c t : quantifying i a of d water s channel s using channel ......cachana 100 95 90 85 80 75 70 65 55...
TRANSCRIPT
Chapter three: QuantIfyIng Intra-Channel arChIteCture Of deep-water slOpe Channel strata usIng Channel MetrICs: a predICtIve MethOd
IntrOduCtIOn
Deep-water slope channel deposits have been the focus of extensive research over the last decade. These complex depositional systems have been thoroughly investigated using vivid three-dimensional images of subsurface turbidite complexes produced from extensive seismic reflection volumes (e.g. Kolla et al., 2001; Abreu et al., 2003; Deptuck et al., 2003; Posmentier and Kolla, 2003; Prather et al., 2003; Samuel et al., 2003; Saller et al., 2004; Schwenk et al., 2005; Gee et al., 2007; Hubbard et al., 2009; Labourdette and Bez, 2010; Sylvester et al., 2011). Despite increases in resolution produced as a result of technological advances in seismic data acquisition and processing, there remains a significant gap in resolution between what is imaged in these surveys and the stratigraphic detail needed to efficiently delineate and develop associated hydrocarbon reservoirs.
During the evaluation of deep-water petroleum reservoirs, seismic datasets are commonly combined with data collected from well penetrations in order to gain an understanding of a particular reservoir interval at multiple scales (e.g., Porter et al. 2006). Well data (ie., wireline or core) is spatially limited, which makes it difficult to predict lateral facies changes and variations in sub-seismic architectural geometries. Supplementing subsurface data with sedimentological insight drawn from outcrop analogues is therefore crucial for the prediction of bed-scale sediment distribution in slope-channel reservoirs (Sullivan et al., 2004; Pringle et al., 2010). Numerous workers have demonstrated the importance of subtle facies characteristics or architectural parameters that impart a strong influence on the connectivity of deep-water channel reservoir bodies (e.g., Barton et al., 2010; Alpak et al., 2011; Li and Caers, 2011). Deep-water architectural elements are commonly characterized with quantifiable metrics in outcrop (e.g., Chapin et al., 1994; Manzocchi et al., 2007; Romans et al., 2009; McHargue et al., 2011; Olariu et al., 2011; Pringle et al., 2010), an approach adopted in order to more objectively describe sedimentary units and generate robust data inputs for reservoir model construction.
The primary focus of this work is to compile quantitative data collected using outcrop observations of a slope channel complex-set 130 m thick from the Cretaceous Tres Pasos Formation of southern Chile (Fig. 3.1). This data characterizes sub-seismic-scale intricacies observed within 18 channel elements in a 2.5 km long outcrop belt. The
43
Lago Toro
10
km
51° 0
0’ S
51° 3
0’ S
72° 3
0’ W
L. S
arm
ient
o
Sou
thA
mer
ica
Ch
ile
1000
km
620
mi
Argentina
Lag
un
aFi
gu
ero
a
Puer
toN
atal
es
Jorg
eM
on
tt
Cer
ro S
ol
Pale
ofl
ow
ro
ug
hly
du
e so
uth
(hig
hly
ob
liqu
e to
ou
tcro
p o
rien
tati
on
)
NO
RTH
SOU
TH
Lege
nd:
chan
nel s
ands
tone
inte
rbed
ded
sand
ston
e an
d m
udst
one
mas
s tr
ansp
ort d
epos
it
B C
10 m
250
m
V.E.
= 9
X
com
plex
bou
ndar
yel
emen
t bou
ndar
y
area
feat
ured
in p
art B
mea
sure
dse
ctio
nlo
catio
ns(s
ee b
lue
lines
& la
bels
in B
)
DS
OP
1Ca
ch 1
Vaca
1Su
b BB
4Su
b BB
1Su
b BB
3KJ
1M
M 1
01M
M 1
02
Vaca
2Pe
q 1
Cach
2
Cac
h 3
Peq
2
OP
2
DS
OP
1O
P 2
Sub
BB3
KJ1
MM
101
MM
102
Sub
BB4
Sub
BB1
Vaca
1Va
ca 2
Peq
1Pe
q 2
Cach
1Ca
ch 2
Cach
3
17
16
14
13
12
10
9
8
7
4
3
2
1
11
12
11
13
15
1818
6
5
15
3 26
9
7
3
2
A
Fig.
3.1
. Stu
dy a
rea
over
view
; (A
) Hig
h-re
solu
tion
sate
llite
imag
e of
a p
ortio
n of
the
Ulti
ma
Espe
ranz
a D
istri
ct o
f Sou
ther
n C
hile
; ins
et m
ap o
f Sou
th A
mer
ica
prov
ides
con
text
. The
red
box
iden
tifies
the
loca
tion
of th
e ou
tcro
p be
lt st
udie
d ad
jace
nt to
Lag
una
Figu
eroa
. (B
) Pho
to-m
osai
c of
Tre
s Pas
os F
orm
atio
n ou
t-cr
op b
elt.
Blu
e lin
es id
entif
y th
e lo
catio
ns o
f eac
h of
the
stra
tigra
phic
sect
ions
mea
sure
d ac
ross
the
stud
y ar
ea. 1
607
m o
f det
aile
d (c
m-s
cale
) mea
sure
d se
ctio
n pr
ovid
es th
e fr
amew
ork
for t
his s
tudy
. (C
) Stra
tigra
phic
cro
ss-s
ectio
n sh
owin
g th
e ei
ghte
en sl
ope
chan
nel e
lem
ents
pre
serv
ed in
the
Tres
Pas
os F
orm
atio
n at
La
guna
Fig
uero
a. T
he 1
30 m
thic
k se
dim
enta
ry p
acka
ge re
pres
ents
a re
serv
oir-s
cale
, cha
nnel
com
plex
-set
. Thi
s com
plex
-set
is d
ivis
ible
into
thre
e ch
anne
l co
mpl
exes
(sho
wn
in d
ashe
d lin
es),
with
bas
al b
ound
arie
s dem
arca
ted
by w
ides
prea
d m
udst
one-
dom
inat
ed u
nits
acr
oss t
he e
ntire
out
crop
bel
t. Th
e no
rthea
st–
sout
hwes
t tre
ndin
g cr
oss-
sect
ion
is o
rient
ed h
ighl
y ob
lique
to p
aleo
flow,
whi
ch w
as ro
ughl
y so
uthw
ard
and
capt
ures
3D
out
crop
per
spec
tives
on
a fla
t pan
el.
44
data is derived from a series of measured sections, comparable to measurements that could be made from cores and wireline logs in subsurface datasets. These data are suited for interpretation of three-dimensional sediment distribution in subsurface reservoirs dominated by analogous slope channel strata (e.g., Mayall et al., 2006). In particular, the dataset compiled provides insight into the extrapolation and prediction of channel element architecture in the subsurface based on diagnostic quantitative criterion defined for intra-channel subenvironments, which include channel axis, off axis and margin.
study area and BaCkgrOund geOlOgy
This study focuses on the Late Cretaceous Tres Pasos Formation, part of a 4-5 km thick succession of deep-marine strata in the Magallanes foreland basin of southern Chile (Fig. 3.1; Romans et al., 2010, 2011). An exceptionally exposed outcrop of the formation located adjacent to Laguna Figueroa provides the foundation for this study (Figs. 3.1A and 3.1B). The Tres Pasos Formation consists primarily of mudstone- and siltstone-dominated strata associated with a graded clinoform system characterized by ~ 870 m of paleobathymetric relief (Hubbard et al., 2010). Architectural analysis was completed on a coarse clastic base of slope deposit that forms an outcrop belt 2.5 km long and ~130 m thick (Fig. 2.1C; Chapter 2). Southward paleoflow was determined from the measurement of hundreds of sole marks, which confirms the generally southward oriented paleoflow trend observed across the basin (Shultz et al., 2005; Shultz and Hubbard, 2005; Romans et al., 2009; Hubbard et al., 2010). The plane of the outcrop belt is oriented north-northeast (27 - 207°N), and is intersected at a highly oblique angle by slope channel bodies preserved in the strata (Fig. 3.1B and 3.1C). Numerous gullies crosscut the outcrop belt roughly perpendicular to paleoflow providing unique 2D and 3D exposures of channel geometries (Fig. 3.1B).
