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Publications List
Posted 07/07/00
Surface Geochemical Exploration
continues to progress global deepwater frontiers
N.R.
Cameron (consultant to TDI-Brooks International, Inc.
and GeoMark Research, Inc.)
James M. Brooks and
Bernie B. Bernard
(TDI-Brooks International, Inc.)
John E. Zumberge and
Stephen Brown (GeoMark
Research, Inc.)
Introduction
This paper is an invited update relating
to a presentation delivered to the 1998 IBC "Worldwide
Deepwater Technologies" forum (Cameron et al., 1998).
Extensive use is also made of two other presentations to IBC,
both given in 1999. These were to the Nigeria Energy Summit
in June (Cameron et al., 1999) and to the Oil and Gas Developments
in West Africa meeting in October (Cameron and White, 1999).
In deepwater exploration a crucial, and arguably
the most critical single issue, is whether oil has been generated,
and if it has, what can be determined, before making costly
decisions, regarding the quality, maturity and the age of
the source succession. With the choicest deepwater acreage
continuing to attract large signature bonuses and with wells
in some cases costing in excess of $US 50-60 million, a reliable
means of assessing source rock risk is required.
Whilst trap geometry details and reservoir
horizons can be predicted from seismic with increasing degrees
of confidence, no fail proof method exists for remotely predicting
the composition of reservoir fluids and gases. AVO theory
provides some degree of control, but continuing dry holes
show that serious interpretational issues persist. Fortunately,
since oil and gas accumulations are invariably leaky, Surface
Geochemical Exploration (SGE) can be used to recover and type
migrant hydrocarbons before committing to either blocks or
wells. The goal is to initially high-grade open acreage and
subsequently rank prospects by means of gas and high molecular
weight hydrocarbon screening of piston-cored samples. Heatflow
surveys and the collection of geological samples for age,
source quality (Total Organic Carbon, etc.) and maturity determinations
(Tmax etc.) are also permitted, together with a wide variety
of geotechnical programmes.
The traditional onset of the deepwater is
the 200-metre (660-feet) shelf edge isobath. Increasingly,
the deepwater commences at the 500 metres (1640 feet) isobath
with the ultra-deepwater commencing at 1500 metres (4920 feet).
Now, as the exploration and technology horizon advances oceanwards,
terms such as ultra-ultradeepwater are emerging for the 2500
metres (8200 feet) plus frontier. These distinctions are not
utilised in this review and all water depths greater than
200 metres are referred to as deepwater.
Since its formation in 1996 TDI-Brooks has
conducted SGE
surveys in the following countries, Angola, Gabon, São
Tome, Equatorial Guinea, Nigeria, Brazil, Trinidad, Barbados,
Colombia, the USA (Gulf of Mexico) and Mexico. A total of
3500 cores have been collected, almost exclusively from deepwater
settings. Additionally, TDI-Brooks has acquired about 500
deepwater heatflow measurements as part of their multiclient
and private programmes.
Why can the deepwater be so rewarding?
As knowledge of the geology of the continental
margins advances it is evident that sands are widely present
in deepwater settings, notably oceanwards of the major river
mouths. However, source rocks, source rock maturity and structural
traps need not be present. Fortunately, many of the world’s
great producing shelf and onshore basins were quickly found
to be associated with prolific deepwater plays. Why this should
be so is outside the scope of this presentation, but ultimately
it relates to two commonly occurring factors:
-
many productive shallow water basins either developed
above source rock rich, deepwater provinces or are greatly
influenced by them, and
-
the oceanwards build-out of basins into deepwater creates
load induced structuring in the deepwater.
Examples are the Gulf of Mexico, the Niger
Delta, northern Angola (the Congo Fan) and the Campos Basin.
The answer to "Why can the deepwater
be so rewarding" question is, as in all of the world’s
great fairways, the simplicity of the resulting play elements.
