http://journal.uir.ac.id/index.php/JGEET 
 

 
 

E-ISSN : 2541-5794  
   P-ISSN : 2503-216X  

Journal of Geoscience,  

Engineering, Environment, and Technology 
Vol 6 No 2 2021 

 

 
Buntoro et al./ JGEET Vol 6 No 2/2020  81 

 

RESEARCH ARTICLE 
 

Feasibility Study on the Application of Dynamic Elastic Rock Properties 

from Well Log for Shale Hydrocarbon Development of Brownshale 

Formation in the Bengkalis Trough, Central Sumatra Basin, Indonesia. 

Aris Buntoro1, C. Prasetyadi2, Ricky Adi Wibowo3, A.M. Suranto1* 
1* Petroleum Engineering Department, Universitas Pembangunan Nasional Veteran Yogyakarta, Indonesia 
2 Geological Engineering Department, Universitas Pembangunan Nasional Veteran Yogyakarta, Indonesia 

3 PT. Pertamina (Persero), Indonesia 

 

*Corresponding author : su_ranto@upnyk.ac.id 

Tel : +62 8179432855 

Received: Nov 30, 2020; Accepted: May 20, 2021. 

DOI: 10.25299/jgeet.2021.6.2.5944 

 

Abstract 

In modeling the hydraulic fracking program for unconventional reservoir shales, information about elasticity rock properties is needed, namely 

Young's Modulus and Poisson's ratio as the basis for determining the formation depth interval with high brittleness. The elastic rock properties 

(Young's Modulus and Poisson's ratio) are a geomechanical parameters used to identify rock brittleness using core data (static data) and well log 
data (dynamic data). A common problem is that the core data is not available as the most reliable data, so well log data is used. The principle of 

measuring elastic rock properties in the rock mechanics lab is very different from measurements with well logs, where measurements in the lab are 

in high stresses / strains, low strain rates, and usually drained, while measurements in well logging use the principle of measured downhole by high 
frequency sonic. vibrations in conditions of very low stresses / strains, High strain rate, and Always undrained. For this reason, it is necessary to 

convert dynamic to static elastic rock properties (Poisson's ratio and Young's modulus) using empirical equations. The conversion of elastic rock 

properties (well logs) from dynamic to static using the empirical calculation method shows a significant shift in the value of Young's Modulus and 

Poisson's ratio, namely a shift from the ductile zone dominance to the dominant brittle zone. The conversion results were validated with the rock 

mechanical test results from the analog outcrop cores (static) showing that the results were sufficiently correlated based on the distribution range. 

 
Keywords: Elastic Rock Properties, Well Log, Shale Hydrocarbon, Brownshale Formation 
 

  

 

1. Introduction  

The development of shale hydrocarbon requires depth 

interval information with high britteness values based on 

knowledge of geology and rock mechanics as a basis for 

hydraulic fracking planning that can connect natural fractures 

to drain hydrocarbons optimally (Grieser and Bray, 2007; Jin et 

al., 2014). This research was conducted on Brownshale 

formation, Pematang Group, Bengkalis Sub- basin as the main 

source rock in the Central Sumatra Basin based on well log data 

of well BS-03 (Carnell, 1997; J. Katz, 1995). The well log data 

from the well BS-03 is the only well that penetrates the 

Brownshale formation which is used to determine the 

brittleness distribution of the Brownshale Formation with the 

crossplot correlation of Poisson's ratio and Young's modulus.  

If complete sonic log data are available, the elastic rock 

properties can be calculated, namely Poisson’s ratio and 

Young's modulus, where the crossplot of these parameters can 

be used to identify ductile and brittle region (Grieser and Bray, 

2007). Grieser & Bray (2007) stated that ductile rocks have low 

Young's Modulus and high Poisson's ratio, whereas brittle rocks 

have high Young's Modulus and low Poisson's ratio. The 

brittleness of shale hydrobarbon can also be calculated from the 

sonic log data based on the transit time (∆t), which is processed 

first to produce P wave velocity (Vp) and S wave velocity (Vs) 

data, then used to calculate the Poisson’s ratio and Young's 

modulus which describe the ease of the rock to crack. The 

crossplot of the Poisson's ratio and Young's modulus shows that 

high Young's modulus and low Poisson's ratio in rocks tend to 

be brittle (Alsaif et al., 2017). 

