Conventional Oil and Gas *This map of North America shows the major onshore oil and gas producing regions. The offshore regions are not shown. *Whether oil/gas is produced onshore or offshore, the truth is that the vast majority of oil/gas is of shallow marine origin!

*Fossil hydrocarbons (oil & gas) are produced from the breakdown of organic material that settles to the ocean floor and gets buried by the inorganic (i.e. clay and dust) sediment that is also settling to the ocean floor. *The water column over the continental shelves is enriched in nutrients that have washed off the continents. These nutrient-rich conditions promote rich populations of algae that settle to the ocean floor upon death. *Terrigenous sediments (i.e. mud, sand, etc. washed off the continents) bury these organics. As an example, 8 km of organic-rich sediment have accumulated off the East Coast of North America in the 200 million years since the Atlantic began to form.

The deeper the sediments are, the older they are and the greater the temperature and pressure they have experienced. With depth the sediments alter to sedimentary rocks: mud goes to mudstone (also called shale) and sand goes to sandstone. The complex organic material is broken down by the action of anaerobic bacteria in the shallow sediment and at depth by high temperature (called thermal maturation). In the shallow sediments the anaerobic bacteria produce methane (CH4) that is naturally stored in methane hydrates (see below). The organics that survive to be buried to greater depths are broken down by the high temperature to oil and gas (thermal maturation).

The oil and gas are not in vast underground caves *The oil and gas are not in vast underground caves. Instead the oil and gas together with seawater are trapped in the almost microscopic spaces between sand grains called interstices. *The oil and gas droplets being lighter than the seawater would tend to float up and out of the sediments and into the ocean except for natural barriers like impermeable rock layers called cap rock. *The shale layers are particularly rich in organics and are called source rocks. The oil and gas flow rapidly out of the sandstone layers; They are called reservoir rocks because it is form them that the oil wells draw the oil/gas out of the ground.

*Finally there have to be natural underground rock structures that allow the oil and gas to concentrate in large enough “pools” or reservoirs to make it economically worthwhile to produce. *In the previous figure the originally flat rock layers have be bent by underground forces into a dome. The oil and gas being lighter than the trapped seawater float under the cap rock to the highest parts of the dome. *Things like cap rock, domes and other structures that concentrate the oil/gas are known as traps. *Again it is important to realize this is not happening in vast underground caves, but through the interstices between sand grains. *Concluding: 4 things are necessary for an economic reservoir: source rocks, reservoir rocks, thermal maturity and traps.

Typical Oil Platform off California

Platform in the Gulf of Mexico

Oil Platform in the North Sea

Gas hydrates: *Gas hydrates form in the subfreezing tundra of Siberia and northern North America, and in the sediments on the continental shelves which are under high water pressure. *The methane (CH4) produced by anaerobic bacteria as they breakdown organic material reacts with water in the sediment to form an ice-like material in which the methane is trapped in “cages” of water molecules. ←Methane hydrate atomic structure. (the blue spheres are CH4 molecules)

JOIDES Resolution research ship drilling into gas hydrates

A piece of gas hydrate brought to the surface. It can be set on fire.

Gas Hydrate: What’s left is a fizzing piece of mud.

Seafloor distribution of gas hydrates

Exploratory drilling for methane hydrate in the Canadian Arctic

Methane hydrate from the permafrost

But at present the technology has not been developed to extract it. Gas hydrates contain centuries worth of burnable natural gas, primarily methane (CH4) But at present the technology has not been developed to extract it.