These are: 1) an abundance of rich, commonly oil-prone source
rocks, 2) the frequent presence of thick clean sands, 3) young
structuring and 4) ongoing hydrocarbons generation.
The application
of seabed sampling to frontier basin exploration
The primary objective of Surface Geochemical
Exploration (SGE) is to reduce risk by defining the regional
distribution and origin of oil, condensate and gas seepages
(Brooks et al., 1997). The goal is to firstly to high-grade
open acreage and subsequently prospects by locating foci of
active oil migration and charge using gas and high molecular
weight hydrocarbon screening of cored samples. The assumption
is that active migration will have previously charged the
underlying reservoirs occupying the same compartments of a
Petroleum System. The value of piston-core programmes to frontier
basin exploration is illustrated in Figure
1. The question at issue here is the prospectivity of
the compound closure labelled A. This hypothetical closure
is positioned in the extensional portion of the Congo Fan
(Henry et al., 1995) and structures of this type were the
primary targets in the 1996 and 1998 TDI-Brooks work programmes
in Angola. Currently the targets are the more oceanwards positioned
compressional portion of the fan and the undeformed sequence
beyond the limit of the salt. For the illustrated example,
the primary drilling objective is a sand positioned just above
the regional Mid-Tertiary break. Examination of the figure
shows that five source units could supply the objective sands.
Success at Site 1 would determine the origin of the oil and
so permit a much improved assessment of the potential of the
target structure. In this example, the optimum charge would
be from the Tertiary aged Malembo Formation since this source
horizon is interbedded with the reservoir objective. Least
preferable are the two Pre-Salt sources due to inefficient
migration pathways through the salt seal section.
The methodology
The piston-coring procedures and laboratory
techniques to be described are those practised by TDI-Brooks
International, Inc. The procedural and geochemical observations
are based on the work of B&B Laboratories (Bernard, 1999)
and GeoMark Research, Inc. The presented methodology is equally
applicable to mature basin studies.
Selecting targets
Core sites are chosen by TDI-Brooks and/or
participant companies, usually from regional 2-D seismic lines.
When cores are collected from optimally located sites, for
example those associated with the seabed intersection of deep
faults, surface amplitude anomalies, wipe-out zones, and Lophelia
mounds, it is often possible, especially from leaky regions
such as the Gulf of Mexico, to obtain 5% or more of the cores
with visible oil-staining from which biomarkers are routinely
discovered . Macroseepages are also characterised by gas expansion
pockets in the cores and by authigenic carbonates produced
from the bacterial breakdown of seepage oil and gas. Microseepages
of oil and gas have been identified by the geochemical techniques
outlined in the following paragraphs. Identical procedures
are used to confirm the macroseep indications.
Enhanced selection is permitted where 3-D
seismic and/or swath bathymetry is available. An excellent
illustration of the additional return from 3-D data is provided
by Haskell et al. (1999) who include TDI-Brooks piston-core
locations on time slices from deepwater Nigeria.
The optimum targets are deep cutting faults
that link the source succession to the seabed. These are best
developed where there is ongoing tectonism. However, even
in tectonically quiet regions breaks are usually present,
especially where the section is thick and/or where there has
been differential movement and reactivation across basement
features such the Benue and Charcot Fracture Zones of the
Nigeria region. The ideal faults are those associated with:
(1) amplitude anomalies ("flags") and/or Bottom
Simulating Reflectors (BSRs) associated with gas hydrates,
(2) seabed constructional features such as carbonate accumulations
and mud-gas mounds, (3) gas vent pits and (4) thermogenic
gas chimneys. Figure 2
illustrates a typical site, this one is positioned on an active
sea bed feature associated with a shale diapir. Further information
on the geology of seeps and slicks (the sea surface manifestation
of a seep) may be found in MacDonald (1998).
Acquiring piston-cores
Core sites are positioned with differential
GPS positioning to a precision of ± 5 metres and generally
within ± 30 metres of the pre-selected locations.