Calculation of the elastic rock properties (Poisson's ratio 

and Young's modulus) from the well log measured by sonic 

high vibration frequencies, the value is not the same as the 

measurement in the lab (core). Thus, a conversion must be done 

from dynamic to static using empirical equations (Basuki, 2017; 

Jin et al., 2014; Luo et al., 2015). The Poisson's ratio value for 

isotropic rocks varies between 0 - 0.5, but in general, Poisson's 

ratio values range from 0.05 - 0.45. For example, shale has a 

Poisson's ratio value ranging from 0.05 - 0.32 (Rai et al, 2011). 

The value of the modulus of rock elasticity varies from one rock 

sample from one geological area to another, due to differences 

in rock formation and the minerals that form it (Alfreds R. 

Jumikis, 1979). 

2. Study Area and Brownshale Formation in the Central 

Sumatra Basin 

2.1.  Study Area of Bengkalis Sub-basin 

The study area is located in Bengkalis Sub-basin, Riau 

Province, Indonesia, where the study site is the work area of 

two oil company operators, which contributed to the research 

data and allowed to publish this paper. 

2.2.  Brownshale Formation of Pematang Group   

The Brownshale formation was deposited in a lacustrine 

depositional environment, which consists of fine layered shale, 

brown to black in color, which indicates a sedimentary 

http://journal.uir.ac.id/index.php/JGEET


 
82  Buntoro et al./ JGEET Vol 6 No 2/2021  
 

environment with calm water conditions, consisting of delta 

deposits and turbidite fans (Heidrick, 2018). The Brownshale 

formation is rich in organic matter, and is the main source rock 

that supply hydrocarbons to oil and gas fields in the Central 

Sumatra area. 

The well BS-03 is located on the margin of the North 

Bengkalis sub-basin depocentre and penetrates the Brownshale 

formation within the Eocene-Oligocene Pematang Group, and 

is deposited in a lacustrine environment (Longley, 1990). 

The Brownshale formation, Pematang Group is only found 

in sub-surface, where the thickness can reach more than 1,800 

meters (Grieser and Bray, 2007), Oil-prone Brownshale 

formation can reach a thickness of more than 580 meters. 

Equivalent lacustrine rock stratigraphy, also characterized as an 

oil source rock, is found in the Karbindo Coal Mine, Kiliranjao 

Sub-basin to the Southwest of the Bengkalis Sub-basin, as a 

location for outcrop analog coring (Heidrick, 2018; Sunardi, 

2015). 

 

Fig 1. Study Area of Bengkalis Sub-basin (Modified from (US Energy Information Administration (EIA), 2015) 

3.  Methodology Overview 

The research workflow is schematically shown in Figure 2. 

Since in-situ core data from the Brownshale Formation 

Pematang Group, Bengkalis Sub-Basin were not available, the 

dynamic to static conversion of elastic rock properties from 

well log data of well BS-03 calculations validated with outcrop 

analog core data.  

Figure 2 describes the process of calculating the static 

(core) and dynamic (well log) elastic rock properties (Poisson's 

ratio and Young's modulus). Dynamic calculations from well 

log calculations must be converted to static, and validated with 

static data from the outcrop analog cores.  

4.  Literature Review  

Determination of rock mechanical properties by laboratory 

tests can be done in the presence of core samples from the wells 

to be analyzed, but not all wells are cored, therefore an 

empirical approach is required in the equation with data 

obtained from well logs. Sonic log is a logging tool that is used 

to determine the mechanical rock properties, whose working 

principle is to use sound speed waves that are sent or 

transmitted into the formation by the transmitter, where the 

sound reflected back will be received by the receiver. The time 

it takes for sound waves to reach the receiver is known as the 

transit time interval (Δt).  

The speed of propagation of waves produces a variety of 

different types of waves, in which the primary wave 

(compression) and secondary wave (transverse) applications 

are the main types of waves. Surface waves are currently more 

focused, namely the ultrasonic wave velocity is determined 

based on the travel time and the length of the path. The P wave 

has a higher velocity than the S wave, so that when it hits rocks, 

different wave types also occur different attenuation. 

Experimentally, the S wave is more difficult to obtain than the 

P wave, but in its application the S wave is more widely used to 

calculate Young's modulus (E) and Poisson's ratio (Ʋ). 

