Hydrocarbons and Energy Flashcards
What is a hydrocarbon?
Naturally occurring compounds containing carbon and oxygen. These may be gaseous, liquid or solid.
Whats the most productive oil country
The middle east, they are in the centre of trade movement
What market do China control?
The rare earth element market
What is the hydrocarbon play?
A play is the particular set of circumstances that have combined to produce a group of oil or gasfields with similar trap structures or reservoir rocks.
What factors must be present to produce a hydrocarbon play?
- Source rock
- Reservoir
- Migration
- Cap/seal rock
- Trap
Structures must be there before hydrocarbon generation occurs.
Define a source rock:
Rocks containing sufficient organic substances to generate oil and gas.
Wheres the best source rock in Britain?
Kimmeridge Clay, organic rich shale, most oil from algae and bacteria
Whats the source for gas
Gas forms if Organic rich material (same that forms oil) like algae and bacteria is buried at depth (deeper than that to form oil)
- Coal is plant matter and also a source rock for gas.
On burial of the plant matter in source rock:
Carbohydrates and proteins of plants are destroyed, remaining organic compounds form Kerogen.
What is the oil and gas window?
At ~100 degrees C it breaks down to oil, at 160 degrees C the long hydrocarbon chains get shorter to give light oil and gas.
Define a reservoir
Its an underground rock formation with sufficient porosity to act as a store for oil or gas
What is porosity:
Not interconnected void space in a rock that can host gas/liquids
What is Permeability:
Ability of a rock to permit flow of fluids through it.
What makes a good reservoir?
- have sufficient porosity and permeability to store and migrate fluid
- best type is poorly stored sandstone
- limestone’s are permeable if they are fractured
What is a suitable cap rock?
Salt - or any impermeable rock
- migration is stopped or slowed
If the rock above and around a reservoir is impermeable it forms?
A trap - in which the seal is known as a cap rock
What is a Trap?
Oilfields and gasfields that are trapped in permeable reservoir rock.
What are the 3 types of trap and give examples:
- Structural (Anticline, fault)
- Salt dome
- Stratigraphic (pinch out)
How is shale gas different from other hydrocarbons
The rock that contains the hydrocarbons is very impermeable and so acts as hydrocarbon source rock, reservoir and seal. The gas is both produced and trapped in the shale.
Give opposition to fracking:
- Earthquakes/subsidence
- Groundwater contamination
- Britain is densely populated unlike America (British Columbia)
How is shale gas extracted?
Shale is drilled and artificially fractured so the gas can be extracted.
Fracking involves a process of pumping high pressure water into the shale along horizontal drill holes, to induce fracturing the rock, and the release of gas.
Whats in the Southern North Sea?
- Most hydrocarbon fields in North sea are gas
- Carboniferous coal measures
- burial beneath Permian sandstones and evaporites (salt)
- parts were at right depth for gas generation, which took place over 140Ma
Whats in the Northern North Sea?
- Oil fields
- buried rift valley, grabens (faults cause traps)
- hydrocarbon deposits occur in a variety of different rock types
- 140Ma Kimmeridge clay
- the most prolific oil bearing reservoirs are the Brent delta deposits (Jurassic)
- Brent delta deposits also contain coal seams from delta swamp
- Cretaceous rocks are the seals (mudstone)
What are the common principles of carbon capture storage (CCS)
Collect and purify CO2 typically from mixed source gases e.g. power station and car exhausts.
CO2 is stored indefinitely, how?
CO2 is piped offshore, its injected under high pressure via a well into the storage site. The site is usually an abandoned rig.
- Abandoned fields refill with saline water to produce saline aquifer which CO2 can be stored
- CO2 stored in gas field, both storage locations have caprocks.
Describe the main process of hydrocarbon exploration
Seismic data is generated by bouncing sound energy off geological layers in the interior of the earth to construct images of the rocks present based on their physical properties (velocity and density).
- In both 2D and 3D
Advantage of using seismic imaging to find hydrocarbons
They provide a useful way of imaging strata in the subsurface, they provide info on stratal geometries and ancient sedimentary systems.
Why don’t we use boreholes instead of seismic imaging
They are very expensive, especially under the sea.
What is seismic reflection imaging?
- It involves the reflection of elastic waves off subsurface geological interfaces.
- By measuring the travel time the distance to the reflector can be calculated
- data must be married to borehole data as rocks have different densities and therefore different velocities
What is coal?
A sedimentary, carbon rich deposit formed from the remains of fossil plants that can be used to produce energy.
How is coal measured?
By its RANK
What are the non-carbon components of coal?
Volatile matter