4320lxr02v02subsurfaceenvts

7/30/2019 4320Lxr02v02SubsurfaceEnvts

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The Subsurface Environment(s) of Petroleum

University of Georgia Department of Geology GEOL 4320/6320 Petroleum Geology


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The Subsurface Environment(s) of PetroleumI. Depth

II. TemperatureIII. Water ChemistryIV. Pressure



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Typical depths:1,000 - 10,000 feet / 300-3000 metersDeepest petroleum well to date:

BPs 2009 Tiber discovery well in Gulf of Mexico35,055 ft / 10,685 m sub-seafloor in 4132 ft / 1259 m of water

in Lower Tertiary strataDrilled by the Deepwater Horizonrig destroyed in April 2010.

Deepest (?) onshore petroleum wellGHK #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)

TemperaturePressure

Water Chemistry



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TemperaturePressure

Water Chemistry



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BPs Tiber discovery well


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TemperaturePressure

Water Chemistry



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(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

PressureWater Chemistry



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(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



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Deepest petroleum well to date:BPs 2009 Tiber discovery well in Gulf of Mexico35,055 ft / 10,685 m sub-seafloor


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 feetDeepest offshore petroleum well: 35 thousand feetDeepest well/borehole of any sort: 40 thousand feet



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II. TemperatureRelevant range: 60-250CGeothermal gradients: 5-100C/km Typically ~25C/kmBottom-hole Temperatures (BHTs)Significance:

(past) Thermal maturation of kerogen to yield petroleum

Oil window: ~65-160CDecreased resistivity of formation watersDegradation / melting of drill bit




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(Lowest T of oil generation to ~metamorphism)


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Geothermal gradients:


From smu.edu/geothermal/heatflow/heatflow.htm


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Both are from smu.edu/geothermal/heatflow/heatflow.htm Heatflow (at right) = conductivity x gradient (at left)


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Alsharhan & Nairn 1997


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Alsharhan & Nairn 1997


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The Subsurface Environment(s) of PetroleumI. DepthII. Temperature

Relevant range: 60-250CGeothermal gradients: 5-100C/km Typically ~25C/kmBottom-hole Temperatures (BHTs)

Measured during logging, well after circulation has stopped.Significance:

(past) Thermal maturation of kerogen to yield petroleumOil window: ~65-160C

Decreased resistivity of formation watersDegradation / melting of drill bit




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Measured during logging, well after circulation has stopped.Significance:





U i i f G i D f G l GEOL 4320/6320 P l G l


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U i it f G i D t t f G l GEOL 4320/6320 P t l G l


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Measured during logging, well after circulation has stopped.Significance of temperature:






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North 1985


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Diagenetic reactions that destroy porosityDecreased resistivity of formation watersDegradation / 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)

and cementation (infiling of pores with minerals).


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North 1985


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The Subsurface Environment(s) of PetroleumI. DepthII. TemperatureIII. Water Chemistry

Increasing total dissolved solids / salinity with depthThus increasing density with depth

Cl- typically the dominant anionNa+ and Ca2+ the dominant cations



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North 1985

sw


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U i i f G i D f G l GEOL 4320/6320 P l G l


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North 1985



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Uni ersit of Georgia Department of Geolog GEOL 4320/6320 Petrole m Geolog


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The Subsurface Environment(s) of PetroleumI. Depth II. Temperature III. Water ChemistryIV. Pressure

Force/area Weight/area (psi)Lithostatic: Weight of overlying rockHydrostatic: Weight of overlying column of fluid

(in which density typically increases downward)

ResultsGreater pressure at depthCompaction of sediments/rocksOverpressure: subsurface liquid/gas pressure greater

than hydrostatic pressurePore fluids sealed below an impermeable stratum are pressurized

a) because of compaction (decrease of pore volume) orb) 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




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ii) Blowout of well




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ii) Blowout of well




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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 porositydecreasing from 25% in the uppermost 1000 feet to 4% at 20,000 feet.



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ii) Blowout of well


These two are not nearly

synonymous in the

isotropic sense

sometimes used in

structural

geology



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ii) Blowout of well



synonymous in the

isotropic sense

sometimes used in

structural

geology



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ii) Blowout of well



synonymous in the

isotropic sense

sometimes used in

structural

geology



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ii) Blowout of well




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North 1985

Note dearthof data in (e).



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ii) Blowout of well




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Dallmus, in Weeks (1958)

Note the inverted vertical scale.



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Dallmus, in Weeks (1958)



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ii) Blowout of well




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U e s ty o Geo g a epa t e t o Geo ogy G O 3 0/63 0 et o eu Geo ogy




Overpressure



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ii) Blowout of well

y g p gy gy



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ii) Blowout of well

y g p gy gy



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y g p gy gy



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y g p gy gy



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Results

Greater pressure at depthCompaction of sediments/rocksOverpressure: subsurface liquid/gas pressure greater




i) Less extensive compaction

ii)Fracturing of rock

y g p gy gy



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Results





i) Less extensive compaction

ii) Fracturing of rock



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Results





i) Less extensive compaction ii) Fracturing of rock

iii) Blowout of well



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200 foot flames at a 1998 natural gas well blowout near Bakersfield, CA.Image from Sandia National Laboratories via a Wilderness Society webpage..


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