Fracture prediction in the tight-oil reservoirs of the Triassic Yanchang Formation in the Ordos Basin, northern China
Fracture prediction in the tight-oil reservoirs of the Triassic Yanchang Formation in the Ordos Basin, northern China
Wen-Tao Zhao 0 1 2
Gui-Ting Hou 0 1 2
0 PetroChina Research Institute of Petroleum Exploration and Development , Beijing 100083 , China
1 China Huaneng Clean Energy Research Institute , Beijing 102209 , China
2 The Key Laboratory of Orogenic Belts and Crustal Evolution of Ministry of Education, School of Earth and Space Sciences, Peking University , Beijing 100871 , China
It is important to predict the fracture distribution in the tight reservoirs of the Ordos Basin because fracturing is very crucial for the reconstruction of the low-permeability reservoirs. Three-dimensional finite element models are used to predict the fracture orientation and distribution of the Triassic Yanchang Formation in the Longdong area, southern Ordos Basin. The numerical modeling is based on the distribution of sand bodies in the Chang 71 and 72 members, and the different forces that have been exerted along each boundary of the basin in the Late Mesozoic and the Cenozoic. The calculated results demonstrate that the fracture orientations in the Late Mesozoic and the Cenozoic are NW-EW and NNE-ENE, respectively. In this paper, the two-factor method is applied to analyze the distribution of fracture density. The distribution maps of predicted fracture density in the Chang 71 and 72 members are obtained, indicating that the tectonic movement in the Late Mesozoic has a greater influence on the fracture development than that in the Cenozoic. The average fracture densities in the Chang 71 and 72 members are similar, but there are differences in their distributions. Compared with other geological elements, the lithology and the layer thickness are the primary factors that control the stress distribution in the study area, which further determine the fracture distribution in the stable Ordos Basin. The predicted fracture density and the two-factor method can be utilized to guide future exploration in the tight-sand reservoirs.
Ordos Basin; Yanchang Formation; Fracture prediction; Finite element modeling; Two-factor method; Tight-sand reservoirs
& Gui-Ting Hou
Unconventional oil and gas resources, such as tight gas,
tight oil and shale oil, have been successfully developed
commercially in the USA, Canada, Australia and some
other countries. The production of tight oil soared from 30
million tons in 2011 to 96.9 million tons in 2012 in the
USA by using new unconventional technologies (Du et al.
2014). In China, the Ordos Basin, the Junggar Basin, the
Songliao Basin, the Sichuan Basin, the Qaidam Basin, etc.,
have abundant tight-oil resources with an output of 97
million tons, accounting for 22% of the nationwide total oil
output (Jia et al. 2014). In the Ordos Basin, the tight-oil
reservoirs in the Triassic Yanchang Formation have
become a major target of petroleum exploration and
development in recent years (e.g., Guo et al. 2012; Yao
et al. 2013).
Since tight-oil reservoirs in the Ordos Basin are of
lowpermeability (\2 9 10-3 lm2) and low-porosity (\10%)
overall, fracturing is crucial for the reservoir
reconstruction, even though the reservoirs are formed with
complicated mechanisms (e.g., Yao et al. 2013; Ezulike and
Dehghanpour 2014). Therefore, it is important to predict
the natural fracture distribution in reservoirs, including
their orientation and density, for future exploration and
development (e.g., Smart et al. 2009). Previous studies
have focused on the geometrical or kinematic models, such
as analyses of seismic techniques or of the layer curvature
(e.g., Zahm et al. 2010; Pearce et al. 2011; Tong and Yin
2011), and fracture prediction in the Ordos Basin has also
been involved in some papers (e.g., Ju et al. 2014a).
However, since earlier fracture prediction was mainly
carried out through layer curvature or two-dimensional
(2D) models, which cannot meet the demands for the
tightoil study and exploration, it is necessary to build
threedimensional (3D) mechanical models in order to achieve
the accuracy needed for further research on the
Various factors, such as the proximity of faults, the
curvature of folds, the layer thickness and the lithology, are
deemed to control the fracture development in tight
reservoirs (e.g., Ju et al. 2013), and the anisotropy or
heterogeneity should also be considered in the modeling
(e.g., Glukhmanchuk and Vasilevskiy 2013). However, it is
difficult for 2D geomechanical models to fully consider all
these factors, and the modeling results cannot be used
successfully for exploration and production. Therefore, 3D
models will be utilized in this paper, which take the
lithology, the thickness and the stress fields into
The study area in this paper, namely the Longdong area,
is located in the southern Ordos Basin, where research on
structural fractures in the tight reservoirs is still deficient
(e.g., Ren et al. 2014; Li et al. 2015). The structural
fractures in the Longdong area were mainly formed after the
Late Triassic, as a result of multiple-stage tectonic events
in the Late Mesozoic and the Cenozoic. These extensively
developed fractures are mostly unfilled and effective,
which noticeably improve the permeability of tight
reservoirs in the Ordos Basin.
2 Geological background
The Ordos Basin, covering an area of 2.6 9 105 km2, is a
large N–S trending basin in the western North China
Craton, which is located between the Siberian Craton and
the South China Craton (Hou et al. 2010) (Fig. 1). Three
orogenic belts have been developed along different
boundaries of the stable basin, including the Yinshan
Mountain in the north, the Qinling Orogen in the south and
the Liupanshan Mountain in the southwest (e.g., Nutman
et al. 2011) (Fig. 2). The basement of the basin is
composed of Archean rocks with Proterozoic sedimentary
cover. Although the margin underwent multiple tectonic
activities, the central part is still stable and is covered by
shallow Paleozoic marine carbonate sediment (Kusky and
Li 2009). Some small-scale paleo-faults exist, but no large
faults have been found within the basin (Wan and Zeng
2002; Yang et al. 2013).
Contrary to the evolution of the eastern North China
Craton including thickening, thinning and destruction, the
Ordos Basin has evolved from three Mesoproterozoic
aulacogens to a Paleozoic–Mesozoic cratonic basin since
the Middle Proterozoic (Menzies et al. 2007; Yang et al.
2013; Wang et al. 2014b). The interior part of the basin is
characterized by horizontal or gently dipping strata (\3 ),
especially for the Mesozoic and Cenozoic strata, whereas
the strata along the margins have been subjected to
significant folding and faulting since the Late Triassic.
Two distinct tectonic events took place from the Late
Mesozoic to the Cenozoic, resulting in two different stress
fields in these periods. In the Late Mesozoic, namely from
the Early Jurassic to the Late Cretaceous, the long-distance
effect of subduction of the Izanagi Plate turned from
northnorthwestward to northwestward when the force arrived at
the Ordos Basin, resulting in the WNW-trending stress
fields and the structural fractures in NW–EW trends (e.g.,
Wan 1994; Hou et al. 2010; Sun et al. 2014; Zhao et al.
2016); while in the Cenozoic, the predominant tectonic
event became the northeastward collision between the
Indian and the Eurasian Plate, which led to the NE-trending
stress fields and the structural fractures in NNE–ENE
trends (e.g., Yuan et al. 2007; Wang et al. 2014b). Two
episodes of fractures are developed under distinct tectonic
events, so the stress fields of different periods should be
taken into consideration during the fracture prediction.
3 Fracture measurement
The parameters of fracture characteristics are important in
the exploration and development of fractured tight
reservoirs. The fracture density is one of the significant indicators
to reflect the failure degree of rocks, which can be divided
into three types, including the linear density, the surface
density and the bulk density of fractures. In this paper, the
surface density is utilized to describe the fracture distribution
in the Ordos Basin. The surface density is defined as the ratio
between the cumulative fracture length and the
cross-sectional area of the matrix, which can better reflect the degrees
of fracture development and be measured more effectively
than others (Golf-Racht 1982). The fracture density from
core observations can be calculated as:
f ¼ PS li ¼ 2pr2 þP2lpi r L ð1Þ
where f is the fracture surface density, li is the length of
each structural fracture, S is the surface area of the
observed core, r is the radius and L is the length of the core.
