10.3 Conventional Petroleum (Oil) and Methane (Natural Gas)
Jeff Simpson
Learning Objectives – By the end of this chapter, you should be able to do the following.
- Describe how petroleum and methane were formed.
- Draw the geology of a methane and petroleum reservoir.
- Describe where petroleum and methane are found in the world.
- List 5 ways we use methane and petroleum.
- List 4 environmental impacts of using methane and petroleum.
- List 4 political and social impacts of using methane and petroleum.
- Describe the production trends and explain why this trend is occurring.
Conventional Petroleum (Oil)
Organic-rich sediments deposited in shallow marine environments formed petroleum and gas, think shallow seas close to the continents. As the organic-rich sediments are buried, the sediments become , that is, converted into rock (typically , , or ) while the organic matter transforms into . The kerogen then changes into oil. The shale, mudstone, or limestone in which hydrocarbons form are the source rock. Once created, the oil and gas leak out of the source rock and migrate to a different rock, usually located above the source (Fig 10.5). The rock that hosts the hydrocarbons is called the reservoir rock.
Reservoir rocks are typically relatively allowing fluids to enter and move; this also facilitates recovery of the oil or gas. Sometimes, the oil liquids and gases make it all the way to the surface, where they sip. Ancient people used oil from sips in different ways. The oil and gas are oxidized at the surface and the carbon eventually returns to the atmosphere. In other cases, the fluids and gasses do not make it to the surface, they are trapped underground. An impermeable layer (e.g. mudstone or claystone) can seal the reservoir, impeding flow and storing the hydrocarbons underneath the Earth. The liquids and gases that are trapped within reservoirs become layered based on their density, with gas rising to the top, oil below it, and water underneath. [3]
Video 10.3.1 – Oil 101(2:16)
Video 10.3.3 – Oil Sands Production 101(2:18)
A trap is a combination of a subsurface geologic structure and an impervious layer that helps block the movement of oil and gas and concentrates it for later human extraction. The development of a trap could be a result of many different geologic situations. Common examples include: an anticline or dome structure, an impermeable salt dome, or a fault-bounded stratigraphic block (porous rock next to non-porous rock). The different traps have one thing in common: they pool the fluid fossil fuels into a configuration in which extraction is more likely to be profitable. Oil or gas in strata outside of a trap renders extraction is less viable.
Where Petroleum Is Found
Petroleum distribution varies widely around the world. This leads to global conflict. When those reserve are gone, they will not be renewed in our lifetime. Countries with proven oil reserves are shown below.
Conventional Methane (Natural Gas)
Figure 10.3.5 – Natural Gas 101 (3:38)
https://www.youtube.com/watch?v=-njmj0diWu8
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Figure 10.3.5 – Hydraulic Fracturing 101 (2:08)
Figure 10.3.7 – LNG 101 (2:23)
Where Methane Is Found
The solidification of loose sediment materials as solid sedimentary rock through compacting pressures and cementation.
A clastic sedimentary rock made of very fine-grained sediments such as muds, clays, and silts.
A rock composed of consolidated mud (clay, silt, or a combination of the two.)
An organic or chemical sedimentary rock that is primarily composed of calcium carbonate (CaCO3). Limestone is a subgroup of rocks that includes chalk, coquina, and fossiliferous limestone.
fossilized insoluble organic material that can be converted to petroleum.
Having permeability. The relative ease of fluid flow in a porous material
