1.Introduction

Introduction

Gas Process Engineering

Solar Energy

• Earth, Water, Air – oxygen-nitrogen • Volcanos, Oceans, Rain, Rivers, winds• Carbon Dioxide, water and Photosynthesis;

releases oxygen• life – trees, fish, animals, humans, waste

accumulation, fermentation, bio gas• Wood, Biomass,Carbohydrates• Peat, lignite, Coal, anthracite• Crude Oil and Natural Gas –hydrocarbons• Oxygen, Combustion – Carbon dioxide, water

Crude Oil and Natural Gas

Petroleum and Gas Fractions

•

Oil & Natural Gas

• Oil and Natural Gas fields can be on-shore or off-shore and are generally in remote areas.

• Fluids produced from oil and gas wells generally constitute mixtures of crude oil, natural gas, salt water and solid particles.

• These mixtures are unsafe and very difficult to handle, meter, or transport to refineries and gas plants for processing.

• Hydrocarbon shipping tankers, oil refineries,and gas plants require certain specifications for the fluids that each receive.

• Also, environmental constraints exist for the safe and acceptable handling of hydrocarbon fluids and disposal of produced salt water.

• It is therefore necessary to process the produced fluids in the field to yield products that meet the specifications set by the customer and are safe to handle.

Oil & Gas Resources

year OilX109 toe

GasX109 toe

1970 70 35

1980 85 70

1990 135 120

Proven Reserves 1000 m3 of NG = 0.85 toe (tons of oil equivalent)

Oil vs Gas Marketed Production 1000 m3 of NG = 0.85 toe

(tons of oil equivalent)

year OilX109 toe

GasX109 toe

1970 2.5 0.8

1980 2.9 1.2

1990 3.2 1.7

2000 2.1

2010 2.6

US Natural Gas Production, Trillion Cubic Feet per Year

Natural Gas

• Natural gas produced along with oil is known as associated gas

• Natural gas produced from gas fields is known as non associated gas.

• Natural gas may contain liquid hydrocarbons (NGL) as well as undesirable components such as H2S,CO2, N2, water and water vapor.

• Field processing of natural gas implies the removal of undesirable components and recovery of higher hydro carbons before the gas can be sold in the market.

• The gas may undergo separation / condensation for the recovery of some hydrocarbon components.

Gas CompositionSome Non-associated Gases

Component Frigg

(NOR)

Lacq

(FRA)

Kapuni

(NZL)

Uch

(PAK)

Methane 95.7 69 45.6 27.3

Ethane 3.6 3 5.8 0.7

Propane 0.9 5.3 0.3

Butanes 0.5 2.1 0.3

C5+ 0.5 0.2 0

N2 0.4 1.5 0.9 25.2

H2S 15.3 0

CO2 0.3 9.3 43.8 46.2

Gas CompositionSome Associated Gases

Component Ekofisk

(NOR)

Parentis

(FRA)

Kirkuk

(IRQ)

Uthmaniyah

(SAU)

Methane 83.3 73.6 56.9 55.5

Ethane 8.5 10.2 21.2 18.0

Propane 3.4 7.6 6 9.8

Butanes 1.5 5 3.7 4.5

C5+ 1 3.6 1.6 1.6

N2 0.3 0.2

H2S 3.5 1.5

CO2 2 7.1 8.9

Classification of Gases

Category 1 2 3 4

Standard Sweet dry gas

Sour Dry gas

Sweet wet gas

Sour wet gas

C2+ <10 <10 >10 >10

H2S <1 >1 <1 >1

CO2 <2 >2 <2 >2

% of fields

47 15.5 23 14.5

% of Types of Natural Gas Available

Region Non Asso. Solution Gas Gas-Cap Gas

N.America 75.5 14.5 10

L.America 32.5 55 12.5

EU 73.5 15 11.5

CIS 94 2.5 3.5

Africa 61.5 19.5 9

Middle East 46 36 18

Aseana 82.5 11.5 6

Total 72 8.5 9

Regions and Acidity factorsRegion Sour Gas

% of totalFrequency Of contam ination

H2S CO2 H2S+CO2

EU 9 7 93

CIS 10 62 38

Africa 5 100

Middle east

78 37 63

Aseana 75 6 94LAmerica 35 100

World 30 45

Gas–Oil Separation Plant (GOSP)

• Crude oil–gas–water mixtures produced from wells are generally directed, through flow lines and manifold system, to a central processing and treatment facility normally called the Gas–Oil Separation Plant (GOSP).

• The first step in processing of the produced stream is the physical separation of the phases (oil, gas, and water) into separate streams.

• This takes place in two-phase gas–oil separators when the produced stream contains no water or three-phase separators when the produced stream contains water.

• The separators are used to relieve the excess pressure due to the gas associated with the produced crude and, consequently, separating it from the oil.

• Fig.1 describes further field treatment of each stream.

An outline of the processing surface field operations

Further treatment of Oil

• After separation also, Oil may contain water as emulsified water

• The presence of this salt water presents serious corrosion and scaling problems in transportation and refinery operations.

• Water remaining in the oil is known as the basic sediments and water (BS&W).

• A maximum of 1% BS&W and in some cases less than 0.5% BS&W is acceptable.

• The limit on the salt content of the remnant water in oils is usually in the range of 10 to 15 PTB (pounds of salt per thousand barrels of oil).

• Treatment involves emulsion treatment/dehydration and desalting processes.

Crude Oil Specifications

Parameter Before Treatment After treatment

Water Emulsion 10%

Free Water 30%

0.3 vol% maximum

Salt 50,000-250,000 mg/L formation water

H2S 1000 ppm 70 ppm

Gas/vapor Pressure 600 scf/bbl crude oil 10 psig (4-5 psi RVP)

Need for Gas dehydration• Water vapor is not objectionable as such;

however, the liquid or solid phase of water is very troublesome.

• This is experienced when the gas is compressed or cooled for the recovery of higher hydrocarbons.

• The liquid form of water accelerates corrosion of pipelines and other related equipment. It also reduces pipeline capacity, because it accumulates in low-point regions.

• Solid hydrates plug valves, fittings, and in some cases the pipe itself.

Acid gas separation

• Acid gases basically imply hydrogen sulfide and carbon dioxide (H2S and CO2).

• Both H2S and CO2 are corrosive, especially in the presence of water.

• Hydrogen sulfide when combusted, produces sulfur oxides- atmospheric pollutants

• H2S could be commercially utilized to produce sulfur.

Natural Gas Treatment

• It is desirable to remove hydrocarbons heavier than methane from natural gas, especially for fuel gasses.

• Heavier hydrocarbons, specifically C3+, on compression tend to condense,forming two-phase flow and thus creating pipeline operating problems.

Natural Gas

Parameter

Natural Gas

Specification

Water Content 7 lbs/MMSCF (in a 1000-psia gas line)

Oxygen (air) 0.2% by volume

H2S 0.25–0.3 grain per 100ft3

(one grain¼64.799 mg)

Total Sulfur 20 grains per 100 ft3

Carbon dioxide 2% by volume

Liquefiable hydrocarbons 0.2 gal per 1000 ft3

Thermal heating value 1150 Btu/ft3

Pipe Line Gas – Liquified Natural Gas