The architecture of channelized deep-water strata is commonly described hierarchically, which provides a means to organize observations and recognize persistent patterns at multiple scales (Mutti and Normark, 1991; Ghosh and Lowe, 1992; Pickering and Clarke 1996; Campion et al., 2000; Gardner and Borer 2000; Hubbard et al., 2008; McHargue et al, 2011). The hierarchical scheme used for the purpose of this study is a slightly modified version of Sprague et al. (2002, 2005). The entire 130 m of outcropping stratigraphy studied is defined as a single complex-set, which in turn, is comprised of three channel complexes 20-68 m thick, differentiated from one another by widespread erosive bases draped by siltstone-dominated deposits (Chapter 2; Fig 2.1C). Complexes are also composite features comprised of genetically related channel elements 6-18 m thick,which consist of sedimentation units measuring 0.1 - 4.5 m in thickness.
45
slOpe Channel MOdel
Slope channel elements in the study area consist of mappable low-sinuosity (1.01-1.05) bodies characterized by little change in internal architecture along the 2.5 km length of the outcrop belt. The cross-sectional fill of each channel is symmetric to slightly asymmetric (Fig 2.2; Chapter 2), and a typical Tres Pasos Formation channelform is ~15 m thick and estimated to be 300 m wide.
These channels are initiated by large, out-sized sediment gravity flows that scour the sea floor (cf., Elliot, 2000). Erosional relief is coupled with constructional internal levee build-up, which focuses turbidity currents and leads to overall aggradation of the channel system (cf., Deptuck et al., 2003; Kane and Hodgson, 2011). Channels largely back-fill with the deposits from collapsing high-concentration turbidity currents (Mutti and Normark, 1991; Clark and Pickering, 1996). An important component of channel fills are fine-grained drape deposits, which mantle the channel base and record deposition from the tails of largely bypassing turbidity currents (Fig. 3.2A; Mutti and Normark, 1987). If preserved, these 10 to 200 cm thick bypass deposits have the potential to impart considerable reservoir heterogeneity and in some instances could compartmentalize a sedimentary body (Figs. 3.1C, 3.2B and 3.2C; cf., Barton et al., 2010).
Channel element fills are composite features comprised of numerous stacked sedimentation units, which individually represent the deposit of a single sediment gravity flow (Fig. 3.2A). These sedimentation units are typically lenticular, thinning from the axis of a channel element towards the margins (Fig. 3.2A). Channel fills commonly transition from thick, amalgamated sandstone beds in the central portion of channel elements to thinly interbedded sandstone and mudstone-dominated deposits in the channelform flanks across < 30 m (Fig. 3.2A). Channel element fill is subdivided into three intra-channel architectural zones, which correspond directly to the sedimentation unit associations described in Chapter 2. For the purpose of this study, these distinct architectural associations are defined as axis, off-axis and margin. These zones are systematically distributed in each channel element (Fig. 3.2A) and are mapped across the outcrop belt (Fig. 3.3). Similar channel element architecture has been identified in numerous outcrop studies, including the Capistrano Formation, California (Campion et al., 2005), the Brushy Canyon Formation, West Texas (Beaubouef et al., 1998; Gardner et al., 2003), and the Ross Formation of Ireland (Sullivan et al., 2004). This internal channel fill architecture is quantitatively characterized in the Tres Pasos Formation by linking architectural observations to the detailed measured section data acquired across the study area (Fig. 1C).
46
05
1015202530354045
55
05
10152025303540455060657075
5 m
25 m
vert
ical
exa
gg
erat
ion
= 2
X
AXIS
OFF
-AXI
SO
FF-A
XIS
MA
RGIN
MA
RGIN
ELEM
ENT
BOU
ND
ARY
erod
ed c
hann
elfo
rm
bypa
ss d
rape
dep
osit
BAC
sedi
men
tatio
n un
it
Fig.
3.2
. (A
) Cha
nnel
ele
men
t arc
hite
ctur
e is
illu
stra
ted
in a
dep
ositi
onal
strik
e or
ient
ed c
ross
-sec
tion.
Cha
nnel
form
geo
met
ry is
ero
ded
by la
rge
out-s
ized
sedi
-m
ent g
ravi
ty fl
ows t
hat p
redo
min
antly
byp
ass t
he c
hann
el e
nviro
nmen
t and
dep
osit
coar
se-g
rain
ed se
dim
ent o
n th
e de
ep se
afloo
r. C
hann
el e
lem
ent b
ases
are
co
mm
only
dra
ped
by si
lt- to
mud
ston
e-do
min
ated
dep
osits
resu
lting
form
the
low
-den
sity
trac
tion
depo
sitio
n an
d he
mip
elag
ic se
ttlin
g as
soci
ated
with
thes
e pr
edom
inan
tly b
ypas
sing
flow
s. C
hann
el e
lem
ent fi
lls a
re c
hara
cter
ized
by
an o
vera
ll co
arse
ning
upw
ard
sequ
ence
, whi
ch p
rese
rves
man
y ep
isod
es o
f ero
sion
, by
pass
and
dep
ositi
onal
bac
kfilli
ng. T
hree
sedi
men
tolo
gica
lly u
niqu
e po
rtion
s of a
cha
nnel
ele
men
t can
be
iden
tified
(axi
s, of
f-ax
is a
nd m
argi
n) a
nd c
hara
cter
-iz
ed q
uant
itativ
ely
by th
e m
etho
d de
scrib
ed in
this
stud
y. (B
) Cha
nnel
ele
men
ts st
ack
into
two
com
posi
te c
hann
el c
ompl
exes
(mea
sure
d se
ctio
n pr
ovid
es v
ertic
al
scal
e).
Das
hed
box
is e
xpan
ded
in p
art C
. (C
) Stra
tigra
phic
sect
ion
mea
sure
d th
roug
h th
e lo
wer
cha
nnel
com
plex
. A
rrow
s ide
ntify
ero
sion
al c
hann
el e
lem
ent
base
s, dr
aped
by
fine-
grai
ned
bypa
ss d
epos
its.
Whe
re p
rese
rved
, the
se fi
ne-g
rain
ed d
rape
s wou
ld p
rovi
de su
bsta
ntia
l ver
tical
bar
riers
to fl
ow.
47
051015202530354045505565707580859095
100
Cach
ana
60
05101520253035404550556065707580859095
100
105
110
115
120Va
ca1
55
Sub
BB4
05
1015202530354045506065707580859095
100
105
110
Sub
BB1
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105
110
115
120
125
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100
105
110
115
Sub
BB3
05101520253035404550556065707580859095
100
105
110
KJ1
05101520253035404550556065707580859095
100
MM
101
05101520253035404550556065707580859095100
105
110MM
102
051015202530354045OP
1
051015
20
2530354045505560657075808590Vaca
2
3035404550556065707580859095
Pequ
ena
0510152025
Cach
ana
2
0510152025303540455055606570
0510
Cach
ana
3
0510152025303540455055606570
051015202530354045
Pequ
ena
2
051015202530354045505560657075OP
2
100
105
110
505560657075808590
DA
RKSI
DE
1
05101520253035404595
100
105
051015
MM
1
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BB2
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0510
DS3
051015
MM
2
0510
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05
DYM
D2
DYM
D3
05
051015
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25 m
250
m
V.E.
= 9
X
1716
14
13
12
10
9
87
4
3
2
1
11
12
11
13
15
1818
6
5
15
3 26
debr
is �
owax
iso�
axi
sm
argi
nin
ner l
evee
Fig.
3.3
. Int
ra-e
lem
ent a
rchi
tect
ure
dist
ribut
ion
char
acte
rized
from
fiel
d ob
serv
atio
ns p
rese
nted
in th
e st
ratig
raph
ic c
ross
-sec
tion
in F
igur
e 3.
1C. R
ecog
nitio
n of
thes
e ar
chite
ctur
al d
ivis
ions
acr
oss t
he o
utcr
op b
elt r
elie
s hea
vily
on
wal
king
out
and
cor
rela
ting
beds
in th
e fie
ld. T
his s
chem
atic
pro
vide
s a si
mpl
ified
up
-sca
led
pers
pect
ive
of th
e ou
tcro
p be
lt, re
mov
ing
sedi
men
tolo
gica
l det
ail.
The
high
est q
ualit
y re
serv
oir r
ocks
are
ass
ocia
ted
with
cha
nnel
axi
s and
off
axis
de
posi
ts, a
nd a
ll ot
hers
wou
ld b
e of
subs
tant
ially
low
er q
ualit
y.