 

  

Fig 2. Research Workflow 

 

Core (Out cr op Analog)

 Poi sson s r at i o (n )

 Young s modul us (E)

v – E Cr osspl ot  (St at i c)

Correl at ed

Wel l Log Dat a

Dynamic t o St at ic Conver si on of El ast ic Rock Propert i es fr om  W el l  Log 

Rel at ed t o Shale Hydr ocar bon Devel opm ent  in t he Bengkal i s Tr ough , 

Cent r al Sumat r a Basi n, Indonesi a 

Val id for i dent ifyi ng t he br it t leness of r ocks 

in Br ow nshale developm ent

 Gamma Ray Log

 Sonic Log

VALIDATION

 Poi sson s r at i o (v)

 Young s modul us (E)

v – E Cr osspl ot  (Dynamic)

Conver si on Dynami c t o 

St at i c

v – E Cr osspl ot  (St at i c)



 
Buntoro et al./ JGEET Vol 6 No 2/2021 83 

 

The empirical equation from the P wave velocity and S 

wave velocity data can be used to calculate the dynamic 

Young’s modulus of rocks, but due to the limitations of the 

sonic log data which only has P wave velocity, the S wave value 

is calculated using the Castagna equation (1985) as follows: 

 

Vs = 0.862 Vp - 1.172    (1) 

 

with dynamic Young's modulus equation proposed by Fjær et 

al. (2008), can be calculated Young’s modulus as follows: 

 

E = ρ𝑉𝑠
2 (3𝑉𝑝

2 − 4 𝑉𝑠
2)

(𝑉𝑝
2 − 𝑉𝑠

2)
    (2) 

where;  

vp  = primary wave velocity (km/sec) 

vs  = secondary wave velocity (km/sec) 

ρ = rock density (g/cc) 

E = Young’s Modulus (MPa)  

 

Dynamic Poisson's ratio of rock can be determined using 

empirical equations obtained from P-wave velocity and S-wave 

velocity data with the equation according to Zoback (2007): 

 

υ = 
1−2 [

𝑣𝑠
𝑣 𝑝

]
2

 

2 [1− [
𝑣𝑠
𝑣𝑝

]
2

]

    or   υ = 
𝑉𝑝

2−2 𝑉𝑠
2

2 (𝑉𝑝
2

− 𝑉𝑠
2)

  (3) 

where; 

vp  = primary wave velocity (km/sec) 

vs  = secondary wave velocity (km/sec) 

υ = Poisson’s ratio (dimensionless) 

 

The principle of measuring elastic rock properties in the 

rock mechanics lab is very different from measurements with 

well log, where the measurement in the lab is in high stresses / 

strains, low strain rates, and usually drained conditions, while 

measurements in well logging use the principle of measuring 

downhole by high frequency sonic vibrations is in very low 

stresses / strains, high strain rate, and always undrained 

condition (Basuki, 2017). For this reason, a dynamic conversion 

to static elastic rock properties (Poisson's ratio and Young's 

modulus) is required using the empirical equation, as follows:  

 Dynamic Poisson’s ratio (𝝂d) to static Poisson’s ratio (𝝂s):  

Wang (2000) proposed the empirical equation of undrained 

dynamic Poisson’s ratio is often comparable to the drained 

static Poisson’s ratio (𝝂d≈𝝂s), in the following relation; 

 

𝑣𝑠 =
3𝑣𝑑−𝛽𝐵(1+𝑣𝑑 )

3−2𝛽𝐵(1+𝑣𝑑 )
   (4) 

 

where; 

𝝂 = Biot’s effective stress constant 

B  = Skempton’s coefficient 

Dynamic Young’s modulus (Ed) to static Young’s modulus 

(Es): 

Eissa & Kazi (1998) proposed the empirical equation of 

Young's Dynamic modulus (Ed) to the static Young 

modulus (Es) for sandstones and shales; 

 

Es=10^(0.02+0.77log (ρb.Ed))  (5) 

 

Dynamic Young’s modulus (Ed) often overestimates rock 

stiffness in general:  Es < Ed. 

5.  Result and Discussion   

5.1. Static Elastic Rock Properties Crossplot of the 

Brownshale Based on Outcrop Analog Core Data 

The Brownshale zone with a thickness of about 56 meters 

at Karbindo Coal Mine (Kiliranjao) is composed of 4 facies 

units, namely: unit E, unit F, unit G, and unit H. Unit E consists 

of an intercalation of red and gray shale, clay-silt grains, 

carbonates and locally containing grains of sand. Unit F 

consists of an intercalation of red, gray to brown shale, the size 

of clay grains - silt, carbonate and contains many gastropods. 

Unit G consists of an intercalation of red and gray shale, the 

size of the clay grains - silt, carbonate and locally containing 

grains of sand. Unit H consists of an intercalation of gray and 

brown shale, grain size of clay - silt, carbonate and locally 

containing grains of sand (Figure 3). 

