Microsoft Word - 05-AJST23134排板.docx


Academic Journal of Science and Technology 
ISSN: 2771-3032 | Vol. 15, No. 1, 2025 

 

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Research	Progress	on	Hydraulic	Fracturing	Test	and	
Numerical	Simulation	of	Fractured	Reservoirs	
Shuo Xu 

School of Civil Engineering, Henan Polytechnic University, Jiaozuo 454000, China 

 

Abstract: Due to the influence of geological conditions, there are a large number of natural fractures or cleats distributed in 
the reservoir, which directly affect the effect of hydraulic fracturing. In order to clarify the mechanism of action between 
hydraulic fractures and natural fractures, the current research on hydraulic fracturing fracture propagation in fractured reservoirs 
is reviewed from two aspects of experiment and numerical simulation. Firstly, the research progress of experiment is introduced. 
Then, the related research of numerical simulation is expounded. Finally, the general conclusions of hydraulic fracturing in 
fractured reservoirs are summarized, and the future research is prospected. 

Keywords: Fractured reservoir; natural fractures; hydraulic fracturing; test; numerical simulation. 
 

1. Introduction 
As an important technology for unconventional oil and gas 

exploitation, hydraulic fracturing has been developed for 
nearly 80 years since its inception in the 1940 s. It injects fluid 
into the target reservoir to exceed the amount of fluid that can 
be accommodated by its pore elasticity, so that the reservoir 
cracks, so as to achieve the purpose of mining unconventional 
oil and gas. With the development of unconventional oil and 
gas resources, under the guidance of China 's " dual carbon 
goal, " the transformation of energy structure is accelerating. 
Natural gas, as a link between traditional fossil energy and 
renewable resources, the importance of hydraulic fracturing 
technology is becoming increasingly prominent. At present, 
hydraulic fracturing has made remarkable progress in theory 
and practice. Due to the key role of hydraulic fracturing in 
unconventional oil and gas exploitation, it has always been a 
hot research field of oil and gas resource exploitation. 

However, due to the influence of geological conditions, 
strong tectonic deformation and physical diagenesis in the 
reservoir, there are a large number of randomly distributed 
natural fractures or cleats in the reservoir[1-2].In the process of 
hydraulic fracturing, the expansion of hydraulic fractures 
must be affected by these fractures and cleats, thus affecting 
the fracturing effect. Therefore, it is very important to 
understand the expansion of hydraulic fractures in fractured 
reservoirs and the interaction mechanism between hydraulic 
fractures and natural fractures and cleats. It directly affects the 
formation of fracture networks and affects the production and 
migration path of gas. 

In recent years, for fractured reservoirs, domestic and 
foreign scholars have carried out a lot of research on hydraulic 
fracturing from the aspects of test and numerical simulation. 
Hydraulic fracturing test is the most direct means to study 
fracture propagation, mainly through similar material test or 
true triaxial test of raw coal samples. The difference between 
the current experimental research is mainly due to the use of 
different loading methods, sample size, stress size, data 
monitoring methods and pump injection during fracturing. 
However, the test may be limited by excessive stress, 
difficulty in sampling or difficulty in loading, which may lead 
to unsatisfactory results. 

Compared with the limited numerical simulation of 

experimental conditions, it has become an ideal means to 
study the hydraulic fracture propagation in fractured 
reservoirs. The classical numerical simulation method of 
hydraulic fracturing is based on the discontinuous 
displacement method to predict the fracture parameters of 
three classical parallel plate fracture models KGD, PKN and 
Radials[3-7]. The main simulation methods are finite element 
method, discrete element method, phase field method and 
lattice model. 

From the perspective of engineering practice, as the 
fracturing process and fracturing parameters become more 
and more complex, the scale of fracturing becomes larger and 
larger, and the study of hydraulic fracturing fractures and the 
development of fracture networks become more important. 
This paper summarizes the current research progress of 
hydraulic fracturing from two aspects of experiment and 
numerical simulation, and introduces the research status of 
hydraulic fracturing in fractured reservoirs. 

