Petroleum Engineering

Presentation:-

Seismic Survey

Rakesh Kumar

Group Members

1. Rajat Sharma (R080114026)2. Rakesh Kumar (R080114027)3. Ram Lakhan Thakur (R080114028)4. Ravi Ranjan Kumar (R080114030)5. Rishabh Tripathi (R080114031)

Topics

1: Origin – How do oil and gas form?

2: Exploration and Production –How do we find oil and gas and how is it produced?

Chemistry Plankton Cooking Migration

Oil Traps Reservoir Rocks Seismic Surveys

Origin (1): Chemistry

Crude Oil

• Oil and gas are made of a mixture of

different hydrocarbons.

• As the name suggests these are large

molecules made up of hydrogen atoms

attached to a backbone of carbon.

Hydrocarbon

Origin (2): Plankton

• Most oil and gas starts life as microscopic plants and animals

that live in the ocean.

Plant plankton Animal plankton

Origin (3): Cooking

As Black Shale is buried, it is heated.

Kerogen

Gas

Oil

Organic matter is first changed by the

increase in temperature into kerogen,

which is a solid form of hydrocarbon

Around 90°C, it is changed into a liquid

state, which we call oil

Around 150°C, it is changed into a gas

A rock that has produced oil and gas in

this way is known as a Source Rock

Origin (4): Migration

• Hot oil and gas is less dense than

the source rock in which it occurs

• Oil and gas migrate upwards up

through the rock in much the same

way that the air bubbles of an

underwater diver rise to the surface

• The rising oil and gas eventually gets

trapped in pockets in the rock called

reservoirs

Rising oil

Exploration and Production (1): Oil Traps

• Some rocks are permeable

and allow oil and gas to freely

pass through them

• Other rocks are impermeable

and block the upward passage

of oil and gas

• Where oil and gas rises up

into a dome (or anticline)

capped by impermeable rocks

it can’t escape. This is one

type of an Oil Trap.

Impermeable

Permeable

Dome Trap

Exploration and Production (2): Reservoir Rocks

• The permeable strata in an oil trap

is known as the Reservoir Rock

• Reservoir rocks have lots of

interconnected holes called pores.

These absorb the oil and gas like a

sponge

This is a highly magnified picture of

a sandy reservoir rock (water-filled

pores are shown in blue)

As oil migrates it fills up the pores

(oil-filled pores shown in black)

Exploration and Production (3): Seismic Surveys

• Seismic surveys are used to locate likely rock structures

underground in which oil and gas might be found

• Shock waves are fired into the ground. These bounce off layers

of rock and reveal any structural domes that might contain oil

Drill here!

What is Seismic Surveying?

• The seismic survey is one form of geophysical survey that aims at measuring the earth’s geophysical properties by means of physical principles such as magnetic, electric, gravitational, thermal, and elastic theories.

• Seismic survey techniques are used to build up an image of the rock formations beneath the seabed during the first part of the exploration phase.

• This technique is used by oil & gas explorers to find the detailed images of rock formation below the earth’s surface, and these information are used in determining location & size of oil reservoirs.

Process

• It is same as we see in the case of bats, which sends waves to locate it’s prey…

• Waves are reflected after striking a surface and we can know it’s location, by the intensity of reflected wave…

Seismic Surveying on Land

• In this sound waves are sent inside the earth, known as “Seismic Waves”.

• Sound producing machines such as Vibrator truck is used to produce Seismic Waves.

• Explosives or vibrating plates (Sledgehammers) generate the waves and a line or grid of geophones records them.

• Density changes between rock or soil layers reflect the waves back to the surface and the speed and strength that the waves are reflected back indicates what geological features lie below.

Seismic Surveying on Land

• Those reflected waves are captured by Geophones, and those waves are recorded in a recording truck.

• Seismic images are produced by generating, recording and analyzing sound waves that travel through the Earth.

• After images are helpful in determining the best places to explore for oil and gas.

What is a marine seismic survey?

• Uses sound energy to map geological structures under the seabed

• Vessels tow devices that use compressed air to produce pulses of high energy, low frequency sound waves

• Sound waves can penetrate more than 6,000 metres below the sea floor

• Travel through the water and into the rock layers beneath the seabed

• Bounce back to receivers (“hydrophones”) that measure strength and return time

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Types of seismic surveys

Two dimensional (2D): Uses one sound source and one set of receivers

Three dimensional (3D): Uses multiple synchronized sound sources and hydrophones

Four dimensional (4D): Uses multiple synchronized sound sources and hydrophones with the added dimension of time (i.e.: a 3D survey is conducted multiple times over the same location at different periods to compare data)

Geohazard or well site survey: Uses one sound source and one set of receivers towed over a small area prior to drilling to check for possible hazards.

Verticial Seismic Profiles: Hydrophones are lowered into a drilled well and sound is produced at the surface to give a detailed view of the geology near the well bore

What are the impacts of seismic surveys on marine life?

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• Current research indicated there is minimal risk of mortality in marine mammals, fish and invertebrates.

• Marine mammals, depending on species and proximity, can experience temporary changes to hearing thresholds and in some extreme cases these effects can be permanent.

• Laboratory research show no mortality among invertebrates (crab etc.) but showed some non-life threatening physical effects.

• Governments, academics and industry continue to invest in research related to seismic impacts to further broaden the body of knowledge.