Introduction of HF

1. NATURAL GAS PROCESSING
AND VALUE ADDITION
Lecture - 1

2. What Is Natural Gas?
• Natural gas is a product of decomposed organic matter, typically from
ancient marine microorganisms, deposited over the past 550 million
years.
• Natural gas is a subcategory of petroleum that is a naturally occurring,
complex mixture of hydrocarbons, with a minor amount of inorganic
compounds.
• The lightest of these hydrocarbons exist in the gaseous state under
normal conditions and are known collectively as natural gas.

3. Types of Natural Gas
• Dry gas: It consists of more methane with little condensable heavier
hydrocarbon compounds such as propane and butane when brought
to the surface. Dry gases are defined as those that contain less than
0.1 gallon of condensable per 1,000 cubic feet of produced gas.
• Associated gas: It is the dissolved natural gas produced along with
crude oil. Associated gas refers to the natural gas found in association
with oil within the reservoir.
• Wet gas: Natural gas that has a lower methane content (typically
below 85%) that is intermixed with water vapor and natural gas
liquids such as propane, butane, and pentane. Wet natural gas often
needs to be further processed to get it pipeline-ready.

4. Shale Gas and Other Unconventional Sources
of Natural Gas
• Unconventional natural gas, which includes shale gas, tight gas, coal bed methane,
and methane hydrates, has been more difficult and costly to exploit than
conventional deposits, until recently.
• Shale gas in highly porous and permeable reservoirs and can be easily tapped by
standard vertical wells, shale gas remains trapped in its original source rock, the
organic-rich shale that formed from the sedimentary deposition of mud, silt, clay, and
organic matter on the floors of shallow seas.
• Tight gas refers to natural gas that has migrated into a reservoir rock with high
porosity but low permeability
• Coal bed methane is often collocated with petroleum, but it can also be found
trapped within coal deposits.
• Methane hydrates, which consist of methane molecules trapped in a cage of water
molecules, occur as crystalline solids in sediments in arctic regions and below the
floor of the deep ocean.
• Such sources could help close the growing gap between domestic production and
consumption

5. Composition of Natural Gas Other Than CH4
• Natural gas can contain a variety of elements and compounds other
than methane.
Organic Inorganic
Water Hydrogen Sulphides
Ethane Carbon-dioxide
Butene Water Vapour
Propane Helium
Pentanes Nitrogen

6. General
Composition of NG

7. Natural Gas Value Chain
• The conversion of natural gas into a liquid has been an elusive
objective for a long time.
• Some parts of the produced gas – Propane, Butane and the natural
condensate, can be shipped as LPG or natural gasoline.
• Ethane can be split out and converted into petrochemicals (ethylene
and its derivatives).
• Methane or C1, portion can be transported by pipeline or by
liquefaction and shipping or it can be chemically converted to
petrochemicals.

8. Mid Stream Gas Sector

9. Down Stream Gas Sector

10. Gas Reserves in India
• India has a bright long term certified gas reserves of over 28 BCM on
a deepwater block in the Krishna/Godavari.
• More than 9 big discoveries have been made in less than 3 years and
a further multi-million deepwater exploration program was kicked off
recently.
• First exploratory venture by RIL in this block has resulted in world’s
largest gas discovery for the year.
• In addition, there is a high probability of success based on the data
available is expected for the unexplored deeper targets. These targets
are expected to yield new discoveries and consequently the resources
from the field are expected to grow with time.

11. New Opportunities in NG in India
• ONGC signed an agreement with L.N. Mittal group to form two joint
venture companies - OMEL (ONGC Mittal Energy Ltd) and OMESL (ONGC
Mittal Energy Services Ltd) for exploration, production and shipping
activities.
• ONGC has offered 26 % partnership in to Coal India Ltd in its Underground
Coal Gasification projects.
• GAIL and EIL have signed a MOU for gas processing and transportation
projects.
• IOC and STATOIL, Norway have formed into a Special Purpose Vehicle for
acquisition of prospective exploration acreage and producing properties.

12. Role of a Production Engineer in NG
• Role of a production
engineer is to maximize oil
and gas production in a cost-
effective manner.
• A complete oil or gas
production system consists
of a reservoir, well, flowline,
separators, pumps, and
transportation pipelines.
• The reservoir supplies well-
bore with crude oil or gas

13. Reservoir
• Hydrocarbon accumulations in geological traps can be classified as
reservoir, field and pool.
• A ‘‘Reservoir’’ is a porous and permeable underground formation
containing an individual bank of hydrocarbons confined by
impermeable rock or water barriers and is characterized by a single
natural pressure system.
• A ‘‘Field’’ is an area that consists of one or more reservoirs all related
to the same structural feature.
• A ‘‘Pool’’ contains one or more reservoirs in isolated structures.
Hydrocarbon accumulations are classified as oil, gas condensate, and
gas reservoirs.

14. Gas Reservoir
• An oil that is at pressure above its bubble point pressure is called an
“unsaturated oil” because it can dissolve more gas at the given
temperature.
• An oil that is at its bubble point pressure is called a “saturated oil”
because it can dissolve no more gas at the given temperature.
• Single phase flow prevails in an under saturated oil reservoir, where
as two-phase (liquid oil and free gas) flow exists in a saturated oil
reservoir.
• The reservoirs at and above dew point are classified as gas reservoirs.

