PART FIVEOff-shore Oil Formation and Reserves

How Oil Is Formed• Millions of years

ago plants and animals of the oceans died & settled on the ocean floor.

Bacterial action, extreme pressure and heat from layers of sediment converted the organic matter to oil & gas.

Oil reserves form when non-porous rock lies above porous rock. Oil seeps up through the porous rock & is trapped by the non-porous rock.

4 Types Oil Reserves Pg. 183

• Fold Trap: the up fold or anticline in the layers of the earth's crust form the reservoir.

• Fault Trap: the vertical movement of the earth's crust forms a pyramid or v-shaped reservoir.

• Salt Dome Trap: The salt dome forms an up-fold in the earth's crust not unlike the anticline caused by tectonic forces.

• Stratigraphic trap: has a former limestone reef as its porous rock feeding the reservoir.

Techniques Used to Locate Reserves

Before 1900’s• The search for oil was limited. Had to look along

fault lines for oil seeping to the surface.

After early 1900’s• Geologists knew to drill in gentle anticlines or

faulted sedimentary rock where reservoirs of oil might occur. (Not always successful).

• “Hit and miss” operations….

Modern oil exploration on the seas

1. Ships tow sound wave equipment over the ocean floor.

2. Sound waves penetraterock and are recorded and plotted.

3. A computer combines hundreds of these to get a3-D image of a rock structure.

4. A wild cat (test) well may be drilled.

Techniques Used to Locate Reserves“Wild cat” wells are drilled to test for oil:

– if they strike oil then delineating wells are drilled to determine the size of the reservoir.

– If they miss oil then the core samples are examined for evidence of oil.

Steps/stages in Oil Exploration: What is the SEQUENCE?????

• Recording sound waves using hydrophones

• Drilling wildcat wells, OIL or NO oil???

• Analyzing the seismic data

• If drilling produces a dry hole, core samples taken

• Directing sounds waves to ocean floor

• Additional wells used to determine size of reserve

Steps/stages in Oil Exploration: The SEQUENCE is…….

• Directing sounds waves to ocean floor

• Recording sound waves using hydrophones

• Analyzing the seismic data

• Drilling wildcat wells, OIL or NO oil???

• Additional wells used to determine size of reserve

• If drilling produces a dry hole, core samples taken

Patterns of Offshore Oil ProductionFIGURE 11.2 PG. 184

Patterns of Offshore Oil Production

FIGURE 11.2 PG. 184

• Most oil regions of the world are on land.

• Oil regions under the ocean floor are concentrated in the North Sea around the UK and in the Gulf of Mexico, and now off the coast of Newfoundland.

Gulf of Mexico North Sea West Africa (Ivory

Coast)

Patterns of Offshore Oil Production

• FIGURE 11.3 PG. 185

• It also reveals that offshore oil production is increasing faster than land production of oil.

• West Africa, especially around the Ivory Coast,

seems to have high oil reserves and is increasing in oil production.

Where are most of the world’s proven oil reserves located?