Cores are acquired with a heavy-duty,
2000 lb. piston-corer with a collapsible piston and six
metres of pipe plus core liner. Although a more expensive
technique, piston-coring offers several advantages over gravity
coring, including: (1) greater penetration depths, (2) better
core recovery, and (3) higher quality (less disturbed) samples.
Using piston- coring to sample depths of up to six metres
significantly reduces intracore variability due to bioturbation,
loss by near surface diffusion of gases, and mixing of natural
hydrocarbon seepage or pollution in the top metre of sea floor
sediments. The length of section allows three sections from
each piston-core to be analysed and depth trends for measured
parameters to be reliably determined and evaluated. Figure
3 illustrates the coring procedure.
Often either precision bathymetric or subbottom
(3.5 kHz or Chirp sonar) profiling is used to further refine
core positions in the field. These techniques, which can also
detect venting trains of gas bubbles, permit cores to be directly
placed on to the seabed features previously identified from
the seismic. After retrieval on deck, the cores are processed
in a clean hydrocarbon sampling laboratory on the vessel.
Samples are immediately frozen (-20º C) for dispatch by airfreight
to Houston for laboratory analyses. Ancillary programmes such
as palaeontology (age determinations of the cored section),
sedimentology/geotechnical, and heat flow measurements are
run as requested. Heatflow techniques are reviewed in the
final section of this paper.
The normal operational window is water depths
between 10-3000 metres. Sampling to depths of up to 4500 metres
is possible, but the core acquisition rate is much lower than
the 8-10 cores/day regularly achieved for shallower depths.
Surface Geochemical
Exploration screening procedures
A three stage investigative procedure is
used for examining piston-cores for migrant, thermally sourced
oils and gases. The first stage is the visual examination
of the cores on site for oil staining and related phenomena.
Hydrocarbons are suspected when dark stained section is present
or gas expansion pockets and authigenic carbonates are observed.
However, visually obvious oil staining is not always present.
In some cases, dark, oil-like staining and fluids are found
by the subsequent testing procedures not to be of thermal
origin. Gas hydrates have been recovered by TDI-Brooks from
the Niger Delta (Brooks et al., in press) and the Gulf of
Mexico.
Upon receipt in the United States, the frozen
cores are sectioned into three portions for the second investigative
phase. This is handled entirely by TDI-Brooks. Three analytical
procedures are utilised: (1) the total scanning fluorescence
intensities of sediment extracts, (2) the C15+
hydrocarbons by gas chromatography in the sediment extracts,
and (3) the light hydrocarbons in separately canned sediment
sections by headspace extraction and gas chromatography.
The third and final stage comprises GC-MS
studies by GeoMark Research Inc. for those samples where one
or more of the TDI-Brooks screening procedures indicates the
presence of oil. Here the objectives are also threefold: (1)
to confirm the occurrence of oil, (2) characterise in terms
of biomarkers the nature of the source rock supplying the
oil, and (3) to determine the maturity of the oil.
Total scanning fluorescence
(TSF)
TSF
provides semi-quantitative measures of petroleum-related aromatic
hydrocarbons. Increasing TSF intensity (expressed in arbitrary
units) generally corresponds to enhanced aromatic hydrocarbon
concentrations in the sediment extracts. Migrant oil samples
contain a higher concentration of larger aromatic compounds
(3 or more benzene rings) and fluoresce at longer wavelengths,
whereas, extracts containing upward-migrated gas or condensate
fluoresce at shorter wavelengths. TSF patterns are insensitive
to bacterial alteration, except in the most severely situations.
Additional information on TSF methodology is provided by Brooks
et al. (1986).
Figure
4 compares the spectral features of background material
with a sample subsequently proven by gc-ms analysis to contain
oil.
