Introduction: Status of Petroleum Refinery, Crude Oil And Natural Gas Origin (Part - 1) | Chemical Technology - Chemical Engineering PDF Download

Introduction

Petroleum and derivatives such as asphalt have been known and used for almost 6000 years and there is evidence of use of asphalt in building more than 600 years ago. Modern petroleum refining began in 1859 with discovery of petroleum in Pennsylvania and subsequent commercialization. The exploration of petroleum originated in the latter part of the nineteenth century 

Crude Oil and Natural Gas Origin, Occurrence, Exploration and Drilling 

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 Petroleum (Crude 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). Table M-VI 1.1 gives more details about composition of petroleum. 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.  

Table M-VI 1.1: Composition of Petroleum 

Hydrocarbons 

Hydrogen Family	Distinguishing characteristics	Major hydrocarbons	Remarks
Paraffins (Alkanes)	Straight carbon chain	Methane, ethane, propane, butane, pentane, hexane	General formula CnH2n+2 Boiling point increases as the number of carbon atom increases. With number of carbon 25-40, paraffin becomes waxy.
Isoparaffins (Iso alkanes)	Branched carbon chain	Isobutane, Isopentane, Neopentane, Isooctane	The number of possible isomers increases        as        in        geometric progression as the number of carbon atoms increases.
Olefins (Alkenes)	One pair of carbon atoms	Ethylene, Propylene	General formula CnH2n Olefins are not present in crude oil, but are formed during process. Undesirable in the finished product because of their high reactivity. Low molecular weight olefins have good antiknock properties.
Naphthenes	5 or 6 carbon atoms in ring	Cyclopentane, Methyl cyclopentane, Dimethyl cyclopentane,	General formula CnH2n+2-2Rn Rn is number of naphthenic ring The average crude oil contains about 50% by weight naphthenes. Naphthenes are modestly good

		cyclohexane, 1,2 dimethyl cyclohexane.	components of gasoline.
Aromatics	6 carbon atom in ring with three around linkage.	Benzene, Toluene, Xylene, Ethyl Benzene, Cumene, Naphthaline	Aromatics are not desirable in kerosene and lubricating oil. Benzene is carcinogenic and hence undesirable part of gasoline.

  

Non Hydrocarbons  

Non-hydrocarbons	Compounds	Remarks
Sulphur compounds	Hydrogen sulphide, Mercaptans	Undesirable due to foul odour 0.5% to 7%
Nitrogen compounds	Quinotine,              Pyradine, pyrrole, indole, carbazole	The presence of nitrogen compounds in gasoline and kerosene degrades the colour of product on exposure to sunlight. They may cause gum formation normally less than 0.2.
Oxygen compounds	Naphthenic acids, phenols	Content traces to 2%. These acids cause corrosion problem at various stages of processing and pollution problem.

Processing Of Petroleum (Crude Oil)  

Processing of Petroleum from drilling: 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. . Figure M-VI 1.1 illustrates the process of oil and gas processing .  

Crude Oil Processed In India  

Both indigenous and imported crude oil are processed in India. Various imported sources of crude oil is given  in Table M-VI 1.2.There has been continuous changes in the crude oil quality.

 

Now imported crude oils are being heavier with higher sulphur content. Changing worldwide crude oil scenario is given in Table M-VI 1.3. Indigenous crude oil is also varying in characteristics. Rajasthan crude oil contains high sulphur and may pose serious challenge to Indian petroleum refining industry Typical characteristics of various indigenous crude oil is given in Table M-VI 1.4.

 

 Figure M-VI 1.1: Oil and Gas Processing

Table M-VI 1.2: Imported Crude Sources  

Middle East	Kuwait, Dubai, S. Arabia( Arab Mix, Arab medium), Iraq, Abu Dhabi, UAE(upper Zakum,Murban,UM Shaif) Iran, Kuwait : Ratawai, Egypt( Suez Mix, Zeit mix),
Mediterranean	Libya - Es Sider
West Africa	Nigeria-Bonny Light, Eseravos, Forcados, Penington, Quaiboe) Angola,           -Cabinda, Palanca, Girassol Eq. Guinea -Ceiba, Zaffiro Congo             -Nikossa, Kitina
Far East	Malaysia         -Labuan, Miri Light Australia         -Barrow Island, Cooper Basin,Chalis Brunei             -Seria Light

 Table M-VI 1.3: Worldwide Crude quality   

Properties	1985	1990	1995	1999	2010
Sulphur,Wt %	1.14	1.12	1.31	1.41	1.51
API gravity	32.7	32.6	32.4	32.2	31.8
Residue in crude ,vol %	19	19.4	19.8	20.2	21.3
‘S’ in residue ,Wt %	3.07	3.26	3.61	3.91	4.0
Metals in residue, ppm	275	286	297	309	320

 

Table M-VI 1.4: Characteristics of Various Crude Oil  

Sources of indigenous crude	Salient features
Assam Crude Nahorkatia/ Moran	31 oAPI, Sulphur 0.3%, Pour point +30 oC, High aromatics, Total distillate yield 65%.
ONGC,                   Lawkwa, Rudrasagar	27 o API, Sulphur 0.3%, High aromatics, Distillate yield 57%.
Ankleshwar Crude	48 oAPI, Sulphur 0.1%, Pour point +18 oC, Distillate

  

	yield 80-82% (Light distillates 24%, Middle distillate 47%), Wax content 9.9%, total sulphur 0.02%.
North Gujarat Crude	28 oAPI, Sulphur content 0.1%, Pour point +27 0C, Distillate yield low 33-35%, High organic acidity.
Bombay High Crude	38 oAPI, Sulphur 0.2%, Pour point +30 oC, Distillate yield 65-70% (Light distillate 24%, Middle distillates 46%), High aromatics.
Narimanam Crude	46 oAPI, Sulphur 0.1%, Pour point 3 oC, Distillate yield 80%.
KG Basin Ravva Crude	36 oAPI, Sulphur 0.1%, Pour point +30 oC, Distillate yield 61%.