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Engineering, Technology & Applied Science Research Vol. 9, No. 1, 2019, 3696-3698 3696  
  

www.etasr.com Irfan & Almufadi: Investigation of Mechanical Properties of Shale Rock in Qassim Region, Saudi Arabia 

 

Investigation of Mechanical Properties of Shale Rock 

in Qassim Region, Saudi Arabia 
 

Mohammad A. Irfan 

Department of Mechanical Engineering 

University of Engineering and Technology 

Peshawar, Pakistan 

mairfan@uetpeshawar.edu.pk 

Fahad A. Almufadi
 

College of Engineering 

Qassim University 

Saudi Arabia 

almufadi@qec.edu.sa 

 

Abstract—An investigation into the mechanical properties of 

shale rock from Qassim Province, Saudi Arabia is presented in 

this paper. Uniaxial compression test, Schmidt hammer test and 

porosity estimation were carried out. Regarding the compression 

test, it was found that the strength ranged from 1.98MPa to 

8MPa and the strain ranged from 0.53% to 2.5%. Regarding the 

Schmidt Hammer test, it was found that the rebound values 

ranged from 22.4 to 25. The measurements of volumetric porosity 

indicated that the porosity in the shale rock ranged between 

19.12% and 24.31%. All the values determined in this project 

match well with the published values of other studies about shale 

rock. 

Keywords-shale rock; mechanical properties; Qassim province; 

Saudi Arabia 

I. INTRODUCTION  

Shale oil and gas production from organic rich shale 
formations is a growing area of technical interest in oil and gas 
exploration. Long horizontal wells with hydraulic fracturing are 
required to bring economic production from shale gas 
reservoirs. Since crack propagation in hydraulic fracturing 
occurs under high strain rates, it is important to understand the 
fracture behavior of shale rock and its mechanical properties. 
The properties of shale rock that are needed in order to be able 
to design the hydraulic fracturing systems include: compressive 
strength, hardness, porosity, modulus of elasticity, Poisson’s 
ratio, fracture toughness and permeability. Rocks in general can 
be classified as: igneous rocks, sedimentary rocks, and 
metamorphic rocks. Sedimentary rocks are made when 
products of weathering are subjected to transportation by water, 
winds or deposition and subsequently are compacted or 
consolidated. Some examples are sandstone, shale, 
conglomerate, breccias, limestone, and coal. Minerals forming 
sedimentary rocks are kaolinite, illite, smectite, hematite, rutile, 
corundum and so on. Shale is basically a sedimentary rock with 
fine grains, composed of mud which is a mixture of flakes of 
clay minerals and small particles of other minerals, mostly 
quartz and calcite. 

Numerous experimental and theoretical investigations have 
demonstrated how mechanical properties in sedimentary rocks 
are affected by porosity [1], clay content [2], overburden stress 
and pore fluid [3]. Further understanding needs to be developed 

on how these parameters control rock strength. The aim of this 
paper is to test the mechanical properties of Saudi shale rock 
from Qassim province, under static loading. Rock samples 
were taken from shale formations in Qassim region, Saudi 
Arabia. Uniaxial compression test, Schmidt hammer test and 
porosity estimation were carried out. 

II. LITERATURE REVIEW 

A. Uniaxial Compression Test of Shale Rock 

Weak rocks are defined by their ultimate compressive 
strength (UCS) in the range of 0.25 to 25MPa [4]. A good 
strength limit for weak rocks may be 20MPa because rocks 
weaker than this behave differently when sheared [5]. 
Sedimentary rocks such as sandstone, siltstone, shale, claystone 
or mudstone, clay-shale fall under the classification of weak 
rocks [6, 7]. The prime factor affecting the strength of weak 
rocks is porosity. Commonly, high porosity gives low strength 
and vice versa. Table I summarizes some available strength 
data for sandstone and shale. It can be seen that higher porosity 
leads to weak compressive strength. 

