PS
Challenging the Paradigm "Missing Section - Normal Fault" - Implications for Hydrocarbon Exploration*
Jean-Yves D. Chatellier1 and Maria Eugenia Rueda2
Search and Discovery Article #40550 (2010)
Posted June 30, 2010
*Adapted from poster presentation at AAPG Annual Convention, New Orleans, Louisiana, April 11-15, 2010
1
2
Talisman Energy, Calgary, AB, Canada ([email protected])
StatoilHydro, Stavanger, Norway
Abstract
In structurally complex areas, seismic interpretation can be misled by wrongly interpreted well data. A common approach in the oil
industry can be summarized by the Spanish sentence “pozo mata sismica” meaning that data from a well must prevail in a seismic
interpretation. A major problem arises when well-based interpretation is taken as data; a missing section is the observation; calling it a
“normal fault” is an interpretation. A series of examples will show, in various structural settings, numerous cases of missing sections
that cannot be attributed to normal faulting. All field names in the text are from Venezuela if not otherwise specified.
The easiest recognizable misinterpretation occurs where wells have missing sections juxtaposed to wells with coeval massive sands;
with enough well control additional support comes from recognizing the typical rhomboidal-shaped blocks; e.g., Dunlin Field, UK.
Synsedimentary activity of horst blocks in the middle of major deposition centers (e.g., Brent delta) is responsible for such
occurrences.
Many tools either alone or combined, can be used to diagnose problematic missing sections; e.g., hydrocarbon-column anomalies
associated with fault-plane mapping, abnormal RFT pressure trends, detailed fault-throw map or perfectly identical TVDss depths of
fault cuts in different stratigraphic units.
Unusual approaches can also be successful at recognizing misinterpreted normal faults, as in the Lama Field: the TDs of every well
that failed to reach their targeted depths were analyzed by plotting their coordinates in 3-D. This revealed the existence of three
Copyright © AAPG. Serial rights given by author. For all other rights contact author directly.
previously unrecognized steeply dipping reverse faults that only one third of the wells had been able to penetrate; each of the latter
group showed missing sections where crossing these faults.
While 3-D seismic is the norm, 2-D lines can be invaluable in better defining the tectonic style of very complex areas. Large amount
of hydrocarbons can be present below faults which have been obliquely reactivated and which appear at first glance to have the
geometry of normal faults (e.g., Western Canada Foothills).
Implications for the examples cited above range from redesign of water injection wells for pressure support (Lama Field) to major
bypassed pay zone (Santa Barbara Field), change in reserve estimates (Dunlin) and finally to a new hydrocarbon discovery (near
Bosque Field).
Selected References
Chatellier, J-Y., Rueda, M.E., Charles, S., and Romero, I., 2008, Why 3D seismic missed a giant field in the Eastern Venezuela thrust
belt; postmortem of a late discovery, CSPG Convention Calgary ( 4-page abstract)
(http://www.cspg.org/conventions/abstracts/2008abstracts/130.pdf) (accessed June 8, 2010).
Chatellier, J-Y., and Zambrano, J., 2007, A multidisciplinary 4D integration delivers a reliable reservoir model for the Santa Barbara
Field, Venezuela: Data Fusion Workshop, SEG-AAPG-SPE, Vancouver, October, 2007
Chatellier, J-Y., and Porras, C., 2004, The Multiple Bischke Plot Analysis, a Simple and powerful graphic tool for integrated
stratigraphic studies: AAPG Search and Discovery Article #40110 (2004)
(http://www.searchanddiscovery.net/documents/2004/chatellier/index.htm)
Chatellier, J-Y., de Sifontes, R., Mijares, O., and Muñoz, P., 1999, Geological and production problems solved by recognizing the
strike slip component on reverse faults, VLA-31, Lake Maracaibo, Venezuela: SPE Annual Technical Conference, Houston, SPE No.
