Oil and Gas – Black Gold!

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NASA

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Origin (1): Chemistry

Crude Oil

Hydrocarbon

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• 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.

OIL AND GAS PRODUCTION

1) What are "fossil fuels" and why are they called that?

The most common fossil fuels are coal, oil and natural gas.

Some other fuels, like oil shale and peat (a very young form of coal), also are fossil fuels.

Formed millions of years ago from plants and animals that died and decomposed beneath tons of soil and rock

2) Why did some decaying material become coal while other ancient material became oil and natural gas?

Coal was formed from plant debris while natural gas and oil were formed from tiny organisms that settled to the bottom of ancient seas and rivers.

Temperatures and pressures, along with the amount of time the organisms decayed underground, typically determined whether oil or natural gas was formed.

Higher temperature or the pressures form natural gas.

Finally concluded that organic source material is probably converted to droplets of crude thro’ thermo chemical reaction (pyrolisis)

Other possible variations in the type of organic source such as Type I,II &IIIType I- Algal, Type II- combination algal and zooplankton and phytoplankton Type III- generally from woody (land) plants

Origin (2): Planktoncache.eb.com/eb/image?id=93510

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• Most oil and gas starts life as microscopic plants and animals that live in the ocean.

Plant plankton Animal plankton

Origin (3): Bloomsserc.carleton.edu/images/microbelife/topics/red_tide_genera.v3.jpg

• Today, most plankton can be found where deep ocean currents rise to the surface

• This upwelling water is rich in nutrients and causes the plankton to bloom

• Blooms of certain plankton called dinoflagellates may give the water a red tinge© Miriam Godfrey

Dinoflagellate bloom

Origin (4): On the sea bedupload.wikimedia.org/wikipedia/en/0/04/Plankton.jpg

When the plankton dies it rains down on sea bed to form an organic mush

Sea bed

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If there are any animals on thesea bed these will feed on theorganic particles

Origin (5): Black Shaleupload.wikimedia.org/wikipedia/en/0/04/Plankton.jpg

• However, if there is little or no oxygen in the water then animals can’t survive and the organic mush accumulates

• Where sediment contains more than 5% organic matter, it eventually forms a rock known as a Black Shale

© Earth Science World Image Bank

Origin (6): Cooking

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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

OIL You wouldn't see a big underground lake, as a lot of people think. Oil doesn't exist in deep, black pools. In fact, an underground oil formation - called an "oil reservoir" - looks very much like any other rock formation.

When reservoir rock is magnified, the tiny pores that contain trapped oil droplets can be seen.

Geological SurveysBegins with geologists examining the surface structure of the earth

Areas are most likely to contain a petroleum or natural gas reservoir.

Information attained from the rock cuttings and samples obtained from the digging of irrigation ditches, water wells, and other oil and gas wells. This information is all combined to allow the geologist to make inferences as to the fluid content, porosity, permeability, age, and formation sequence of the rocks underneath the surface of a particular area.

Seismic ExplorationSeismology refers to the study of how energy, in the form of seismic waves, moves through the Earth's crust and interacts differently with various types of underground formations.

Placing GeophonesSeismic waves, emitted from a source, will travel through the earth, but also be reflected back towards the source by the different underground layers.

It is this reflection that allows for the use of seismology in discovering the properties of underground geology.

Create vibrations on the surface and record how these vibrations are reflected back to the surface. – rubber ball

Placing Geophones

Seismology in Practice

Onshore SeismologyArtificially creating seismic waves, the reflection of which are then picked up by sensitive pieces of equipment called 'geophones', imbedded in the ground.

A Seismic Vibrator Truck Due to environmental concerns and improved technology, it is often no longer necessary to use explosive charges to generate the needed seismic waves.

Instead, most seismic crews use non-explosive seismic technology.

Thumper

A Seismic Vibrator Truck

Offshore SeismologyInstead of using dynamite or impacts on the seabed floor, the seismic ship uses a large air gun, which releases bursts of compressed air under the water, creating seismic waves that can travel through the Earth's crust and generate the seismic reflections that are necessary.

Offshore Seismic Exploration

MagnetometersMagnetic properties of underground formations can be measured to generate geological and geophysical data.

Magnetometers are devices that can measure the small differences in the Earth's magnetic field.

Satellite, called Magsat, allows for the study of underground rock formations and the Earth's mantle on a larger scale, and provides clues as to tectonic plate movement and the location of deposits of petroleum, natural gas, and other valuable minerals.

