Oil Seeps – the only real Direct Hydrocarbon
Indicator
Chris Parry,
Regional and New Ventures Exploration,
E.ON Exploration & Production
chris.parry@eon.com
“A look at the exploration history of the important oil areas of the world proves
conclusively that oil and gas seeps gave the first clues to most oil producing
regions. Many great oil fields are the direct result of seepage drilling.”
Link (1952).
FORCE “Underexplored Plays”, Stavanger, April 8/9th, 2015.
Presentation Outline
Hydrocarbon Seeps:
- Macroseepage,
- Microseepage.
Onshore hydrocarbon macroseepage detection:
- Seeps,
- Mud volcanoes.
Offshore hydrocarbon seepage detection:
- Mud volcanoes,
- Pockmarks,
- Gravity coring.
Summary and Conclusions
2
Exploration Success Rates – Risk Reduction
Typical Exploration Failures
Charge
(30%)
Seal
(45%)
Most wildcat failures are due to the
fluid component of the petroleum
system:
- Hydrocarbon charge
or
Trap
(10%)
Reservoir
(15%)
- Retention
Hydrocarbon Seepage:
Oil or gas fields emit a continuous stream of light hydrocarbon gases
to the earth's surface known as macro- and microseepages.
3
Hydrocarbon Seepage.
Macroseepage illustrate the presence of hydrocarbons
in a basin but may have travelled long distances, while
microseepage travels vertically from charged reservoirs
and thus are true Direct Hydrocarbon Indicators.
Macroseepage:
- large concentrations of migrated hydrocarbons,
- visible oil staining and odour,
- migrate laterally via porous, permeable damage
zones of faults, injectites or vents,
- can be detected at the surface.
Microseepage:
- chemically detectable,
- concentrations lower than macroseepage,
- no visible hydrocarbons or odour,
- migrate vertically via grain boundaries in the
rock,
- diagenetically altering the rocks through which
they pass,
- can be detected at the surface.
4
Fant olje i
første forsøk
I mange av
steinprøvene fra
de utgående
lagene på ØstGrønland kan
geologene både
se og lukte olje.
Her er det
Reidun
Myklebust i
TGS som gleder
seg over et
«oljefunn».
- Det lukter olje!
Macroseepage - Oil
La Brea Tar Pit Museum (California)
“A look at the exploration history of the important oil areas of the
world proves conclusively that oil and gas seeps gave the first clues
to most oil producing regions. Many great oil fields are the direct
result of seepage drilling.” Link (1952).
Natural oil seeps such as these in California were exploited by the
native Americans (Achomawi and Maidu tribes) who used Asphaltum
for face painting, waterproofing boats and baskets and even chewing
gum!
Oil seep McKittrick area (California)
The European immigrants used it to grease their wagon wheels and
later the seeps were mined by settlers, and crudely refined oil to
pave roads, to burn in oil lamps, and as a lubricant for machinery.
In the Middle East, the Dead Sea was exploited from the earliest
times. The supply of asphalt was so well known that the Romans
called it Lacus Asphaltites:
- Genesis 6:14 “make the ark with rooms, and shall cover it inside
and out with pitch”
USGS: oil seep origins (1907)
- Genesis 11:3 “and they used brick for stone, and they used
bitumen for mortar“
- Genesis 14:10 “the Valley of Siddim was full of tar pits"
- Exodus 2:3 “she got a papyrus basket for him and coated it with
tar and pitch”
5
Open pit seep mining (1850’s)
By the 1850's and 60's some of the early California
settlers were mining oil from natural seeps.
The oil was mined by digging pits and tunnels at
seep sites, and, eventually, by drilling under natural
seeps in search of underground oil reservoirs.
Prospector mine shaft (1860’s)
Most early discoveries of oil in California were found
in this way.
Top figure: oil prospectors first mined asphaltum by
digging open pits where seeps occurred
La Brea oil derricks (1910)
Middle figure: This mine shaft in the McKittrick
asphaltum mine (Kern County) was built in the
1860's with redwood timbers. Oil prospectors were
often former gold miners, so they tried to use hardrock mining methods for extracting asphaltum and
heavy oil.
