Chapter 1

 In order to have hydrocarbon to accumulate we need to have sediment basin, High level of organic materials, and temperature/pressure.  Source Rock is sedimentary materials made of organic-rich matters.  Maturity describes the degree to which petroleum generation has occurred.

 Heavy, thick oil is considered immature, having been generated at relatively low temperature. Mature oil—lighter or less viscous—forms at higher temperature.  Migration is the process of hydrocarbons moving out of source rock through cracks, faults, and fissures into the porous and permeable reservoir rock.  Reservoir rock immobilizes the reservoir within structure called trap.

 Bacterial processes deep in seabed mud convert organic matter into a waxy material called kerogen.  Different periods of geological eras effect creation of kerogen; Middle Cretaceous about 100 million years ago account for 30% and late Jurassic about 150 million years ago account for 25%.

 Kerogen concentrations as low as 1 % to 3 % make source rock (shake or limestone) suitable for commercial exploitation of crude oil and natural gas.  Black shale is most common kind of source rock.  Geothermal Gradient of earth happens as the organic-rich source rock undergoes progressive burial (i.e., as additional sediments are laid down above it), the rock becomes hotter.

 From the surface to a depth of about 60 meters (200 feet), ground temperature maintains a relatively constant 11°C (55°F).  The term oil window is used to describe the range of temperature or depth within which most of oil’s complex constituents are produced. This window is typically (176– 428°F) or (7,200–18,000 feet).

 Maturation is the process where Kerogen in source rock undergoes conversion to petroleum due to pressure (imposed by overlying rock and sediment), the presence of heat-tolerant bacteria that act on the oil, and the presence of hydrogen and oxygen (from water and surrounding minerals).  Peak kerogen to petroleum conversion occurs at about 100°C (212°F).

 If the temperature rises above 130°C (266°F) for even a brief time, then crude oil itself begins to break into smaller molecules, and gas starts to be produced.  Virtually all commercially viable oil reservoirs result from migration that takes the hydrocarbons away from the source rock and into reservoir rock.  Notable clastic depositions are found in the Gulf Coast and several Venezuelan coastal fields, the Niger River delta in Africa, and the south Caspian Sea.

 Carbonate rock is typically formed by a chemical reaction between calcium and carbonate ions in shallow seas, or by a process called biomineralization.  In a promising hydrocarbon-bearing formation, oil and gas have migrated into what is called a trap.  By some estimates, nearly 80% of the world’s largest oil reservoirs are found in anticlinal traps.

 Hydrocarbon accumulations are typically associated with normal and thrust faults.  Stratigraphic traps are created when a seal or barrier is formed above and around an oil- or gas-bearing formation by sedimentary deposition of impermeable rock.  Most wells pump not only oil and gas but also mineral-laden water called brine.

 By some estimates, an average of about 10% of all the gas and oil that forms in a sedimentary basin ever reaches a trap.