WB Ordos Basin
In this paper, the Longdong area was selected as the
study area to carry out fracture measurements (Fig. 2).
Sixty-six wells were chosen to study the distribution of
structural fractures in the Chang 71 and 72 members
(Fig. 3). As shown in Fig. 4, the fracture density in the
tight-sandstone cores is relatively low (smaller than
0.5 m-1), representing the general condition in the
Longdong area. The fracture density of the Chang 72
member is more concentrative than that of Chang 71
member, even though their average densities are similar
in general (0.071 m-1 for the Chang 71 member and
0.081 m-1 for the Chang 72 member). The difference of
fracture distribution between the Chang 71 and 72
members is obvious: The highest fracture density in the
Chang 71 member lies in the Laocheng and Qingyang
areas, while that in the Chang 72 member lies in the
Laocheng, the Qingyang and the Zhengning areas
4 Modeling approach
Methods such as geological analysis, physical modeling
and numerical simulation including the finite element
method (FEM) can be applied in the study of stress fields,
which is the foundation of fracture prediction. In this study,
the finite element software ANSYS is used to calculate the
stress field and predict the fracture distribution (Vela´zquez
et al. 2009; Jarosinski et al. 2011). The basic concept of
FEM is that a geological body can be discretized into finite
continuous elements connected by nodes. The geometrical
and mechanical parameters allocated on each element are
consistent with the properties of real rocks. The continuous
field function of the geological area is first transformed into
linear functions at every node that contain displacement,
stress and strain variables resulting from the applied forces
(Jiu et al. 2013), and then all these elements are used to
obtain the stress distribution over the entire area.
Qinling Orogen Belt
Yinshan Orogen Belt
4.1 Geometrical model
The Ordos Basin is a near-rectangular basin in the western
part of the North China Craton (Li and Li 2008; Tang et al.
2012) (Fig. 2). Although the Ordos Basin underwent
multistage tectonic movements in the Late Mesozoic–Cenozoic
eras, the deformation was confined to the western margin
and no significant tectonic events occurred in the central
part. Therefore, the outline of the basin remained
unchanged in these periods (Sun et al. 2014) (Fig. 5a). Since no
large faults or folds have been recorded inside the Ordos
Basin, the sedimentary facies, the lithology and the
distribution of sand bodies are the key factors to determine the
In this paper, the Chang 71 and 72 members in the
Triassic Yanchang Formation, the major tight-oil members in
Fig. 3 Synthetical stratigraphic column and depositional environment of the Upper Triassic—Middle Jurassic in the Ordos Basin (after Duan
et al. 2008)
the Ordos Basin, are selected as the study strata, and the
Longdong area is chosen to discuss the stress fields and the
fracture distribution (Figs. 2, 3, 5). Since the Yanchang
Formation is characterized by strong heterogeneity with
facies change, the simplified model with only one rock
mechanical property is no longer suitable for the complex
interior of the Ordos Basin (Yang and Deng 2013). Based
on the sandstone-mudstone ratio, it is assumed that the
ratios between the sandstone and mudstone layers are
0.43–4.26 (average 1.27) in the Chang 71 member and
0.54–9.00 (average 1.70) in the Chang 72 member (e.g.,
Guo et al. 2012; Li et al. 2015), and multiple-layer
constructions (four sandstone layers in Chang 71 member and
three sandstone layers in Chang 72 member) are applied in
X73 Qingcheng Z200
the geometrical model to simulate the sandstone-mudstone
interlayers (Fig. 5). To avoid the boundary effect, forces in
the models are set on the boundaries of the Ordos Basin,
and the study area is nested inside the basin (Fig. 5). The
sandstone layers, which are also the main layers in fracture
development, in the middle of each member, are selected to
display the modeling results in the following text,
representing the general situation of fracture development in the
Chang 71 and 72 members.
4.2 Boundary conditions and modeling
In order to predict the fracture distribution of the Ordos
Basin, it is assumed that the upper crustal thickness of the
basin in the Late Mesozoic–Cenozoic era is 25 km (e.g.,
Liu et al. 2006). The top of the model is set as a free
surface, and the entire model is subjected to gravity load.
The average density of the upper crust, which mainly
consists of sedimentary cover, greenschist and granite, is
2750 kg/m3 (Hou et al. 2010; Wang et al. 2014b). Based on
the velocities of P and S waves, the calculated average
Poisson’s ratio is 0.20 and the average Young’s modulus is
80 GPa for the whole basin (Liu et al. 2006).
To subtly depict the distribution of structural fractures in
the Longdong area, four more kinds of material elements
are involved in the 3D geometrical model, including the
sandstones/mudstones of the Chang 71 member and the
sandstones/mudstones of the Chang 72 member. Tri-axial
rock mechanical experiments were carried out by the
Institute of Acoustics, Chinese Academy of Sciences, on 62
core samples collected from observed wells in the
Longdong area (Fig. 4). In order to simulate the real conditions
underground, in these experiments, confining pressures
corresponding to the original depth of the Yanchang
Formation are applied in the radial directions, and vertical
pressures are applied in the axial directions of all samples.
Through statistical analysis and geological classification,
five sets of rock mechanical properties, the average density,
Young’s modulus, Poisson’s ratio, internal friction angle
and cohesion, are listed in Table 1 by layer and lithology.
Because the stress fields in the Late Mesozoic and
the Cenozoic are strikingly different and both of them
had a significant effect on the fracture development in
the Ordos Basin, the boundary conditions during these
two episodes along the basin need to be defined (Zhao
et al. 2016).
As a result of intense compression from the Early
Jurassic to the Middle Cretaceous, the Yinshan Orogen
Belt was developed as thrust faults with dextral shearing
features in the Late Mesozoic (Darby and Ritts 2002;
Zhang et al. 2007; Faure et al. 2012). A uniform direction
and a constant magnitude of a 40 MPa normal component
with a 10 MPa dextral shearing component are applied
along the northern side of the Ordos Basin (L1) (Fig. 6a).
The east-dipping thrusts, the NWW-dipping back-thrusts
and the associated folds developed along the Lu¨liang
Mountain in the Jurassic show that the stress regime in the
eastern margin was related to the long-distance effect of the
push from the northwestward subduction of the Izanagi
Plate in the Late Mesozoic (Zhang et al. 2007; Hou and
Hari 2014). Hence, it is a compressive boundary with a
sinistral shearing component along the eastern edge of the
basin. A deviatoric stress of an approximately 150 MPa
normal component with a 45 MPa shearing component is
set along the eastern boundary (L2) (Fig. 6a). Based on the
paleo-magnetic constraints, geological evidence and
40Ar/39Ar and U–Pb dating, it can be assumed that in the
southern part of the Ordos Basin, the Qinling Ocean finally
closed during the Late Jurassic-Early Cretaceous period.
This indicates that the collision between the North China
Craton and the South China Craton continued up to the
Cretaceous period (Huang et al. 2005; Liu et al. 2015). And
due to this collision, thrust faults with sinistral strike-slip
features were developed along the northern margin of the
Qinling Orogen Belt (Malaspina et al. 2006; Yuan et al.
2007). Therefore, a constant magnitude of normal stress
(60 MPa) with sinistral shearing stress (30 MPa) is applied
along the southern margin of the basin (L3) (Fig. 6a). In
the western and southern margins, the long-distance effect
of collision from the Qiangtang Massif affected the Ordos
Young’s modulus, GPa
Internal friction angle,
Basin (Zhang et al. 2007; Li and Li 2008), so a
compressive traction with a uniform direction and a constant
magnitude of deviatoric stress of 30 MPa on the
southwestern boundary (L4) and 75 MPa on the western
boundary (L5) are applied along the basin (Fig. 6a). On the
basis of SHRIMP zircon U–Pb ages and other
geochronological data, it can be presumed that the closure of the
Paleo-Asian Ocean finally took place after the Early
Permian. Due to this episode of closure, the northward
movement of the Alashan Block (Fig. 2) was arrested by
the Siberian Craton in the Late Mesozoic (e.g., Zheng et al.
