University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth
II. Temperature
III. Water Chemistry
IV. Pressure
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth
Typical depths:
1,000 - 10,000 feet / 300-3000 meters
Deepest petroleum well to date:
BP’s 2009 Tiber discovery well in Gulf of Mexico
35,055 ft / 10,685 m sub-seafloor in 4132 ft / 1259 m of water
in Lower Tertiary strata
Drilled by the Deepwater Horizon rig destroyed in April 2010.
Deepest (?) onshore petroleum well
GHK #1-27 Bertha Rogers in Washita County, Oklahoma
(Anadarko Basin) (1974)
31,441 feet / 9583 m, P&A in molten sulfur
Deepest drillhole to date:
Kola Superdeep Borehole in Kola Peninsula, Russia (1989)
40,230 ft / 12,262 m (drilled non-rotary with a mud-motor bit)
Temperature
Pressure
Water Chemistry
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth
Typical depths:
1,000 - 10,000 feet / 300-3000 meters
Deepest petroleum well to date:
BP’s 2009 Tiber discovery well in Gulf of Mexico
35,055 ft / 10,685 m sub-seafloor in 4132 ft / 1259 m of water
in Lower Tertiary strata
Drilled by the Deepwater Horizon rig destroyed in April 2010.
Deepest (?) onshore petroleum well
GHK #1-27 Bertha Rogers in Washita County, Oklahoma
(Anadarko Basin) (1974)
31,441 feet / 9583 m, P&A in molten sulfur
Deepest drillhole to date:
Kola Superdeep Borehole in Kola Peninsula, Russia (1989)
40,230 ft / 12,262 m (drilled non-rotary with a mud-motor bit)
Temperature
Pressure
Water Chemistry
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
BP’s Tiber discovery well
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth
Typical depths:
1,000 - 10,000 feet / 300-3000 meters
Deepest petroleum well to date:
BP’s 2009 Tiber discovery well in Gulf of Mexico
35,055 ft / 10,685 m sub-seafloor in 4132 ft / 1259 m of water
in Lower Tertiary strata
Drilled by the Deepwater Horizon rig destroyed in April 2010.
Deepest (?) onshore petroleum well
GHK #1-27 Bertha Rogers in Washita County, Oklahoma
(Anadarko Basin) (1974)
31,441 feet / 9583 m, P&A in molten sulfur
Deepest drillhole to date:
Kola Superdeep Borehole in Kola Peninsula, Russia (1989)
40,230 ft / 12,262 m (drilled non-rotary with a mud-motor bit)
Temperature
Pressure
Water Chemistry
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth
Typical depths:
1,000 - 10,000 feet / 300-3000 meters
Deepest petroleum well to date:
BP’s 2009 Tiber discovery well in Gulf of Mexico
35,055 ft / 10,685 m sub-seafloor in 4132 ft / 1259 m of water
in Lower Tertiary strata
Drilled by the Deepwater Horizon rig destroyed in April 2010.
Deepest (?) onshore petroleum well
GHK #1-27 Bertha Rogers in Washita County, Oklahoma
(Anadarko Basin) (1974)
31,441 feet / 9583 m, P&A in molten sulfur.
Deepest drillhole to date:
Kola Superdeep Borehole in Kola Peninsula, Russia (1989)
40,230 ft / 12,262 m (drilled non-rotary with a mud-motor bit)
Temperature
Pressure
Water Chemistry
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth
Typical depths:
1,000 - 10,000 feet / 300-3000 meters
Deepest petroleum well to date:
BP’s 2009 Tiber discovery well in Gulf of Mexico
35,055 ft / 10,685 m sub-seafloor in 4132 ft / 1259 m of water
in Lower Tertiary strata
Drilled by the Deepwater Horizon rig destroyed in April 2010.
Deepest (?) onshore petroleum well
GHK #1-27 Bertha Rogers in Washita County, Oklahoma
(Anadarko Basin) (1974)
31,441 feet / 9583 m, P&A in molten sulfur.
Deepest drillhole to date:
Kola Superdeep Borehole in Kola Peninsula, Russia (1989)
40,230 ft / 12,262 m (drilled non-rotary with a mud-motor bit)
Temperature
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth
Deepest petroleum well to date:
BP’s 2009 Tiber discovery well in Gulf of Mexico
35,055 ft / 10,685 m sub-seafloor
Deepest (?) onshore petroleum well
GHK #1-27 Bertha Rogers in Washita County, Oklahoma
31,441 feet / 9583 m, P&A in molten sulfur.