2. Hydraulic Fracturing Test Research 
Status 

Heng et al.[8] used the indoor large-scale true triaxial 
hydraulic fracturing test system, and used the outcrop shale to 
process the fracturing sample with a size of 300mm × 300mm 
× 300m to carry out the hydraulic fracturing test with bedding. 
The hydraulic fracture expands along the parallel bedding 
direction and the approximate vertical bedding direction at the 
wellbore, which illustrates the influence of fracture toughness 
on the fracture propagation. The hydraulic fracture encounters 
the bedding surface with small fracture toughness during the 
propagation. It will turn and bifurcate, further communicate 
the natural fractures to form a complex fracture network and 
form volume fracturing.  

Ma et al.[9] used hydraulic fracturing test system to study 
the propagation characteristics of hydraulic fractures in 
natural fractured reservoirs using similar material samples of 
prefabricated fractures, and used clear water with dye as 
fracturing fluid to observe fracture morphology. The sample 
size is 200 mm × 200 mm × 200 m cube, and the ratio is 
cement : gypsum : pulverized coal : water = 2 : 1 : 1 : 2, and 
the ratio is obtained by mechanical property test. The test 
results show that in the samples with prefabricated vertical 



 

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fractures, the expansion of hydraulic fractures presents three 
expansion modes due to the presence of natural fractures. It 
stops at natural fractures, expands along natural fractures, 
extends to the tip of natural fractures, and then expands. The 
pump pressure curves and fracture expansion of different 
samples are different, indicating that the mechanical 
properties of the reservoir will affect the fracturing effect. In 
the specimens with prefabricated horizontal fractures, the 
results are different from those of prefabricated vertical 
fractures, indicating that the location of natural fractures also 
affects the fracturing effect. 

Zhou et al.[10] studied the influence of natural fractures on 
the propagation behavior and geometry of hydraulic fractures 

in fractured reservoirs through a triaxial fracturing test system 
( Fig.1 ).In the fracturing process, the effects of horizontal 
stress field, approaching angle and shear strength of 
prefabricated natural fractures on the propagation of 
hydraulic fractures were considered. The results show that the 
higher the shear strength of the prefabricated natural fracture, 
the more easily the hydraulic fracture propagation is 
prevented by the natural fracture. The shape of the hydraulic 
fracture in the reservoir with natural fracture is mainly 
controlled by the in-situ stress and the natural fracture 
approaching angle. When the hydraulic fracture encounters 
the natural fracture, it is possible to offset and produce 
bending fracture. 
 

 
Figure 1. Triaxial fracturing test system diagram[10] 

 
Zhang et al.[11] used the triaxial fracturing system 

monitored by acoustic emission to discuss the influence of 
closed cemented natural fractures on the propagation of 
hydraulic fractures in tight sandstone, and studied the 
influence of natural fractures in different directions on 
hydraulic fractures. The results show that when the angle 
between the natural fracture and the direction of the 
maximum principal stress is 30°-60°, the geometric shape of 

the hydraulic fracture is the most complex, and the number of 
activated natural fractures is the most, while the deflection 
conditions are different under other angles. There are four 
interaction modes between natural fractures and hydraulic 
fractures, namely, deflection along natural fractures, stopping 
after expansion along natural fractures, directly passing 
through natural fractures, and extending along natural 
fractures + directly passing through natural fractures. 
 

 
Figure 2. Fracture morphology[11] 



 

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Jiang et al.[12] used the self-developed multi-functional 

fluid-solid coupling true triaxial test system, based on the 
theory of tensile fracture induced by stress concentration on 
the hole wall, and combined with fracture mechanics to study 
the fracture propagation law of hydraulic fracturing coal. The 
results show that natural fractures will induce hydraulic 
fractures to expand along natural fractures, which can reduce 
the initiation pressure, and the initiation pressure is the 
smallest when natural fractures are perpendicular to the 
minimum principal stress. 

3. Numerical Simulation of Hydraulic 
Fracturing in Fractured Reservoir 

Zhu et al.[13] established a seepage-stress-damage coupled 
finite element-discrete fracture network model to study 
fracture propagation, and verified the correctness of the 
model by using the analytical solution of the KGD model. The 
effects of natural fracture approximation angle, cluster 
spacing, horizontal stress difference and displacement on 
fracture propagation were studied. The results show that the 
larger the approaching angle is, the more easily the hydraulic 
fracture propagation is affected by natural fractures, or even 
blocked, resulting in shorter fracture length. The larger the 
cluster spacing is, the weaker the inhibition of crack 
propagation is ; the increase of flow rate will not change the 
mechanism between natural fractures and hydraulic fractures. 
The final results show that there are three main mechanisms 
between hydraulic fractures and natural fractures : passing 
through natural fractures, opening natural fractures and being 
prevented by natural fractures. 