56558
Challenging the Paradigm
“Missing Section – Normal Fault”
Implications for Hydrocarbon Exploration
Jean-Yves Chatellier
Talisman Energy Inc. Calgary
[email protected]
Maria Eugenia Rueda
Statoil Hydro
W
Abstract
In structurally complex areas, seismic interpretation can be misled by wrongly interpreted well
data. A common approach in the oil industry can be summarized by the Spanish sentence “pozo
mata sismica” meaning that data from a well must prevail in a seismic interpretation. A major
problem arises when well-based interpretation is taken as data; a missing section is the
observation, calling it a normal fault is an interpretation. A series of examples will show, in various
structural settings, numerous cases of missing sections that cannot be attributed to normal faulting.
All field names in the text are from Venezuela if not otherwise specified.
The easiest recognizable misinterpretation occurs where wells have missing sections juxtaposed
to wells with coeval massive sands; with enough well control additional support comes from
recognizing rhomboidal shaped blocks as in the Upper Ness E of the Dunlin Field - UK. Log facies
maps are most effective at indicating these occurrences because of the patterns on the maps; this
also works well in compressive structural settings as in one Oligocene unit of El Furrial Field.
Synsedimentary activity of horsts in the middle of major deposition centers (e.g., Brent delta) is
responsible for such occurrences.
Problems at same
stratigraphic levels
E
2km
(Furrial Field)
Many wells are missing sands from the exact same stratigraphic interval
TVD(ss)
9000
9500
10000
10500
Pressure problems
at same depth
Detachment
Despegue
15000
RFT
16000
An unusual approach was successful at recognizing misinterpreted normal faults in the Lama
Field: the TDs of every well that failed to reach its targeted depth were analyzed by plotting their
coordinates in 3-D. This revealed the existence of three major steeply dipping reverse faults that
only one third of the wells had been able to penetrate; each of the latter showed missing sections.
Oblique slip associated with these Riedel Shears has been invoked for the missing section along
reverse faults.
SBC-96 (02-99)
Y
SBC-52 (08-96)
SBC-61 (03-97)
Legend
5000’
While 3-D seismic is the norm, 2-D lines can be invaluable in defining the tectonic style in very
complex areas. Large amount of hydrocarbons can be present below faults which have been
obliquely reactivated and which appear at first glance to have the geometry of normal faults (e.g.,
Western Canada Foothills).
Implications for the examples cited above range from redesign of water injection wells for pressure
support (Lama Field) to major bypassed pay zone (Santa Barbara Field) and finally to a new
hydrocarbon discovery (near Bosque Field).
11500
14000
(Santa Barbara Field)
In the Western part of El Furrial Trend, different tools either alone or combined, were used to
diagnose problematic missing sections; e.g., hydrocarbon column anomalies associated with faultplane mapping, abnormal RFT pressure trends, detailed fault-throw map or perfectly identical
TVDss depths of fault cuts in different stratigraphic units. When dealing with problematic missing
sections, core observations may also help significantly as in the Carito Field where timing and
geometry of deformation bands revealed by a diagenetic study indicate a multiphase complex
tectonic history with rotation of transport direction.
11000
Drilling problems
on single plane
(Lama Field)
X
10000’
Z
15000’
Abnormally
short TDs
(Jammed)
Fault-plane dip different
from bed dip
(modelling)
PSI
Syn-sedimentary tectonic activity
Keywords
Pattern on maps
Blocky sands
Same units missing
Borehole geometry (especially in offshore wells)
Observations
Reverse fault
with
Missing section
In particular instances
the well trajectory could
lead to misinterpretation
Normal fault
with
Repeat section
Synsedimentary tectonic activity creating havoc
Furrial Field
W
E
Venezuela
OGIP = 7.5 Billion bbls
Best blocky sands are
missing at the same
stratigraphic level
2km
SANTA BARBARA
CARITO
Best sand in Furrial
(zoomed view)
FURRIAL
Many more wells are missing sands at the exact same stratigraphic interval
Paleosoil
Dunlin Field
UK North Sea
OGIP = 0.827 Billion bbls
Blocks in blue indicate
where the blocky sands
of the upper Ness E
(Brent Group)
are missing
In the Dunlin Field, all of
the red dots correspond
to wells drilled and for a
while misinterpreted.