Deepest drillhole to date:
Kola Superdeep Borehole in Kola Peninsula, Russia (1989)
40,230 ft / 12,262 m (drilled non-rotary with a mud-motor bit:
With a lot of rounding:
Deepest onshore petroleum well: 30 thousand feet
Deepest offshore petroleum well: 35 thousand feet
Deepest well/borehole of any sort: 40 thousand feet
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth
II. Temperature
Relevant range: 60-250°C
Geothermal gradients: 5-100 °C/km Typically ~25 °C/km
Bottom-hole Temperatures (BHTs)
Significance:
(past) Thermal maturation of kerogen to yield petroleum
Oil window: ~65-160°C
Decreased resistivity of formation waters
Degradation / melting of drill bit
Pressure
Water Chemistry
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth
II. Temperature
Relevant range: 60-250°C
Geothermal gradients: 5-100 °C/km Typically ~25 °C/km
(Lowest T of oil generation to ~metamorphism)
Bottom-hole Temperatures (BHTs)
Significance:
(past) Thermal maturation of kerogen to yield petroleum
Oil window: ~65-160°C
Decreased resistivity of formation waters
Degradation / melting of drill bit
Pressure
Water Chemistry
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth
II. Temperature
Relevant range: 60-250°C
Geothermal gradients: 5-100 °C/km Typically ~25 °C/km
Bottom-hole Temperatures (BHTs)
Significance:
(past) Thermal maturation of kerogen to yield petroleum
Oil window: ~65-160°C
Decreased resistivity of formation waters
Degradation / melting of drill bit
Pressure
Water Chemistry
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
Geothermal gradients:
From smu.edu/geothermal/heatflow/heatflow.htm
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
Geothermal gradients:
Both are from smu.edu/geothermal/heatflow/heatflow.htm
Heatflow (at right) = conductivity x gradient (at left)
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
Geothermal gradients:
Alsharhan & Nairn 1997
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
Geothermal gradients:
Alsharhan & Nairn 1997
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth
II. Temperature
Relevant range: 60-250°C
Geothermal gradients: 5-100 °C/km Typically ~25 °C/km
Bottom-hole Temperatures (BHTs)
Measured during logging, well after circulation has stopped.
Significance:
(past) Thermal maturation of kerogen to yield petroleum
Oil window: ~65-160°C
Decreased resistivity of formation waters
Degradation / melting of drill bit
Pressure
Water Chemistry
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth
II. Temperature
Relevant range: 60-250°C
Geothermal gradients: 5-100 °C/km Typically ~25 °C/km
Bottom-hole Temperatures (BHTs)
Measured during logging, well after circulation has stopped.
Significance:
(past) Thermal maturation of kerogen to yield petroleum
Oil window: ~65-160°C
Decreased resistivity of formation waters
Degradation / melting of drill bit
Pressure
Water Chemistry
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth
II. Temperature
Relevant range: 60-250°C
Geothermal gradients: 5-100 °C/km Typically ~25 °C/km
Bottom-hole Temperatures (BHTs)
Measured during logging, well after circulation has stopped.
Significance of temperature:
(past) Thermal maturation of kerogen to yield petroleum
Oil window: ~65-160°C
Decreased resistivity of formation waters
Degradation / melting of drill bit
Pressure
Water Chemistry
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth
II. Temperature
Relevant range: 60-250°C
Geothermal gradients: 5-100 °C/km Typically ~25 °C/km
Bottom-hole Temperatures (BHTs)
Measured during logging, well after circulation has stopped.
Significance of temperature:
(past) Thermal maturation of kerogen to yield petroleum
Oil window: ~65-160°C
Decreased resistivity of formation waters
Degradation / melting of drill bit
Pressure
Water Chemistry
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
North 1985
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth
II. Temperature
Relevant range: 60-250°C
Geothermal gradients: 5-100 °C/km Typically ~25 °C/km
Bottom-hole Temperatures (BHTs)
Measured during logging, well after circulation has stopped.
Significance of temperature:
(past) Thermal maturation of kerogen to yield petroleum
Oil window: ~65-160°C
Diagenetic reactions that destroy porosity
Decreased resistivity of formation waters
Degradation / melting of drill bit
*Diagenesis: the physical and chemical modification of sediments that turns them into sedimentary rocks,
including but not limited to compaction (lessening of bulk volume)
Pressure
Water Chemistry
and cementation (infiling of pores with minerals).