TABLE I.  COMPRESSIVE STRENGTH AS RELATED TO POROSITY  

Reference Location Porosity % Compressive strength (MPa) 

[5] Kidderminster (UK) ~31 2 to 3 

[8] 
Bringelly Shale, 

Australia 
7% to 14% 2.4 to 49 

 

B. Schmidt Hammer Test 

Schmidt Hammer test is commonly used for testing 
different rocks and has a strong correlation with UCS through 
numerous empirical equations. Schmidt hammer rebound (R) 
values were directly used in the analysis and were not 
converted to UCS, since there is no standard conversion 
designated for shale. Table II shows the range of R values for 
Sevier and Rome shale [9].  

TABLE II.  SHALE ROCK COMPRESSIVE STRENGTH ESTIMATION [9] 

Type of Shale Schmidt Hammer Rebound (R) 

Sevier Shale 30 

Rome Shale 38 

Corresponding author: M. A. Irfan



Engineering, Technology & Applied Science Research Vol. 9, No. 1, 2019, 3696-3698 3697  
  

www.etasr.com Irfan & Almufadi: Investigation of Mechanical Properties of Shale Rock in Qassim Region, Saudi Arabia 

 

C. Porosity 

Porosity is defined as the fraction of a rock occupied by 
pores. It is a static property which can be measured by various 
methods in the absence of fluid flow. To find effective porosity 
fluid flow is required to ascertain whether the pores are 
interconnected. Table III presents some data on average 
porosity. Nearly all the measurements were made at room 
temperature and pressure of 1 atmosphere [10]. 

TABLE III.  AVERAGE POROSITY FOR SHALE ROCK [10] 

Title Average Porosity (ф) 

Shale (Near Ponca City, Oklahoma) 42.5% 

Shale (Eastern Venezuela) 33.5% 

Shale (Los Manueles field, Venezuela) 20.0% 

Shale (Ponca City and Garber areas, Oklahoma) 17.0% 

Weston Shale (Bonner Springs, Kansas) 15.8% 

Chanute Shale (Independence, Kansas) 14.9% 
 

III. MATERIALS AND METHODS 

Shale rock samples were collected from a local cement 
quarry in Qassim, Saudi Arabia. A total of 40 samples were 
obtained for initial testing.  

A. Specimens Preparation  

The cutting of samples was completed in the Civil 
Engineering lab at Qassim University, using its sample 
preparation machine. It took five days to complete prepare the 
specimens to finally obtain only 20 proper samples out of 40. 
Figure 1 shows the shale samples before they were cut into 
cubical shapes. The specimens were cut as 
50mm×50mm×50mm cubes as per ASTM C 109/C 109M. 
There may be some errors in the dimensions due to the 
difficulty in precision cutting of soft rocks. Also, there is a 
maximum expected dimension error of ±2mm. 

 

 
Fig. 1.  Samples before cutting 

IV. RESULTS AND DISCUSSION 

A. Uniaxial Compression Test  

The laboratory uniaxial compressive strength is the 
standard strength parameter of intact rock material. An MTS 
universal tensile testing machine used with capacity of 25kN 
was used. Table IV shows the results of the compression test. 
The average strength of the 4 samples used is 2.5MPa. Table 
IV also shows the strain values of the 4 samples. The 
maximum is 2.5% for sample 3 and the minimum is 0.91% for 
sample 1, while the average is 1.46%. It is important to 
compare the results with previous ones, to observe and discuss 
their differences. Table V represents the uniaxial compressive 
strength of shale rock and its associated porosity, from [5], in 
comparison with Qassim shale results investigated in this 

paper. The average porosity of Qassim shale was 22.54%. The 
average UCS of Qassim shale was 2.5MPa which is well within 
the range of internationally published values as shown in Table 
V. 