2014). The final closure of the Qilian Ocean took place at
the end of the Ordovician, and after that, the Qaidam
Block, which was adjacent to the Alashan Block, restricted
the southward movement of the Alashan Block (Song et al.
2013). The nonidentical apparent polar wandering paths of
the Tarim Block and the Alashan Block up to the Jurassic
period clearly indicates that the amalgamation of these two
blocks might have occurred during the Jurassic (Gilder
et al. 2008). As a result of amalgamation in the Jurassic, the
wedge-shaped Alashan Block was trapped between the
Siberian Plate, the Qaidam Block, the Tarim Block and the
Ordos Block (Zhang et al. 2007). Therefore, the
northwestern boundary (L6) is kept fixed as the Alashan Block
was locked by the adjacent blocks in the Late Mesozoic
The stress field in the Cenozoic era, which is regarded as
a consequence of the Indo-Asian collision, is strikingly
different from that in the Late Mesozoic era (e.g., Darby
and Ritts 2002; Bao et al. 2013) (Fig. 6b). During the
Cenozoic, the extension along the margins of the Ordos
Basin triggered the formation of the Hetao, the Weibei and
the Yinchuan Grabens, which in turn transposed reverse
faults to normal faults in the Helan Mountain and the
Qinling Mountain (Rao et al. 2014). Therefore, a tensile
traction with a uniform direction and a constant magnitude
of 5 MPa is applied on the northern, the southern and the
northwestern margins, respectively (L7, L9 and L12)
(Fig. 6b). The subduction of northwestern Pacific Plate
restricted the further eastward movement of the Ordos
Basin (Fournier et al. 2004; Schellart and Lister 2005). The
current GPS horizontal velocity field map shows that the
eastward velocity of the Shanxi Block (Fig. 2) is relatively
smaller than that of the Ordos Basin (e.g., Zhu and Shi
2011; Wang et al. 2014c). The velocity differences
between the Shanxi Block and the Ordos Basin suggest that
the northeastward motion of the Ordos Basin, which was
pushed by the Tibet Plateau, was restricted by the Shanxi
Table 2 Shortening rates of
different profiles in the
midsouth section of the western
margin (L11) in the Ordos Basin
(Source: Feng et al. 2013)
Shortening rate, %
Average shortening rate, %
Block due to the westward subduction of the Pacific Plate
in the Cenozoic (Hou et al. 2010). Accordingly, the eastern
edge of the basin is kept fixed for the Cenozoic era (L8)
(Fig. 6b). On the basis of massive fault-striation data, it can
be interpreted that the southern margin, namely the Weihe
Graben, turned into a sinistral shearing tensile boundary
(e.g., Mercier et al. 2013; Rao et al. 2014), and hence, a
constant left-lateral shearing stress of 30 MPa is set on the
southeastern border of the basin (L9) (Fig. 6b).
Due to the impact of collision between the Indian Plate
and the Eurasian Plate, the Liupanshan Thrust-Fold Belt
(namely the Liupan Mountain in Fig. 2) was developed
along the southwestern margin of the Ordos Basin, which
resulted in the transformation of the west-southwestern
margin into a strongly compressive boundary during the
Cenozoic era (Yuan et al. 2007; Li and Li 2008). When the
western boundary of the basin is taken into consideration,
as the shortening rate of the northern section (Tianshuibao
Profile: 30.4%–50.6%) is greater than that of the southern
one (Pengyang Profile: 12.9%–17.9%) (Feng et al. 2013)
(Table 2; Fig. 7), a compressive traction with a uniform
direction and a gradient magnitude from 80 to 55 MPa is
applied on the western boundary (L11), whereas a
compressive traction with a constant magnitude of 80 MPa is
applied on the southwestern margin (L10) (Fig. 6b).
4.3 Theory of fracture prediction Lagrangian formulations are used in ANSYS to simulate the three-dimensional, plane strain deformation, applying
C P T
Shortening rate: 30.41 %-50.62 %
Shortening rate: 12.87 %-17.91 %
8-node isotropic elements to represent each lithological
layer. The mechanical behavior in the elastic domain is
dominated by the generalized Hook’s law. As the Yanchang
Formation is generally less than 3000 m in depth where the
plastic deformation is not obvious and the structural fractures
in the Chang 71 and 72 members are chiefly shearing
fractures based on field measurements and core observations
(Fig. 8), the mechanical behavior follows the elastic model,
which is described by the generalized Hook’s law.
Various methods for fracture prediction have been
proposed in previous literature, such as the conventional logging
method, the stress field method, the principle curvature
method, the geostatistical method, etc. (e.g., Savage et al.
2010; Zahm et al. 2010; Jiu et al. 2013). The two-factor
method, involving the rupture value and the strain energy
density, is used in this paper to predict the distribution of
structural fractures in the Ordos Basin (Ding et al. 1998).
4.3.1 Rupture value Tensile fractures and shearing fractures conform to different criteria. Griffith’s criterion, which is derived from the micro
mechanism, is an effective criterion to predict the
development and the distribution of tensile fractures; however, this
criterion, which in nature is equivalent with the theory of
maximum tensional stress, is only suitable for the tensile
fractures (Griffith 1920). Although tensile fractures are found
in some areas of the Ordos Basin, they are limited to the
contact surfaces of sandstone and mudstone layers, and more
than 95% of structural fractures in the Longdong area are
shearing fractures, whose rupture is controlled by the Mohr–
Coulomb failure criterion (Xie et al. 2008). Therefore, only
Mohr–Coulomb failure criterion is taken into consideration in
this study, which follows the equation (Coulomb 1776):
where [s] represents the critical shearing stress, C
represents the cohesion, rn represents the stress normal to the
shearing fractures and u represents the internal friction
angle (Table 1). Shearing fracture is triggered once the
shearing stress exceeds the critical shearing stress ([s]) in
Eq. (2). rn can be obtained via the maximum principal
stress (r1) and the minimum principal stress (r3) according
to Wang et al. (2004):
rn ¼ ðr1 þ r3Þ=2 ðr1 r3Þ sin u=2 ð3Þ
The shearing stress (sn) can also be obtained via the two
principal stresses according to Wang et al. (2004):
sn ¼ ðr1 r3Þ ð4Þ
Following the Mohr–Coulomb failure criterion, the rock
will break when the shearing stress is equal or greater than
the critical shearing stress in Eq. (2), so the rupture value
(I) is introduced in order to measure the probability of
rock’s rupture according to Ding et al. (1998):
I ¼ sn=½s ð5Þ
The possibility of rock’s failure is very small when the
rupture value (I) is far smaller than 1, whereas the
possibility is relatively larger when the rupture value (I) exceeds
1. The fracture density (f) and the rupture value (I) may
have a positive correlation, so the rupture value (I) is an
effective index for fracture prediction through empirical
formulas established between them.
4.3.2 Strain energy density
It is generally accepted that the rocks with relatively high
strain energy density are more likely to develop structural
fractures than those with a lower one. The strain energy
density, namely the strain energy per unit volume, is
described as follows (Prince and Rhodes 1966):
U ¼ r2X þ r2Y þ r2Z 2vðrX rY þ rY rZ þ rZ rX Þ
þ 2ð1 þ vÞ s2XY þ s2YZ þ s2ZX =2E
where U is the strain energy density, v is Poisson’s ratio,
rX, rY and rZ are the normal stress components in x, y and
z directions, respectively, and sXY, sYZ and sZX are the
shearing stress components in the corresponding directions.
Strain energy density (U) could be utilized to indicate the
Rupture value (I) stands for the possibility of rock
failure, whereas the strain energy density (U) stands for the
developing ability of structural fractures. In this study,
(Zhou et al., 2009b)
40.0-70.0 MPa (Zhou et al., 2009b)
(Wang et al., 2014c) Wuqi
(Zhang et al., 2014)
(Zhou et al., 2009a)
syntheses of the rupture value and the strain energy density,
namely the two-factor method, are applied, in order to
build finite element models for fracture prediction in the
Ordos Basin (Ding et al. 1998).
