World Geography

Unit 4: Primary ResourcesEnergy from the Oceans

How Oil Is Formed

►The formation of oil takes millions of years.►Most geologists believe that the formation of

petroleum began when plants and animals of the oceans died and settled on the ocean floor millions of years ago.

►Over many thousands of years bacterial action and extreme pressure from layers of sediment converted the organic matter to oil and gas.

►The pressure also created tremendous amounts of heat which helped the process along.

Forming Oil Reservoirs

► For oil recovery to be a profitable venture the oil needs to collect in pools under the rock.

►These pools form where Non-Porous rock lie above Porous sedimentary rock

►Water and pressure drive the oil up through the sedimentary rock until it pools under the cap rock.

►This is called a Oil and Natural Gas Trap.►There are four main types of oil and natural

gas traps.

Forming Oil Reservoirs

►Reserve – the amount of oil in a reservoir that can be brought to the surface.

►Due to limiting factors in reservoir characteristics and extraction technology, not all the oil in a reservoir can be extracted.

►The size of the reserve can be increased through investment in extraction technology. This is what is meant by “recoverable barrels of oil” when governments talk about oil fields.

The Four Main Types of Oil and Natural Gas Traps

►There are four common types of oil and natural gas traps: Fold trap Fault trap Salt dome trap Stratigraphic (Limestone Relief) trap

Fold Trap

Fault Trap

Salt Dome Trap

Strategraphic Trap(Limestone Relief)

Finding Oil and Gas Reserves

►Before the 1900’s the search for oil was limited to areas of fault lines where residue seeped to the surface.

►Geologists soon started to look in areas of gentle aniticlines or faulted sedimentary rock where reservoirs of oil might occur. They drilled many wells without knowing if they would eventually hit some oil.

►Today offshore oil and gas companies make use of many modern tools in their search for oil.

How We Find Oil Under the Seabed

► Ships tow sound emitters through the water;► Sound penetrates the different rocks that

makes up the seabed and upper crust► The sound bounces back reflecting specific

signatures for each type of rock, and the depth of the rock

► The reflections are recorded by hydrophones and plotted on seismograms to create cross sections of the rock. (a side on view of the rock)

► Hundreds of cross sections are taken and combined to make a 3-D image of what the rock looks like

► The image is analyzed by geologists and the best possible place for oil deposits to be is determined

► Test wells called “wild cat wells” are drilled► There is a 10% chance that there will be oil in

the well

Patterns in the Distribution of Offshore Oil and Gas Reserves

►Different regions of the world have different amounts of offshore oil.

►The biggest producers can be found around the North Sea, the Gulf of Mexico and West Africa around the Ivory Coast.

►The production of these areas is measured in millions of barrels a day.

►Look at figures 11.2 and 11.3 in your text for specifics.