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International Journal of Engineering & Technology IJET-IJENS Vol:09 No:10
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Characterization, Pressure, and Temperature
Influence On The Compressional and Shear
Wave Velocity in Carbonate Rock
Jarot Setyowiyoto 1) and Ariffin Samsuri *)
Department of Petroleum Engineering, Faculty of Chemical and Natural Resources Engineering, Universiti
Teknologi Malaysia, 81310 UTM Skudai, Johor Bahru, Malaysia.
Abstract-- Rock characterization and acoustic wave velocity
analysis are very important stage in the petroleum reservoir
characterization and seismic exploration. Meanwhile carbonate
rocks are worthy of attention since they contain at least 40% of
the world’s known hydrocarbon reserve and have some
complexity in porosity, lithology facies and acoustic wave
behavior. This paper present detail relationship between
porosity and permeability, effect of pressure and temperature to
the acoustic wave parameters such as compressional and shear
wave velocities. Data collected includes petrography analysis,
S EM image, detail core description, and laboratory
experimental of acoustic wave velocities measurements in
variation of overburden pressure and temperature. S ome
acoustic wave parameters were simulated as close as possible to
the reservoir conditions. Based on the petrophysical data and
acoustic wave measurement, the porosity is the main controlling
factor of acoustic wave parameter. A plot of porosity versus
velocity displays a clear inverse trend to porosity which an
increasing of porosity resulting in decreasing of velocity. In
addition, increasing of permeability will results in decreasing
velocity value. The overburden pressure causes compaction,
porosity reduction and increasing in velocity. This performance
is slightly changed when temperature increase from 28.73 oC to
62.07 oC, generally both Vp and Vs value become lower. The
results can be used for better seismic analysis performance,
correspond to increase hydrocarbon discovery from the
carbonate rock in the future.
Index Term--
Acoustic wave velocity; Carbonate rock;
Petrophysic properties; Pressure and temperature.
1.
INTRODUCTION
With the rapid development in seismic exploration and
petroleum reservoir characterization, detailed studies on
acoustic wave velocity and its controls parameters such as
pressure and temperature are getting more attention. There are
* ) Corresponding author: Prof. Dr. Ariffin
Samsuri , Email address: [email protected]
T el : +60122105171
1) Permanent Address: Department of
Geological Engineering, Faculty of
Engineering, Gadjah Mada University,
Yogyakarta, Indonesia. Email address:
[email protected]
some researches focused on igneous rocks, sandstones, and
unconsolidated carbonate sediments but few on carbonate
rocks or core.
Carbonate rock result mainly from biochemical and biological
processes in warm shallow marine and lacustrine environments
and prone to rapid and pervasive diagenetic alterations that
change the mineralogy and pore type within carbonate rocks. It
is volumetrically a most significant part of the geological
record and possesses much of the fossil record of life on this
planet. Their deposition involves a more complex suite of
processes than many other sediment types [1].
They hold more than half of the world’s petroleum reserves.
However geophysical applications in carbonate reservoirs are
less mature and abundant than those associated with
siliciclastic reservoirs. It because carbonate reservoirs offer
unique geophysical challenges with respects to reservoir
characterization and are notoriously more difficult to
characterize than siliciclastic reservoirs [2]. Adding complexity
to reservoir quality prediction is that carbonate which
producing organism have evolved through time [3].
Carbonate diagenetic processes continuously modify the pore
structure to create or destroy porosity. Cementation diagenetic
processes for instance are prone to reduce porosity while
dissolution will enlarge porosity. All these modifications will
effect seismic wave velocity such as compressional wave
velocity and shear wave velocity [4].
Pressure and temperature strong influence in determining the
acoustic velocity in rocks. Reference [5] has measured Vp and
Vs on unconsolidated carbonate mud to completely lithified
limestones under variable confining and pore-fluid pressures.
