Upload
didina
View
37
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Possible effects of glacial events on hydrocarbon accumulations. Pressure loss, adjustment to hydrostatic or underpressure Temperature loss. Erosion. Gascap expansion and gas exsolution. Transient effects: Pressure gradients, difference in contacts across subtle barriers - PowerPoint PPT Presentation
Citation preview
Possible effects of glacial events on hydrocarbon accumulations
ErosionPressure loss, adjustment to hydrostatic orunderpressure Temperature loss
Transient effects: Pressure gradients, difference in contacts across subtle barriersHigh temperature gradient
Gascap expansion and gas exsolution
1000
2000
3000
1 20
Volumøkning av gassekspansjon, 1500 m erosjon
Dyp i meter
Barents Sea: Cooling commonly results in net leakage of gas from traps
Residual oil
Ice cover and cold periods
Low temperaturePossible permafrost and gas hydratesPossible pressure build-upPossible stress changeTransient low temperature
Hydrostatic pressure increasePossible gas hydratesPossible pressure build-upTransient slightly lower temperature ?
Vol gas = constant
Vol oil = constant
Tilting of oil – gas accumulation
Residual oil in water
When the field is tilted, the gas and oil will adjust to the new trap volume. If there is no migration, leakage or pressure change, the volume is preserved. When oil is swept by gas or water, some residual oil is left. Gas sweeps oil more efficiently than water, so oil shows in the gas zone are expected to be weaker than in the water.The paleo-contact reveals the position of the original contact. However, the paleocontact is not necessarily of the same age everywhere.
W E
Residual oil in gas
Sketch profile of Hammerfest Basin Fields
Snøhvit Askeladd Albatross Goliat
1500
2500
2000
1000
Fast migration and spill of hydrocarbons:
The impact of Plio-Pleistocene history on oil zones and residual oil in the Troll Field
Janka RomWenche Tjelta JohansenTrond Brekke (Brekke Chemo) Fridtjof Riis
Stavanger
Bergen
Troll field
35x55 km,
Located in the glacially eroded Norwegian channel (Norskerenna),
50 km from the coast
Belongs to the rim zone of Scandinavia which was affected by Cenozoic uplift
20 km
500 ms
Troll
migration
tilting
erosion
Viking Graben
Troll: Tectonic setting and migration routes
1km
2km
GNSR-119A
Northern connection Middle connection
Southern connection
TROLL EASTGas, 0 – 6 m oil
TROLL WESTGas province, 13-14 m oil
TROLL WESTOil province, 22-27 m oil
Pr/n-C17
9.0 (oil)
4.64.93.8
4.0 (Sognefj.)1.1 - 2.7
5.3
0.9 - 1.7
2.2 Sognefjd. and oil)
1.5 (Water zone)
19.0 (oil)2.5
1.5 (water zone)
1.9 (oil)
0.7 (Sognefjd.)
2.0 (oil)
1.10- 1.8
3.5 (Sognefjd.)2.3 (oil)
5.5 – 14.4 (Water zone
%CO2 in gas
2.3
1.7 0.6
1.2
2.0
0.3 – 0.6
1.2
1.7 – 3.0 0.50.3
0.3 –0.4
0.1 – 0.3
0.1
0.5 – 1.1
Biodegradation
Oil and residual oil: strong biodegradation in the W, weak in the east
Temperature from DSTBiodegradation is observed in shallow North Sea fields, limited to approx 1700 m below sea floor
Less biodegradation in Troll East than Troll west – supports a deeper initial burial of Troll East
Troll Paleo oil Well observations: thickness of residual oil below oil zone
,
Residual oil and paleo contacts in wells EOM data from Horstad et al.
0 50 mg/g EOM
1600
1550
?
?
4D seismic effect (1991-2005)
Low water saturations - orange colours.Residual oil zone - purple colour.
W E
Smoothed time thickness map of the difference between the black and the red reflector. Reflects thickness of paleo oil zone
Water saturation profile
Troll Paleo oil
STOIIP in paleo oil zone, assuming average Sw = 0,2
• TWOP: 125 mill Sm3
• Total: 423 mill Sm3
Map of Troll showing depth of conceptual paleo oil water contact
Vol gas = constant
Vol oil = constant
Tilting of oil – gas accumulation
Residual oil in water
When the field is tilted, the gas and oil will adjust to the new trap volume. If there is no migration, leakage or pressure change, the volume is preserved. When oil is swept by gas or water, some residual oil is left. Gas sweeps oil more efficiently than water, so oil shows in the gas zone are expected to be weaker than in the water.The paleo-contact reveals the position of the original contact. However, the paleocontact is not necessarily of the same age everywhere.
W E
Residual oil in gas
Top Sognefjordpresent60 m120 m
180 m250 m300 m500 m
Tilting of Troll
The animation starts with present day and geometrically tilts the structure back to 500 m tilt.(Mid Miocene?)
Reference level (grey horisontal surface) is based on the spill in the northern connection
Holocene tiltIsobases at the end of the Weichselian glaciation
20 m contours
Submerged beach
Younger Dryas isobases
Glaciation – tilting combined with pressure effects
100 m lowering of eustatic sea level:
10 bar pressure reductionTroll example: 7 % gas cap expansion4-5 m deeper gas oil contact
Ice stream in Norwegian channel 300 m higher than present sea level:
28 bar pressure increaseTroll example: 15 % gas cap contraction10 m shallower gas oil contact
Eustatic fallGlacial load
Glaciation effectson contact movements
40 m tilt
Eustatic fall
4-5 m downMax 25 m down
Glacial load
10 m upMax 10 m down
WEST
Eustatic fall
4-5 m downMax 15 m up
Glacial load
10 m upMax 30 m up
EAST
Timing of events
0
100
200
300
400
500
600
700
800
024681012
Ma
Tilt
re
lati
ve
to
pre
se
nt
da
y
800 m tilt Pliocene tilt 0,25 mm/year 500 m tilt 500m constant rate
Examples of possible uplift curves
Between 1,8 and 7,2 Ma
Between 1,2 and 4,4 Ma
First spill into Troll East
Between 180 and 300 m tilt
180 m300 m
• The paleo oil water contact in Troll was formed in the Neogene, probably prior to the Pleistocene and later than 6 Ma.
• At this time the field was tilted between 180 m and 300 m, and the gas volume was less than 60 % of the present volume. The corresponding rate of gas migration is in the order of 0,2 Mm3/year
• Glacial effects are not big enough to explain the paleo oil water contact
• In the western part of Troll, the oil zone may have been 20 – 25 m deeper in the Weichselian
• Oil shows in the gas zone mainly occur in the eastern part of Troll West, and were most likely formed during the Neogene tilt. A further study of these oil shows could give information about the thickness of the ice stream.
Conclusions