Geochemical Logging: A Valuable Tool for Exploring Complex Reservoirs

1. 1
Primary funding is provided by
The SPE Foundation through member donations
and a contribution from Offshore Europe
The Society is grateful to those companies that allow their
professionals to serve as lecturers
Additional support provided by AIME
Society of Petroleum Engineers
Distinguished Lecturer Program
www.spe.org/dl

2. 2
Society of Petroleum Engineers
Distinguished Lecturer Program
www.spe.org/dl
Jim Galford
Geochemical Logging: A Valuable Tool
for Exploring Complex Reservoirs

3. 3
Outline
• What is geochemical logging?
• Measurement theory
• Complex reservoir challenges
• Case studies
• Summary remarks

4. 4
What is geochemical logging?
• Measurement principles
– Neutron-induced gamma ray spectroscopy
– Natural gamma ray spectroscopy
• Output logs
– Elemental yields
– Dry rock and wet rock elemental weight fractions
• Application
– Quantitative estimate of formation mineralogical composition
• Improved accuracy and assurance for evaluations in simple
mineralogy formations
• Improved volumetric petrophysical evaluations in complex
mineralogy formations

5. 5
Measurement Theory – Neutron
Interactions
Chemical or Pulsed
Neutron Source
Inelastic 
Capture 
Inelastic Neutron Scattering
neutron energies
100keV - 14 MeV
Thermal Neutron Absorption
neutron energy ~0.025 eV
neutron energy reaches
thermal level 0.025 eV
followed by diffusion for
a few microseconds
neutron energy
decreases with
time and scattering
Elastic Neutron Scattering
all neutron energies
0.025 eV - 14 MeV

6. 6
Which elements are measured?
Si
K
Mg Al
Ti Fe
Gd
S
MnCa

7. 7
Measured Elemental Weight % of Eight
Most Common Elements in the Earth’s Crust
Weight %
O 46.60
Si 26.72
Al 8.13
Fe 5.00
Ca 3.63
Na 2.83
K 2.59
Mg 2.09
98.59
Magnesium
Potassium
Sodium
Calcium
Iron
Aluminum
Silicon
Principles of Geochemistry, 4th ed., 1982
B. Mason and C. B. Moore

8. 8
Data Flow
Acquisition
Spectral
Fitting
Oxides
Closure
Model
Elements
to Mineral
Interpretation
Gamma Ray
Spectra
Relative
Elemental
Yields
Elemental
Weight Fractions
Mineral Volume
Fractions
PROCESS
RESULTS
Real Time Post Acquisition

9. 9
The Complex Reservoir
Challenge:
In conventional and unconventional reservoirs, reliable reserves and
production estimates are difficult to achieve
 Resistivity, density, neutron, sonic, dielectric, NMR, …
 Mineral analysis and grain density
 More reliable reserves estimates from improved porosity and
saturation
 Better completion and stimulation designs to optimize the asset
Solution:
Geochemical logs provide information for formation evaluation in
conjunction with other measurements:

10. 10
Downstream Applications
Geochemical Logs
• Mg, Al, Si, S, K, Ca, Ti,
Mn, Fe, Gd, etc.
• Th, U, K
Formation
Evaluation
• Mineralogy
• Porosity, permeability
• Fluid Characterization
(typing, saturation, etc.)
Geo-Mechanics
• Mechanical Properties
• Frac Parameters

11. 11
Elemental Concentrations Identify
Mineralogy
Mineral Chemical Formula Identifying Elements
Quartz SiO2 Silicon
Calcite CaCO3 Calcium
Dolomite CaMg(CO3)2 Calcium + Magnesium
Anhydrite CaSO4 Calcium + Sulfur
Pyrite FeS2 Iron + Sulfur
Ankerite Ca(Mg,Fe,Mn)(CO3
)2
Calcium + Magnesium + Iron + Manganese
Kaolinite Al4
(Si4
O10
)(OH)8 Silicon + Aluminum
Ilmenite FeTiO3
Iron + Titanium
Orthoclase KAlSi3
O8
Potassium + Aluminum + Silicon
Gadolinium(III) oxide Gd2
O3
Gadolinium

12. 12
Case Studies
 Carbonate Reservoir
 Conventional Complex Sandstone Reservoir
 Shale Gas Play