Li et al.[14] used the finite element RFPA2D-Flow software 

to study the influence of natural fracture filling, stress 
difference and the angle between natural fracture and 
hydraulic fracture on the propagation of hydraulic fracture. It 
is considered that there are three modes of crossing, turning 
and migration when hydraulic fracture and natural fracture 
meet. 

Wasantha et al.[15] used two-dimensional discrete element 
method to study the geometric shape of hydraulic fractures 
with or without natural fractures in the reservoir. It was found 
that natural fractures have a significant effect on the 
symmetry of hydraulic fractures. The stiffness of natural 
fractures, the approaching angle, and the distance between the 
wellbore and natural fractures will affect the propagation of 
hydraulic fractures. It is considered that the asymmetry of 
hydraulic fracture propagation can be reduced by increasing 
the stiffness and approaching angle of natural fractures, and 
the influence of natural fractures more than 50 m away from 
wellbore on hydraulic fracture propagation can be neglected. 
It is found that it is difficult to further expand after the 
intersection of hydraulic fractures and natural fractures. 

Based on the discrete fracture network model, Li et al.[16] 
established a three-dimensional model and used the 
displacement discontinuity method to simulate the expansion 
of hydraulic fractures in fractured reservoirs and the 
interaction between hydraulic fractures and natural fractures. 
The results show that the strong interaction between hydraulic 
fractures and natural fractures makes the fracture network 
complex. The increase of liquid injection displacement can 
increase the complexity of fractures, and the complexity of 
fractures in the horizontal direction is less than that in the 
vertical direction. 

 

 
Figure 3. Hydraulic fracture propagation process[16] 

 
Zhang et al.[17] used the continuous-discontinuous element 

method to establish the model, and discussed the mechanism 
of hydraulic fracture propagation and the influence of natural 
fracture characteristics on hydraulic fracture propagation. The 
results show that when the hydraulic fracture is close to the 
natural fracture, the natural fracture preferentially occurs 
shear failure, and the propagation speed of the hydraulic 

fracture slows down. When the natural fracture density is high, 
the hydraulic fracture is more likely to activate the natural 
fracture to form a curved fracture morphology, but it is not the 
higher the natural fracture density, the higher the degree of 
fracture. The length of the natural fracture also affects the 
scope of the fracturing, but it has little effect on the fracturing 
effect. 
 



 

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Figure 4. Fractured reservoir fracturing process[17] 

 

4. Conclusion and Prospect 
At present, great progress has been made in the 

experimental and numerical simulation of reservoirs with 
natural fractures. However, with the adjustment of the world 
energy structure, how to develop efficiently remains to be 
solved. This paper reviews some research progress in samples 
and numerical simulation of reservoirs with natural fractures. 
It is found that there are four main mechanisms of interaction 

between hydraulic fractures and natural fractures, namely, 
hydraulic fractures directly pass through natural fractures, 
hydraulic fractures are captured by natural fractures ( natural 
fractures prevent the expansion of hydraulic fractures ), 
hydraulic fractures turn to expand along natural fractures, 
hydraulic fractures first expand along natural fractures and 
then turn to the direction of maximum principal stress, as 
shown in Figure 5. 

 

 
(a)pass-through  (b)capture    (c)diversion      (d)offset 

Figure 5. Interaction mechanism between hydraulic fracture and natural fracture[18] 

 
At present, most of the natural fracture tests carried out 

have fewer prefabricated natural fractures, and cannot show 
the impact of the density of natural fractures contained in real 
reservoirs. The numerical simulation is mostly two-
dimensional model to study the role of hydraulic fractures and 
natural fractures, ignoring the possibility of other forms of 
expansion in the real three-dimensional case. Therefore, the 
next step is to carry out three-dimensional simulation work 
consistent with the test and simulation, which can further 
discover new results, increase the reliability of data, and lay 
the foundation for increasing the fracturing effect. 

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