5 Results and analyses
Because the orientation and the distribution of structural
fractures are the key elements in fracture prediction, the
fracture orientation and the estimated density have been
calculated with the finite element modeling and will be
compared with the observed data in outcrops and cores.
With the two-factor method, modeling results, including
the principal compressive stress orientations, the rupture
values, the strain energy density and the fracture density,
are presented as maps, which can imply the relative
degrees of fracture development in the Longdong area.
5.1 Validity of models
Since reliable numerical models are the basis of further
study on the fracture prediction in the Longdong area, it is
necessary to verify the correctness of the two models
proposed in this paper, including the Late Mesozoic and
the Cenozoic ones, by comparing the results of finite
element modeling with earlier published data.
The calculated displacement directions reveal that the
relative rotation directions in these periods are (1)
anticlockwise from the Early Jurassic to the Cretaceous and (2)
clockwise in the Cenozoic era (Fig. 9). These results are in
good agreement with earlier findings (e.g., Pei et al. 2011;
Li et al. 2014; Yang et al. 2014).
Acoustic Emission (AE) is an important technique in
rock mechanics and experimental seismology, which can
offer rock mechanical parameters, such as the maximum
principal stress magnitudes generated in the geological
history. The maximum principal stress magnitudes of the
Late Mesozoic era after pore-pressure correction range
from 40.0 to 103.9 MPa in the Yanhewan, the Dingbian,
the Dongsheng areas, etc. (Fig. 10a). The Cenozoic stress
magnitudes remain in a limited range of 22.3–58.5 MPa
within the Wuqi-Yanhewan, the Zhenyuan, the Wushengqi
areas, etc. (Zhou et al. 2009a, b; Wang et al. 2014a; Zhang
et al. 2014) (Fig. 10b). The calculated maximum principal
stress magnitudes in the Late Mesozoic and the Cenozoic
are in agreement with the range of stress magnitudes
measured by AE technology (Fig. 10). The
above-mentioned evidence strengthens the validity of our calculated
results in the models.
In addition, earlier published stress orientation data
(Wan 1994; Hou et al. 2010; Sun et al. 2014) are also used
as evidence to substantiate our models (Fig. 11a). These
stress orientation data suggest that the dominant orientation
of maximum principal compressive stress in the Late
Mesozoic is WNW. Current stress field data can also be
utilized to interpret the Cenozoic stress fields because the
basin has been stable during this period (Wang et al. 2008;
Xie et al. 2011; Sun et al. 2014; Yang et al. 2014). Based
on the borehole collapse and multiple strain analyses in the
Yanhewan area, it can be inferred that the dominant
orientation of maximum principle compressive stress in the
Cenozoic is NE (Zhou et al. 2009a). All these orientations
are presented in the stereonets (Fig. 11). The differences
between the calculated orientations of maximum
compressive stress and the measured ones, including the
stress orientations in previous literature (e.g., Wan 1994;
Hou et al. 2010; Sun et al. 2014) and the measured data in
the present study, are in general less than 5 , proving the
reliability of the Late Mesozoic and Cenozoic models
Evidence including the rotation directions, the measured
maximum principal stress magnitudes and the previous
stress data is gathered to prove the authenticity of the two
stress fields in the Late Mesozoic–Cenozoic models, and it
is found that the calculated results are reliable. Despite
slight differences between the calculated and observed
maximum principal compressive stress, the modeling
results of the Late Mesozoic stress fields indicate that the
orientation of the maximum principal compressive stress in
the Ordos Basin is WNW, whereas in the Cenozoic model,
the orientation is NE. Based on the above-mentioned
proofs, the validity of the two models in the Late Mesozoic
and the Cenozoic can be corroborated.
5.2 Maximum principal stress orientations
Tectonic events of different episodes have distinct effects
on the principal stress orientations in the Ordos Basin.
Since there is little difference between the Chang 71 and 72
members except for lithology and layer thickness, the
pattern of principal stress orientation during the same
period is similar in each layer of the Longdong area. Thus,
the Chang 71 member is taken as an example to
demonstrate the distribution of maximum principal compressive
stress in the study area (Fig. 12).
On the basis of paleo-magnetic evidence in earlier
studies, although the Ordos Basin experienced rotation in
different directions from the Late Mesozoic to the
Cenozoic, the rotation angle of the basin is less than 5 in the
Late Mesozoic–Cenozoic eras (e.g., Huang et al. 2005).
Therefore, the present stress data, including fracture trends
and Formation Microscanner Image (FMI) data, can also be
utilized to indicate the stress orientations in the Late
Mesozoic–Cenozoic. From numerical modeling, the
orientations of calculated maximum compressive stress in the
Late Mesozoic are mainly WNW, while those in the
Cenozoic are mainly NE (Zhao et al. 2013, 2016) (Fig. 12).
In outcrops and cores, the observed fractures developed in
the Late Mesozoic are chiefly in NW–EW trends and those
in the Cenozoic are chiefly in NNE–ENE trends (Fig. 8).
Our field measurements also corroborate that the
ENEtrending structural fractures developed later than the
NWtrending ones. Therefore, it can be concluded that the NW
to EW fractures were developed in a Late Mesozoic stress
field, whereas the NNE to ENE ones were developed in a
Cenozoic stress field. Despite tiny differences between the
calculated and the observed data, in general, modeling
results fit well with the dominant orientations of observed
fractures which are obtained from the FMI technology
Structural fractures in the Ordos Basin were developed
in multiple orientations under different stress fields,
primarily in the Late Mesozoic and the Cenozoic episodes,
and this intersection pattern will contribute to wider
opening and better connectivity of the fractures. The
formed fracture networks provide a path for fluid
transmission and enhance the permeability, which will have
notably improved the fractured tight-oil reservoirs in the
Ordos Basin (e.g., Izadi and Elsworth 2014).
5.3 Rupture values
Since the rupture value is an important parameter to
indicate the fracture development in the study area, comparison
between the calculated rupture values and the observed
core fracture density is informative to help analyze the
reliability of the models (Figs. 13, 14).
In the maps of rupture values in the Chang 71 member
during the Late Mesozoic–Cenozoic era, the highest
rupture values are situated in the east and center of the
study area, mainly concentrated in the Qingyang, the
Laocheng and the Zhengning areas (Fig. 13a, b), while
the highest rupture values in the Chang 72 member are
chiefly situated in the mid-southern area, particularly in
the Qingyang-Heshui and the Ningxian areas (Fig. 13c,
0.95 0.98 1.01 1.04 1.07 1.10 1.13 1.16 1.19 1.22
Chang 7 2 in Late Mesozoic
0.95 0.98 1.01 1.04 1.07 1.10 1.13 1.16 1.19 1.22
d). The distribution of sand bodies and the thickness of
sandstone layers have a distinct impact on the distribution
of rupture values within the Longdong area. Both in the
Chang 71 and 72 members, the rupture values are
relatively higher where sand bodies are developed and the
thickness of sandstone layers is relatively larger, due to
the brittleness of sandstones (Fig. 4). The regional stress
fields during different periods also influence the rupture
values, resulting in the Cenozoic rupture values being
smaller than the Late Mesozoic ones. However, the
influence of regional stress fields is not as remarkable as
that of lithology, because regional stress fields determine
only the magnitudes, not the distribution of rupture values
in the Chang 71 and 72 members within the study area
5.4 Strain energy density
Because rocks with higher strain energy density are more
likely to form structural fractures than those with a lower
one, the strain energy density can be used as another
parameter to predict the fracture density.