13. 13
West Texas Carbonate Geochemical Logs
Dolomite
Limestone
4900
5000
5100
5200
Magnesium
Silicon
Aluminum
Sulfur
Potassium
Calcium
Titanium
Iron
Manganese
Gamma KT
Gamma KT
Caliper
Total Gamma Ray
Thorium
Uranium
Potassium
LLS
LLD
PE
Neutron LS Porosity
Bulk Density
0 api 150
0 api 150
6 in 16
0 ppm 60
‐10 % 10
‐10 ppm 30
0.2 ohmm 2000
0.2 ohmm 2000
0 b/e 20
1.94 g/cc 2.97
0.45 decp ‐0.15
0.6 decp 0
GR Spectroscopy Resistivity Density / Neutron Dry Elemental WFDepthCorrelation

14. 14
Geochemical PE Log
PE logs derived from
geochemical logs can
be substituted for
lithodensity PE logs in
wells drilled with
heavy muds or when
borehole conditions
are poor.
4900
5000
5100
5200
Magnesium
Silicon
Aluminum
Sulfur
Potassium
Calcium
Titanium
Iron
Manganese
Gamma KT
Gamma KT
Caliper
Total Gamma Ray
Thorium
Uranium
Potassium
LLS
LLD PE
Neutron LS Porosity
Bulk Density
0 api 150
0 api 150
6 in 16
0 ppm 60
‐10 % 10
‐10 ppm 30
0.2 ohmm 2000
0.2 ohmm 2000 0 b/e 20
1.94 g/cc 2.97
0.45 decp ‐0.15
0.6 decp 0
Geochemical PE
0 b/e 20
GR Spectroscopy Resistivity Density / Neutron Dry Elemental WFDepthCorrelation

15. 15
Mineralogy Analysis
4900
5000
5100
5200
Magnesium
Silicon
Aluminum
Sulfur
Potassium
Calcium
Titanium
Iron
Manganese
Illite
Orthoclase
Anhydrite
Dolomite
Calcite
Quartz
Clay Bound Water
Free Water
Oil
Gamma KT
Gamma KT
Caliper
Total Gamma Ray
Thorium
Uranium
Potassium
LLS
LLD
PE
Neutron LS Porosity
Bulk Density
App. Matrix Density
0 api 150
0 api 150
6 in 16
0 ppm 60
‐10 % 10
‐10 ppm 30
0.2 ohmm 2000
0.2 ohmm 2000
0 b/e 20
1.94 g/cc 2.97
0.45 decp ‐0.15
1.9 g/cc 2.9
0 decp 10.6 decp 0
GR Spectroscopy Resistivity Density / Neutron Dry Elemental WFDepthCorrelation Wet Rock VF
Mineralogy from
geochemical
logs can be used
to calculate a
variable matrix
density like the
one shown in
Track 4.

16. 16
Complex Sandstone Mineralogy Analysis
250
300
350
Magnesium
Silicon
Aluminum
Sulfur
Potassium
Calcium
Titanium
Iron
Manganese
Kaolinite
Anhydrite
Illite
Dolomite
Calcite
Quartz
Clay Bound Water
Free Water
Gas
Gamma KT
Gamma KT
Caliper
Total Gamma Ray
Thorium
Uranium
Potassium
RT10
RT60
PE
Neutron LS Porosity
Bulk Density
0 api 150
0 api 150
6 in 16
0 ppm 60
‐10 % 10
‐10 ppm 30
0.2 ohmm 2000
0.2 ohmm 2000
0 b/e 20
1.94 g/cc 2.97
0.45 decp ‐0.15
0 decp 10.6 decp 0
RT90
0.2 ohmm 2000
App. Matrix Density
1.9 g/cc 2.9
GR Spectroscopy Resistivity Density / Neutron Dry Elemental WFDepthCorrelation Wet Rock VF
XRD results
indicated a
mixture of
kaolinite and
illite clay
minerals with
a small
amount of
anhydrite

17. 17
Complex Sandstone Mineralogy Analysis
250
300
350
Magnesium
Silicon
Aluminum
Sulfur
Potassium
Calcium
Titanium
Iron
Manganese
Kaolinite
Anhydrite
Illite
Dolomite
Calcite
Quartz
Clay Bound Water
Free Water
Gas
Gamma KT
Gamma KT
Caliper
Total Gamma Ray
Thorium
Uranium
Potassium
RT10
RT60
PE
Neutron LS Porosity
Bulk Density
0 api 150
0 api 150
6 in 16
0 ppm 60
‐10 % 10
‐10 ppm 30
0.2 ohmm 2000
0.2 ohmm 2000
0 b/e 20
1.94 g/cc 2.97
0.45 decp ‐0.15
0 decp 10.6 decp 0
RT90
0.2 ohmm 2000
App. Matrix Density
1.9 g/cc 2.9
GR Spectroscopy Resistivity Density / Neutron Dry Elemental WFDepthCorrelation Wet Rock VF
Reservoir
matrix
density
increases to
~2.69 g/cc
because of
anhydrite