They reported that pure carbonate rocks show, unlike
siliciclastic or shaly sediments, little direct correlation between
acoustic properties (Vp and Vs) with age or burial depth of the
sediments so that velocity inversions with increasing depth are
common.
Reference [6] reported the effect of temperature and pressure
on sonic wave velocities in sandstone. They showed that
sonic velocity in the liquid saturated sandstone increases with
increased pressure and decreasing velocity with increased
temperature. Reference [7] investigated the effect of pressure
on compressional and shear wave velocity in modern
carbonate sediment and rock. They concluded that the wave
velocities increase with increasing pressure. More over,
reference [8] researched on the effect of pressure and
95510-9393 IJET-IJENS © December 2009 IJENS
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International Journal of Engineering & Technology IJET-IJENS Vol:09 No:10
temperature to the acoustic wave velocity in marble and calcschist. They reported that the velocity includes compressional
and shear waves will increase with increasing pressure and
decrease with increased temperature.
The objective of this study includes detail relationship among
pressure, temperature, and petrophysisc parameters such as
porosity and permeability to the acoustic wave parameter, i.e
compressional and shear wave velocity in Miocene carbonate
core taken from around 2800 meter deep.
2. M ETHOD AND DATA COLLECTION
Twenty one carbonate core samples have been prepared for
analysis of detail core description, petrophysic, petrography,
and Scanning Electron Microscope (SEM). Twelve cylindrical
core-plug samples from those were analyzed in the Wave
Inversion and Subsurface Fluid Imaging Research Laboratory
to obtain the value of compressional wave velocity (Vp) and
shear wave velocity (Vs) in variation of overburden pressure,
pore pressure and also temperature. Some acoustic wave
parameters were simulated as close as possible to the reservoir
conditions.
The samples were cleaned in methanol and dried in a vacuum
oven at 85oC for period of twenty-four hours and than
saturated with brine/formation water of 16,271.67 mg/liter. The
acoustic velocity measurement on the carbonate samples have
been performed under brine saturated conditions at
frequencies of about 10 Hz, the overburden pressure range
from 50 – 460 bar, the pore pressure range from 40-400 bar, and
temperature range from 28-57oC. These procedures were run in
Wave Inversion and Subsurface Fluid Imaging Research
Laboratory, Institute Technology of Bandung.
Petrographic analysis was undertaken on all the cores which
had been impregnated with araldite resin to maintain the
existing natural porosity and staining for carbonate minerals
with solution of Alizarin Red-S. The carbonate coloration given
by this staining is as follows; pink color for calcite, bluish pink
to blue for ferroan calcite, dark blue to greenish blue for ferroan
dolomite and unstained for dolomite.
In order to obtain an understanding of diagenetic fabrics,
particularly clay and micrite, and their roles with respect to
reservoir quality, SEM-EDX analysis was also conducted. The
samples were cleaned using organic solvents and ultrasound
treatment, then were broken to create fresh surface and
mounted on10 mm Cu-stub. They were air brushed free of dust
and other contaminants, placed under vacuum overnight to
remove most remaining volatile, and electrostatically coated
with both carbon and gold alloy.
3. RESULT AND DISCUSSION
3. 1 Rock Characterization
Detail descriptions of the carbonate core samples include rock
texture, sedimentary structure, composition and fossil content
had been analyzed. Supported by integrated petrography and
Scanning Electron Microscopy (SEM) analysis, it has
identified seven carbonate rock types.
3.1.1 Bedded Large Forams Grainstone
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Large forams grainstone in general is a grayish white in colour.
Inclined parallel bedding indicated by changes in sediment
grain size may represent considerable periods of time when
there was little deposition, and then tilted due to endogenic
uplifting force. The grain size ranges from 0.52mm – 1.8mm,
dominantly point type grain contact, moderately sorted and
mostly abraded (rounded). It is composed mainly of skeletal
grains such as large forams and red algae, and associated with
minor amount of echinoid, bryozoans, brachiopods, and
indeterminate bioclast. Pore system is dominated by vuggy
porosity, some intercrystalline and intragranular pore ty pes.