48
dataset and MethOds
Over 1600 m of detailed measured section were collected at the cm-scale, documenting sedimentation unit thickness, grain-size, primary sedimentary structures, and the nature of bed contacts across study area (Fig. 3.1C and 3.2C). Measured section through 185 channel elements were taken, and 3656 sedimentation units were documented. Lateral spacing between measured sections ranges from 100 to 250 m, although localized channel margins were characterized by 10-20 m section spacing (Fig. 3.1C). Measured sections were correlated through field and photomosaic mapping (Chapter 2; Fig. 2.1C).
Eighteen channel elements are present, defined through stratigraphic correlations, delineation of channel edges, facies analysis and paleocurrent measurements (Fig. 3.1C). Each channel fill is subdivided into axis, off axis and margin architectural zones along the length of the outcrop belt (Fig. 3.3). These architectural divisions are the foundation of the quantitative metrics tabulated. Linking the intra-element architecture to the bed-scale measurements collected allows these different zones to be differentiated based on a series of quantified 1-D characteristics. These characteristics, or metrics, include net-to-gross ratio, amalgamation ratio, and maximum amalgamated sandstone thickness.
Net-to-Gross Ratio Net-to-gross ratio (NTG) is a common quantitative parameter used to describe one-dimensional stratigraphic sections (from outcrop or subsurface) collected from deep-water strata. It is a measure of sandstone richness, recorded as a ratio of the total thickness of sandstone divided by the gross thickness of the interval of interest. In this study, channel element thickness is used to define the gross interval (Fig 3.1C and 3.2C), and net-to-gross values tabulated are expressed as a decimal between 0 and 1 (Fig. 3.4).
Amalgamation ratioAmalgamation ratio (AR) is a quantitative parameter defined by the number of
amalgamation surfaces in a gross interval (ie, sandstone on sandstone bedding contacts) divided by the number of sedimentation units in that same interval minus one (Fig. 3.4). Subtracting one from the denominator of the ratio normalizes the metric since there is always one fewer bed contact than sedimentation unit in an interval. The calculated value is also presented as decimal between 0 and 1 for ease of comparison with NTG. This metric is useful for the evaluation of vertical connectivity in deep-water sandstone accumulations (e.g., Chapin et al., 1994; Manzocchi et al., 2007; Romans et al., 2009).
49
Fig. 3.4. Quantitative metrics calculated in three stratigraphic sections measured through the axis to margin transition of a channel element. At left, graphic logs of sections indicate sedimentary unit thick-ness, grain-size, primary sedimentary structures, the nature of bed contacts and number of sedimenta-tion units in the interval of interest. To the right of the graphic logs, each sedimentation unit within the interval is classified Type 1 – 5. Net sandstone is tabulated and compared to the overall interval thick-ness to calculate net-to-gross ratio. Amalgamation surfaces (sandstone on sandstone contacts identified by arrows) are counted and compared to the number of beds in an interval to calculate an amalgamation ratio, and the maximum thickness of amalgamated sandstone is tabulated.
MM
2M
M 1
MM
102
0
5
10
0
5
10
0
5
cmfvfsltmud
cmfvfsltmud
cmfvfsltmud1
2
3
4
5
6
7
8
9
10
11
12 13 14 151617
1
2
3
4
5
6
7
89 10 11 12 131415
16
1718
2019
1 23
45 67 89 10 11 12 131415
1617
18
2019
2122
24
23
26 2725 28
measured section
measured section
measured section
sedimentationunit type
sedimentationunit type
sedimentationunit type
net sand
net sand
net sandcompiled metrics
compiled metrics
compiled metrics
Net to Gross Ratio:
Amalgamation Ratio:
0.97
0.63
Max. Amalgamated Sst. Thickness:
11.3 m
Total Unit Thickness:
11.6 m
Type 1:
73.6%Type 2:
24.1%Type 3:
1.1%Type 4:
1.2%
Net to Gross Ratio:
Amalgamation Ratio:
0.95
0.60
Max. Amalgamated Sst. Thickness:
7.5 m
Total Unit Thickness:
11.3 m
Type 1:
52.5%Type 2:
40.2%Type 3:
1.5%Type 4:
4.8%
Net to Gross Ratio:
Amalgamation Ratio:
0.53
0.11
Max. Amalgamated Sst. Thickness:
1.2 m
Total Unit Thickness:
6.3 m
Type 1:
4.8%Type 2:
27.1%Type 3:
15.0%Type 4:
53.1%
net sssed. unit type 3 sed. unit type 4sed. unit type 2sed. unit type 1 gross amalg. surface max. amalg. sst
Axis
O�-Axis
Margin
50
Maximum thickness of amalgamated sandstone The maximum thickness of amalgamated sandstone is defined as the greatest
thickness of continuous amalgamated sandstone present within a channel element succession. This metric is a useful measure of sandstone connectivity complimentary to both AR and NTG.
sedIMentatIOn unIts
Sedimentation units are the fundamental division used to capture stratigraphic details in the channelized deep-water deposits studied, and are defined using the well-established bed classification schemes of Lowe (1982) and Bouma (1964). Five sedimentation unit types characterize the channel elements of the Tres Pasos Formation (Table 3.1):
Type one: Type one sedimentation units consist of thick-bedded (25 – 450 cm) amalgamated sandstone with sharp, erosive bases. Beds contain a coarse- to very coarse-grained basal lag with occasional scattered granules, which normally grades into upper fine- to upper medium-grained structureless to planar laminated sandstone. Moderate to high concentrations of mudstone intraclasts (up to 25 cm in diameter) are commonly observed at the base of sandstone beds, rarely comprising layers > 20 cm thick. Intraclasts are sub-angular to sub-rounded and in some instances, where they are elongate, they are crudely aligned to imbricated. Bed tops are typically truncated by the erosive base of the overlying bed.
These highly erosive, amalgamated sedimentation units record deposition from erosive high-density turbidity currents (Lowe, 1982). Basal mudstone intraclast lags are locally transported by tractional processes on the channel floor. The structureless portions of sedimentation units record the rapid collapse of suspended material from the sediment-laden turbidity current (Ta division of Bouma, 1962; S3 division of Lowe, 1982) and planar laminations preserve waning stage traction sedimentation (Tb division of Bouma, 1962). Fine-grained deposits associated with the dilute low-density tails (ie, Td-e) of the large turbidity currents are usually absent due to erosion by subsequent high-density turbidity currents.
51
Tabl
e 3.
1. D
escr
iptio
n of
sedi
men
tatio
n un
it ty
pes a
nd in
terp
rete
d se
dim
enta
ry p
roce
sses
, Tre
s Pas
os F
orm
atio
n, L
agun
a Fi
guer
oa.
unit
disc
riptio
nTy
peD
omin
ant g
rain
-siz
eSe
dim
enta
ry s
truc
ture
sTu
rbid
ite
divi
sion
sBo
undi
ng
surf
aces
Thic
knes
sra
nges
Seco
ndar
y fe
atur
esD
epos
ition
al p
roce
ss
Thic
k-be
dded
sa
ndst
one
1U
pper
fine
to u
pper
m
ediu
m-g
rain
ed
sand
ston
e, c
oars
e to
ve
ry c
oars
e-gr
aine
d sa
ndst
one
and
gran
ules
at s
ed. u
nit
base
s
Nor
mal
ly g
rade
d;
stru
ctur
eles
s to
pla
ne
lam
inat
ed; c
rude
al
ignm
ent o
f cla
sts
and
rare
cla
st im
bric
atio
n in
sed.
uni
t bas
es; b
ed
amal
gam
atio
n co
mm
on
S1, T
a &
Tb
Eros
ive
base
; gr
adat
iona
l to
shar
p to
p
Mud
ston
e in
trac
last
s (u
p to
25
cm
in le
ngth
) com
mon
at s
ed. u
nit
base
s; ra
re d
ewat
erin
g st
ruct
ures
; m
inor
sof
t sed
imen
t def
orm
atio
n
Mix
ture
of t
ract
ion
and
rapi
d su
spen
sion
sed
imen
tatio
n fr
om h
igh-
dens
ity tu
rbid
ity c
urre
nts
2Lo
wer
fine
to u
pper
m
ediu
m-g
rain
ed
sand
ston
e
Nor
mal
ly g
rade
d;
stru
ctur
eles
s or
pla
ne-
lam
inat
ed to
ripp
le
lam
inat
ed; b
ed
amal
gam
atio
n co
mm
on
Ta, T
b &
TcSh
arp,
flat
ba
ses;
gr
adat
iona
l to
shar
p to
p
Min
or lo
w d
ensi
ty o
r iso
late
d m
udst
one
intr
acla
sts
(up
to 1
5 cm
in
leng
th) fl
oatin
g in
mat
rix o
r at s
ed.