Similar to the rupture value, there is obvious positive
correlation between the strain energy density and the
thickness of sandstone layers. The strain energy density is
0 50 100 200 km
0.95 0.98 1.01 1.04 1.07 1.10 1.13 1.16 1.19 1.22
Chang 7 2 in Cenozoic
0.95 0.98 1.01 1.04 1.07 1.10 1.13 1.16 1.19 1.22
0 50 100 200 km
4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 5.7 5.9
Chang 7 1 in Late Mesozoic Chang 7 1 in Cenozoic
Table 3 Curve-fitting
relationships of the measured
fracture densities, the calculated
rupture values and the strain
energy densities of Chang 71
and 72 members in the
DM = 3.493 I2 - 0.049 U2 - 6.241 I ? 0.695 U ? 0.270
DC = 3.581 I2 - 0.123 U2 - 7.105 I ? 3.240 U ? 1.054
DM = 48.429 I2 - 0.039 U2 - 100.308 I ? 0.734 U ? 48.585
DC = 22.944 I2 ? 0.450 U2 - 46.876 I - 4.094 U ? 33.241
DM (m-1) and DC (m-1) represent the measured fracture densities in cores of the Late Mesozoic and the
Cenozoic periods, respectively. I and U denote the calculated rupture values and the strain energy densities
(104 J/m3), respectively
higher where the sand bodies are developed as a whole
(Figs. 4, 14). Although the Cenozoic stress field of the
Ordos Basin is strikingly different from the Late Mesozoic
one, the impact of regional stress is mainly limited to the
magnitudes, not the distribution of strain energy density in
the Longdong area. The distribution of strain energy
density in the Late Mesozoic and the Cenozoic periods is
similar, but the Late Mesozoic strain energy density is
larger than the Cenozoic one both in the Chang 71 and 72
members, implying that the strain energy density is more
influenced by the movement in the Late Mesozoic than that
in the Cenozoic (Fig. 14).
5.5 Predicted fracture distribution
In order to predict the fracture distribution in the Yanchang
Formation within the Longdong area, connection between
the calculated and the measured fracture density in cores
must be established to study their relationship. In this
paper, the two-factor method is utilized to compare the
calculated data (including the rupture value and the strain
energy density) and the measured fracture density (Ding
et al. 1998). Since structural fractures in the Ordos Basin
were chiefly developed during two stages of stress fields,
namely the Late Mesozoic and the Cenozoic ones, two
episodes of fractures should be fitted separately and then be
added up by weight.
By multiple regression analyses, bi-quadratic
relationships between the rupture values, the strain energy
density and the measured fracture density in the Chang
71 and 72 members of different episodes have been built
and the empirical formulas are shown in Table 3.
Correlation coefficients in all curve-fitting relationships are
larger than 0.87, which means that there is a significant
correlation between the calculated and the measured
To further illustrate the reliability of our models, error
analyses are carried out as follows. Both the absolute error
and the relative error were applied to reflect the accuracy of
fracture prediction. Absolute error is calculated by:
And relative error can be described as follows:
D denotes the absolute error and e denotes the relative
error. DP and DM represent the predicted and the measured
fracture densities, respectively. Generally, when e is less
than 50%, we can consider that the predicted data match
the measured ones and the modeling results are reliable to a
The differences between the measured and the predicted
fracture densities are shown in Tables 4 and 5. For most of
the wells in the Chang 71 member, the predicted and the
measured data match quite well. In the 54 measured wells,
only 2 wells exceed 0.05 m-1 in absolute errors and 3
wells exceed 50% in relative errors (Table 4). The
differences between them may be caused by the stress
concentration in some areas, such as Well Z47 and Z78, where
numerous fractures are found. As for the Chang 72
member, predicted data of only 8 wells in the 39 measured
wells are more than 0.05 m-1 in absolute errors, and data
of only 5 wells are more than 50% in relative errors
(Table 5). Most of these wells are with extraordinarily high
fracture density, which results in large errors between the
predicted and the measured fracture densities. Some large
errors may be caused by non-structural factors, such as
various sedimentary phenomena. Cross bedding and
lenticular bedding appeared widely in Well Ze77, etc., which
may lead to the difference between the predicted and
measured data. Despite these differences, the tendency of
predicted fracture distribution is still in accordance with the
measured one. In short, the errors between the predicted
and the measured fracture densities are within
acceptable limits, implying that the modeling results are
suitable for the fracture prediction in the Yanchang Formation
of the Ordos Basin.
As is shown in the maps of maximum principal
compressive stress orientations in the Chang 71 and 72 members in
the Longdong area, the dominant orientations of the Late
Mesozoic fractures are NW–EW (Fig. 12a) and those of
the Cenozoic ones are NNE–ENE (Fig. 12b) which are
consistent with the regional stress fields of the Ordos Basin
in the corresponding periods (e.g., Zhang et al. 2003). In
the maps of predicted fracture density in different periods,
the average density of the Cenozoic fractures is larger than
that of the Late Mesozoic ones (Fig. 15). By comparison
between the distribution maps of predicted total fracture
densities in the Chang 71 and 72 members within the study
area (Fig. 16), the predicted fracture density in each
member is alike as a whole; however, their fracture
distributions are significantly distinct. In the Chang 71
member, the maximum fracture density is located in the center
and the east of the Longdong area (Fig. 16a), while in the
Chang 72 member, the maximum density is situated in the
southern-central section of the study area (Fig. 16b).
In addition, by comparing the predicted fracture density
with the distribution of sand bodies, their similarity reveals
that the lithology is a key factor in controlling the fracture
distribution in the Ordos Basin. Structural fractures are
more likely to be developed in the sandstones rather than in
the mudstones. Where thicker sandstone layers are
developed, the fracture density is relatively higher than other
areas (Figs. 4, 16). However, there is still a difference
between the predicted fracture distribution and the outline
of sand bodies, indicating that the regional stress field also
Chang 7 1 in Late Mesozoic
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18
Chang 7 1 in Cenozoic
0 50 100 200 km
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18
Chang 7 2 in Cenozoic
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18
plays a role in the fracture development, even though its
influence is limited compared with the lithology and the
In brief, the stress fields determine the overall fracture
orientations, and the lithology distribution and the
thickness of sandstone layers in the study area play a
predominant role in the distribution of predicted fracture density.
Some potential factors which are not covered in these
numerical models may restrict the accuracy of predicted
The complicated heterogeneity of each layer;
The extreme stress in some areas;
The interaction between the two episodes of structural
The influence of deep paleo-faults.
Since the modeling is on a relatively large-scale while the
outline of sand bodies is depicted in considerable detail, the
modeling results, including the rupture values and the strain
energy density, can still be used to guide further exploration
in spite of the four above-mentioned restrictions.
Meanwhile, the qualitative fracture prediction obtained from the
numerical modeling may also be applicable. These results
act as a reference for future regional-scale petroleum
exploration, while the method of fracture prediction,
including the two-factor method and the empirical formulas
can be used at well scale. Structural fractures play an
important role in reconstructing the tight clastic reservoirs,
especially in their permeability (Re´da 2013).
The controlling factors of fracture development are
complex owing to the complicated geological background.
Fault systems can be a vital factor in developing fractures
where tectonic movements are strong such as the Kuqa
Depression of the northern Tarim Basin in the northwestern
China (Ju et al. 2014b) and the Upper Rhine Graben in
France and Germany (Johanna et al. 2015); flow may
notably promote fracture development where fluid flow or
lava flow appears (e.g., Agosta et al. 2010). However, in
the Ordos Basin, where the tectonic events are rather weak
and the dips of the Mesozoic–Cenozoic strata are less than
3 , the lithology and the layer thickness are the dominant
factors in governing the distribution of fracture density.
The relationship between the lithology and the fracture
density is still obscure, but it may be related to the
difference of rock physical parameters (Table 1) according to
previous study (e.g., Zeng et al. 2008). The different grain
Chang 7 1
0 50 100
Ze97 Z57 X25Z978 Z87 Z47
X2X62163 QXX2i37n33gchZe7n9Zg1Z524Z200 LaoZc1h8T6e1n5Tg2
X19B5an1X21H40eZs1h7u2i Z1Z21448 ZN237Z06233
0.00 0.04 0.08 0.12 0.16 0.20 0.24 0.28 0.32 0.36
Chang 7 2
0.00 0.04 0.08 0.12 0.16 0.20 0.24 0.28 0.32 0.36
Fig. 16 Distribution of predicted total fracture density (m-1) in a the Chang 71 and b Chang 72 members within the Longdong area. Black solid
dots represent the measured wells in the study area
sizes in various clastic rocks may be the micro-mechanism
that causes the distribution of fracture density in the Ordos
Basin (Zhao et al. 2013; Ju et al. 2015).