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
North 1985
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth
II. Temperature
Relevant range: 60-250°C
Geothermal gradients: 5-100 °C/km Typically ~25 °C/km
Bottom-hole Temperatures (BHTs)
Measured during logging, well after circulation has stopped.
Significance of temperature:
(past) Thermal maturation of kerogen to yield petroleum
Oil window: ~65-160°C
Diagenetic reactions that destroy porosity
Decreased resistivity of formation waters
Degradation / melting of drill bit
Pressure
Water Chemistry
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth
II. Temperature
Relevant range: 60-250°C
Geothermal gradients: 5-100 °C/km Typically ~25 °C/km
Bottom-hole Temperatures (BHTs)
Measured during logging, well after circulation has stopped.
Significance of temperature:
(past) Thermal maturation of kerogen to yield petroleum
Oil window: ~65-160°C
Diagenetic reactions that destroy porosity
Decreased resistivity of formation waters
Degradation / melting of drill bit
Pressure
Water Chemistry
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth
II. Temperature
III. Water Chemistry
Increasing total dissolved solids / salinity with depth
Thus increasing density with depth
Cl- typically the dominant anion
Na+ and Ca2+ the dominant cations
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
sw
North 1985
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth
II. Temperature
III. Water Chemistry
Increasing total dissolved solids / salinity with depth
Thus increasing density with depth
Cl- typically the dominant anion
Na+ and Ca2+ the dominant cations
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth
II. Temperature
III. Water Chemistry
Increasing total dissolved solids / salinity with depth
Thus increasing density with depth
Cl- typically the dominant anion
Na+ and Ca2+ the dominant cations
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth
II. Temperature
III. Water Chemistry
Increasing total dissolved solids / salinity with depth
Thus increasing density with depth
Cl- typically the dominant anion
Na+ and Ca2+ the dominant cations
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
North 1985
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth II. Temperature III. Water Chemistry
IV. Pressure
Force/area Weight/area (psi)
Lithostatic: Weight of overlying rock
Hydrostatic: Weight of overlying column of fluid
(in which density typically increases downward)
Results
Greater pressure at depth
Compaction of sediments/rocks
Overpressure: subsurface liquid/gas pressure greater
than hydrostatic pressure
Pore fluids sealed below an impermeable stratum are pressurized
a) because of compaction (decrease of pore volume) or
b) because of diagenetic chemical reactions
that release liquid or gas (increase of fluid volume)
Potential results of overpressure:
i) Fracturing of rock
ii) Blowout of well
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth II. Temperature III. Water Chemistry
IV. Pressure
Force/area Weight/area (psi)
Lithostatic: Weight of overlying rock
Hydrostatic: Weight of overlying column of fluid
(in which density typically increases downward)
Results
Greater pressure at depth
Compaction of sediments/rocks
Overpressure: subsurface liquid/gas pressure greater
than hydrostatic pressure
Pore fluids sealed below an impermeable stratum are pressurized
a) because of compaction (decrease of pore volume) or
b) because of diagenetic chemical reactions
that release liquid or gas (increase of fluid volume)
Potential results of overpressure:
i) Fracturing of rock
ii) Blowout of well
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth II. Temperature III. Water Chemistry
IV. Pressure
Force/area Weight/area (psi)
Lithostatic: Weight of overlying rock
Hydrostatic: Weight of overlying column of fluid
(in which density typically increases downward)
Results
Greater pressure at depth
Compaction of sediments/rocks
Overpressure: subsurface liquid/gas pressure greater
than hydrostatic pressure
Pore fluids sealed below an impermeable stratum are pressurized
a) because of compaction (decrease of pore volume) or
b) because of diagenetic chemical reactions
that release liquid or gas (increase of fluid volume)
Potential results of overpressure:
i) Fracturing of rock
ii) Blowout of well
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The dashed curve labeled “Natural water” is the pressure trajectory of a water column with porewaters
increasing from G = 1.00 in the uppermost 1000 feet to 1.08 at 20,000 feet depth. The dashed curve labeled
“Natural strata” is the pressure trajectory of a stratigraphic section with a mineral G of 2.65 with porosity
decreasing from 25% in the uppermost 1000 feet to 4% at 20,000 feet.