unit
boun
darie
s; ra
re lo
adin
g an
d so
ft-s
edim
ent d
efor
mat
ion
Dep
osite
d ra
pidl
y fr
om s
uspe
nsio
n by
hig
h-de
nsity
turb
idity
cur
rent
s
Thic
k- to
thin
-bed
ded
non-
amal
gam
ated
sa
ndst
one
Low
er fi
ne to
upp
er
med
ium
-gra
ined
sa
ndst
one,
silt
ston
e to
m
udst
one
com
mon
ly
inte
rbed
ded
Nor
mal
ly g
rade
d;
stru
ctur
eles
s or
pla
ne-
lam
inat
ed to
ripp
le
lam
inat
ed; b
ed
amal
gam
atio
n ra
re
Part
ial t
o co
mpl
ete
Boum
a se
quen
ces
Shar
p, fl
at
base
s;
grad
atio
nal t
op
Abu
ndan
t pre
serv
atio
n of
silt
ston
e at
sed
. uni
t top
; mud
ston
e in
trac
last
s ar
e ra
re; r
are
load
ing
and
soft
-sed
imen
t def
orm
atio
n
Dep
osite
d ou
t of s
uspe
nsio
n by
a
mix
ture
of h
igh
and
low
den
sity
tu
rbid
ity c
urre
nts,
trac
tion
depo
sitio
n fr
om b
y-pa
ssin
g flo
ws
Shal
e w
ith ra
re
silts
tone
Pred
omin
antly
sha
le
with
rare
silt
ston
e an
d ve
ry fi
ne-g
rain
ed
sand
ston
e
Stru
ctur
eles
s to
fain
tly
lam
inat
ed; r
are
norm
al
grad
ing
Gra
datio
nal t
o sh
arp
base
s;
shar
p to
p
Rare
ver
y fin
e to
fine
-gra
ined
sa
ndst
one
beds
com
mon
ly <
10
cm th
ick
Dep
osite
d un
der n
orm
al m
arin
e co
nditi
ons
from
hem
ipel
agic
set
tling
or
by
colla
psin
g lo
w-d
ensi
ty
turb
idity
cur
rent
s, d
epos
ition
from
by-p
assi
ng �
ows
Chao
tic m
udst
one-
rich
depo
sits
Com
ingl
ed s
hale
, si
ltsto
ne a
nd
sand
ston
e
Non
e; c
haot
ic, f
olde
d an
d de
form
ed b
eddi
ngVa
riabl
e to
p an
d ba
seRa
re s
ands
tone
and
silt
ston
e ra
fted
bl
ocks
; poo
rly s
orte
d m
ixtu
res
of
sedi
men
t with
var
ying
pro
port
ions
of
san
d, s
ilt a
nd s
hale
; com
mon
so
ft s
edim
ent d
efor
mat
ion
Mas
s w
astin
g (b
ank
colla
pse,
sl
umpi
ng, s
lidin
g); d
epos
ition
by
mud
-ric
h de
bris
flow
s
3 4 5
Sedi
men
tatio
n
25 -
450
cm
10 -
250
cm
10 -
200
cm
0.5
- 10
cm
20 -
500
cm
52
Type two Type two sedimentation units consist of thick-bedded (10 to 250 cm) sandstone with flat bases, which commonly grade normally from upper medium- to upper fine-grained sandstone. These units are typically amalgamated. Sandstone is predominantly structureless with planar laminations common in the upper 5 to 30 cm of the unit, occasionally overlain by ripple lamination. Soft-sediment deformation characterizes sandstone bed tops in some instances. Thin siltstone beds rarely cap sedimentation units. Isolated mudstone intraclasts up to 15 cm in length are present at the tops of beds or in basal lags. Intraclasts are commonly angular and rarely imbricated.
Type two sedimentation units record rapid suspension sedimentation from high-density turbidity currents (dominated by S3/Ta divisions). Planar and ripple laminations (Tb and Tc divisions of Bouma, 1962) record traction deposition from waning turbulent flows.
Type three Type three sedimentation units are thin- to thick-bedded (5 to 200 cm), with sharp, flat bases. They are not typically associated with amalgamated, sand-on-sand bedding contacts. Sandstone beds normally grade from upper medium to upper fine-grained, are commonly structureless or faintly laminated, and grade rapidly to siltstone or mudstone deposits 2 to 10 cm thick. Planar and ripple lamination are sometimes preserved in the upper 10 to 15 cm of sedimentation units, and are often associated with soft sediment deformation. The siltstone- to mudstone-dominated intervals at the top of each sedimentation unit are occasionally characterized by diffuse planar laminations. Mudstone intraclasts are rare, randomly distributed in the upper half of sandstone beds.
Type three sedimentation units are the result of deposition from high to low-density turbidity currents. Thick structureless sandstone deposits record rapid sedimentation from the head of a large high-density turbidity current (Ta/S3). Waning of the current is recorded by the Tb, Tc and Td divisions of Bouma (1962).
Type four Type four sedimentation units consist of thinly interbedded (0.5-10 cm thick), non-amalgamated siltstone and very fine-grained sandstone. Units exhibit flat bases and where thicker than 5 cm, normal grading is typical. The upwards transition from sandstone to siltstone is gradational; sandstones are planar- to ripple-laminated and siltstones are diffusely laminated to massive.
Thin-bedded siltstone and sandstone units with gradational tops were deposited
53
by traction, associated with dilute, low-density turbulent gravity flows (Tb - Te divisions of Bouma, 1962). In some instances, these beds originated from the dilute tails of large, erosive turbidity currents, which predominantly bypassed the channel environment (cf., Mutti and Normark, 1987).
Type five Type five sedimentation units consist of poorly sorted mudstone-dominated deposits 20-500 m thick. They are chaotically bedded, characterized by folded and internally deformed fabric locally. Basal and upper contacts are sharply defined and often undulous. Small blocks (up to 40 cm in diameter) of rafted sandstone or siltstone are occasionally observed within a poorly sorted muddy matrix.
Chaotic deposits are attributed to mass wasting or slumping. They also could be the result of deposition by mud-rich debris flows (Lowe, 1982). Mass wasting deposits are an important constituent of many deep-water channel fills (e.g., Mayall et al., 2006; Hubbard et al., 2009), however they make up a minor proportion (1.2%) of the strata studied.
applICatIOn Of MetrICs tO well-expOsed Channel transeCts
In order to demonstrate the quantification of intrachannel architectural detail, the analysis of two channel axis to margin transects are described below (Fig. 3.5).
MM Margin Measured sections from the MM Margin characterize internal element architecture as it transitions from margin to axis (Fig. 3.5A). NTG increases systematically from 0.53 at the channel margin, to 0.95 in the off-axis position and then to 0.97 in the channel axis (Fig. 3.5A). AR also increases from 0.11 at the margin, to 0.60 in the off-axis section and 0.63 in the axial-most portion of the channel (Fig. 3.5A). Maximum amalgamated sandstone thicknesses increases from 1.2 m in the margin to 7.5 m in the off-axis position and 11.3 m in the axis. The characterization of the MM Margin produces idealized results, where all three quantitative metrics increase systematically from the channel margin to axis (Fig. 3.5A).