Gas chromatography
Gas
chromatography (GC) provides a separate means of detecting
and characterising petroleum-related hydrocarbons. The output,
the gas chromatogram, is a plot on which the vertical axis
records abundances and the horizontal axis positions the hydrocarbon
components of the sample. Background samples produce a flat
basal trace with scattered peaks unrelated to thermogenic
products. Fresh oil, which is only rarely recovered from seabed
settings, is characterised by a regular train of peaks all
related to known thermogenic products and which rise from
a flat baseline. Most of these peaks are formed by alkanes
(normal paraffins). They, together with lesser components,
such as pristane and phytane, are used to study the origin
and maturity of the source succession (Brooks et al., 1986).
Almost all seabed oils are moderately to
severely modified by bacterial attack. In a few cases, sufficient
alkanes and related compounds remain to demonstrate the thermogenic
origin of the sample. However, in most examples all the molecular
components of the oil are lost and the sample acquires properties
akin to modern seabed organic matter.
The process of bacterial attack is termed
biodegradation. Biodegraded oils are characterised by the
increasingly "moth-eaten" appearance of the alkane
peaks and the appearance of a pronounced hump below the initially
flat base of the trace. The hump represents the by-products
from the bacterial attack. These are termed the Unresolved
Complex Mixture or UCM.
Figure
5 presents an example of gas chromatograms for: (1) a
background sample and (2) a severely biodegraded oil. Gc-ms
analysis (see below) was used to type the origin of the oil.
Barnard et al. (2000) include a TSF-UCM cross-plot that distinguishes,
for the Niger Delta, background from anomalous samples.
Headspace gas analysis
Headspace
gas analysis relates to the determination of interstitial
light hydrocarbon gases. Various gas parameters such as total
alkanes, total non-methane alkane gases (C2+) and
ethane/ethene ratios are used to separate thermogenic from
biogenic gas seepages. Methane can be thermal or bacterial
origin. Ethane is a stable thermogenic product, ethene is
formed by bacterial fermentation and does not persist at depth.
Thus the higher the ethane/ethene ratio the more likely is
the thermal origin o f the sample.
Figure
6 relates, for a large (n=363) data set, the ethane/ethene
ratio to the maximum TSF intensity. The linkage with enhanced
ethane/ethene ratios to migrant oils is readily apparent.
The less pronounced ethane/ethene peak in the central region
of the plot is associated with migrant thermogenic gas.
Biomarker analysis
Biomarkers are organic molecules whose chemistry
is specific to life. Most originate from the thermal degradation
of bacteria, algae and vegetal debris. The resulting biomarker
suites are diagnostic, provided that a sample is either not
too severely affected by biodegradation by bacterial action
or is a condensate, of the depositional setting of source
rocks, their relative thermal maturity, and, in some cases,
the geological age of the source. Biomarkers are routinely
analysed by Gas Chromatography-Mass Spectrometry (gc-ms).
In this technique, a mass spectrometer is used to split the
biomarker portion of a gas chromatograph’s output into diagnostic
molecular fragments. Figure
7 demonstrates how the resulting ratios of biomarkers
may be used in the form of cross-plots to determine oil source
environments. Figure 8
shows two examples of the biomarker traces used to build the
cross-plots.
Locations containing confirmed oil are termed
macroseeps, locations containing probable oil are termed microseeps.
Macroseep and most microseep samples contain sufficient quantities
of biomarkers to allow them to be readily typed to their source
rocks. It is often helpful to compare, for example when building
play maps, the piston-core samples with oils from producing
shallow water or onshore fields. Figure
9 compares the gc-ms trace of a macroseep oil with a produced
oil. In this case, a common Tertiary source is indicated by
the enhanced amounts of the age diagnostic biomarker oleanane.