Figure 4 shows the crossplot of elastic rock properties 

(Poisson's ratio vs Young's modulus) from the results of rock 

mechanics tests based on shale outcrop analog cores at the 

Karbindo Coal Mine (Kiliranjau) which represents each facies 

unit of shale hydrocarbon, which consists of six core samples, 

namely: cores B-2A, B-6, B-8, B-15, B-17, B-21, and B-22.  

 

Fig 3. Outcrop of Brownshale formation and profiles at the Karbindo Coal Mine, Kiliranjao Area 



 
84  Buntoro et al./ JGEET Vol 6 No 2/2021  
 

 

Fig 4. Static elastic rock properties (Poisson's ratio vs Young’s 

Modulus) crossplot of the Brownshale based on outcrop analog cores 
data 

5.2. Dynamic Elastic Rock Properties Crossplot of the 

Brownshale Based on Well Log Data 

Geomechanical analysis of well log data from well BS-03 

as the only well that penetrated the Brownshale formation in the 

Bengkalis Sub-basin area with a depth interval of 10,420 - 

11,642 feet (thickness: 1,222 feet) can be used as a basis for the 

development of shale hydrocarbon. 

Crossplot of dynamic elastic rock properties (Dynamic 

Poisson's ratio vs Dynamic Young's Modulus) from the results 

of the geomechanical analysis of BS-03 well log data on the 

Brownshale formation from all depth intervals is shown in 

Figure 4, where the distribution of elastic rock properties is 

more dominant in the ductile region, with Dynamic Poisson's 

ratio values at several depth intervals can reach 0.4, because of 

the intercalation laminated shale / sand section. The Poisson's 

ratio (Ʋ) for shale only varies between 0.05 and 0.32, and 

sandstones have a Poisson's ratio value in the range 0.05 to 0.4 

(Rai, et al, 2014). 

Figure 5 shows the influence of the intercalation laminated 

shale / sand section which causes the Dynamic Poisson's ratio 

value to reach 0.4, so it can be concluded that not all 

Brownshale formation intervals are brittle, but at some depth 

intervals are ductile. 

5.3. Dynamic to Static Conversion of Elastic Rock 

Properties Crossplot of the Brownshale Based on Well Log 

Data  

The principle of measuring elastic rock properties in a rock 

mechanics lab is very different from measuring with a well log. 

Therefore, it is necessary to convert dynamic to static elastic 

rock properties (Poisson's ratio and Young's modulus) using the 

empirical equation proposed by Wang (2000) for Poisson's 

ratio, and the empirical equation proposed by Eissa & Kazi 

(1998) for Young's modulus. The crossplot resulting from the 

conversion of dynamic elastic rock properties to static 

Brownshale formation from well log data is shown in Figure 5. 

 

Fig 5. Dynamic elastic rock properties (Poisson's ratio vs Young’s 

Modulus) crossplot in the Brownshale formation interval from the 

well log data of well BS-03 

From Figure 6, it is very clear that there is a change in the 

crossplot value from dynamic to static of elastic rock properties, 

where the Poisson’s ratio value shifts to the left significantly, 

and Young's modulus value goes downward, where in dynamic 

conditions the distribution is more dominant in ductile region 

and after converting in static conditions the distribution 

becomes more dominant in brittle region. 

5.4.  Validation of Static Elastic Rock Properties of Well 

Log Data Using Outcrop Analog Cores Data 

From the results of the dynamic to static conversion of 

elastic rock properties (Poisson's ratio and Young's modulus) 

using empirical equations, it is very clear that there is a change 

in the crossplot value from dynamic to static elastic rock 

properties, where the Poisson's ratio values shifts to the left is 

quite significant, and the Young's modulus values shifting 

downward, which in dynamic conditions the distribution is 

more dominant towards the ductile region and after converting 

in static conditions, the distribution becomes more dominant 

towards the brittle region. Regarding of shale hydrocarbon 

development in the Brownshale formation, Pematang Group, 

Bengkalis Sub-basin, validation must be carried out with core 

data, so that it is more accurate to identify brittleness rock, 

because core data is not available, outcrop analog cores data is 

used.  

 

Fig 6. The crossplot conversion of dynamic to static of elastic rock properties, where in dynamic conditions the distribution is more dominant in 

ductile region and after converting in static conditions the distribution becomes more dominant in brittle region. 