15. Gas Reservoir Classification
• When the reservoir temperature is above the critical temperature of
the hydrocarbon system, the reservoir is classified as a natural gas
reservoir.
• On the basis of their phase diagrams and the prevailing reservoir
conditions, natural gases can be classified into four categories:
1. Retrograde gas-condensate
2. Near-critical gas-condensate
3. Wet gas
4. Dry gas

16. Retrograde Gas-condensate Reservoir
• When the reservoir temperature lies between the critical
temperature and cricondentherm of the reservoir fluid, the
reservoir is classified as a retrograde gas-condensate reservoir.
• This category of gas reservoir is a unique type of hydrocarbon
accumulation in that the special thermodynamic behavior of the
reservoir fluid is the controlling factor in the development and the
depletion process of the reservoir.
• When the pressure is decreased on these mixtures, instead of
expanding (if a gas) or vaporizing (if a liquid) as might be
expected, they vaporize instead of condensing. Consider that the
initial condition

17. • When the reservoir pressure is above the upper dew-point pressure,
the hydrocarbon system exists as a single phase (i.e., vapor phase).
• As the reservoir pressure declines isothermally during production
from the initial pressure (point 1) to the upper dew-point pressure
(point 2), the attraction between the molecules of the light and heavy
components causes them to move further apart further apart.
• As this occurs, attraction between the heavy component molecules
becomes more effective; thus, liquid begins to condense.

18. Pressure-Temperature Phase Diagram

19. Near-critical Gas-condensate
• When the reservoir temperature is near the critical temperature the
hydrocarbon mixture is classified as a near-critical gas-condensate.
• The volumetric behavior of this category of natural gas is described
through the isothermal pressure declines by the vertical line.
• Because all the quality lines converge at the critical point, a rapid liquid
buildup will immediately occur below the dew point as the pressure is
reduced to point 2.
• This behavior can be justified by the fact that several quality lines are
crossed very rapidly by the isothermal reduction in pressure. At the
point where the liquid ceases to build up and begins to shrink again,
the reservoir goes from the retrograde region to a normal vaporization
region.

20. Pressure-Temperature Phase Diagram

21. Wet-gas Reservoir
• A typical phase diagram of a wet gas have a reservoir temperature
above the cricondentherm of the hydrocarbon mixture.
• Because the reservoir temperature exceeds the cricondentherm of
the hydrocarbon system, the reservoir fluid will always remain in the
vapor phase region as the reservoir is depleted isothermally, along
the vertical line A-B. As the produced gas flows to the surface,
• however, the pressure and temperature of the gas will decline. If the
gas enters the two-phase region, a liquid phase will condense out of
the gas and be produced from the surface separators.

22. Pressure-Temperature Phase Diagram

23. Dry-gas Reservoir
• The hydrocarbon mixture exists as a gas both in the reservoir and in
the surface facilities. The only liquid associated with the gas from a
dry-gas reservoir is water.
• Usually a system having a gas-oil ratio greater than 100,000 scf/STB is
considered to be a dry gas.
• Kinetic energy of the mixture is so high and attraction between
molecules so small that none of them coalesce to a liquid at stock-
tank conditions of temperature and pressure.
• The classification of hydrocarbon fluids might be also characterized by
the initial composition of the system.

24. Pressure-Temperature Phase Diagram

25. Gas-Well
• Oil and gas wells are drilled like
an upside-down telescope.
• The large-diameter borehole
section is at the top of the well.
• Each section is cased to the
surface or a liner is placed in the
well that laps over the last casing
in the well.
• Each casing or liner is cemented
into the well.

26. Well
• Gas wells are drilled like an upside-down telescope.
• The large-diameter borehole section is at the top of the well. Each section
is cased to the surface, or a liner is placed in the well that laps over the last
casing in the well.
• Each casing or liner is cemented into the well
The ‘wellhead’ is defined as the surface equipment set below the master
valve. It includes casing heads and a tubing head.
• The casing head (lowermost) is threaded onto the surface casing. This can
also be a flanged or studded connection. A ‘‘casing head’’ is a mechanical
assembly used for hanging a casing string.
• Depending on casing programs in well drilling, several casing heads can be
installed during well construction.

27. Well Head

28. Tubing Head
• Most flowing wells are
produced through a string of
tubing run inside the
production casing string.
• At the surface, the tubing is
supported by the tubing
head (i.e., the tubing head is
used for hanging tubing
string on the production
casing head.

29. Christmas Tree
• The equipment at the top of the producing wellhead is called a
‘‘Christmas tree’’ and it is used to control flow.
• The ‘‘Christmas tree’’ is installed above the tubing head. It may have
one flow outlet (a tee) or two flow outlets (a cross).
• It consists of a main valve, wing valves and a needle valve which are
used for closing the well when needed.
• At the top of the tee structure, there is a pressure gauge that
indicates the pressure in the tubing.
• The wing valves and their gauges allow access (for pressure
measurements and gas or liquid flow) to the annulus spaces.

30. Christmas Tree

31. Surface Choke Valve
• Surface choke (i.e., a restriction in the flow line) is a piece of
equipment used to control the flow rate.
• In most flowing wells, the oil production rate is altered by adjusting
the choke size.
• The choke causes back-pressure in the line. The back-pressure
(caused by the chokes or other restrictions in the flowline) increases
the bottom hole flowing pressure.
• Increasing the bottom-hole flowing pressure decreases the pressure
drop from the reservoir to the wellbore (pressure drawdown).

32. Surface Choke Valve