Bacteria have attacked the piston-core oil and many of the
peaks on the right hand portion of the trace represent remnants
of the original biomarkers. In addition, new peaks, labelled
with stars (*), have appeared in the field occupied in fresh
oils by biomarkers known as pentacyclic terpanes – the starred
peaks are related to seabed products. Fortunately, the left
portion of the trace, which is occupied by biomarker compounds
unpalatable to bacteria and known as the tricyclic terpanes,
has not been affected. The pattern of the tricyclic peaks
indicates derivation from a marine claystone containing terrestrially
derived detritus. More on this subject may be found in Brooks
et al. (1986). In some frontier basins the piston-core oils
may provide the first evidence of entirely new Petroleum Systems.
Multivariant statistics
Multivariant statistics provide a powerful
means of compiling Oil Families from suites of biomarker environmentally
diagnostic components that best explain the geological variation
in the data. The effectiveness of this approach is illustrated
on Figure 10, which
presents a cluster analysis dendrogram prepared by Schiefelbein
et al. (1999) for a GeoMark oils set from the South Atlantic
region. This methodology clearly separates marine from lacustrine
sourced oils. The data set does not include the deepwater
oils from the South Atlantic. Most of these are marine oils,
but lacustrine oils are the source in the deepwater Campos.
For much of Brazil and in West Africa north of the Namibia/Angola
border many of the Cretaceous and older Tertiary marine sources
are richly oil prone and since they are regional in their
extent they will generate hydrocarbons wherever there is sufficient
cover for maturity.
Oil quality: determining
from seeps the commercial value of deepwater oils
Provided the recovered oil is not too severely
biodegraded, it is possible to determine the ultimate commercial
value of many deepwater oils from their seep geochemistry.
Thus in relation to Closure A on Figure
1, it may be possible by sampling Site 1 to determine
the API, the ppm metals content, the saturate/aromatic ratio,
the wax content and the sulphur content of the migrating oil.
Once again a Malembo source would be ideal, though there is
risk, if the reservoir is too shallow, of biodegradation of
the type present in Elf’s Block 17 lowering the oil’s value.
Biodegraded oils have high TAN (Total Acid Number) values
and require more expensive pipework and topside facilities
than pH neutral oils. The origins of acidic biomarkers are
described, in a timely paper on this topic, by Nascimento
et al. (1999).
In the Gulf of Mexico many deepwater oils
originate from late Jurassic shale sources with carbonate-marl
affinities (Zumberge et al., 1998 and 1999). Typical products
are low maturity and, therefore, low API oils high in sulphur.
These contrast with the more valuable, higher API, low sulphur
oils derived from the Cretaceous and Tertiary shale succession
that supplies the shallower water fields. Figure
11 summarises the relative commercial value of Jurassic
and Cretaceous/Tertiary oils in terms of their APIs and sulphur
contents.
The definition of
slicks from radarsat imagery and other techniques
Identification of surface slicks using radar
satellite images or other sensing methods offers an alternative
and substantially cheaper method for initially screening seepage
in a frontier basin. However, slick supply is not necessarily
continuous, calmish waters are required for their development
and slick-like features can result from dry gas plumes.
Slick surveys are an important initial screening
tool that requires subsequent ground truthing using the piston-coring
techniques previously outlined. Sophisticated add-ons such
as heat flow measurements are rarely practical in surface
slick programmes.
Even after seeps have been located at sea
it can be difficult to locate the source. For example, in
Angola a seep could not be tracked to its source despite two
days of Chirp subbottom surveying and the recovery of fifteen
cores from potential leakage features. Interestingly, slick
oils, because they are the frequently the product of transient
events, tend to be fresher than seep oils. Thus slick oils
should always be sampled.
Heatflow programmes
Of at least equal importance to the previously
described SGE work in deepwater exploration evaluations is
the determination of heatflow.
Unless reference DSDP (Deep-Sea Drilling Project) sites are
present, the information needed to control basin models is
not available until the first wells have been drilled. The
maturity and origin of a recovered oil provides clues to the
heatflow, but since biodegradation frequently affects the
biomarker ratios used for maturity studies, direct determinations
of heatflow at the pre-bid stage are highly desirable.
Heatflow information is obtained by implanting
up to eleven outrigger-style thermistors along the core barrel.