Gold Margin Four measured sections, A through D, are used to characterize Gold Margin architecture (Fig. 3.5B). Section A was measured through the margin and Section D
54
MM MARGIN
5 m
5 m
VE=1.5
5 m
5 m
VE=1.5
GOLD MARGIN
Max. Amalgamated Sst:
1.2 m
Net to Gross Ratio:
Amalgamation Ratio:
0.53
0.11Max. Amalgamated Sst:
7.5 m
Net to Gross Ratio:
Amalgamation Ratio:
0.95
0.60Max. Amalgamated Sst:
11.3 m
Net to Gross Ratio:
Amalgamation Ratio:
0.97
0.63
Max. Amalgamated Sst:
10.1 m
Net to Gross Ratio:
Amalgamation Ratio:
0.90
0.23Max. Amalgamated Sst:
8.8 m
Net to Gross Ratio:
Amalgamation Ratio:
0.88
0.37Max. Amalgamated Sst:
6.2 m
Net to Gross Ratio:
Amalgamation Ratio:
0.90
0.24Max. Amalgamated Sst:
0.88 m
Net to Gross Ratio:
Amalgamation Ratio:
0.56
0.05
0
2
4
6
8
10
12
0.0
0.2
0.4
0.6
0.8
1.0
01020304050607080
net t
o gr
oss
/ am
alg.
ratio
max
. am
alg.
sst
. (m
)
0
2
4
6
8
10
12
0.0
0.2
0.4
0.6
0.8
1.0
(m)
01020304050607080
net t
o gr
oss
/ am
alg.
ratio
max
. am
alg.
sst
. (m
)
amalgamation ratio max. amalgamation ss thicknessnet to gross
margin axis
margin axis
margin axis
east west
eastwest
B
0
5
0
5
10
MM 2
0
5
10
MM 1MM 102
0
5
10
D
0
5
10
15
C
0
5
10
A
0
5
10
B
A
Fig. 3.5. Stratigraphic cross-sections across two well-preserved channel margins in the study area. The graph beneath each channel element illustrates changes in channel metrics across the transition from margin to off-axis to axis.
55
towards the channel element axis, with sections B and C capturing characteristics of the intermediate off axis portion of the channel element (Fig. 3.5B). NTG values generally increase from margin to axis, from 0.56 to 0.90; intermediate values calculated in the off-axis position decrease from 0.90 in Section B to 0.88 in Section C (Fig. 3.5B). Minor variation in the systematic increase in NTG from margin to axis is locally recorded. AR increases as expected from Section A (0.05), through sections B (0.24) and C (0.37); however, the transition from Section C to Section D is characterized by a decrease in AR to 0.23 (Fig. 3.5B). With AR highly dependent on the number of sedimentation units present, the reduced amalgamation ratio in Section D results from a relatively high number of thin beds preserved within the drape deposits in the most deeply incised, axial-most portion of the channel element described. Maximum amalgamated sandstone values increase from 0.88 m in the margin (Section A), to 6.2 m and 8.8 m in the off-axis positions (sections B and C), and finally to 10.1 m as the channel axis is approached (Fig. 3.5B).
Comparison of the two margins The Gold and MM margin case examples demonstrate how quantitative metrics computed from measured sections help differentiate intra-channel architectural zones (Fig. 3.2A and 3.5). Perturbations in expected trends can commonly be attributed to increased presevation of drape deposits locally within the channel, however, an increase in NTG and AR is generally expected across the transition from margin to axis. With little variation in gross intra-element fill trends observed across the study area (Fig. 3.1C and 3.2A), this relationship forms the basis for computation of quantitative metrics for each intra-element architectural zone (axis, off-axis or margin). Examining the relative proportion of each sedimentation unit type across the channel fills also provides complimentary results that should add another quantifiable attribute to help differentiate each subdivision in poorly constrained reservoirs (Fig. 3.4).
results
Statistical analysis was completed on the tabulated channel metrics produced from the robust dataset collected at the Laguna Figueroa study area (Table 3.2). For the purpose of this discussion, NTG is considered high, moderate or low, when characterized by values of > 0.8, 0.5 to 0.8 and < 0.5, respectively. AR results are similarly subdivided into high (> 0.5), moderate (0.2 to 0.5) and low (< 0.2) degrees of amalgamation. Channel Axis Data
56
Eleme
nt
E186.7
016.
250.0
05.5
50.0
02.5
0--
----
--2.2
53.9
00.3
53.8
03.9
55.6
01.6
03.1
50.8
52.7
5--
----
----
----
----
----
----
--E17
----
3.00
6.55
1.80
11.30
1.65
5.00
2.30
6.15
1.10
5.60
1.50
5.25
4.60
4.60
3.63
6.95
5.85
7.30
5.60
6.95
3.10
5.20
----
2.70
7.20
0.00
4.77
----
----
E165.7
010.
003.5
86.8
01.9
56.8
03.9
010.
353.2
59.1
52.1
59.3
03.1
08.1
00.0
03.5
5--
----
----
----
----
----
----
----
----
--E15
0.10
3.10
5.15
5.15
0.80
5.90
0.00
3.65
0.00
3.60
0.00
3.50
0.00
1.65
0.00
3.70
5.65
8.10
4.10
6.25
6.75
9.95
8.20
11.00
----
4.10
10.00
0.19
9.19
----
----
E140.0
03.0
52.5
02.5
00.0
02.5
00.0
01.8
53.3
04.9
00.8
06.1
02.9
510.
705.9
011.
957.1
57.1
50.0
07.1
55.8
07.0
55.9
56.4
0--
--3.5
04.6
00.0
03.5
6--
----
--E13
0.30
3.45
6.85
6.85
5.45
7.55
7.20
7.20
3.75
3.75
2.10
2.10
0.00
1.30
2.50
3.25
1.90
4.20
0.68
2.75
1.90
3.90
3.20
3.20
----
3.85
4.10
0.81
6.48
----
----
E120.0
06.8
58.7
08.7
08.2
08.2
06.8
06.8
04.2
04.2
02.4
54.7
54.0
04.8
52.3
54.0
53.1
05.5
02.2
59.2
510.
6510.
6512.
5512.
55--
--12.
8012.
808.3
79.5
7--
----
--E11
1.70
11.65
4.30
4.30
7.90
10.95
3.70
4.70
5.85
6.45
0.95
3.10
0.00
2.00
0.00
2.65
0.00
4.45
4.05
4.05
2.75
2.90
4.05
4.05
----
5.40
5.40
4.30
6.91
----
----
E10--
----
----
--3.8
56.6
50.2
27.8
53.1
510.
152.5
38.4
02.8
05.4
01.5
51.5
5--
----
----
----
----
----
----
----
--E9
0.80
6.75
----
1.95
3.70
4.00
7.45
12.40
12.40
7.90
11.20
10.65
12.90
4.00
15.20
1.50
16.45
5.30
16.30
10.90
15.20
6.95
13.45
0.00
6.45
0.70
11.35
5.47
13.09
0.00
14.05
----
E89.4
016.
50--
--10.
2013.
101.3
05.4
00.0
01.4
00.0
05.2
5--
----
----
----
----
----
----
----
----
----
----
--E7
0.08
4.45
----
1.70
2.00
7.80
13.05
6.90
12.35
7.85
13.30
11.55
15.35
4.75
14.00
5.10
13.05
4.19
11.90
2.85
11.10
2.55
8.60
1.60
8.15
4.90
8.35
4.66
8.00
0.00
7.25
----
E61.6
08.5
0--
----
--3.0
05.3
52.0
05.2
56.0
07.7
52.0
58.6
50.0
06.8
00.0
02.9
5--
----
----
----
----
----
----
----
--E5
0.00
2.30
----
----
0.00
6.05
0.45
5.95
1.45
3.95
0.00
4.55
0.00
3.20
0.00
2.97
0.00
4.95
0.33
1.50
0.00
3.75
2.33
6.00
1.05
4.90
0.00
3.14
0.00
3.20
----
E4--
----
----
----
----
--0.7
50.7
51.9
04.5
07.9
09.0
56.0
012.
536.8
010.
654.8
713.
1211.
8011.
807.2
511.
20--
--2.7
111.
013.7
58.5
0--
--E3
2.90
7.40
----
----
0.85
8.15
0.69
7.55
9.65
13.10
6.45
6.45
7.95
8.35
3.75
8.50
3.75
5.55
6.18
6.93
8.50
8.50
3.05
8.20
----
8.08
8.26
9.35
9.95
2.85
11.50
E23.3
03.3
0--
----
--5.7
012.
855.1
05.7
59.2
09.2
04.9
013.
054.7
010.
258.0
511.
0513.
5017.
15--
--6.1
016.
907.6
07.6
0--
--8.1
512.
134.7
618.