Fig. 1, detail petrography analysis shows a grainstone mainly
consist of large forams (C-I, 5-6; C-G, 2-4; K-L, 8-9) and less of
red algae (F-G, 8-9; J-M, 6; A-B, 4-5).
3.1.2 Cross-Bedded Large Foram Grainstone
The carbonate rock of this type in general is light grey to grey,
commonly grainstone texture. Cross bedding sedimentary
structures were observed in this rock. This sedimentary
structure indicated that there are changes of flow velocity or
depth during their deposition. The grains size range 0.22 mm 3.75 mm, point type grain contact, and moderately sorted and
mostly abraded (rounded). This rock contains commonly large
forams, and less of red algae, echinoderms, small benthonic
forams, planktonic forams, and bryozoan. Moldic pore type is
dominant, mostly filled by mosaic calcite cement type which is
overgrowth on some echinoderms grains.
Diagenetic
processes include micritization of grains; also fill intraparticle
voids and cause reducing porosity.
3.1.3 Red Algal Packstone
Generally, the red algal packstone to floatstone is grey in
colour. Minor discontinous thin laminae of detrital clay and
carbonaceous materials are present in this rock. The grain size
ranges from 0.3 mm - 3.75 mm, mostly abraded. Grain to grain
contact is dominated by floating type and some of them are
point type. Composition of the rock is predominantly red algae
and larger forams. Other grain constituents are minor amount
of echinoderms, brachiopods, coral debris and indeterminate
bioclasts. The porosity type is predominantly mouldic and
interparticle pores which are mostly filled by calcite cement
type. Detail petrography analysis as shown in Fig. 2 reveals a
packstone mainly consist of red algae (D-I, 6-7; A-C, 6-9) and
some of large forams (A-F, 3-4; C-I, 4-5).
3.1.4
Bioclastic Grainstone
In general the rock type is light grey in colour, common
grainstone texture. The rock shows grains -supported fabric,
grain size range from 0.8mm – 3.2mm, moderate sortation,
abraded and point type grains as shown in Fig. 3. Petrog raphy
analysis as presented in Fig. 4 reveal that the main composition
of this carbonate is indeterminate bioclasts grains / fragments
that is underwent neoformism diagenetic changed into calcitesparite and micrite. Other components are mollusk fragments
and benthic forams. Petrography analysis reveals that the
forming of calcite-sparite and micrite due to neomorfism
diagenetic process (A-D, 4-9; G-M, 1-9; photo A). Calcite
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cement (G-M, 1-5; photo B) and calcite-sparite of carbonate
mud (A-M, 1-9; Foto B) are present in the rocks as pore filling
of intercrystalline pore types.
3.1.5 Mollusc Corraline Rudstone
This rock type is dark grey in colour, has grain-supported
fabric, moderate sortation, grain size range from 1.8mm – 6.2mm
, mostly abraded and point type grains. The main composition
of this rock is molusc and corral fragments and benthic forams.
Other components are forams and undetermined bioclasts.
Calcite-sparite and micrite of carbonate mud distributed in the
rock as pore filling of vuggy and intercrystalline porosity are
formed by recrystallization process.
3.1.6 Corraline Rudstone
In general this rock type is dark grey in colour, has grain
supporting fabric, grain size range from 0.14mm – 5.71mm, poor
to moderate sortation and point type grain, and dominantly the
grains were abraded. Other components are brachiopods, red
algae, and benthic forams. Porosity is dominated by mouldic
and vuggy pore types. Some of them filled by carbonate mud
and grain that are underwent micritization process.
3.1.7
Red Algae Floatstone
This rock type is dark grey in colour, has grain size ranging
from 0.5mm – 11.42mm, poor sortation, and dominantly the
grains were abraded and floating in the mud carbonate,
predominantly consists of red algae fragments and
undetermined bioclastics. Other components are micritization
of forams. Carbonate mud and calcite sparite are underwent
micritization and fill some of the porosity that is dominated by
mouldic and intercrystalline pore type.