Missing sections commonly
misinterpreted as being
associated with normal
faults
Lessons
Ø Major mistakes in reserve estimates can be linked to syn-sedimentary tectonics
Ø Missing sections are often found in horst blocks next to the thickest and best sands of a field
Ø Development scheme can aim at sands that do not exist
Ø Blocky sands next to missing sections should trigger your attention
Ø Same pattern is usually found at the same stratigraphic level in various neighboring fields
Missing Sections in Strike-Slip Regimes
Example from the Lama Field (Block VLA 31) Lake Maracaibo, Venezuela
Observations
Key points
Oblique slip
MBPA
Lama Field
Lama Field
Misoa C4 facies map
Venezuela
Fault
OOIP = 7.6 Billion bbls
Block VLA 31
Fault
Final
Lama
Field
Interpretation
Lake
Maracaibo
9 wells with missing sections
Outer fault
Channels dissecting
the marine bars.
1 well with a small repeat
Icotea
fault
29 wells not reaching the objective (jamming)
More than 15 years of water injection has not
helped maintain the pressure of the field
47 wells
Geological Model is wrong
Resolving the
Problems
Displaced facies
Channels are
perpendicular to
the Icotea Fault
Estuarine channels
C4
Interval
Marine bars
Multiple Bischke Plot Analysis
3D analysis of all abnormally short TD
Disagrees with normal faulting
delivers 3 perfect fault planes
Dd
Dd
753 vs 861
Y
753 vs 867
100
400
0
200
0
X
+
-100
-200
-200
6250
Dd
7500
depth
5250
8750
6000
Dd
753 vs 902
100
X
Y
Y
X
6750
7500
depth
753 vs 515
-200
0
-300
Z
Z
Fault 1
375
2 .7
6327
Fault 3
Fault 2
300
4 .1
Legend
1 0 4 9 6 .1
806
5439
2 4 .1
-100
Z
5000’
485
-400
6 4 1 3 .9
-7 . 4
-200
469
-1 0 . 9
1 0 4 9 9 .7
-500
10000’
316
7 .3
6000
7000
depth
8000
9000
6000
7000
depth
8000
9 0 5 6 .3
9000
15000’
The stratigraphy of Well 753 is compared to four non-faulted wells
Conclusion = the red marker is misinterpreted
MBPA graphical method allowed confirmation of the position of the
faults where missing sections are found; however, the MBPA
6 abnormally short TDs
11 abnormally short TDs
12 abnormally short TDs
Each of the fault cut-out fits on one of the three planes defined by the abnormal
TD of the wells that did not reach the planned objective (the Guasare Formation)
demonstrates that these are not missing sections but miscorrelations.