TABLE IV.  TENSILE TEST SUMMARY 

Sample No. Strength (MPa) Strain (%) 

1 2.13 0.91 

2 2.38 1.26 

3 3.53 2.5 

4 1.98 1.16 

TABLE V.  RESULTS COMPARISON 

Reference Location Porosity % 
Compressive strength 

(MPa) 

[5] Kidderminster (UK) ~31 2 to 3 

[8] 
Bringelly Shale, 

Australia 
7% to 14% 2.4 to 49 

Current 
study 

Qassim, 
Saudi Arabia 

19% to 24% 1.98 to 3.53 

 

B. Schmidt Hammer Test  

Three samples were tested by Schmidt hammer. The 
dimensions of the samples were 50mm×50mm×50mm. An N-
type Schmidt hammer with an impact energy of 2.2N.m was 
used to measure rock hardness. Table VI shows pictures of the 
three samples before and after the test. It also shows the 
rebound and strength values obtained. The maximum rebound 
value was in sample 2, where sample 3 had the minimum 
value. Note that the empirical relation used to estimate the 
compressive strength in [11] could not be valid for the 
specimens used in this test.  

TABLE VI.  SCHMIDT HAMMER TEST RESULTS 

Name Before test After test 
Rebound 

value (R) 

S
H
-2
0
1
6
-0
1
 

  

23.5 

S
H
-2
0
1
6
-0
2
 

  

25 

S
H
-2
0
1
6
-0
3
 

  

22.4 

 

Tables VII-VIII show the results of this study in 
comparison with previously published results [9]. 



Engineering, Technology & Applied Science Research Vol. 9, No. 1, 2019, 3696-3698 3698  
  

www.etasr.com Irfan & Almufadi: Investigation of Mechanical Properties of Shale Rock in Qassim Region, Saudi Arabia 

 

TABLE VII.  RESULTS COMPARISON WITH SEVIER SHALE [9] 

Sample Number 

of current study 

Absolute Difference of 

Schmidt Hammer 

Rebound Value (R) 

Difference of Schmidt 

Hammer Rebound 

Value (%) 

SH-2016-01 6.5 21 

SH-2016-02 5 16 

SH-2016-03 7.6 25 

TABLE VIII.  RESULTS COMPARISON WITH ROME SHALE [9] 

Sample Number 

of current study 

Absolute Difference of 

Schmidt Hammer 

Rebound Value (R) 

Difference of Schmidt 

Hammer Rebound 

Value (%) 

SH-2016-01 14.5 38 

SH-2016-02 13 34 

SH-2016-03 15.6 41 
 

C. Determination of Porosity 

Mathematically, porosity can be defined by (1): 

�������� = 	ф =	
��

�
=

�
���

�
    (1) 

where ф: porosity (%), Vb: bulk volume (cm
3
), Vp: pore volume 

(cm
3
), and Vm: matrix volume (grain volume) (cm

3
). Vb of the 

sample was measured by the volumetric displacement method. 
Vm was measured by crushing the sample to grain size and 
immersing it in a container filled with water. Substituting the 
results in (1) we have the results shown in Table IX: 

TABLE IX.  SUMMARY OF RESULTS 

Sample No. Porosity (ф) 

1 19.12% 

2 24.15% 

3 24.31% 
 

Table X shows the porosity results comparison of shale 
rock in current study and in [10]. It can be seen that porosity 
measured values lie within the range of other published values. 

TABLE X.  COMPARISON WITH [10] 

Title Average ф[10] Qassim average ф 
Percent 

difference 

Shale (Near Ponca 
City, Oklahoma) 

42.5% 

22.53% 

+20.03% 

Shale (Eastern 

Venezuela) 
33.5% +10.03% 

Shales (Los 
Manueles field, 

Venezuela) 

20% -2.53% 

Shale (Ponca City 

and Garber areas, 
Oklahoma.) 