Temperature measurements are recorded in-situ using a digital
thermograd. Ambient temperatures below the seabed are derived
by tracking for ten minutes the heat decay induced by the
frictional energy of the core barrel and mathematically projecting
the resulting decline curve to infinity. A known heat pulse
is then applied to the thermisters enabling the conductivity
of each section to be calculated using an identical ten minute
sampling procedure. Heatflow (HF) is determined by combining
the site thermal conductivity (k) with the geothermal gradient
(G) determined from the thermistors according to the relationship
HF = kG. Water depth is measured by pressure and the angle
of tilt of the core barrel is monitored to obtain true vertical
depths. Heatflow measurements are possible in water depths
of up to 6000 metres. More details on the technology may be
found in Hutchison and Owen (1989).
Once criticism of the technique is that the
six metre maximum penetration may not permit measurements
below the water saturated bottom coating oozes so commonly
seen on seismic. This problem can be minimised by selecting
sites from the seismic where these oozes are of minimal thickness
such as on the crests of an active shale diapir or along the
walls of fault scarps. During the later stages of exploration,
direct well becomes possible.
Cost benefits
Given the necessity of mobilising an ocean
going vessel and operating safely and efficiently in remote
settings, the cost of mounting piston-core surveys approaches
those of seismic operations. As each core requires to be treated
as potentially hydrocarbon bearing at all stages of the TDI-Brooks
screening programme, the total cost of acquisition and analysis
varies from $3,000 to $5,000/core. Using an overall 5% success
rate for biomarker typed oils, each success or "hit"
will cost on average between $60,000 and $100,000. Though
these are sizeable sums, a $100,000 hit represents 0.2% of
the cost of a $50,000,000 deepwater well. Multiple oil "hits"
and the availability of oil analyses from wells permit the
source risk to be further refined through the supply of corroborative
detail.
Since their initiation SGE programmes have
exercised significant impact on the progress of deepwater
exploration in West Africa and the Gulf of Mexico. This is
because of their ability to delineate areas of active migration
in undrilled acreage almost regardless of water depths. Figure
12 illustrates a success – in this case the recovered
oil was typed to it source. Thus dollars were initially saved,
for example by getting the value of the bid correct, and potentially
earned, for example by setting the scene for a future commercial
discovery.
References
Bernard B.B., J.M. Brooks, T. McDonald and
N. Cameron, 2000. Threshold vs anomalous concentrations of
near-surface hydrocarbons in the ultradeepwater, offshore
Nigeria. Petroleum Systems and Evolving Technologies in African
E&P, Geological Society/PESGB, Burlington House, London,
May 16-18, 2000, extended abstract, p.3.
Bernard B. B., 1999. Core Sampling – Summary
Methodology. B&B Laboratories, Inc., pp. 20.
Brooks J.M., M.C. Kennicutt II and B.D. Carey
Jr., 1986, Offshore surface geochemical exploration. Oil and
Gas Journal, 20 October, pp. 6.
Brooks J.M., W.R. Bryant, B.B. Bernard and
N.R. Cameron, in press. The nature of gas hydrates on the
Nigerian continental slope. The New York Academy of Sciences.
Third International Conference of Gas Hydrates, Park City,
Utah, July 18-22 1999.
Brooks J.M., B.B. Bernard, J.D. Stonebraker,
C. F. Schiefelbein, K.A. Allen, and T.J. McDonald, 1997. Design
of multidisciplinary surface geochemical exploration surveys
to identify active Petroleum Systems offshore West Africa,
Hedberg Research Symposium, "Petroleum Systems of the South
Atlantic Margin", Rio de Janeiro, 16-19 November, extended
abstract, pp. 3.
Cameron N.R., C.F. Schiefelbein, J.M. Brooks
and M.G.P. Brandão, 1998. The application of seabed
sampling and organic geochemistry to frontier basin exploration
in Angola. 3rd Annual Forum Worldwide Deepwater
Technologies, London, 17-18 February 1998, pp. 8.