83--
--E1
----
----
----
----
----
----
2.40
2.40
5.25
10.25
4.65
4.65
7.55
12.30
----
4.65
6.20
----
----
----
2.30
9.62
----
Darks
ideOP
1OP
2MM
102MM
101KJ1
Sub BB
3Sub
BB1
Pequen
a 2 Up
perCac
hana
Cachan
a 2Cac
hana 3
Sub BB
4Vac
a 1Vac
a 2Peq
uena
Pequen
a 2 Lo
wer
Eleme
nt
E18
0.31
0.72
0.00
0.16
0.00
0.45
----
----
0.64
0.69
0.06
0.32
0.15
0.89
0.05
0.80
0.50
0.31
----
----
----
----
----
----
----
E17
----
0.50
0.46
0.08
0.40
0.15
0.51
0.15
0.59
0.44
0.83
0.80
0.93
1.00
1.00
0.24
0.91
0.63
0.91
0.70
0.88
0.33
0.81
----
0.22
0.76
0.00
0.67
----
----
E16
0.70
0.69
0.35
0.82
0.19
0.79
0.21
0.78
0.37
0.58
0.64
0.72
0.39
0.78
1.00
1.00
----
----
----
----
----
----
----
----
----
E15
0.08
0.13
0.09
0.24
0.04
0.30
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.80
0.70
0.21
0.72
0.44
0.72
0.54
0.80
----
0.27
0.63
0.13
0.52
----
----
E14
0.00
0.36
0.13
0.74
0.00
0.85
0.00
1.00
0.53
0.80
0.20
0.47
0.30
0.84
0.42
1.00
1.00
1.00
0.00
0.59
0.55
0.98
0.63
0.94
----
0.30
0.89
0.00
0.29
----
----
E13
0.07
0.59
0.38
1.00
0.47
0.97
0.73
1.00
1.00
1.00
1.00
1.00
0.00
0.50
0.13
0.82
0.50
0.96
0.10
0.94
0.19
0.88
1.00
1.00
----
0.63
0.95
0.09
0.25
----
----
E12
0.00
0.31
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
0.25
0.91
0.61
0.85
0.50
0.58
0.13
0.95
0.11
0.98
1.00
1.00
1.00
1.00
----
1.00
1.00
0.80
1.00
----
----
E11
0.04
0.71
1.00
1.00
0.67
0.79
0.25
0.88
0.20
0.96
0.33
0.34
0.00
0.40
0.00
0.17
0.00
0.42
1.00
1.00
0.67
0.95
1.00
1.00
----
1.00
1.00
0.11
0.91
----
----
E10
----
----
----
0.93
0.89
0.04
0.24
0.05
0.69
0.10
0.78
0.19
0.85
1.00
1.00
----
----
----
----
----
----
----
----
E90.0
20.2
8--
--0.1
70.6
30.6
10.9
71.0
01.0
00.9
00.7
10.3
50.8
50.2
50.8
50.1
70.8
10.1
40.8
80.4
20.8
80.0
70.7
60.0
00.2
90.2
40.6
70.3
70.6
40.1
10.5
2--
--E8
0.61
0.87
----
0.75
0.82
0.82
0.79
0.00
0.14
0.00
0.00
----
----
----
----
----
----
----
----
----
----
----
E70.0
80.3
9--
--0.8
90.9
50.5
30.8
50.3
00.8
30.4
70.7
20.6
70.8
90.5
80.7
90.5
40.9
20.2
20.9
00.3
30.5
90.0
80.7
50.2
50.5
50.5
50.7
00.4
40.7
90.1
30.7
7--
--E6
0.14
0.72
----
----
0.50
0.56
0.40
0.44
0.17
0.81
0.15
0.75
0.00
0.00
0.00
0.65
----
----
----
----
----
----
----
----
E50.0
00.2
8--
----
--0.0
00.2
00.0
50.2
90.0
30.7
30.0
00.2
70.0
00.0
00.0
00.0
00.0
00.3
91.0
00.7
80.1
70.4
50.1
40.5
00.0
80.4
30.0
00.0
00.0
00.0
0--
--E4
----
----
----
----
----
1.00
1.00
0.25
1.00
0.90
0.97
0.17
0.91
0.46
0.99
0.53
0.99
1.00
1.00
0.43
0.98
----
0.55
0.94
0.74
0.72
----
E30.2
10.6
7--
----
--0.3
80.3
70.0
40.5
70.1
60.8
01.0
01.0
01.0
00.9
50.2
80.6
50.2
20.7
90.5
00.9
71.0
00.9
50.4
50.7
1--
--0.8
90.9
80.5
70.9
70.4
21.0
0E2
1.00
1.00
----
----
0.50
0.98
0.57
0.99
1.00
0.99
0.37
0.99
0.41
1.00
0.26
0.99
0.58
0.88
----
0.28
0.91
1.00
1.00
----
0.85
0.99
0.49
0.76
----
E1--
----
----
----
----
----
--1.0
00.7
90.5
00.9
71.0
01.0
00.3
90.9
7--
--0.8
20.9
0--
----
----
--0.8
00.2
4--
--
Darks
ideOP
1OP
2MM
102
MM10
1KJ
1Su
b BB3
Sub B
B1Pe
quen
a 2 U
pper
Cach
ana
Cach
ana 2
Cach
ana 3
Sub B
B4Va
ca 1
Vaca
2Pe
quen
aPe
quen
a 2 Lo
wer
BA
Axi
sO
�-ax
isM
argi
n
Mx Am
SS (m
)Thic
kness
(m)
Mx Am
SS (m
)Thic
kness
(m)
Mx Am
SS (m
)Thic
kness
(m)
Mx Am
SS (m
)Thic
kness
(m)
Mx Am
SS (m
)Thic
kness
(m)
Mx Am
SS (m
)Thic
kness
(m)
Mx Am
SS (m
)Thic
kness
(m)
Mx Am
SS (m
)Thic
kness
(m)
Mx Am
SS (m
)Thic
kness
(m)
Mx Am
SS (m
)Thic
kness
(m)
Mx Am
SS (m
)Thic
kness
(m)
Mx Am
SS (m
)Thic
kness
(m)
Mx Am
SS (m
)Thic
kness
(m)
Mx Am
SS (m
)Thic
kness
(m)
Mx Am
SS (m
)Thic
kness
(m)
Mx Am
SS (m
)Thic
kness
(m)
Mx Am
SS (m
)Thic
kness
(m)
AmRat
NTG
AmRat
NTG
AmRat
NTG
AmRat
NTG
AmRat
NTG
AmRat
NTG
AmRat
NTG
AmRat
NTG
AmRat
NTG
AmRat
NTG
AmRat
NTG
AmRat
NTG
AmRat
NTG
AmRat
NTG
AmRat
NTG
AmRat
NTG
AmRat
NTG
Tabl
e 3.
2. C
hann
el m
etric
s com
pute
d fo
r eac
h ch
anne
l ele
men
t fro
m F
ig 3
.1C
and
tabu
late
d in
col
umns
cor
resp
ondi
ng to
eac
h m
easu
red
sect
ion.
Eac
h el
emen
t is
cla
ssifi
ed b
y in
tra-e
lem
ent a
rchi
tect
ure
clas
sifie
d in
Fig
. 3.3
. NTG
= n
et-to
-gro
ss. A
mR
at =
Am
alga
mat
ion
ratio
. Max
Am
SS
= M
axim
um a
mal
gam
ated
sa
ndst
one.
Thi
ckne
ss =
Tot
al e
lem
ent t
hick
ness
. Blu
e bo
xes =
axi
s. R
ed b
oxes
= o
ff-ax
is. G
reen
box
es =
mar
gin.
57
Channel element axes are characterized by moderate to high NTG (0.71 to 1.00) with a mean value of 0.95 (Fig. 3.6 and 3.7A). The frequency distribution graph of NTG for channel element axes shows that >90% of the measurements are 0.8 or higher (Fig 3.7A). Amalgamation ratios within channel element axes are highly variable, with computed values ranging from low to high (0.1 to 1.00); however, channel element axes generally exhibit a high degree of amalgamation with a mean value of 0.68 (Fig. 3.6 and 3.7B). Maximum amalgamated sandstone measurements vary greatly within the axis of the channel elements studied, with values ranging from 0.1 m up to 12.8 m and an average value of 6.91 m (Fig 3.8A). The sedimentation unit proportions that characterize the axis of a channel element are: 61.4% type one, 23.2% type two, 8.1% type three, 7.3% type four and < 0.1% type five (Fig. 3.9). Based on the metrics tabulated, channel element axes are associated with the best reservoir properties within the studied strata (Fig. 3.6).Channel Off-axis Data Channel off-axis units are characterized by NTG ranging from low to high (0.29 to 1.00) with a mean of 0.81 (Fig. 3.7C). Distribution graphs indicate that > 50% of off-
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
10.00
Axis Off-Axis Margin
Intra-Element Architecture
Net
-to-g
ross
& A
mal
gam
atio
n R
atio
s(d
ec)
Max
imum
Am
alga
mat
ed S
S Th
ickn
ess
(m)
Amalgamation Ratio
Net-to-gross Ratio
Max Am. SS Thickness
MEAN METRIC VALUES
Fig. 3.6. Overview of mean quantitative metrics values tabulated from the Tres Pasos Formation.