18. 18
Heterogeneity: A Problem for Core - Log
Comparisons

19. 19
Core – Log Comparison Issue: Volume
Sampling
• Log measurements tend
to homogenize formation
properties
• Tool’s sensitive area is
several times larger than
the cross-sectional area
of a 4-in. core
• Results for a given depth
sample are derived from
~4-ft length of borehole at
normal logging speeds
4-in. Core
Geochemical Tool
8-in. Borehole
9 – 12 inches
Sensitive Area
Borehole
Gamma-ray Shield

20. 20
Haynesville Shale Geochemical Logs
Haynesville
Shale
Deep
Cotton Valley
Limestone
700
800
900
Magnesium
Silicon
Aluminum
Sulfur
Potassium
Calcium
Titanium
Iron
Manganese
Gamma KT
Gamma KT
Caliper
Total Gamma Ray
Thorium
Uranium
Potassium
RT90 PE
Neutron LS Porosity
Bulk Density
0 api 150
0 api 150
6 in 16
0 ppm 60
‐10 % 10
‐10 ppm 30
0.2 ohmm 2000 0 b/e 20
1.94 g/cc 2.97
0.45 decp ‐0.15
0.6 decp 0
GR Spectroscopy Resistivity Density / Neutron Dry Elemental WFDepthCorrelation

21. 21
Geochemical Log – Core Comparison
700
800
900
Gamma KT
Caliper
6 in 16
Gamma KT
Total Gamma Ray
0 api 150
0 api 150
GEM Al
Core Al
0 decp 0.15
0 decp 0.15
GEM Si
Core Si
0 decp 0.4
0 decp 0.4
GEM S
Core S
0 decp 0.04
0 decp 0.04
GEM K
Core K
0 decp 0.05
0 decp 0.05
GEM Ca
Core Ca
0 decp 0.4
0 decp 0.4
GEM Ti
Core Ti
0 decp 0.01
0 decp 0.01
GEM Fe
Core Fe
0 decp 0.05
0 decp 0.05
Spectral GR U
Core U
0 ppm 10
0 ppm 10
Spectral GR Th
Core Th
0 ppm 20
0 ppm 20
DepthCorrelation Al Si S K Ca Ti Fe U Th
Red symbols
represent
Inductively
Coupled
Plasma
Spectroscopy
(ICP)
measurements
done on core
material

22. 22
Haynesville Shale Mineralogy Analysis
700
800
900
Gamma KT
Caliper
6 in 16
Gamma KT
Total Gamma Ray
0 api 150
0 api 150
Core Porosity
Total Porosity
20 p.u. 0
20 p.u. 0
Core Rhoma
Matrix Density
2.6 g/cc 2.85
2.6 g/cc 2.85
XRD Quartz
Dry Quartz
0 % 50
0 % 50
XRD Calcite
Dry Calcite
0 % 100
0 % 100
XRD Illite
Dry Illite
0 % 50
0 % 50
XRD Mg Chlorite
Dry Mg Chlorite
0 % 50
0 % 50
XRD Albite
Dry Albite
0 % 50
0 % 50
XRD Pyrite
Dry Pyrite
0 % 20
0 % 20
Magnesium
Silicon
Aluminum
Sulfur
Potassium
Calcium
Titanium
Iron
Manganese
0.6 decp 0
Mg Chlorite
Pyrite
Illite
Albite
Calcite
Quartz
Clay Bound Water
Free Water
Gas
0 decp 1
Kerogen
DepthCorrelation Dry Elemental WF Wet Rock VF Porosity Grain Density Quartz Calcite Illite Chlorite Albite Pyrite

23. 23
Summary
• Multi-mineral petrophysical evaluations are essential in
complex reservoirs
• Geochemical logs provide valuable inputs to the
formation evaluation process
• A good workflow is important to define mineral and fluid
response parameters
• Core – log comparisons can sometimes be challenging
and the results can depend on the core sampling method

24. 24
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