Lower figure: The Tar Pits in 1910; oil derricks can
be seen in the background
6
Macroseepage - Gas
Temple of Eternal Fire (Baku), 1860
Mud Volcanoes are low-temperature examples of seepage
related geomorphological features and exhibit the most
spectacular evidence of subsurface fluid venting, with
powerful eruptions sometimes accompanied by flames of up
to several hundreds of meters.
Vented fluids are a complex mixture of hydrocarbon gases
(methane and wet hydrocarbons), hydrogen sulphide,
carbon dioxide, petroleum, pore waters and mud.
Comprehensive literature of numerous mud volcano
provinces demonstrate ovewhelming evidence for role of
hydrocarbon gases in their formation (biogenic and thermal
methane have different 13C content).
Direct evidence of generation, migration and
hydrocarbon potential of deeper subsurface sediments.
Lokbatan 2010 eruption (Azerbaijan)
7
World’s most active mud volcano
Conical mud volcano: basic structure & main elements
(simplified after Dimitrov, 2002)
Onshore to Offshore
1 BBOR+ Oil field area
"smelled of petroleum"
Gas bubbles – no
associated oil
8
Offshore Macroseepage
Active mud volcano fluid leakage
(Black Sea)
WD 2080m
Greinert et al., 2006
Mud Volcanoes are mainly found in active accretionary
prisms or compressional settings:
vented fluids document subsurface petroleum systems
mud flows often contain litho clasts of the underlying
geology (Black Sea mud volcanoes have erupted both
the Oligo-Miocene Maikop Fm super source rock and
several different reservoir rocks).
Dredge samples Stock-on-Trent mud volcano,
(United Nations Rise, Mediterranean Sea)
(adapted and simplified after Dimitrov, 2002)
Sandstone
Active pockmark fluid leakage
(Vestnesa Ridge)
Shale
Sandstone
Bünz et al., 2012
Shale
WD 1200m
9
Pockmarks: mainly found in unconsolidated fine-grained
siliciclastic setting in a wide range of tectono-stratigraphic
settings associated with structural or stratigraphic
discontinuities:
unconformities,
faults,
anticlines,
diapirs and
shallow buried channels..
Offshore Macroseepage Detection
Seepage mapping is much more difficult offshore
but has been documented off California, the Gulf of
Mexico (first described by the Spanish explorers in
16th century), the Labrador Sea, deepwater West
Africa (Angola, Nigeria) and the Barents Sea.
Surface slick
suppresses wind
ripple waves
Sea surface wind
ripple waves
Oil coated gas
bubbles
Current
Macroseepage
Gas Chimney
LEGEND
Oil coated
gas bubble
Pock mark
Macroseepage
Microseepage
Backgroud
seepage
10
Seafloor hydrocarbon escape features are pock
marks or mud volcanoes:
- Gas bubbles with oil film burst at surface
Bragg scatter
creating an oil ‘pancake’,
from wind ripples
- Sustained seepage results in ‘pancakes’
coalescing into a slick, which dampens wind
Fresnel scatter
from oil film
ripples and can be observed from space.
Synthetic Aperture Radar (SAR) is an excellent tool
for detecting oil slicks and vessels:
- Covers large geographic areas,
- Independent of day light,
- Sees through cloud and fog.
SAR can distinguish between natural occuring
seeps versus man-made pollution:
- fresh oil is much thicker than the natural film of
oil associated with an active oil seep.
Natural Oil Seep
(click on image for video controls)
Courtesy Alan Williams, NPA Satellite Mapping, CGG
11
Natural Oil Seepage
Detecting Offshore Oil Seepage
Proven low cost, high coverage
technique for exploring new
basins.
Very effective in deep and ultra
deep offhsore basins.
Reduces exploration risk on
source rock presence and
maturity.