58
0.10.20.30.40.50.60.70.80.91.0 0.00
5
15
25
35
45
20
10
30
40
0.10.20.30.40.50.60.70.80.91.0 0.00
5
15
25
35
45
20
10
30
40
0.10.20.30.40.50.60.70.80.91.0 0.00
5
15
25
35
45
20
10
30
40
N = 56mean = 0.68median = 0.65
N = 82mean = 0.40median = 0.32
N = 64mean = 0.17median = 0.04
Axis Amalgamation Ratio
Margin Amalgamation Ratio
Off-axis Amalgamation Ratio
Amalgamation Ratio
Amalgamation Ratio
Amalgamation Ratio
Freq
uenc
yFr
eque
ncy
Freq
uenc
y
0.10.20.30.40.50.60.70.80.91.0 0.00
5
15
25
35
45
20
10
30
40
0.10.20.30.40.50.60.70.80.91.0 0.00
5
15
25
35
45
20
10
30
40
0.10.20.30.40.50.60.70.80.91.0 0.00
5
15
25
35
45
20
10
30
40 N = 56mean = 0.95median = 0.98
N = 82mean = 0.81median = 0.81
N = 64mean = 0.39median = 0.38
Margin Net to Gross
Off-axis Net to Gross
Axis Net to Gross
Net-to-Gross Ratio
Net-to-Gross Ratio
Net-to-Gross Ratio
Freq
uenc
yFr
eque
ncy
Freq
uenc
y
BA
C
E
D
F
Fig. 3.7. Histograms of net-to-gross and amalgamation ratios computed from the Laguna Figueroa study area. N = the number of calculated ratios. SD = standard deviation. (A) Distribution of net-to-gross ratio tabulated from channel element portions characterized as axis. (B) Amalgamation ratio distribution tabu-lated from each channel element axis. (C) Distribution of net-to-gross ratio tabulated from channel ele-ment portions characterized as off-axis. (D) Amalgamation ratio distributions tabulated from each channel element portion label off-axis. (E) Distribution of net-to-gross ratios calculated from each channel element margin. (F) Amalgamation ratio distributions tabulated from channel element margins. Intra-element archi-tecture is classified in Figure 3.
59
axis NTG ratios are high (> 0.8), and 98% are above the moderate NTG cut off of 0.5. Off-axis portions of channel elements comprise highly variable AR ranging from 0.0 and 1.00. The mean is 0.40 indicating a moderate degree of amalgamation within this portion of the channel element (Fig. 3.6D). Maximum amalgamated sandstone measurements vary greatly from 0.0 m to 9.65 with a moderate mean value of 3.56 m (Fig. 3.8B). The sedimentation unit proportions that characterize the transitional off-axis portion of a channel element are: 36.1% type one, 30.1% type two, 11.6% type three, 21.4% type four and 0.8% type five (Fig. 3.9). Channel element off-axis intervals are commonly characterized by ideal reservoir metrics (Fig. 3.6); however, the preservation of fine-grained deposits interbedded between sandstone units leads to locally variable vertical sandstone bed connectivity.
Channel Margin Data Channel margin deposits are characterized by generally low NTG with a mean value of 0.39 (Fig. 3.6) and a range from low to high (0.29 to 0.99; Fig. 3.7E). AR is highly variable, ranging from 0.0 to 0.60, with a mean AR of 0.17 although it is typically < 0.1 (Fig. 3.7F). In this case the median (0.04) provides a much closer approximation to a typical AR. Maximum amalgamated sandstone measurements are generally low, characterized by a mean value of 0.93 m (Fig 3.8C). The sedimentation unit proportions that characterize the margins of channel elements are: 9.0% type one, 13.4% type two, 8.9% type three, 65.6% type four and 3.1% type five (Fig. 3.9). The margins of channel elements are of low reservoir quality, dominated by generally fine-grained deposits and low levels of sedimentation unit amalgamation (Fig. 3.6).
Amalgamation ratio vs net-to-grossAR versus NTG is plotted in order to emphasize the distinguishing characteristics
of intra-channel architectural zones (Fig. 3.10A). Overall, channel axis deposits possess both high net-to-gross and high amalgamation ratios, with the contrary characteristic of channel margin deposits where low values for both metrics are expected. Some discrepancies to expected end-member characteristics are notable (Fig 3.10A). For example, the moderate to high NTG in some channel margins is unexpected; however, these values usually reflect very thin or eroded channel margin packages (with low gross thickness) that preserve a high number of thin sandstone beds. As described, low amalgamation ratios in channel axial positions are controlled primarily by the presence of numerous non-amalgamated thin beds in drape deposits (Fig. 3.5). This perturbation in the data is also exacerbated where a significant portion of the channel element top
60
0
5
15
25
35
45
20
10
30
40
55
50
0
5
15
25
35
45
20
10
30
40
55
50
0
5
15
25
35
45
20
10
30
40
55
50
0
5
15
25
35
45
20
10
30
40
55
50
2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.00.00
5
15
25
35
45
20
10
30
40
55
50
0
5
15
25
35
45
20
10
30
40
55
50
2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.00.0
2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.00.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.00.0
2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.00.0
2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.00.0
N = 56mean = 6.91median = 6.75
N = 82mean = 3.82median = 3.67
N = 56mean = 9.86median = 10.10
N = 82mean = 8.19median = 7.68
N = 64mean = 4.56median = 4.00
N = 64mean = 0.93median = 0.32
Axis
Freq
uenc
yFr
eque
ncy
Freq
uenc
y
Freq
uenc
yFr
eque
ncy
Freq
uenc
y
Max amalgamated ss thickness
Max amalgamated ss thickness
Max amalgamated ss thickness Element thickness
Element thickness
Element thickness
Axis
Off-axisOff-axis
MarginMargin
B
A
C
E
D
F
Fig. 3.8. Histograms of maximum amalgamated sandstone thicknesses and element thicknesses from the Laguna Figueroa study area. N = the number of thickness measurements through each channel division. SD = standard deviation. (A) Distribution of maximum amalgamated sandstone thicknesses measured in chan-nel element axes. (B) Maximum amalgamated sandstone thickness distribution (off-axis). (C) Maximum amalgamated sandstone thicknesses measured in channel element margins. Element thickness distributions tabulated from each channel element division: axis (D) axis, off-axis (E) and margin (F).
61
has been removed by erosion at the location analyzed. Despite these discrepancies, it is possible to readily identify fields associated with intra-channel architectural end-members. Because off-axis deposits are intermediate between margin and axis architectural zones, they are more difficult to specifically delineate using these two metrics alone (Fig. 3.10A).
Maximum amalgamated sandstone vs. channel element thicknessMaximum amalgamated sandstone thickness versus overall element thickness
is presented in Figure 3.10B. If an element is preserved completely and not impacted by erosion from successive channel incision, it will be thickest in an axial position, tapering towards the margins (Fig. 3.2A). Likewise, a similar increase in amalgamated sandstone thickness is expected across this same transition. Two distinct data clusters are recognized in the graph associated with the two intra-channel architectural end members: axis and margin. The area between these two zones represents the intermediate off-axis architecture, although off-axis measurements are widely distributed (Fig 3.10B). Perturbations to the expected trends are exclusively due to differential erosion of the upper portions of channels, leaving a partially preserved record of the original channel fill.
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Axis Off-axis Margin
Type 5
Type 4
Type 3
Type 2
Type 1
SEDIMENTATION UNIT PROPORTIONS
Fig. 3.9. Bar graph of the relative proportions of sedimentation unit types in each intra-element subdivision: axis, off-axis or margin.
