Topic
Planning Geochemical Evaluation
of a Basin
Specific applications depend on
stage of exploration
Geochemistry in an exploration program
Combine geochemistry with geology and geophysics
FRONTIER AREA
GENERAL PRINCIPLES
DEVELOPING PLAY
MATURE AREA
DETAILED ANALYSIS
Frontier area: before
the first wildcat
 Surface geology / seismic
 Outcrop samples
 Surface seeps
 Surface microseeps “surface geochemistry”
 Tentative thermal modeling
Surface Geochemistry
Outcrop Samples
Tie surface units into the subsurface with seismic
NEED TO BE AS FRESH AS POSSIBLE:
use mines, roadcuts, etc.
PROVIDES INFORMATION ON:
organic matter content
organic matter type
maturity
Van Krevelen diagrams for outcrop samples
Developing play: limited subsurface data
 Extending and refining
quantitative modeling
 Source rock richness and maturity
 Oil characteristics – and inferred
source rock lithology/environment
 Correlation to give number of oil families
and from this number of source rocks
 Oil-versus-gas potential of the area
Mature exploration area: abundant data
 Refine maturity modeling to extend
exploration to adjacent areas
 Extend correlation studies
 Improved definition of migration
pathways
 Define patterns of oil quality
(e.g., biodegraded oils)
Reservoir geochemistry
 Recognize reservoir compartments
 Document compositional differences that
lead to differences in physical properties
which could affect flow models
 Investigate tar layers that can influence
water drive and water flooding
How Do I Initiate and Complete
a Geochemical Study?
 Consult with a geochemist early to determine:
objectives
sampling strategy, analytical scheme
 Initiate the project:
formalize objectives, costs, and timing
agree on expected final product
 Supply carefully labeled samples, geology
 Maintain communication during analysis
 Integrate geochemistry and geology with geochemist
for final interpretative report
Data Quality Depends on Collection
Procedures and Sample Containers
Sample
Comment
Ideal Container
Oil/Seep
Any clean, gas-tight container;
avoid contact of sample with cap.
Metal is best, glass is good if
packed not to break
Clean metal vessel;
gas-tight screw cap
Do not use newspaper to wrap
rocks or pens to mark directly
on rocks. Avoid waxed cores!
Cloth rock bag
quality paper OK
Sample unweathered rock; dig to
expose fresh surfaces at roadcuts,
river banks, low-dip outcrops
Cloth rock bag,
quality paper OK
Source rock
(General)
Source rock
(Outcrop)
Data Quality Depends on Collection
Procedures and Sample Containers
Sample
Comment
Ideal Container
Source rock
(cuttings)
Wash cuttings to remove drilling
mud and contaminants
Cuttings envelope
or small vial
Reservoir
rock (core)
Foil wrapped and sealed samples Cloth rock bag,
are best. Avoid waxed cores!
quality paper OK
Gas
Sample at well head if possible
Pressure bomb
Gas seep
Any gas-tight container. Samples
should be shipped upside-down
with water/bacteriocide
Sampling bottle
Sampling
OILS
Produced samples (e.g., DSTs) are best
RFTs or SFTs are next best
— often contaminated by diesel when
oil-based mud is used
Core or sidewall core extracts are next best
— chose least flushed material by sampling core center
Cuttings are the least desirable sample type
— Poor vertical resolution
— High surface to volume of cuttings causes
hydrocarbon flushing by drilling fluid and
contamination by drilling additives
Sampling
OILS (cont)
Collect oil/condensates in glass bottles
or metal cans
NEVER use plastic bottles
(e.g., Cloxox bottles, plastic soda bottles)
NEVER use containers with plastic-lined tops
Label samples with: date, field, well, depth,
formation, section, township & range (or
lat. And long.), and country or state
Pack glass containers in absorbent material
(e.g., Vermiculite)
Sampling
GAS/CONDENSATE
Gases should be collected in
steel cylinders or gas bags
Cylinders must be ordered several
weeks in advance
Cylinders are assembled and evacuated,
then shipped to the field location
When condensate is collected from a
separator, collect near the
END of the production test
Sampling
Collect samples of organic well additives!
— oil-based muds (diesel, pipe dope, etc)
— lost circulation material
(walnut hulls, fibres, plastics, etc)
— gilsonite
If samples of additives are collected, then
even contaminated oil samples can often be
made useful
Classical Geochemistry
Books:
J. M. Hunt, 1979, Petroleum Geochemistry and Geology
B.Tissot and D. H. Welte, 1984, Petroleum Formation
and Occurrence
D. W. Waples, 1985, Geochemistry in Petroleum
Exploration
K. E. Peters and J. M. Moldowan, 1993, The Biomarker
Guide