The predicted fracture distribution provides a clear view of
the fracture concentration and fracture development.
Several primary conclusions can be drawn from the modeling
A finite element modeling technique, applying the
twofactor method, is suitable for the fracture prediction of
the Ordos Basin, based on comparison between the
calculated and the measured fracture densities of the
Chang 71 and 72 members in the Longdong area.
Two episodes of structural fractures have been
developed since the Late Triassic: The dominant
orientations of the Late Mesozoic fractures in the Yanchang
Formation are NW–EW, whereas those of the
Cenozoic fractures are NNE–ENE, both of which are in
agreement with the modeling results.
Structural fractures in the Ordos Basin are controlled
by the regional stress fields, and the lithology and the
layer thickness have a significant impact on the
distribution of structural fractures, because the stress
distribution will be affected by the inhomogeneity of
lithology and layer thickness. This conclusion is shown
in the similarity between the maps of predicted fracture
density and observed sand bodies in the Yanchang
Formation within the study area.
The average fracture density is close in the Chang 71
and 72 members, but there are obvious differences in
their fracture distributions. In the Chang 71 member,
the maximum fracture density is concentrated in the
center and the east of the Longdong area, particularly
in the Qingyang, the Laocheng and the Zhengning
areas (up to 1.5 m-1), while in the Chang 72 member,
the maximum value is located in the central and
southern part of the area.
The modeling results and the predicted fracture density
can be utilized to guide future regional exploration,
and the method of fracture prediction, namely the
twofactor method, can be referred for further study of the
Acknowledgements The authors would like to thank Drs. Wei Ju,
Peng Zhang, Yan Zhan and Xuan Yu for their help in the core
observation and modeling. This research was funded by the National
Natural Science Foundations of China (Grant Nos. 40772121 and
41530207), State Key Projects of Petroleum (Nos.
2008ZX05029001, 2011ZX05029-001 and 2014A0213) and Research and
Development Foundations of the Huaneng Clean Energy Research Institute
Open Access This article is distributed under the terms of the
Creative Commons Attribution 4.0 International License (http://crea
tivecommons.org/licenses/by/4.0/), which permits unrestricted use,
distribution, and reproduction in any medium, provided you give
appropriate credit to the original author(s) and the source, provide a
link to the Creative Commons license, and indicate if changes were
Agosta F , Alessandroni M , Antonellini M , et al. From fractures to flow: a field-based quantitative analysis of an outcropping carbonate reservoir . Tectonophysics . 2010 ; 490 ( 3-4 ): 197 - 213 . doi:10.1016/j.tecto. 2010 .05.005.
Bao XW , Song XD , Xu MJ , et al. Crust and upper mantle structure of the North China Craton and the NE Tibetan Plateau and its tectonic implications . Earth Planet Sci Lett . 2013 ; 369 - 370 : 129 - 37 . doi:10.1016/j.epsl. 2013 .03.015.
Coulomb CA . Essai sur une application des regles des maximas et minmas a quelques problemes de statique relatifs a l'architecture, vol. 7. Divers Savanta: Mem. Acad. Roy. Pres. 1776.
Darby BJ , Ritts BD . Mesozoic contractional deformation in the middle of the Asian tectonic collage the intraplate Western Ordos fold thrust belt , China. Earth Planet Sci Lett . 2002 ; 205 ( 1-2 ): 13 - 24 . doi:10.1016/ S0012-821X(02)01026-9.
Ding ZY , Qian XL , Huo H , et al. A new method for quantitative prediction of tectonic fractures-the two-factor method. Oil Gas Geol . 1998 ; 19 ( 1 ): 1 - 8 (in Chinese).
Du JH , Liu H , Ma DS , et al. Discussion on effective development techniques for continental tight oil in China . Pet Explor Dev . 2014 ; 41 ( 2 ): 217 - 24 . doi:10.1016/S1876-3804(14)60025- 2 .
Duan Y , Wang CY , Zheng CY , et al. Geochemical study of crude oils from the Xifeng Oilfield of the Ordos Basin , China . J Asian Earth Sci . 2008 ; 31 : 341 - 56 . doi:10.1016/j.jseaes. 2007 .05.003.
Ezulike DO , Dehghanpour H. A model for simultaneous matrix depletion into natural and hydraulic fracture networks . J Nat Gas Sci Eng . 2014 ; 16 : 57 - 69 . doi:10.1016/j.jngse. 2013 .11.004.
Faure M , Lin W , Chen Y. Is the Jurassic (Mesozoic) intraplate tectonics of North China due to westward indentation of North China block? Terra Nova . 2012 ; 24 ( 6 ): 456 - 66 . doi:10.1111/ter. 12002.
Feng JP , Ouyang ZY , Huang ZL . The application of balance geological section technology in the mid-south section of the western margin of Ordos Basin . Geotecton Metallog . 2013 ; 37 ( 3 ): 393 -7 (in Chinese).
Fournier M , Jolivet L , Davy P , et al. Back-arc extension and collision: an experimental approach to the tectonics of Asia . Geophys J Int . 2004 ; 157 : 871 - 89 . doi:10.1111/j.1365-246X.2004.02223.x.
Gilder SA , Gomez J , Chen Y , et al. A new paleogeographic configuration of the Eurasian landmass resolves a paleomagnetic paradox of the Tarim Basin (China) . Tectonics . 2008 ; 27 ( 1 ): 1256 . doi:10.1029/2007TC002155.
Glukhmanchuk ED , Vasilevskiy AN. Description of fracture zones based on the structural inhomogeneity of the reflector deformation field . Russ Geol Geophys . 2013 ; 54 ( 1 ): 82 - 6 . doi:10.1016/j. rgg. 2012 .12.007.
Golf-Racht TDV . Fundamentals of fractured reservoir engineering . Amsterdam: Elsevier; 1982 . p. 1 - 12 .
Griffith AA . Phenomena of rupture and flow in solids . Fish Manage Ecol . 1920 ; 16 ( 2 ): 130 - 8 . doi:10.1098/rsta.1921.0006.
Guo YR , Liu JB , Yang H , et al. Hydrocarbon accumulation mechanism of low permeable tight lithologic oil fields in the Yanchang Formation , Ordos Basin , China. Pet Explor Dev . 2012 ; 39 ( 4 ): 447 - 56 . doi:10.1016/S1876-3804(12)60061- 5 .
Hou GT , Hari KR . Mesozoic-Cenozoic extension of the Bohai Sea: contribution to the destruction of North China Craton . Front Earth Sci . 2014 ; 8 ( 2 ): 202 - 15 . doi:10.1007/s11707- 014 - 0413 -3.
Hou GT , Wang YX , Hari KR . The Late Triassic and Late Jurassic stress fields and tectonic transmission of North China Craton . J Geodyn . 2010 ; 50 ( 3-4 ): 318 - 24 . doi:10.1016/j.jog. 2009 .11.007.
Huang BC , Shi RP , Wang YC , et al. Palaeomagnetic investigation on early-middle Triassic sediments of the North China block: a new early Triassic palaeopole and its tectonic implications . Geophys J Int . 2005 ; 160 : 101 - 13 . doi:10.1111/j.1365-246X.2005.02496.x.
Izadi G , Elsworth D. Reservoir stimulation and induced seismicity: roles of fluid pressure and thermal transients on reactivated fractured networks . Geothermics . 2014 ; 51 : 368 - 79 . doi:10.1016/ j.geothermics. 2014 .01.014.
Jarosinski M , Beekman F , Matenco L , et al. Mechanics of basin inversion: finite element modeling of the Pannonian Basin system . Tectonophysics . 2011 ; 502 ( 1-2 ): 121 - 45 . doi:10.1016/j. tecto. 2009 .09.015.