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth II. Temperature III. Water Chemistry
These two are not nearly
IV. Pressure
synonymous in the
“isotropic” sense
Force/area Weight/area (psi)
sometimes used in
Lithostatic: Weight of overlying rock
structural
Hydrostatic: Weight of overlying column of fluid
geology
(in which density typically increases downward)
Results
Greater pressure at depth
Compaction of sediments/rocks
Overpressure: subsurface liquid/gas pressure greater
than hydrostatic pressure
Pore fluids sealed below an impermeable stratum are pressurized
a) because of compaction (decrease of pore volume) or
b) because of diagenetic chemical reactions
that release liquid or gas (increase of fluid volume)
Potential results of overpressure:
i) Fracturing of rock
ii) Blowout of well
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth II. Temperature III. Water Chemistry
These two are not nearly
IV. Pressure
synonymous in the
“isotropic” sense
Force/area Weight/area (psi)
sometimes used in
Lithostatic: Weight of overlying rock
structural
Hydrostatic: Weight of overlying column of fluid
geology
(in which density typically increases downward)
Results
Greater pressure at depth
Compaction of sediments/rocks
Overpressure: subsurface liquid/gas pressure greater
than hydrostatic pressure
Pore fluids sealed below an impermeable stratum are pressurized
a) because of compaction (decrease of pore volume) or
b) because of diagenetic chemical reactions
that release liquid or gas (increase of fluid volume)
Potential results of overpressure:
i) Fracturing of rock
ii) Blowout of well
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth II. Temperature III. Water Chemistry
These two are not nearly
IV. Pressure
synonymous in the
“isotropic” sense
Force/area Weight/area (psi)
sometimes used in
Lithostatic: Weight of overlying rock
structural
Hydrostatic: Weight of overlying column of fluid
geology
(in which density typically increases downward)
Results
Greater pressure at depth
Compaction of sediments/rocks
Overpressure: subsurface liquid/gas pressure greater
than hydrostatic pressure
Pore fluids sealed below an impermeable stratum are pressurized
a) because of compaction (decrease of pore volume) or
b) because of diagenetic chemical reactions
that release liquid or gas (increase of fluid volume)
Potential results of overpressure:
i) Fracturing of rock
ii) Blowout of well
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The dashed curve labeled “Natural water” is the pressure trajectory of a water column with porewaters
increasing from G = 1.00 in the uppermost 1000 feet to 1.08 at 20,000 feet depth. The dashed curve labeled
“Natural strata” is the pressure trajectory of a stratigraphic section with a mineral G of 2.65 with porosity
decreasing from 25% in the uppermost 1000 feet to 4% at 20,000 feet.
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth II. Temperature III. Water Chemistry
IV. Pressure
Force/area Weight/area (psi)
Lithostatic: Weight of overlying rock
Hydrostatic: Weight of overlying column of fluid
(in which density typically increases downward)
Results
Greater pressure at depth
Compaction of sediments/rocks
Overpressure: subsurface liquid/gas pressure greater
than hydrostatic pressure
Pore fluids sealed below an impermeable stratum are pressurized
a) because of compaction (decrease of pore volume) or
b) because of diagenetic chemical reactions
that release liquid or gas (increase of fluid volume)
Potential results of overpressure:
i) Fracturing of rock
ii) Blowout of well
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
North 1985
Note dearth
of data in (e).
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth II. Temperature III. Water Chemistry
IV. Pressure
Force/area Weight/area (psi)
Lithostatic: Weight of overlying rock
Hydrostatic: Weight of overlying column of fluid
(in which density typically increases downward)
Results
Greater pressure at depth
Compaction of sediments/rocks
Overpressure: subsurface liquid/gas pressure greater
than hydrostatic pressure
Pore fluids sealed below an impermeable stratum are pressurized
a) because of compaction (decrease of pore volume) or
b) because of diagenetic chemical reactions
that release liquid or gas (increase of fluid volume)
Potential results of overpressure:
i) Fracturing of rock
ii) Blowout of well
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
Dallmus, in Weeks (1958)
Note the inverted vertical scale.
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
Dallmus, in Weeks (1958)
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth II. Temperature III. Water Chemistry
IV. Pressure
Force/area Weight/area (psi)
Lithostatic: Weight of overlying rock
Hydrostatic: Weight of overlying column of fluid
(in which density typically increases downward)
Results
Greater pressure at depth
Compaction of sediments/rocks
Overpressure: subsurface liquid/gas pressure greater
than hydrostatic pressure
Pore fluids sealed below an impermeable stratum are pressurized
a) because of compaction (decrease of pore volume) or
b) because of diagenetic chemical reactions
that release liquid or gas (increase of fluid volume)
Potential results of overpressure:
i) Fracturing of rock
ii) Blowout of well
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
Overpressure
The dashed curve labeled “Natural water” is the pressure trajectory of a water column with porewaters
increasing from G = 1.00 in the uppermost 1000 feet to 1.08 at 20,000 feet depth. The dashed curve labeled
“Natural strata” is the pressure trajectory of a stratigraphic section with a mineral G of 2.65 with porosity
decreasing from 25% in the uppermost 1000 feet to 4% at 20,000 feet.