B-22

B-21

B-2A

B-6

B-8

B-15

B-17

0

20

40

60

80

100

0 0,1 0,2 0,3 0,4 0,5

S
ta

ti
c
 Y

o
u

n
g

's
 M

o
d

u
lu

s
(M

P
a
)

Static Poisson's Ratio

Outcrop Core Data
(Surface)

Brittle Region Ductile Region

Static

Outcrop Analog

(Modified from Perez & Marfurt, 2013)

0

20

40

60

80

100

0 0,1 0,2 0,3 0,4 0,5

D
y
n

a
m

ic
 Y

o
u

n
g

's
 M

o
d

u
lu

s
 
(M

P
a
) 

Dynamic Poisson's Ratio

Well Log Data
(Subsurface)

Brittle Region Ductile Region

Dynamic

(Modified from Perez & Marfurt, 2013)

Shale Sand
Composite Log

Static

Shale Sand

(Modified from Perez & Marfurt, 2013)

0

20

40

60

80

100

0 0,1 0,2 0,3 0,4 0,5

S
ta

ti
c

 Y
o

u
n

g
's

 M
o

d
u

lu
s

(M
P

a
)

Static Poisson's Ratio

Well Log Data
(Subsurface)

Outcrop Core Data
(Surface)

Brittle Region Ductile Region

0

20

40

60

80

100

0 0,1 0,2 0,3 0,4 0,5

D
y
n

a
m

ic
 Y

o
u

n
g

's
 M

o
d

u
lu

s
 
(M

P
a
) 

Dynamic Poisson's Ratio

Well Log Data
(Subsurface)

Brittle Region Ductile Region

Dynamic

(Modified from Perez & Marfurt, 2013)

Shale Sand



 
Buntoro et al./ JGEET Vol 6 No 2/2021 85 

 

Figure 7 shows the validation of the crossplot static elastic 

rock properties of the well log data using outcrop analog cores 

data. From Figure 6, it is confirmed that the validation of the 

static elastic rock properties of the well log data with the rock 

mechanics test results from the outcrop analog cores has a 

strong correlation, so that the outcrop analog data is valid and 

representative to be used in the initial study of shale 

hydrocarbon development in the Brownshale formation, 

Pematang Group, Bengkalis Sub-basin. 

 

Fig 7. The validation of the crossplot static elastic rock properties 

(Poisson's ratio vs Young’s Modulus) of the well log data using an 

outcrop analog cores. 

6. Conclusions 

Crossplot dynamic elastic rock properties of the 

Brownshale formation in the well BS-03 has an intercalation of 

the laminated shale / sand section from the top to the bottom 

interval, where the distribution of dynamic elastic rock 

properties is more dominant in the ductile region, so it can be 

concluded that not all Brownshale formations are brittle, but 

some depth intervals are ductile. 

The value of dynamic elastic rock properties (Dynamic 

Poisson's ratio and Dynamic Young's modulus) calculated from 

the well log data is higher than the static value of the core 

measurements in the rock mechanics lab, so a conversion must 

be done from dynamic to static using core data to validate.     

From the results of the dynamic to static conversion of 

elastic rock properties (Poisson's ratio and Young's modulus), 

there is a change in the crossplot value from dynamic to static 

elastic rock properties, where the Poisson's ratio value shifts to 

the left significantly, and the Young's modulus value shifts 

downward, where in dynamic conditions the distribution is 

more dominant in ductile region and after converting in static 

conditions the distribution becomes more dominant in brittle 

region. 

Validation of the static elastic rock properties crossplot of 

the well log data using the outcrop analog cores data, it is 

confirmed that the validation results have a strong correlation, 

so that the outcrop analog data is valid and representative to be 

used in the initial study of shale hydrocarbon development in 

the Brownshale formation, Pematang Group, Bengkalis Sub-

basin. 

Acknowledgments 

This work was carried out with support from Kementerian 

Riset dan Teknologi / Badan Riset dan Inovasi Nasional - 

Indonesia that has given funding for this research and Malacca 

Strait EMP Group and CPP Block BOB PT. Bumi Siak Pusako-

Pertamina Hulu for contributing data and permission for 

publication. 

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© 2021 Journal of Geoscience, Engineering, 

Environment and Technology. All rights 
reserved. This is an open access article 

distributed under the terms of the CC BY-SA License 

(http://creativecommons.org/licenses/by-sa/4.0/). 

 
 

B-22

B-21

B-2A

B-6

B-8

B-15

B-17

0

20

40

60

80

100

0 0,1 0,2 0,3 0,4 0,5

S
ta

ti
c

 Y
o

u
n

g
's

 M
o

d
u

lu
s

(M
P

a
)

Static Poisson's Ratio

Well Log Data
(Subsurface)

Outcrop Core Data
(Surface)

Brittle Region Ductile Region

Static

Shale Sand
Composite Log

Outcrop Analog

(Modified from Perez & Marfurt, 2013)

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http://creativecommons.org/licenses/by-sa/4.0/