Jia CZ , Zhang YF , Zhao X. Prospects of and challenges to natural gas industry development in China . Nat Gas Ind B . 2014 ; 1 ( 1 ): 1 - 13 . doi:10.1016/j.ngib. 2014 .10.001.
Jiu K , Ding WL , Huang WH , et al. Simulation of paleotectonic stress fields within Paleogene shale reservoirs and prediction of favorable zones for fracture development within the Zhanhua Depression, Bohai Bay Basin, east China . J Pet Sci Eng . 2013 ; 110 : 119 - 31 . doi:10.1016/j.petrol. 2013 .09.002.
Johanna FB , Silke M , Sonja LP . Architecture, fracture system, mechanical properties and permeability structure of a fault zone in Lower Triassic sandstone , Upper Rhine Graben. Tectonophysics . 2015 ; 647 - 648 : 132 - 45 . doi:10.1016/j.tecto. 2015 .02. 014.
Ju W , Hou GT , Hari KR . Mechanics of mafic dyke swarms in the Deccan Large Igneous Province: palaeostress field modeling . J Geodyn . 2013 ; 66 : 79 - 91 . doi:10.1016/j.jog. 2013 .02.002.
Ju W , Hou GT , Feng SB , et al. Quantitative prediction of the Yanchang Formation Chang 63 reservoir tectonic fracture in the Qingcheng-Heshui area, Ordos Basin . Earth Sci Front . 2014a ; 21 ( 6 ): 310 - 20 (in Chinese).
Ju W , Hou GT , Zhang B. Insights into the damage zones in fault-bend folds from geomechanical models and field data . Tectonophysics. 2014b; 610 : 182 - 94 . doi:10.1016/j.tecto. 2013 .11.022.
Ju W , Sun WF , Hou GT . Insights into the tectonic fractures in the Yanchang Formation interbedded sandstone-mudstone of the Ordos Basin based on core data and geomechanical models . Acta Geol Sin (Engl Ed) . 2015 ; 89 ( 6 ): 1986 - 97 . doi:10.1111/ 1755 - 6724 .12612.
Kusky TM , Li JH . Paleoproterozoic tectonic evolution of the North China Craton . J Asian Earth Sci . 2009 ; 22 ( 4 ): 383 - 97 . doi:10. 1016/S1367-9120(03)00071- 3 .
Kusky TM . Geophysical and geological tests of tectonic models of the North China Craton . Gondwana Res . 2011 ; 20 ( 1 ): 26 - 35 . doi:10. 1016/j.gr. 2011 .01.004.
Li HB , Guo HK , Yang ZM , et al. Tight oil occurrence space of Triassic Chang 7 member in Northern Shaanxi Area , Ordos Basin , NW China. Pet Explor Dev . 2015 ; 42 ( 3 ): 434 - 8 . doi:10. 1016/S1876-3804(15)30036- 7 .
Li RX , Li YZ . Tectonic evolution of the western margin of the Ordos Basin (Central China) . Russ Geol Geophys . 2008 ; 49 ( 1 ): 23 - 7 . doi:10.1016/j.rgg. 2007 .12.002.
Li YH , Wang QL , Cui DX , et al. One feature of the activated southern Ordos Block: the Ziwuling small earthquake cluster . Geod Geodyn . 2014 ; 5 ( 3 ): 16 - 22 . doi:10.3724/SP.J. 1246 . 2014 .03016.
Liu MJ , Mooney WD , Li SL , et al. Crustal structure of the northeastern margin of the Tibetan plateau from the SongpanGanzi terrane to the Ordos basin . Tectonophysics . 2006 ; 420 ( 1-2 ): 253 - 66 . doi:10.1016/j.tecto. 2006 .01.025.
Liu SF , Li WP , Wang K , et al. Late Mesozoic development of the southern Qinling-Dabieshan foreland fold-thrust belt, Central China, and its role in continent-continent collision . Tectonophysics . 2015 ; 644 - 645 ( 3 ): 220 - 34 . doi:10.1016/j.tecto. 2015 .01.015.
Malaspina N , Hermann J , Scambelluri M , et al. Multistage metasomatism in ultrahigh-pressure mafic rocks from the North Dabie Complex (China) . Lithos . 2006 ; 90 ( 1-2 ): 19 - 42 . doi:10.1016/j. lithos. 2006 .01.002.
Menzies M , Xu YG , Zhang HF , et al. Integration of geology, geophysics and geochemistry: a key to understanding the North China Craton . Lithos. 2007 ; 96 ( 1-2 ): 1 - 21 . doi:10.1016/j.lithos. 2006 .09.008.
Mercier JL , Vergely P , Zhang YQ , et al. Structural records of the Late Cretaceous-Cenozoic extension in Eastern China and the kinematics of the Southern Tan-Lu and Qinling Fault Zone (Anhui and Shaanxi provinces , PR China). Tectonophysics . 2013 ; 582 : 50 - 75 . doi:10.1016/j.tecto. 2012 .09.015.
Nutman AP , Wan YS , Du LL , et al. Multistage late Neoarchaean crustal evolution of the North China Craton, eastern Hebei . Precambr Res . 2011 ; 189 ( 1-2 ): 43 - 65 . doi:10.1016/j.precamres. 2011 .04.005.
Pearce MA , Jones RR , Smith SAF , et al. Quantification of fold curvature and fracturing using terrestrial laser scanning . AAPG Bull . 2011 ; 57 : 2367 - 85 . doi:10.1306/11051010026.
Pei JL , Sun ZM , Liu J , et al. A paleomagnetic study from the Late Jurassic volcanics (155 Ma), North China: implications for the width of Mongol-Okhotsk Ocean . Tectonophysics. 2011 ; 510 ( 3-4 ): 370 - 80 . doi:10.1016/j.tecto. 2011 .08.008.
Prince NJ , Rhodes FH . Fault and joint development in brittle and semi-brittle rock . London: Pergamon Press ; 1966 . p. 110 - 64 . doi:10.1016/B978-0- 08 - 011275 -6. 50009-4 .
Rao G , Lin AM , Yan B , et al. Tectonic activity and structural features of active intracontinental normal faults in the Weihe Graben, central China . Tectonophysics. 2014 ; 636 ( 1 ): 270 - 85 . doi:10. 1016/j.tecto. 2014 .08.019.
Re´da SZ. Fracture density estimation from core and conventional well logs data using artificial neural networks: the CambroOrdovician reservoir of Mesdar oil field, Algeria . J Afr Earth Sci . 2013 ; 83 : 55 - 73 . doi:10.1016/j.jafrearsci. 2013 .03.003.
Ren JH , Zhang L , Ezekiel J , et al. Reservoir characteristics and productivity analysis of tight sand gas in Upper Paleozoic Ordos Basin China . J Nat Gas Sci Eng . 2014 ; 19 : 244 - 50 . doi:10.1016/j. jngse. 2014 .05.014.
Santosh M , Liu SJ , Tsunogae T , et al. Paleoproterozoic ultrahightemperature granulites in the North China Craton: implications for tectonic models on extreme crustal metamorphism . Precambr Res . 2012 ; 222 - 223 : 77 - 106 . doi:10.1016/j.precamres. 2011 .05. 003.
Savage MH , Shackleton JR , Cooke LM , et al. Insights into fold growth using fold-related joint patterns and mechanical stratigraphy . J Struct Geol . 2010 ; 32 ( 10 ): 1466 - 76 . doi:10.1016/j.jsg. 2010 .09.004.
Schellart WP , Lister GS . The role of the East Asian active margin in widespread extensional and strike-slip deformation in East Asia . J Geol Soc . 2005 ; 162 : 959 - 72 .
Smart KJ , Ferrill DA , Morris AP . Impact of interlayer slip on fracture prediction from geomechanical models of fault-related folds . AAPG Bull . 2009 ; 93 ( 11 ): 1447 - 58 . doi:10.1306/05110909034.
Song SG , Niu YL , Su L , et al. Tectonics of the North Qilian orogen, NW China. Gondwana Res . 2013 ; 23 ( 4 ): 1378 - 401 . doi:10.1016/ j.gr. 2012 .02.004.