Cross-section of final model
- Missing sections associated with reverse faults
- Repeats not recognized because the repeats are from different facies
Ø The Multiple Bischke Plot analysis can help review the stratigraphy
Ø TDs of jam-terminated wells can indicate the presence of faults
SW
Eocene Miocene
Lessons
Ø Lateral motion along faults in strike-slip settings can induce :
NE
Post-Lagunillas
Lagunillas Superior
Lagunillas Inferior
Misoa “B”
Misoa “C”
Guasare
Paleo
Cret. Cogollo
BASEMENT
X
Multiphase Deformation on Low Angle Reverse Faults
Key points
Pressure trends
Fault cut-out on planes
Polyphase deformation
Carito Field
Each well on the following maps
exhibits missing sections
Venezuela
SANTA BARBARA
OOIP = 6.7 Billion bbls
CARITO
FURRIAL
Problem 1
Each was first interpreted as normal fault
depths in feet are indicated on map
Quartz-cemented band within a
sandstone layer
Fault planes linking
missing sections
N-6
N-3
Normal Fault
Interpretation
N-6
N-6
N-6
Reverse Fault
with missing section
Each fault cut-out corresponds
to a different fault
N-3
N-8
N-6
A
Northern Flank of Carito Central
A
Reverse Fault
Interpretation
N-8
Several fault cut-outs
fit on one fault plane
Detachment plane marked by
slickensides
(view from below)
Fault
A
Fractures
M UC-4 5
15560
I-3
M UC-4 2
14601
I-6
No recognized
detachment planes
within the Naricual
M UC-4
13866
I-6
M UC-5 0
14199
I-6
F UC-1 6
14316
F UC-1 5
14126
I-6
F UC-2 5
13712
M UC-1 E
13809
I-3
F UC-7
13632
F UC-2 6
13505
M UC-5 7
12456
Carap ita-E
M UC-3 7
12991
I-8
F UC-6
12866
I-6
CRC-7
12613
I-8
M UC-6 6
12499
Carap ita-E
A’
see location map below
Reactivated
fault
Proposed mechanism (detail)
Projected cross-section
N
SBC-20
Santa Barbara Field
j2
Problem 2
Venezuela
SBC-103
j1
43 degrees dip
for fault plane
43 Fault
First order polynomial
Perfect fit
Fault plane generated by first deformation phase
CARITO
SBC-45
14 degrees bed dip
OOIP = 6.1 Billion bbls
+ OGIP = 21 Tcf
Total = 9.6 Billion BOE
SANTA BARBARA
SBC-16
S
Oblique slip was generated by the
second phase of deformation
FURRIAL
j1
j2
Each fault is associated with a missing section at a different stratigraphic level
SBC-116 was a very successful infill well drilled as a follow-up of that new interpretation
(8000 bopd)
Missing sections associated with strike-slip or oblique slip
RFT pressures
Prof.
ft
PSI
11300
11400
11500
11600
11700
13000
Fault 1
13500
14000
“Hanging wall”
Fault 2
14500
Beds with
14 dip
15000
Well SBC-02
(West of the location map)
“Footwall”
Fault with 43 dip
Tectonic post-hydrocarbon emplacement is reflected in the pressure trends
Reverse faulting is interpreted from pressure data (despite a missing section)
Lessons
Ø Planar alignments of fault cut-outs can help indentify misinterpretations :
- Fault planes between 30º and 60º can be associated with multiphase deformation
- Missing section is obtained by sedimentary sequences gliding obliquely on a preexisting fault plane
Ø Large untapped hydrocarbon pools are found below such faults (e.g., SBC-116 with 8000 bopd)
Ø Sealing capacity of these faults is common and can be related to reactivation and cataclasis
Missing Sections Associated with Detachments
Key points
at same depths
Pressure problems
Gradual throw change
Santa Barbara Field
Venezuela
Example from Santa Barbara block 3
Example from Santa Barbara block 1
Problem 1
OOIP = 6.1 Billion bbls
+ OGIP = 21 Tcf
Total = 9.6 Billion BOE
Projected well
see to the right
Detachment
Damaged
zone
SANTA BARBARA
CARITO
Detachment
FURRIAL
SANTA BARBARA FIELD
Seismic line
Bosque
Block 1
Block 2
X-section
Block 3
RFT pressures (psi)
Missing sections at the same depth in every well
Very different units are missing
Detachment as seen on seismic
Missing sections observed (see right)
Note the “Herringbone” pattern
Example from Santa Barbara block 2
Example from Santa Barbara block 2
North
16415.5
1067600
15235.4
15362.5
Note the very high similarity
of depth of fault cutouts:
All points are close to 14970’
or between 15100’ and 15300’
Only variant = fault in PIC-01
1067600
N
Intra-Carapita
Marker A
CARAPITA SHALES
250
490
1067200
14987.3
Problem 2
Repetitions
510
South
Intra-Carapita
Marker A
1067200
15368
250
Nar Sup
15223
Nar Sup
>-2000
-1600
Nar Inf
14960.8
1066800
N
14972
KT
1066800
-135
0
15170
1 km
-260
Top NS @ 14970’
416250
Missing sections
-50
No fault recognized
417500
418750
Section from 3-D modelling
420000
416250
417500
418750
420000
Depths of major faults in the wells located at the limit between Block2 and Block 4
Faults with missing sections and faults with repeats
at nearly the same depth in every well.