3D visualization

Reservoir RockTrap Rock

Reservoir Rock Classification

• Clastic Rocks (broken pieces of older rock)– Sand / sand stone

• Carbonate rocks– Lime Stone/ Dolomite

• Reef Rocks (a ridge of jagged rock)– This is fractured basement rock; – Porous and permeable rock that contains the pool of petroleum

Porosity

• Porosity or pore space or void space is expressed in percentage as the ratio of total volume of pore space to total volume of rock.

• The ratio of interconnected pore space to the total bulk volume of rock is termed effective porosity. • The porosity of most reservoirs range from 5-30% most commonly 10-30%. • 15-20% of porosity - Good;

• 20-25% of porosity - very good

• >25% of porosity - excellent

Permeability

• Another important factor to be considered in a reservoir rock. It is the property that permit the passage of any fluid thro’ the interconnected pores of a rock with out damage to the frame work of the rock.

• The ability, or measurement of a rock's ability, to transmit fluids, typically measured in darcies or milli darcies.

• A rough appraisal of reservoir permeabilities is– 1.0 to 10 md- Fair; – 10 to 100 md – Good;– 100 to 1000 md- Very good.

Origin (7): Migrationwww.diveco.co.nz/img/gallery/2006/diver_bubbles.jpg • 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

Traps

• Beneath the earth's surface, oil will ooze through rocks if there is enough space between them, but this oil will not accumulate into large quantities unless something traps it in a particular place. There are a variety of geologic traps, which themselves can be broken into categories:

• Structural trap types: anticline, fault trap, salt dome • Stratigraphic trap types: unconformity, lens, pinch-out• Combination traps

Structural Trap

Anticline Trap

An anticline is an example of rocks which were previously flat, but have been bent into an arch. Oil that finds its way into a reservoir rock that has been bent into an arch will flow to the crest of the arch, and get stuck (provided, of course, that there is a trap rock above the arch to seal the oil in place).

A cross section of the Earth showing typical Anticline Traps. Reservoir rock that isn't completely filled with oil also contains large amounts of salt water.

Normal Fault Normal fault.

•The main varieties of faults are normal or gravity faults, reverse or thrust faults and strike-slip faults.

•The hanging wall moves down relative to the footwall of a normal fault.

•These faults are formed the trap for many gas or oil pools.

•Pools trapped by normal faulting are almost always on the upper side of the fault.

•Trap associated with thrust or reverse faulting may form either above or below the fault plane.

Schematic Diagram of Growth Fault

A cross section of rock showing a fault trap - in this case, an example of gouge. This is because the reservoir rock on both sides of the fault would be connected, if not for the fault separating the two. In this example, it is the fault itself that is trapping the oil.

Fault traps are formed by movement of rock along a fault line. In some cases, the reservoir rock has moved opposite a layer of impermeable rock. The impermeable rock thus prevents the oil from escaping. In other cases, the fault itself can be a very effective trap. Clays within the fault zone are smeared as the layers of rock slip past one another. This is known as fault gouge.

Here we see salt that has moved up through the Earth, punching through and bending rock along the way. Oil can come to rest right up against the salt, which makes salt an effective trap rock.

However, many times, the salt chemically changes the rocks next to it in such a way that oil will no longer seep into them. In a sense, it destroys the porosity of a reservoir rock.

Salt Dome Trap

Photograph of fractures in Jebel Hafit (UAE)

Fracture. A fracture is a surface of breakage in rock, but differs from a fault in that there is no movement of the rocks on either side of the fracture.

Stratigraphic Trap

Origin (9): Source of North Sea Oil

Ancient Earth

© Ian and Tonya West

The Kimmeridge Clay is a Black Shale with up to 50% organic matter. It is the main source rock for the North Sea Oil & Gas

Province

Black Shale

Exploration and Production (3): Seismic Surveys

Earth Science World Image Bank Image #h5inpjEarth Science World Image Bank Image #h5inor

• 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!

Exploration and Production (5): Enhanced Recovery

© California Department of Conservation

• Although oil and gas are less dense than water and naturally rise up a well to the surface, in reality only 40-50% of the total will do so.

• To enhance recovery, a hole is drilled adjacent to the well and steam is pumped down. The hot water helps to push the oil out of the rock and up into the well.

Exploration and Production (6): Transport

United States Geological Survey

• Once extracted oil and gas must be sent to a refinery for processing

• Pipelines transport most of the world’s oil from well to refinery

• Massive Oil Tankers also play an important role in distribution

Trans-Alaskan Pipeline

Exploration and Production (8): Early History

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Abraham Gesner (1797-1864)

Californian oil gusher

• The modern era of oil usage began in 1846 when Gesner perfected the art of paraffin distillation.

• This triggered a massive worldwide boom in oil production.

• California was centre of activity in the early 1900s, famous for its gushers.

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