3.2 Correlation between Porosity and
Permeability
Correlation between porosity and permeability as shown in Fig.
5 show that porosity is directly proportional to the
permeability. The increasing of porosity results in increasing
permeability. All of the carbonate samples studied show
heterogeneity in porosity and permeability related to the
preburial factors of depositional texture and diagenesis
process, including the compaction and creation of mouldic or
vuggy porosity by leaching [5].
3.3 The Effect of Pressure on the Acoustic Wave Velocity
Fig. 6 shows the effect of overburden pressure to the
compressional wave velocity. Generally, the velocity increases
with increasing pressure. From the graph it can be analyzed
that velocity drastically increases with pressure (3650 m/s to
3900 m/s) in the low pressure range (50 bar to 200 bar), because
the thinnest pores close at low pressures and the compacted
rocks will have higher acoustic velocity. Further increasing of
pressure in the higher pressure range has less effect on the
velocities because cracks may have already been closed [4].
The effect of overburden pressure to the shear wave velocity
is relatively similar to compressional wave velocity. Fig. 7
demonstrates shear velocity drastically increases (1840 m/s to
1940 m/s) even in the lower pres sure range (50 bar to 200 bar).
69
At higher pressure range, the velocities are slightly more
gradually constant.
3.4 The Influence of Pressure and Temperature on Acoustic
Wave Velocity
Fig. 8 shows that Vp increases range from 3660 m/s to 4100
m/s, and Vs also increases slowly with range from 1840 m/s to
2020 m/s when overburden pressure increase from 50 Bar to
460 Bar. The overburden pressure causes compaction, porosity
reduction and increasing in velocity. This performance is
slightly changed when temperature increase from 28.47 oC to
57.10 oC, generally both Vp and Vs value become lower. The Vp
increases with range from 3480 m/s to 3820 m/s and Vs values
range from 1780 m/s to 1950 m/s (Fig. 9).
Fig. 10 shows that when pore pressure increase from
40 Bar to 400 Bar, Vp decreased with range from 3950 m/s to
3600 m/s, and Vs also decreased slowly with range from 2015
m/s to 1850 m/s. This behavior changed when temperature
increase from 28.47 oC to 57.10 oC. Generally both Vp and Vs
value become lower. The Vp decreased with range from 3910
m/s to 3480 m/s and Vs values slightly decreased from 1965 m/s
to 1780 m/s (Fig. 11).
3.5 The Effect of Porosity and Permeability to the Acoustic
Wave Velocity
Velocity is strongly dependent on the rock-porosity [4]. A plot
of porosity versus compressional wave velocity (Vp), as
shown in Fig. 12 displays a clear inverse trend; an increase in
porosity from (5% to 20%) will resulting a decrease in velocity
from 4500m/s to 2000m/s. Increasing porosity will create a
mount of pore space that cause slow of acoustic velocity [9].
For the shear wave velocity (Vs), as illustrated in Fig. 13 also
demonstrated a clear inverse trend; an increase in porosity (5%
to 20%) will resulting a decrease in velocity (2300m/s to
1000m/s).
The same phenomenon also occurs in the correlation
between permeability and acoustic wave velocity. Fig. 14
shows an increase in permeability (1.8mD to 10.2mD) will cause
a decrease in velocity from 4600m /s to 2000m /s. For the shear
wave velocity (Vs), as illustrated in Fig. 15 also demonstrated a
clear inverse trend; an increase in permeability (5% to 20%) will
caused a decrease in velocity from 2300mD to 1000mD.
CONCLUSION
The porosity and permeability are the main factor in
determining acoustic wave velocity in carbonate rocks. An
increase in porosity and permeability will decrease in velocity
both compressional and shear waves. Velocity is also strong
influenced by pressure and temperature. Increasing
overburden pressure will result in increasing of velocity, on the
other hand increasing of pore pressure produce decreasing of
velocity and increasing temperature will also resulting in
decreasing of velocity.