Sun YJ , Dong SW , Zhang H , et al. Numerical investigation of the geodynamic mechanism for the late Jurassic deformation of the Ordos Block and surrounding orogenic belts . J Asian Earth Sci . 2014 ; 114 : 623 - 33 . doi:10.1016/j.jseaes. 2014 .08.033.
Tang X , Zhang JC , Shan YS , et al. Upper Paleozoic coal measures and unconventional natural gas systems of Ordos Basin , China. Geosci Front . 2012 ; 3 ( 6 ): 863 - 73 . doi:10.1016/j.gsf. 2011 .11.018.
Tong HM , Yin A. Reactivation tendency analysis: a theory for predicting the temporal evolution of preexisting weakness under uniform stress state . Tectonophysics . 2011 ; 503 : 195 - 200 . doi:10. 1016/j.tecto. 2011 .02.012.
Vela´zquez SM , Vicente G , Elorza FJ . Intraplate stress state from finite element modeling: the southern border of the Spanish Central System . Tectonophysics. 2009 ; 473 ( 3-4 ): 417 - 27 . doi:10.1016/j. tecto. 2009 .03.024.
Wan TF . Intraplate deformation, tectonic stress field and their application for Eastern China in Meso-Cenozoic . Beijing: Geological Publishing House ; 1994 . p. 230 .
Wan TF , Zeng HL . The distinctive characteristics of the Sino-Korean and the Yangtze plates . J Asian Earth Sci . 2002 ; 20 ( 8 ): 881 - 8 . doi:10.1016/S1367-9120(01)00068- 2 .
Wang J , Ye ZR , He JK . Three-dimensional mechanical modeling of large-scale crustal deformation in China constrained by the GPS velocity field . Tectonophysics . 2008 ; 446 ( 1-4 ): 51 - 60 . doi:10. 1016/j.tecto. 2007 .11.006.
Wang LJ , Wang HC , Wang W , et al. Relation among three dimensional tectonic stress field, fracture and migration of oil and gas in oil field . Chin J Rock Mech Eng . 2004 ; 23 ( 23 ): 4052 -7 (in Chinese).
Wang CL , Zhou W , Li HB , et al. Characteristics and distribution of multiphase fractures in Yanchang Formation of Zhenjing Block in Ordos Basin, China . J Chengdu Univ Technol (Sci Technol Ed). 2014a; 41 ( 5 ): 596 - 603 (in Chinese).
Wang CY , Sandvol E , Zhu L , et al. Lateral variation of crustal structure in the Ordos block and surrounding regions, North China, and its tectonic implications . Earth Planet Sci Lett. 2014b; 387 : 198 - 211 . doi:10.1016/j.epsl. 2013 .11.033.
Wang W , Wang DJ , Zhao B , et al. Horizontal crustal deformation in Chinese Mainland analyzed by CMONOC GPS data from 2009-2013. Geod Geodyn . 2014c ; 5 ( 3 ): 41 - 5 . doi:10.3724/SP.J. 1246 . 2014 .03041.
Xie FR , Zhang HY , Cui XF , et al. The modern tectonic stress field and strong earthquakes in China . Recent Dev World Seismol. 2011 ; 1 : 4 - 12 (in Chinese).
Xie HP , Ju Y , Li LY , et al. Energy mechanism of deformation and failure of rock masses . Chin J Rock Mech Eng . 2008 ; 27 ( 9 ): 1729 - 40 (in Chinese).
Yang H , Deng XQ. Deposition of Yanchang Formation deep-water sandstone under the control of tectonic events in the Ordos Basin . Pet Explor Dev . 2013 ; 40 ( 5 ): 549 - 57 . doi:10.1016/S1876- 3804(13)60072- 5 .
Yang MH , Li L , Zhou J , et al. Segmentation and inversion of the Hangjinqi fault zone, the northern Ordos basin (North China) . J Asian Earth Sci . 2013 ; 70 - 71 : 64 - 78 . doi:10.1016/j.jseaes. 2013 . 03.004.
Yang SX , Huang LY , Xie FR , et al. Quantitative analysis of the shallow crustal tectonic stress field in China mainland based on in situ stress data . J Asian Earth Sci . 2014 ; 85 : 154 - 62 . doi:10. 1016/j.jseaes. 2014 .01.022.
Yao JL , Deng XQ , Zhao YD , et al. Characteristics of tight oil in Triassic Yanchang Formation , Ordos Basin . Pet Explor Dev . 2013 ; 40 ( 2 ): 161 - 9 . doi:10.1016/S1876-3804(13)60019- 1 .
Yuan YS , Hu SB , Wang HJ , et al. Meso-Cenozoic tectonothermal evolution of Ordos basin, central China: insights from newly acquired vitrinite reflectance data and a revision of existing paleothermal indicator data . J Geodyn . 2007 ; 44 ( 1-2 ): 33 - 46 . doi:10.1016/j.jog. 2006 .12.002.
Zahm KC , Zahm CL , Bellian AJ . Integrated fracture prediction using sequence stratigraphy within a carbonate fault damage zone , Texas, USA. J Struct Geol . 2010 ; 32 ( 9 ): 1363 - 74 . doi:10.1016/j. jsg. 2009 .05.012.
Zeng LB , Zhao JY , Zhu SX , et al. Impact of rock anisotropy on fracture development. Prog Nat Sci . 2008 ; 18 : 1403 - 8 . doi:10. 1016/j.pnsc. 2008 .05.016.
Zhang C , Zhou W , Xie RC , et al. Fracture prediction of the Ma 51-2 tight carbonate reservoir in gentle structure zone , Daniudi Gas Field. J Northeast Pet Univ . 2014 ; 38 ( 3 ): 9 - 17 (in Chinese).
Zhang YQ , Liao CZ , Shi W , et al. Jurassic deformation in and around the Ordos Basin , North China. Earth Sci Front . 2007 ; 14 ( 2 ): 182 - 96 . doi:10.1016/S1872-5791(07)60016- 5 .
Zhang YQ , Ma YS , Yang N , et al. Cenozoic extensional stress evolution in North China . J Geodyn. 2003 ; 36 ( 5 ): 591 - 613 . doi:10.1016/j.jog. 2003 .08.001.
Zhao GC , Sun M , Wilde SA , et al. Late Archean to Paleoproterozoic evolution of the North China Craton: key issues revisited . Precambr Res . 2005 ; 136 ( 2 ): 177 - 202 . doi:10.1016/j.precamres. 2004 .10.002.
Zhao WT , Hou GT , Hari KR . Two episodes of structural fractures and their stress field modeling in the Ordos Block, northern China . J Geodyn . 2016 ; 97 : 7 - 21 . doi:10.1016/j.jog. 2016 .02.005.
Zhao WT , Hou GT , Sun XW , et al. Influence of layer thickness and lithology on the fracture growth of clastic rock in east Kuqa . Geotecton Metallog . 2013 ; 4 : 603 - 10 (in Chinese).
Zheng RG , Wu TR , Zhang W , et al. Late Paleozoic subduction system in the northern margin of the Alxa block, Altaids: geochronological and geochemical evidences from ophiolites . Gondwana Res . 2014 ; 25 ( 2 ): 842 - 58 . doi:10.1016/j.gr. 2013 .05.011.
Zhou XG , Zhang LY , Huang CJ , et al. Paleostress judgement of tectonic fractures in Chang 61 low permeable reservoir in Yanhewan area, Ordos Basin in main forming period . Geoscience . 2009a; 23 ( 5 ): 843 - 51 (in Chinese).
Zhou XG , Zhang LY , Qu XF , et al. Characteristics and quantitative prediction of distribution laws of tectonic fractures of lowpermeability reservoirs in Yanhewan area . Acta Pet Sin . 2009b; 30 ( 2 ): 195 - 200 (in Chinese).
Zhu SB , Shi YL . Estimation of GPS strain rate and its error analysis in the Chinese continent . J Asian Earth Sci . 2011 ; 40 ( 1 ): 351 - 62 . doi:10.1016/j.jseaes. 2010 .06.007.