Cameron N.R., Brooks J.M. and J.E. Zumberge, 1999. Deepwater
Petroleum Systems in Nigeria: their identification and characterisation
ahead of the drill bit using SGE technology. IBC Nigeria Energy
Summit, London, 15-16 June 1999, pp. 20.
Cameron N.R. and K. White, 1999. Exploration opportunities
in offshore deepwater West Africa. Oil and Gas Developments
in West Africa, IBC, 25-26 October 1999, pp. 28.
Haskell N., S. Nissen, M. Hughes, J. Grindhaug,
S. Dhanani, J. Kantorowicz, L. Antrim, M. Cubanski, R. Nataraj,
M. Schilly and S. Wigger, 1999. Delineation of geologic drilling
hazards using 3-D seismic attributes. The Leading Edge, 18,
3, p. 373-374, 376, 378, and 381-382.
Henry S.G., W.D. Brumbaugh and N.R. Cameron,
1995. Pre-salt source rock development on Brazil's conjugate
margin: West African examples. 1st Latin American Geophysical
Conference, Rio de Janeiro, August, extended abstract, pp.3.
Hutchison I. and T. Owen, 1989. A microprocessor
heat flow probe. In: Handbook of Seafloor Heat Flow. J.A.
Wright and K.E. Louden (editors), CRC Press, Baton Rouge,
USA.
MacDonald I.R., 1998. Natural Oil Spills. Scientific American,
November 1998, p. 31-35.
Nascimento L.R., L.M.C. Rebouças,
L. Kolke, F. de A.M. Reis, A.L. Soldan, J.R. Cerqueira and
A.J. Marsaiola, 1999. Acidic biomarkers from Albacora oils,
Campos Basin, Brazil. Organic Geochemistry, 30, p. 1175-1191.
Schiefelbein C.F., J.E. Zumberge, N.R. Cameron
and S.W. Brown, 1999. Petroleum Systems in the South Atlantic
Margins. In: Cameron N.R., R.H. Bate, and V.S. Clure (editors).
The Oil and Gas Habitats of the South Atlantic. Special Publication
of the Geological Society No. 153, p. 169-180.
Zumberge J., H. Illich, C. Pratsch, S. Brown
and N. Cameron, 1998. Origin of oil in the Gulf of Mexico:
exploration significance. Petroleum Exploration Society of
Great Britain, PETEX 98 Conference and Exhibition, London,
1-3 December 1998, Paper E5, pp. 2 (abstract).
Zumberge J., H. Illich, C. Pratsch, S. Brown
and N. Cameron, 1999. Origin of oil in the Gulf of Mexico:
exploration significance. Bulletin of the American Association
of American Petroleum Geologists, 83, 8, p. 1346 (abstract).
Acknowledgements
We wish to thank Mabon Limited for permission
to include a section of one of their seismic lines.
Contacts
Nick Cameron is the UK representative for
TDI-Brooks International, Inc. and GeoMark Research, Inc.
Contact options include: +44-(0)1494-776850 (telephone/fax)
and nick@topaz.primex.co.uk.
Information relating to TDI-Brooks International 1996, 1998,
and 1999-2000 coring programmes may be obtained from either
Dr. Jim Brooks [+1-409-695-3634 (telephone), +1-409-695-5168
(fax), Drjmbrooks@aol.com]
or Dr. Bernie Bernard [+1-409-693-3446 (telephone), +1-409-693-6389
(fax), berniebernard@tdi-bi.com].
The GeoMark Research, Inc contacts are: Stephen Brown and
Dr. John Zumberge, +1-281-856-9333 (telephone), +1-281-856-2987
(fax), or <biomarkers@aol.com>.
The figures and the talk graphics were prepared
by Steve King (+44-(0)1442-825128 and steve@topaz.primex.co.uk).
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