Footwalls and hangingwalls associated with each fault cut-out
do not exhibit any drag folding
Whereas the sequence of reservoir is 4000 feet thick
These are the only faults interpreted in each of these wells.
A major detachment is responsible for all of the missing sections
and repeat sections
Fault throws are gradually changing on a map view.
Very different units are missing
Lessons
Ø Missing sections occurring at the very same depth are linked to detachment planes
- No drag folding and gradual thickness change is found on either side of the fault
- Bed dip can be different above and below the fault
Ø Pressure data can be very helpful in determining the depth of the detachments
Ø Fault-throw maps can validate the newly developed geological model
Implications for Hydrocarbon Exploration
Implications for
hydrocarbon exploration
Reserves overestimation
and far from optimum
development scheme
Main lessons
You may want to be aware of:
Missing sections at the same stratigraphic
level in many wells
Best sands
are absent
on the horsts
(Dunlin and Furrial fields)
Missing sections at the same
depth in neighbouring wells
Non-official interpretation
Wrong injection
scheme
And wrong
structural model
(Lama Field)
Pressure before injection
Pressure after injection
Water-cut after injection
Missing sections on a
well defined plane
Pressures
Pressures
PSI
2500
2400
2300
2200
2100
2000
1900
1800
1700
1600
1500
1400
1300
1200
PSI
4000
3800
3600
3400
3200
3000
2800
2600
2400
2200
2000
1800
1600
1400
1200
Water cut
Color Range
0%
50%
Reservoir pressure problems
Injection wells
Useless water injection
100%
Contouring using the new fault pattern
Drilling problems (Jamming)
Missing a giant field
(Bosque Field North of
Santa Barbara Field, block 2)
A few selected references
Chatellier, J-Y., Rueda, M.E., Charles, S. and Romero, I., 2008, Why 3D seismic missed a giant field in the Eastern
Venezuela thrust belt; postmortem of a late discovery, CSPG Convention C4lgary, 4 page Abstract
http://www.cspg.org/conventions/abstracts/2008abstracts/130.pdf
Chatellier, J.Y. and Zambrano, J. 2007, A multidisciplinary 4D integration delivers a reliable reservoir model for the Santa
Barbara Field, Venezuela, Data Fusion Workshop, SEG-AAPG-SPE, Vancouver, October 2007
Chatellier, J-Y and Porras C., 2004, The Multiple Bischke Plot Analysis, a Simple and Powerful Graphic Tool for Integrated
Stratigraphic Studies, AAPG Search and Discovery Article #40110 (www.searchanddiscovery.com)
Misunderstanding
of by-passed zones
Chatellier, J-Y., de Sifontes, R., Mijares, O. and Muñoz, P., 1999, Geological and production problems solved by
recognizing the strike slip component on reverse faults, VLA-31, Lake Maracaibo, Venezuela, SPE Annual Technical
Conference, Houston, SPE No. 56558
(Santa Barbara Field, block 1)
Acknowledgments
Much by-passed oil below the fault plane
The authors would like to thank Petroleos de Venezuela and Talisman Energy Inc. for permission to present this material.
All but one of the examples are taken from various Venezuelan structural settings and were presented in different forms at
various meetings; all of these with permission from PDVSA Intevep.