Pollution: Fresh oil is much thicker than the natural film of oil associated with an active oil seep
Seismic evidence of hydrocarbon leakage used to design
seabed geochemical surveys
- Biological build-ups at or near sea floor:
- amplitude anomalies,
- time pull-ups,
- Mechanical disturbance of shallow sediments:
- mud volcanoes,
- pock marks,
- Diagenetic alteration of shallow sediments (Methane Derived Authigenic
Carbonates - MDACs):
- commonly carbonate precipitation,
- Shallow gas,
- Gas chimneys,
- Hydrocarbon-Related Diagenetic Zones (HRDZs),
- Rock property variations due to hydrocarbon presence (DHIs):
- bright spots,
13
- flat spots.
Offshore Seep Sampling
14
Gravity Piston Coring: Seafloor Geochemistry
Gravity piston core samples:
- Grid covering prospect and background,
- Headspace gas analyses (C1 – C5),
- Gas Chromatography Mass Spectroscopy,
- TOC/Rock-Eval,
- Vitrinite reflectance,
- Biostratigraphy
- XRD,
- Porosity/permeability,
- Petrography,
- SEM.
Microseepage
Background
LEGEND
Core location
Pock mark
Macroseepage
Source rock characteristics revealed by
biomarkers (fingerprinting):
- Relative abundance oil-prone vs. gas-prone
organic matter,
- age,
- environment of deposition (marine,
lacustrine, fluvio-deltaic or hypersaline),
- lithology (carbonate vs. shale vs. coal),
- thermal maturity during generation.
Microseepage
Backgroud
seepage
15
15
Calibrate basin modeling results.
Micro seepage Rate: Keta Dome Gas Storage Reservoir (Iowa)
Surface Ethane Anomalies
Saint Peter Sandstone (Ordovician) ca 300m below surface)
Empty
Geochemical
Survey Grid
July 1988
Charged for
winter use
October 1988
3 months (90 days)
Empty after
winter use
Winter use
January 1989
3 months (90 days)
April 1989
4 months (120 days)
Vertical movement due to gravity of gas bubbles
Migration Type?
- Buoyancy,
- Effusion (1 m/day),
- Dispersion (1 mm/year).
Keta Dome microseepage rate: between 2.5 - 3.33 m/day
16
Redrawn and symplified after: Tedesco, (1999)
Summary and Conclusions
- Most of the world’s major hydrocarbon provinces are characterised by oil
seepage.
- Offshore, satellite detection of oil seepage can identify prospectivity in new
basins or identify regions to explore in areas previously dismissed as nonproductive (due to prevailing paradigms).
- Surface geochemical surveying can ground
Typical Exploration Failures
truth the satellite observations. Results need
to be fully integrated into the petroleum
system analysis:
Charge
(30%)
Seal
(45%)
- Seismic interpretation and
- Basin modeling.
Oil Seeps – the only real
Direct Hydrocarbon Indicator!
17
Trap
(10%)
Reservoir
(15%)
May the Source be with you!
Acknowledgements:
 E.ON management for support for this presentation,
 Alan Williams, NPA Satellite Mapping, CGG,
Jane Whaley, GeoExpro.
Bibliography
Bünz, S. & Mienert, J., 2012, Gas hydrate and shallow gas reservoirs in the
Barents Sea and on the Svalbard Margins: an unconventional resource or a
geohazard?
Carsten, H., 2012, Fant olje i første forsøk. Geo365.
Dimitrov, L.I., 2002, Mud volcanoes – the most important pathways for
degassing deeply buried sediments. Earth Sci. Rev., v.59, 49-76.
Greinert, J., Artemov, Y., Egorov, V., De Batist, M., & McGinnis, D., 2006, 1300m
high rising bubbles from mud volcanoes at 2080m in the Black Sea:
Hydroacoustic characteristics and temporal variability. Earth & Plan. Sci. Letters,
v.244, 1-15.
Link, W.R., 1952, Significance of Oil and Gas Seeps in World Oil Exploration.
AAPG., v.36(8), 1505-1540.
Tedesco, S.A., 1999, Anomaly shifts indicate rapid surface seep rates. Oil & Gas
Journal, 97 (13).
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