, classify the oil (for example, West Texas Intermediate or Oman) and determine an appropriate price for it.
The properties of oil include its density, called the API gravity (named after the American Petroleum Institute), sulphur content, nitrogen content, carbon residue and distillation range. Each of these properties is important for different reasons.
For example, the sulphur content of oil is important because it determines the kind of treatment that it will require at a refinery. The higher the sulphur level, the bigger the effect it will have on the environment—and the more corrosive effect it will have on equipment.
API gravity is also important. It is essentially a measure of density. It determines whether a specific type of crude oil has a higher or lower boiling range (or distillate yields), which is important for separating and extracting different parts (or fractions).
Different oil-producing areas produce different kinds of crude oil. And depending on its mixture of hydrocarbons, crude oil can vary in colour, composition and consistency
Processing of Crude Oil
When petroleum is drilled and brought to the surface, the pressure drops resulting in separation of gases from the crude oil. Further processing of crude involves separation of water and oil and salt.
Associated natural gas is further processed for separation of natural gas, condensate, acid gases. Crude oil varies in appearance from brownish green mobile liquid to black viscous and sometimes semisolid.