Generation of crude oil
Organic material in shale averages approximately one (1) percent of the shale rock
volume. Clay mineral constituents comprise the remaining 99 percent.
Kerogen is an insoluble, high molecular weight, polymeric compound which comprises
about 90 percent of the organic material in shale. The remaining 10 percent comprises
bitumens of varying composition, which, according to some researchers, is thermally
altered kerogen. As alteration occurs, kerogen is developed by the increasing temperature
in the closed system.
Temperature increases with depth. Normal heat flow within the earth’s crust produces an
average geothermal gradient of approximately 1.5 oF for each 100 feet of depth.
Maturation studies on various crude oil types indicate that temperatures required to
produce oil occur between the depth of approximately 5,000 feet and 20,000 feet under
average heat-flow conditions.
Pressure, like temperature, is a function of depth and increases 1 psi for each foot of
depth. Pressure is caused by the weight of the sedimentary overburden.
Bacterial action is important in the conversion of organic material to petroleum at shallow
depths. It is involved in the process of breaking down the original material into
hydrocarbon compounds, which eventually become biogenic gas.
Kerogen is a primary factor in forming bitumens that increase and migrate to accumulate
as crude oil. Thermal conversion of kerogen to bitumen is the important process of crude
oil formation. Thermal alteration increases the carbon content of the migratable
hydrocarbons, which leaves the unmigratable kerogen components behind.
Maturation of kerogen is a function of increased burial and temperature and is
accompanied by chemical changes. As kerogen thermally matures and increases in carbon
content, it changes from an immature light greenish-yellow color to an overmature black,
which is representative of a higher coal rank
Organic material in shale averages approximately one (1) percent of the shale rock
volume. Clay mineral constituents comprise the remaining 99 percent.
Kerogen is an insoluble, high molecular weight, polymeric compound which comprises
about 90 percent of the organic material in shale. The remaining 10 percent comprises
bitumens of varying composition, which, according to some researchers, is thermally
altered kerogen. As alteration occurs, kerogen is developed by the increasing temperature
in the closed system.
Temperature increases with depth. Normal heat flow within the earth’s crust produces an
average geothermal gradient of approximately 1.5 oF for each 100 feet of depth.
Maturation studies on various crude oil types indicate that temperatures required to
produce oil occur between the depth of approximately 5,000 feet and 20,000 feet under
average heat-flow conditions.
Pressure, like temperature, is a function of depth and increases 1 psi for each foot of
depth. Pressure is caused by the weight of the sedimentary overburden.
Bacterial action is important in the conversion of organic material to petroleum at shallow
depths. It is involved in the process of breaking down the original material into
hydrocarbon compounds, which eventually become biogenic gas.
Kerogen is a primary factor in forming bitumens that increase and migrate to accumulate
as crude oil. Thermal conversion of kerogen to bitumen is the important process of crude
oil formation. Thermal alteration increases the carbon content of the migratable
hydrocarbons, which leaves the unmigratable kerogen components behind.
Maturation of kerogen is a function of increased burial and temperature and is
accompanied by chemical changes. As kerogen thermally matures and increases in carbon
content, it changes from an immature light greenish-yellow color to an overmature black,
which is representative of a higher coal rank
