Oil and Gas - Exploration Flashcards
What is prospecting?
The search for crude oil and natural gas in the Earth using highly sophisticated petroleum engineering technology.
Prospecting will only be feasible if these 4 basic geological factors are present
(Aka a hydrocarbon system)
- Source rock and sufficient thermal maturation
- Organic-rich rock that can form hydrocarbons when subject to heat and pressure over time
1a. Thermal maturation
- As the source rock is buried deeper in the Earth, its temperature and pressure rises
- Natural gas formation already starts at the surface, but oil formation is only possible when the source rock is buried deep enough to reach 60C and no more than 160C (oil window) (around 2 - 5km)
- Below the oil window, any oil is broken down into lighter and shorter chains of hydrocarbons.
- Oil Production = Time spent within the oil window
- Time needed not only to produce the oil, but for it to migrate into the reservoir rock
- Reservoir rock
- A good reservoir rock acts like a sponge, holding a lot of oil and gas in a limited area
- The hydrocarbons collect in the pores of a reservoir rock or the open fractures in non-porous rocks - Migration pathway
- A pathway for oil and gas to migrate into the reservoir rock
- A good migration pathway will ideally divert oil and gas directly into reservoir rock - Cap rock
- An impermeable rock that layers over the reservoir rock and is resistant to oil and gas penetration
- Together with the trap rock, the cap rock prevents vertical and lateral escape of oil and gas (a dead end), and allows oil and gas to accumulate in large quantities
How do oil and gas form in nature?
Plankton, the most abundant form of life.
The offshore is the kitchen.
An abundance of plankton fossilised on the seabed rock.
The seabed rock is buried under layers and layers of sediments.
The pressure and high temperatures ‘cook’ the fossils, breaking them down into hydrocarbons.
It is possible to obtain oil and gas directly from the source rock
Yes, but you have to drill much deeper. In recent years however, it has become more economically feasible. Today, most production methods today still drill for reservoir rocks as it is still more feasible than drilling the source rock.
What are the qualities of a good reservoir rock?
High porosity
- Many open spaces in the rock that can hold oil and gas
High permeability
- The connectivity between the pore spaces
- Will affect the ease in which oil and gas can be extracted from the rock
What are the 3 types of reservoir rocks?
Limestone, shale, and sandstone
Why is shale an unconventional reservoir rock?
- It has very high porosity, but poor permeability
2. It also functions as a source rock
How do geologists make an educated guess of potential oil and gas reservoirs?
- Start with satellite images
- Measure subtle changes in the Earth’s gravity, caused by subtle variations in sub-surface rock. - Conduct seismic reflection mapping
- Energy waves travel down the subsurface of the rock, reflect off the interfaces of subsurface rock, and are recorded by arrays of pressure sensors that extend away from the energy source
- Produces a sedimentary profile.
- White area shows where the oil and gas is. - Compare with any data logged by previous drilling attempts in the vicinity
- Any seismic model will be more accurate if there is an existing well that the seismic data crosses.
- If the well was logged, the geophysical data of the surrounding rock types can be used to compare with the seismic data.
- Any core samples of actual rock - Study physical formations at the area
- Rivers, ancient rocks outcropped above ground - Develop detailed model of subsurface feature structure and rock composition and make an educated gas of location
What are the two types of property rights: Mineral rights and surface rights?
Mineral rights that allow the owner to exploit the subsurface beneath the land for minerals it may contain
Surface rights cover the land, soil and groundwater beneath it.
The government owns all mineral rights, while surface rights belong to landowner. T/F?
True
What does a company need to offer in order to lease the mineral rights from the government or private landowner?
Bonus (one-time payment)
Royalty (% of sales of oil and gas from drilling)
Primary term (the duration of the lease while the company is exploring for oil and gas)
Delay rentals (payment to owner if the company decides to postpone drilling during lease period)
Secondary term (extended term of lease if exploration is successful and a producing well is established)
Companies do not typically buy mineral rights. They seek to lease them instead. T/F?
True. Buying mineral rights outright is too risky. Mineral rights are also not valuable once all the oil and gas have been extracted.
Why is it better to have reservoir rock that is permeable and porous?
So that when holes are created in the target reservoir, oil can easily flow out into the well.
If the target reservoir is not sufficiently permeable or porous, then hydraulic fracking may need to be done to increase the permeability of the rock.
How has fracking revolutionised the oil and gas industry?
It has allowed oil and gas production to take place on low-permeability rock, such as shale rock.
What isolates the interior of an oil/gas well from the surrounding rock and fluids?
Casing made up of steel and cement