62
Sedimentation unit proportions The proportion of each sedimentation unit type (1 through 5) within a measured interval can also be used to characterize intra-element architectural zones (Table 3.1; Fig. 3.9). Channel element margin deposits are associated with the most unique sedimentation unit signature, composed predominantly (> 65% by proportion) of thinly interbedded sandstone and mudstone deposits (type four sedimentation units) (Fig. 3.9). The thick-bedded sandstone deposits (type one and type two sedimentation units) dominate axis and off-axis architectures (> 65% by proportion; Fig 3.9). Channel element axes are
0
2
4
6
8
10
12
14
16
0 2 4 6 8 10 12 14 16 18 20
Element Thickness (m)
Max Amalgamated SS Thickness (meters)
Max
. Am
alga
mat
ed S
S Th
ickn
ess
(m)
axis
off a
xis
mar
gin
B
Am
alga
mat
ion
Rat
io
Net to Gross
axis
off axis
margin
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00
Amalgamation Ratio (dec)
Axis
O� Axis
Margin
A
Fig. 3.10. (A) Scatter plot of amalgamation ratio vs. net-to-gross ratio; data points are classified to identify data fields for each zone: axis, off-axis or margin; see part A in Table 3.2. (B) Scatter plot of the maximum amalgamated sandstone vs. channel element thickness; data points are classified to identify data fields for each zone: axis, off-axis or margin; see part B in Table 3.2
63
impacted by the highest energy during deposition and are therefore dominated by type one sedimentation units (> 60% by proportion; Fig. 3.9), which have erosive bases and preserve the coarsest grained detritus. Off-axis architectural zones are characterized by a higher proportion of flat bedded, non-erosive, type two sedimentation units when compared to channel axis (30% in off-axis, 23% in axis; Fig. 3.9). This is attributed to the waning depositional energy away from the axis of the channelform (Chapter 2). In many instances it is straightforward to qualitatively distinguish off-axis architecture from axis architecture; however, in some cases it is particularly difficult. Sedimentation unit proportions are particularly useful for differentiating axis and off-axis architectural zones in the data collected.
pOtentIal applICatIOns Of results
Predicting/interpreting depositional model from limited well and seismic dataIntegrating this method with traditional subsurface exploration datasets (seismic
and well data) allows for the prediction of deep-water facies at the bed-scale. Seismic reflection surveys are useful for imaging system-scale depositional architecture, including the aerial extent of a deep-water slope channel complex or complex-set. Channel elements represent reservoir-scale sedimentary bodies (commonly < 15 m) thick with complex internal characteristics commonly not resolved in these surveys. Knowledge of critical bed-scale information, such as the distribution and character of shale drapes, is necessary for construction of reservoir models yet only available from core data in many instances. Predicting lateral facies changes beyond the well-bore from limited well data can be facilitated by using metrics data to determine what intra-element architecture zones are intersected by a core sample (axis, off-axis or margin). For example, based on the Tres Pasos Formation intra-element characteristics, if a channel margin is intersected by a wellbore, a substantial reservoir body is likely in close proximity because the transition to off-axis or axial sandstone commonly occurs across < 30 m (Fig. 3.5). It is important to note that thin sandstone beds in margin packages are connected with thicker, more aerially extensive channel axis deposits across the outcrop belt (Fig. 3.1C).
In many cases, discerning element boundaries is difficult in well data; however, their recognition is critical for the application of the metrics data tabulated from the Tres Pasos Formation. Element boundaries derived from outcrop mapping are highlighted in measured section data from the Tres Pasos Formation in Figure 3.11. A variety of intra-element architectural zones from successive channels are discerned in most cases through identification of the drape deposits at the base of each element (see OP2, Sub
64
BB3, and Vaca1 in Fig. 3.11). In areas where the axes of successive channel elements are vertically stacked, element boundaries are difficult to decipher due to erosion of drapes and amalgamation of sandstone units (see OP2, Vaca1 and Cach1 in Fig. 3.11). The preservation potential of basal drape deposits is greater in off-axis and margin deposits due to the lower energy imparted on the channel floor by turbidity currents (see OP2, MM 101, and Cach 1 in Fig. 3.11). This in practice should make identifying them in a subsurface dataset straightforward; however, these channel portions can potentially be very difficult to identify without lateral context (see MM101 and Vaca 1 in Fig. 3.11). All of the intra-element architectural zones can be recognized by an overall upward coarsening trend or upwards decrease in gamma-radiation through an individual channel element in cases where a basal drape is preserved (Fig. 3.12). In practice, evaluating and identifying architectural boundaries from limited subsurface datasets is difficult yet necessary in order to predict channel facies beyond the well-bore.
Incorporation of metrics data into reservoir modelsNumerous reservoirs on continental margins world round, target deep water
channel deposits (e.g., Samuel et al., 2003; Sullivan et al., 2004; Mayall et al., 2006; Porter et al., 2006). The architectures of these reservoirs are captured three-dimensionally in reservoir models by industry geoscientists and engineers for numerous reasons, which include development well planning and reservoir forecasting. Despite the importance of these models, they are commonly limited by a lack of available facies and architecture information. The high-resolution cross-section along the Laguna Figueroa outcrop belt records the architectural detail that should be expected in some deep-water channel reservoirs. The data is logically up-scaled across the transect into fundamental intra-channel divisions (ie., axis, off-axis or margin), providing a perspective of facies distribution (Fig. 3.3). Although it was not an objective of this study, the effectiveness of integrating traditional sedimentological data like that collected from the Laguna Figueroa outcrop belt into a high-resolution subsurface reservoir model has been demonstrated in numerous instances (e.g., Sullivan et al., 2004; Pringle et al., 2011)
Without direct information available for input from cores, reservoir models can be improved through incorporation of robust data collected from outcrop analogues. If the channel complex-set strata examined in this study of the Tres Pasos Formation is deemed an architecturally suitable analogue to a given reservoir, than the detailed metrics tabulated provide reasonable input values for the model constructed (Figs. 3.6-3.10).
65
MM
101
0510152025
Sub
BB3
404550556065
Vaca
1
657075808590
Cach
1
45
50
55
65
70
Elem
ent b
ound
ary
O�-axisAxis
Margin O�-axisMarginMargin
AxisAxis
AxisAxis O�-axis
Axis O�-axis
cm
fvf
slt
mu
d
cm
fvf
slt
mu
d
cm
fvf
slt
mu
dc
mf
vfsl
tm
ud
Axis
OP2
2025303540
cm
fvf
slt
mu
d
45
O�-axis
60
upward coarseningupward coarsening
upward coarseningupward coarseningupward coarsening
upward coarsening
Dra
peD
rape
Dra
pe
Dra
peD
rape
Dra
pe
Am
alga
mat
ed e
lem
ent
Dra
pe
Dra
pe
Fig.
3.1
1. S
ectio
ns m
easu
red
at th
e ce
ntim
eter
-sca
le fr
om th
e La
guna
Fig
uero
a st
udy
area
illu
stra
ting
chan
nel e
lem
ent
base
s, w
hich
are
com
mon
ly d
rape
d by
fine
-gra
ined
byp
ass d
epos
its.
With
out i
nsig
ht fr
om o
utcr
op th
ese
boun
darie
s are
dif-
ficul
t to
defin
e. O
rigin
al n
amin
g sc
hem
e an
d m
easu
rem
ents
are
show
n fo
r com
paris
on to
Fig
ure
3.1C
.
66
suMMary
• 3656 sedimentation units were documented in >1600 m of stratigraphic section, collected through 185 different portions of 18 slope channel elements exposed in an outcrop of the Tres Pasos Formation at Laguna Figueroa.• The quantitative metrics tabulated from this database, can be used to differentiate and characterize intra-channel architectural zones (ie, axis, off-axis, margin).• NTG is highest in channel axes (mean = 0.95), decreases towards the channel off-axes (mean = 0.81) and channel margins (mean = 0.39)• AR follows the same trend, of highest in channel axes (mean = 0.68), decreasing towards the channel off-axes (mean = 0.40) and channel margins (mean = 0.17) • Maximum amalgamated sandstone thicknesses also repeat this gradational trend, with mean measurements of 6.91 m in channel axes, 3.36 m in channel off-axes, and 0.93 in channel margins.• Proportions of sedimentation unit types can also be used distinguish intra-channel architecture, and are particularly useful in differentiating axis from off-axis deposits. • This robust database presents realistic input variables for reservoir models of slope channel deposits and illustrates the utility of this outcrop as a reservoir analog. • Finally, it is essential that the architectural boundaries separating elements be chosen precisely for this method to accurately predict intra-element architecture.
~10
m
~50 m
Gamma-Ray Curves
Fig. 3.12. Schematic cross-section of a representative channel element from the Laguna Figueroa study area. Theoretical gamma ray curves reflect grain-size trends observed in the outcrop belt across the transi-tion from channel axis to margin. Note the overall coarsening upward trend evident, especially in channel margins.
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