17% -5.53% 

Weston Shale 

(Bonner Springs, 
Kansas) 

15.8% -6.73% 

Chanute Shale 

(Independence, 

Kansas) 

14.9% -7.63% 

 

V. CONCLUSION AND FUTURE WORK 

Uniaxial compressive strength was tested for 4 different 
samples, ranged from 1.98MPa to 5MPa and with an average 
of 2.5MPa, while the strain ranged between 0.91% and 2.5% 
and had an average of 1.46%. The Schmidt hammer test results 

found that the rebound values ranged from 22.4 to 25. 
Displacement method was used to determine the Qassim shale 
rock porosity, the results were 19.12%, 24.15% and 24.31% 
and the average porosity was 22.53%. The samples for this 
study were taken from a cement quarry. In future, samples can 
be derived from the drilling core, because that would give more 
meaningful results for shale gas exploration. Another 
suggestion is to calculate shale rock’s modulus of elasticity and 
Poisson's ratio. Schmidt hammer can be done with a lighter L-
type Schmidt hammer, which has impact energy 0.735N.m. In 
addition, impact tests can also be conducted. 

ACKNOWLEDGEMENT 

Authors would like to thank undergraduate students Suhail 
A. Aswailem, Abdurehman S. Alquba and Ahmed M. Alhasan 
for conducting the experiments as a part of their senior project. 

REFERENCES 

[1] M. R. Wyllie, A. R. Gregory, G. H. F. Gardner, “An experimental 
investigation of factors affecting elastic wave velocities in porous 
media”, Geophysics, Vol. 23, pp. 459-493, 1957 

[2] D. Han, A. Nur, D. Morgan, “Effect of porosity and clay content on 
wave velocity in sandstones”, Geophysics, Vol. 51, pp. 2093-2017, 1986 

[3] M. S. King, “Static and dynamic elastic properties of rocks from the 
Canadian Shield”, International Journal of Rock Mechanics and Mining 
Sciences & Geomechanics Abstracts, Vol. 20, No. 5, pp. 237-241, 1983 

[4] R. Ulusay, The ISRM Suggested Methods for Rock Characterization, 
Testing and Monitoring: 2007-2014, Springer, Switzerland, 2015 

[5] L. Dobereiner, M. H. de Freitas, “Geotechnical properties of weak 
sandstones”, Geotechnique, Vol. 36, pp. 79-94, 1986 

[6] J. C. Jaeger, N. G. W. Cook, R.W. Zimmerman, Fundamentals of Rock 
Mechanics, Blackwell Publishing, 2007 

[7] S. Klein, “An approach to the classification of weak rock for tunnel 
projects”, 2001 Rapid Excavation and Tunneling Conference, San 
Diego, USA, June 11-13, 2001 

[8] W. Ezzat, Engineering Performance of Bringelly Shale, PhD Thesis, 
University of Sydney, 2005 

[9] A. Nandi, C. M. Liutkus, M. J. Whitelaw, “Geotechnical 
characterization of Sevier and Rome shale, East Tennessee”, 43rd U.S. 
Rock Mechanics Symposium and 4th U.S. –Canada Rock Mechanics 
Symposium, Asheville, USA, June 28-July 1, 2009 

[10] G. E. Manger, Porosity and Bulk Density of Sedimentary Rocks, US 
Government Printing Office, 1963 

[11] F. I. Shalabi, E. J. Cording, O. H. Al-Hattamleh, “Estimation of rock 
engineering properties using hardness tests”, Engineering Geology, Vol. 
90, No. 3-4, pp. 138-147, 2007 

 
AUTHORS PROFILE 

 

Mohammad A. Irfan did his PhD in Mechanical Engineering from Case 
Western Reserve University, Cleveland, OH, USA in 1998. Following his 
PhD he worked for 2 years in the US industry. His work was related to the 
design of industrial burners. He has been awarded with the Fulbright 
postdoctoral fellowship in 2008. During his post doc he conducted research on 
reducing porosity in aluminum die castings. He joined Qassim University, in 
2010. Currently he is working as a Professor of Mechanical Engineering at the 
University of Engineering and Technology, Peshawar, Pakistan. 

 

Fahad A. Almufadi did his PhD from Ohio University, USA in 2004. He 
joined Qassim University, Saudi Arabia in 2009 where he was in charge of 
different academic and administration positions starting with mechanical 
engineering department head, then vice dean and currently he is the dean of 
the Engineering College.