A CKNOWLEDGEM ENT
We wish to thank Pertamina for their permission to
publish these data and Laboratory of Wave Inversion
and Subsurface Fluid Imaging Research, Institut
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Teknologi Bandung, Indonesia for seiscore analysis, and
we also extend our thanks to IRPA Malaysia.
Permeability (mD)
REFERENCES
[4]
[5]
[6]
[7]
[8]
[9]
8
6
4
por vs. perm
2
Linear (por vs. perm)
0
0
5
Fig. 5.
4200
10
15
20
25
Porosity (%)
Correlation between porosity and permeability.
y = 221.59Ln(x) + 2719.2
R2 = 0.9092
4100
4000
Vp (m/s)
[3]
3900
3800
3700
Vp (m/s)
3600
Log. (Vp (m/s))
3500
0
100
200
300
400
500
Overburden pressure (bar)
Fig. 6. Effect of overburden pressure to the compressional wave
velocity.
2050
y = 82.469Ln(x) + 1498.7
R2 = 0.9591
2000
A
Vs (m/s)
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1950
1900
1850
Vs (m/s)
Log. (Vs (m/s))
1800
0
100
200
300
400
500
Overburden pressure (bar)
Fig. 7. Effect of overburden pressure to the shear wave
velocity.
B
4200
4100
4000
Vp (m/s)
[1]
y = 0.5661x - 2.3622
R2 = 0.8342
10
3900
3800
3700
3600
Vp at 28.47 degC
3500
Vp at 57.10 degC
3400
0
100
200
300
400
500
Overburden pressure (bar)
Fig. 4. Petrography analysis of bioclastic grainstone.
Fig. 8. T he effect of overburden pressure to compressional wave
velocity in different temperatures.
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2050
71
5250
4500
2000
Vp (m/s)
1900
y = -147.15x + 5400.5
R2 = 0.9126
3000
2250
1500
1850
Vp (m/s)
1800
Vs at 28.47 degC
750
Vs at 57.10 degC
0
Linear (Vp (m/s))
1750
0
0
100
200
300
400
5
10
500
15
20
25
Porosity (%)
Overburden pressure (bar)
Fig. 12. Cross plot between porosity and compressional wave
velocity
Fig. 9. T he effect of overburden pressure to shear wave velocity (Vs) in
different temperatures.
2500
Vs (m/s)
2000
4000
3900
Vp (m/s)
y = -61.423x + 2584.7
R2 = 0.7969
1500
1000
3800
500
3700
0
Vs (m/s)
Linear (Vs (m/s))
0
3600
5
10
15
20
25
Porosity (%)
Vp at 28.47 degC
3500
Fig. 13. Cross plot between porosity and shear wave
velocity.
Vp at 57.10 degC
3400
0
100
200
300
400
500
5000
Pore pressure (bar)
2050
Vp (m/s)
4000
Fig. 10. T he effect of pore pressure to compressional wave velocity in
different temperatures.
3000
2000
y = -221.25x + 4525.9
R2 = 0.7104
1000
2000
Vp (m/s)
Linear (Vp (m/s))
.
0
1950
0
2
4
6
8
10
12
Permeability (mD)
1900
Fig. 14.
1850
Vs at 28.47 degC
1800
2000
1750
0
100
200
Correlation between permeability and compressional wave
velocity.
2500
Vs at 57.10 degC
300
400
500
Pore pressure (bar)
Vs (m/s)
Vs (m/s)
Vs (m/s)
3750
1950
Fig. 11. T he effect of pore pressure to shear wave velocity in different
temperatures.
1500
1000
y = -105.25x + 2288.8
R2 = 0.8057
Vs (m/s)
500
Linear (Vs (m/s))
0
0
2
4
6
8
10
Permeability (mD)
Fig. 15.
Correlation between permeability and shear wave velocity.
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