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth II. Temperature III. Water Chemistry
IV. Pressure
Force/area Weight/area (psi)
Lithostatic: Weight of overlying rock
Hydrostatic: Weight of overlying column of fluid
(in which density typically increases downward)
Results
Greater pressure at depth
Compaction of sediments/rocks
Overpressure: subsurface liquid/gas pressure greater
than hydrostatic pressure
Pore fluids sealed below an impermeable stratum are pressurized
a) because of compaction (decrease of pore volume) or
b) because of diagenetic chemical reactions
that release liquid or gas (increase of fluid volume)
Potential results of overpressure:
i) Fracturing of rock
ii) Blowout of well
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth II. Temperature III. Water Chemistry
IV. Pressure
Force/area Weight/area (psi)
Lithostatic: Weight of overlying rock
Hydrostatic: Weight of overlying column of fluid
(in which density typically increases downward)
Results
Greater pressure at depth
Compaction of sediments/rocks
Overpressure: subsurface liquid/gas pressure greater
than hydrostatic pressure
Pore fluids sealed below an impermeable stratum are pressurized
a) because of compaction (decrease of pore volume) or
b) because of diagenetic chemical reactions
that release liquid or gas (increase of fluid volume)
Potential results of overpressure:
i) Fracturing of rock
ii) Blowout of well
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth II. Temperature III. Water Chemistry
IV. Pressure
Force/area Weight/area (psi)
Lithostatic: Weight of overlying rock
Hydrostatic: Weight of overlying column of fluid
(in which density typically increases downward)
Results
Greater pressure at depth
Compaction of sediments/rocks
Overpressure: subsurface liquid/gas pressure greater
than hydrostatic pressure
Pore fluids sealed below an impermeable stratum are pressurized
a) because of compaction (decrease of pore volume) or
b) because of diagenetic chemical reactions
that release liquid or gas (increase of fluid volume)
Potential results of overpressure:
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth II. Temperature III. Water Chemistry
IV. Pressure
Force/area Weight/area (psi)
Lithostatic: Weight of overlying rock
Hydrostatic: Weight of overlying column of fluid
(in which density typically increases downward)
Results
Greater pressure at depth
Compaction of sediments/rocks
Overpressure: subsurface liquid/gas pressure greater
than hydrostatic pressure
Pore fluids sealed below an impermeable stratum are pressurized
a) because of compaction (decrease of pore volume) or
b) because of diagenetic chemical reactions
that release liquid or gas (increase of fluid volume)
Potential results of overpressure:
i) Less extensive compaction
ii)Fracturing of rock
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth II. Temperature III. Water Chemistry
IV. Pressure
Force/area Weight/area (psi)
Lithostatic: Weight of overlying rock
Hydrostatic: Weight of overlying column of fluid
(in which density typically increases downward)
Results
Greater pressure at depth
Compaction of sediments/rocks
Overpressure: subsurface liquid/gas pressure greater
than hydrostatic pressure
Pore fluids sealed below an impermeable stratum are pressurized
a) because of compaction (decrease of pore volume) or
b) because of diagenetic chemical reactions
that release liquid or gas (increase of fluid volume)
Potential results of overpressure:
i) Less extensive compaction
ii) Fracturing of rock
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
The Subsurface Environment(s) of Petroleum
I. Depth II. Temperature III. Water Chemistry
IV. Pressure
Force/area Weight/area (psi)
Lithostatic: Weight of overlying rock
Hydrostatic: Weight of overlying column of fluid
(in which density typically increases downward)
Results
Greater pressure at depth
Compaction of sediments/rocks
Overpressure: subsurface liquid/gas pressure greater
than hydrostatic pressure
Pore fluids sealed below an impermeable stratum are pressurized
a) because of compaction (decrease of pore volume) or
b) because of diagenetic chemical reactions
that release liquid or gas (increase of fluid volume)
Potential results of overpressure:
i) Less extensive compaction ii) Fracturing of rock
iii) Blowout of well
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology
200 foot flames at a 1998 natural gas well blowout near Bakersfield, CA.
Image from Sandia National Laboratories via a Wilderness Society webpage..
University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology