Microscopic mechanism of water flooding
in tight reservoirs
Cite as: AIP Advances 10, 015042 (2020); https://doi.org/10.1063/1.5131775
Submitted: 17 October 2019 • Accepted: 16 December 2019 • Published Online: 17 January 2020
Haibo Li (李海波), Hekun Guo (郭和坤), Zhengming Yang (杨正明), et al.
COLLECTIONS
Paper published as part of the special topic on Fluids and Plasmas
ARTICLES YOU MAY BE INTERESTED IN
Evaluation of oil production potential in fractured porous media
Physics of Fluids 31, 052104 (2019); https://doi.org/10.1063/1.5089157
Spatially multi-scale artificial neural network model for large eddy simulation of
compressible isotropic turbulence
AIP Advances 10, 015044 (2020); https://doi.org/10.1063/1.5138681
Effects of variable density on oscillatory flow around a non-conducting horizontal circular
cylinder
AIP Advances 10, 015020 (2020); https://doi.org/10.1063/1.5127967
AIP Advances 10, 015042 (2020); https://doi.org/10.1063/1.5131775
© 2020 Author(s).
10, 015042
AIP Advances
ARTICLE
scitation.org/journal/adv
Microscopic mechanism of water flooding in tight
reservoirs
Cite as: AIP Advances 10, 015042 (2020); doi: 10.1063/1.5131775
Submitted: 17 October 2019 • Accepted: 16 December 2019 •
Published Online: 17 January 2020
Haibo Li (李海波),1,2,a)
Hekun Guo (郭和坤),1,2 Zhengming Yang (杨正明),1,2 Lixin Meng (孟立新),3
4
Qingqiao Zeng (曾庆桥), Hongcheng Xu (胥洪成),2 Hewen Zhang (张合文),2 Yuping Sun (孙玉平),2
Haibing Lu (卢海兵),2 Xuewu Wang (王学武),5 and Huan Meng (孟焕)2
AFFILIATIONS
1
Institute of Flow and Fluid Mechanics, Chinese Academy of Sciences, Langfang 065007, Hebei Province,
People’s Republic of China
2
Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083, People’s Republic of China
3
Research Institute of Exploration and Development of PetroChina Dagang Oilfield Company, Tianjin 300280,
People’s Republic of China
4
Research Institute of Exploration and Development of PetroChina Huabei Oilfield Company, Renqiu 062552,
Hebei Province, People’s Republic of China
5
Shengli College China University of Petroleum, Shengli 257061, Shandong Province, People’s Republic of China
a)
Author to whom correspondence should be addressed: lihaibo05@petrochina.com.cn
ABSTRACT
Based on cores from tight oil reservoirs in Ordos Basin, water flooding experiments with both low and high displacement pressures were
carried out. Combined with NMR, quantitative analysis approaches for produced oil under different microscopic effects were established
for quantitative research of the microscopic mechanism of water flooding in tight reservoirs. The research indicated that under low displacement pressure, oil recovery mechanisms of hydrophilic cores mainly include displacement, imbibition, and denudation, and those of
wetting cores mainly include displacement and imbibition. After increasing the displacement pressure, both hydrophilic and neutral wetting
cores have a certain increase in oil recovery. The common point is that both oil controlled by small throats and remaining oil droplets
controlled by traps in large pores have been activated, while the discrepancy is that the oil film of the neutral wetting core boundary
layer becomes thinner, which improves oil recovery ratio, and these mechanisms have less effect on hydrophilic cores. The amount of
oil produced by each type of oil recovery mode was quantitatively analyzed. Percentages of produced oil in hydrophilic cores by flooding and imbibition and denudation are 15% and 12%, respectively, which are the main oil recovery mechanisms; percentages of produced
oil in neutral wetting cores by displacement and imbibition are 25% and 2%, respectively, with displacement as the main oil recovery
mechanism. After increasing the displacement pressure, oil produced by hydrophilic and neutral wetting cores increased by 6% and 9%,
respectively, indicating that with increasing the displacement pressure, a part of the boundary layer of oil could be produced in neutral wetting
cores.
© 2020 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license
(http://creativecommons.org/licenses/by/4.0/). https://doi.org/10.1063/1.5131775., s
I. INTRODUCTION
Tight oil, whose strategic significance has become increasingly
prominent due to its effective development in domestic China, is
widely distributed (Jia et al., 2012; Zou et al., 2012; Wu et al.,
2016; Zhang et al., 2016; 2018, Yang et al., 2013; Guo et al., 2016;
Wu et al., 2015; and Dejam et al., 2018). Tight oil reservoirs have
AIP Advances 10, 015042 (2020); doi: 10.1063/1.5131775
© Author(s) 2020
complex pore structures, poor physical characteristics (Yao et al.,
2013; Bai et al., 2013; Dejam et al., 2017a; 2017b; Zhao et al., 2015;
Ghanizadeh et al., 2015; and Yang et al., 2012), small pores in crude
oil occurrence, and large fluid seepage resistance, leading to difficulty in establishing an effective displacement system (Li et al., 2016;
2006; Zhao et al., 2015; Ghanizadeh et al., 2015; Wang et al., 2015;
2009; Yang et al., 2014; 2007; 2009; Yu et al., 2012; Loucks et al.,
10, 015042-1
AIP Advances
ARTICLE
2009; Law and Curtis, 2002; Mullen, 2010; Zhong et al., 2012; Yao
et al., 2013; and Quan et al., 2011). A microseepage mechanism of
oil and water is the theoretical basis for water flooding recovery in
oilfields. Understanding the micromobility laws and driving mechanisms of water-flooding in tight reservoirs is of great significance for
the rational and effective development of reservoirs. Some scholars
have carried out a lot of research on the micromechanism of waterflooding in low-permeability reservoirs. Xueling et al. (2018) studied
liquid flow in nano- or microsized circular tubes. Wei et al. (2014)
analyzed influencing factors on water-oil displacement. Suleimanov
et al. (2017) studied fluid properties near to the phase transition
point. Datta et al. (2014) studied the fluid flow mechanism from a
three-dimensional porous medium. De Paoli et al. (2016) and Chen
and Yan (2015) studied the flow behavior of fluids in heterogeneous
porous media. Qu et al. (2018) believed that the static imbibition
recovery factor is closely related to the reciprocal of the irreducible
number. The optimal value of the reciprocal of irreducible is about 1.
Jianming et al. (2019) studied the impact of the energy supplement
from the unreturned fluid during volume fracturing in horizontal
wells on the development effect. Qu et al. (2017) explored the influence of fractures on the seepage characteristics of dense rock water
flooding. Wei et al. (2016) studied the effect of reservoir properties
on imbibition recovery. Gu et al. (2017) revealed the microscopic
influence mechanism of the permeability of tight reservoirs on the
efficiency of oil imbibition recovery. Pan et al. (2016) adopted the
combination of nuclear magnetic resonance test and displacement
test to study the displacement process of medium injection and
crude oil under different injection conditions and clarified the producing rules of crude oil in different pores under water injection
and CO2 injection. Qualitative visual observation and theoretical
analysis of the microscopic mechanism of water flooding in low
permeability reservoirs (Huang, 1999; Guo et al., 1990; and Wang
and Sun, 2010) with different wettability values have been done.
However, there are few research studies on the microscopic recovery mechanism of water flooding in tight reservoirs with no report
on the quantitative characterization of oil recovery in the micro-
scitation.org/journal/adv
scopic mechanism, and it is necessary to explore the quantitative
characterization of different recovery mechanisms in water flooding.
Targeting at tight cores with different wettability values, this
study combined nuclear magnetic resonance technology with water
flooding experiments under different pressures to establish a quantitative analysis approach for oil production from different microscopic actions and quantitatively analyze the microscopic mechanism of water flooding. The production mechanism of hydrophilic
cores and neutral wetting cores under low displacement pressure is
studied quantitatively (flooding, imbibition, and denudation), and
the main mechanism is clarified. The mechanism of improving water
displacement recovery of hydrophilic core and neutral wetting core
after increasing the displacement pressure is studied quantitatively
(production from small pore throats, boundary layers, and large
pores controlled by small throats), and the similarities and differences between them are analyzed. Figure 1 shows the general sketch
of the physical model.
The steps of this work are as follows: First, the experimental
core and fluid data are presented. Then, cores are saturated with
kerosene, and the T 2 spectrum is measured. Next, cores are redried
and saturated with heavy water. Afterward, cores of saturated water
are flooded by kerosene to establish irreducible water, and the T 2
spectrum is measured. Finally, the water flooding experiment under
the pressure of 0.32 MPa and 5.12 MPa is carried out for each
core, and the nuclear magnetic resonance T 2 spectrum is measured
separately.
II. EXPERIMENTAL CORE DATA AND FLUID DATA
In this study, eight tight oil reservoir cores from the Ordos
Basin were selected for water flooding experiments under low displacement pressure and high displacement pressure, and nuclear
magnetic resonance detection was performed on each state of the
cores. The porosity of the eight cores ranges from 5.4% to 12.5%
with an average of 9.9%, and the gas measured permeability range
is (0.035–0.21) mD with an average of 0.12 mD (see Table I).
FIG. 1. The schematic diagram of the experimental system.
AIP Advances 10, 015042 (2020); doi: 10.1063/1.5131775
© Author(s) 2020
10, 015042-2
AIP Advances
ARTICLE
scitation.org/journal/adv
TABLE I. Quantitative statistics of the microscopic mechanism of water flooding in cores.
Oil recovery ratios through different actions (%)
Porosity Permeability
No. (%)
(mD)
1
2
3
4
5
6
7
8
10.27
12.45
5.37
9.44
11.66
11.54
9.78
8.90
0.192
0.175
0.088
0.210
0.102
0.035
0.039
0.120
Wettability
Hydrophilic
Hydrophilic
Hydrophilic
Hydrophilic
Hydrophilic
Weakly hydrophilic
Neutral
Neutral
Wetting
Production from Production from large
angle Imbibition +
small pore throats
pores controlled
Residual
(deg) denudation Displacement (boundary layers)
by small throats
oil
20.3
22.5
34.6
21.6
28.5
65.6
88.9
96.6
14.27
17.71
9.80
11.42
7.47
10.31
3.76
0.47
The experimental water is standard brine with a mineralization
degree of 50 g/l (NaCl: 22.5 g/l; KCl: 22.5 g/l; CaCl2 : 3.8 g/l; and
MgCl2 : 1.2 g/l. Heavy water does not contain H core, and so no
nuclear magnetic signal is generated during nuclear magnetic resonance testing). The experimental oil is aviation kerosene with similar
properties to the crude oil of the reservoir, with the physical parameters such as viscosity being basically the same as those of the actual
crude oil, 2.65 cP at 25 ○ C. The gas medium used in the experiment
is nitrogen.
III. EXPERIMENTAL PRINCIPLE
The application of nuclear magnetic resonance in the
petroleum industry is to make full use of the relaxation of NMR to
detect and analyze the occurrence state and properties of oil and
water in rocks. The T 2 relaxation time of fluids in rocks can be
expressed by the following formula:
(
1
1
1
1
)
=( ) +( ) +( ) .
T2 total
T2 S
T2 D
T2 B
(1)
In formula (1), ( T12 ) is the relaxation contribution of fluid
S
from the surface of rock particles, ( T12 ) is the relaxation contriB
bution of bulk fluid itself, and ( T12 ) is the relaxation contribution
D
from self-diffusion of fluid molecules. When the static magnetic field
is uniform, ( T12 ) is close to zero and negligible. The relaxation of
D
bulk fluids is much weaker than that of rock surface fluids, which can
be neglected in petroleum nuclear magnetic research and application. For surface fluid relaxation in the presence of a single channel,
the following expression can be used:
M(t) = Aexp(−
t
).
T2
(2)
The rock pore is composed of different sizes of pores. Each size
of pore has its own characteristic relaxation time T 2i under different
occurrence conditions. Therefore, there are many exponential decay
processes in rock. The total relaxation is the superposition of these
relaxations,
AIP Advances 10, 015042 (2020); doi: 10.1063/1.5131775
© Author(s) 2020
14.19
12.83
16.26
19.88
13.25
11.60
20.54
28.39
1.06
2.66
2.85
0.84
3.64
2.04
7.05
4.46
6.53
2.60
4.45
4.81
3.38
3.78
2.47
4.12
M(t) = ∑ Ai exp(−t/T2i ).
29.77
24.31
30.47
31.00
28.28
24.24
30.48
27.94
(3)
In formula (3), Ai is the proportion of component i and T 2i
is the relaxation time of component i, which is related to the specific surface S/V or pore size of the rock. When the fluid is in close
contact with the solid surface in large pores or fluid in small pores,
the nuclear magnetic transverse relaxation time of the fluid is small.
Conversely, when the fluid is not in close contact with the pore surface in large pores, the nuclear magnetic transverse relaxation time
of the fluid is large.
IV. EXPERIMENTAL METHODS AND STEPS
1 core marking, oil washExperimental steps are as follows: ⃝
ing (Dean Stark extraction), drying and weighing dry weight, and
2 achieving gas measurement
measuring core length and diameter; ⃝
porosity and gas measured permeability (steady state gas-perm; the
3 vacuum pressurized and saturated with
gas medium is nitrogen); ⃝
kerosene, calculating kerosene porosity (using the core weight difference between saturated kerosene and dry weight to calculate core
pore volume and using core length and diameter to calculate core
4 measuring the nuclear magnetic resonance T 2 specvolume); ⃝
trum under saturated oil state (using the Reccore-04 core NMR
5 core redrying; ⃝
6 vacuum
analyzer for T 2 spectrum detection); ⃝
pressurized and saturated with heavy water at a mineralization of
50 000 mg/l, calculating the porosity (water measured porosity) by
using the difference between the wet weight and the dry weight of
7 loading the core into the displacement stream, selectthe core; ⃝
ing an appropriate displacement pressure, flooding the core of the
saturated water by kerosene, and establishing the state of the saturated oil of the core under irreducible water state (the displacement
experiment is completed by using the SL-2012 nonlinear test system; the displacement multiple is about 10 PV, measuring the dis8 measuring the T2
placed water volume and the core weight); ⃝
spectrum of NMR under the condition of the saturated oil under
9 based on core parameters including
irreducible water state; and ⃝
physical properties, each core is subject to the water flooding experiment under the pressure of 0.32 MPa and 5.12 MPa, separately, and
each displacement pressure is driven until no more oil is produced
(the displacement volume is about 5 PV). Measure the amount of
10, 015042-3
AIP Advances
ARTICLE
produced oil, measure the core weights, and test the NMR T 2
spectrum, separately.
V. ANALYSIS OF MICROSCOPIC MECHANISMS
OF WATER FLOODING
A. Microscopic mechanism of low displacement
water flooding
Figure 2 shows the NMR T 2 spectra of No. 5 and No. 8 specimen under the conditions of saturated oil, saturated oil under irreducible water, and 0.32 MPa water flooding. The wettability of No.
5 was hydrophilic (wetting angle 28.5○ , Fig. 3), and the wettability of No. 8 was neutral (wetting angle 96.6○ ). It can be seen from
this figure that there are significant discrepancies in the T 2 spectra of the different states of the hydrophilic and neutral cores. The
right peaks of No. 8 saturated oil state and the saturated oil under
irreducible water state T 2 spectrum (corresponding to the macropores) are basically coincident, indicating that the crude oil in partial
large pores of the neutral cores has been fully filled, while partial
large pores of the hydrophilic cores have not been fully filled. After
0.32 MPa displacement, the right peak of No. 8 sample decreased
greatly and the decrease in gradient of the left peak was lower, indicating that the producing degree of the crude oil in partial large pores
scitation.org/journal/adv
was relatively high, while the left and right peaks of No. 5 sample
decreased by an equivalent amplitude. According to the principle of
nuclear magnetic resonance, small relaxation time corresponds to
the fluid in small throats or at the surface of the large pore throats
of the cores. Further comparative analysis shows that the produced
crude oil in the pore space below 10 ms in No. 8 specimen was little (corresponding to Fig. 2, right panel), indicating that the crude
oil in small throats or on the surface of large pore throats in No. 8
specimen was rarely produced. Since the displacement pressure is
only 0.32 MPa, which is relatively low, the absorption at the surface of the pores in the tight reservoir is very strong, suggesting that
such displacement pressure cannot drive out the oil on the surface of
the large pores of the cores; on the other hand, the tight reservoir is
featured by mixed wettability, with some of the pore throats showing hydrophilic characteristic and some of the pore throats showing
lipophilic characteristic. For the lipophilic small throats, the small
displacement pressure cannot overcome the capillary resistance and
drive out the oil in the small throat, and so the oil in the small throats
can only be produced by the imbibition of the hydrophilic capillary
portion; therefore, the mechanism of the crude oil in the pore space
below 10 ms in No. 8 specimen is imbibition.
The volume of crude oil produced from the pore space below
10 ms in No. 5 specimen is relatively high (corresponding to Fig. 2,
FIG. 2. The NMR T 2 spectra of the two cores under oil saturated state, saturated oil and irreducible water state, and state after 0.32 MPa.
FIG. 3. Wetting angle tests of 4 cores.
AIP Advances 10, 015042 (2020); doi: 10.1063/1.5131775
© Author(s) 2020
10, 015042-4
AIP Advances
ARTICLE
scitation.org/journal/adv
FIG. 4. The NMR spectra of 2 cores under oil saturated state, oil saturated and irreducible water state, and different stages of water flooding.
left panel). Due to the hydrophilicity of No. 5 specimen, the small
displacement pressure can also drive out the oil on the surface of
the large pores through denudation action. Therefore, the crude oil
in the pore space of No. 5 specimen below 10 ms is the result of the
combined mechanism of denudation and imbibition. Figure 2 shows
that the T 2 spectrum amplitude of the irreducible water under saturated oil state below 10 ms in No. 5 specimen is relatively large, indicating that the effect of oil recovery through denudation is relatively
strong.
B. The microscopic mechanism of water flooding
under increased displacement pressure
Figure 4 shows the NMR T 2 spectra of No. 4 and No. 7 under
conditions of saturated oil state, saturated oil under irreducible
water state, and states after flooding at different displacement pressures. The wettability of No. 4 was hydrophilic (wetting angle 21.6○ ,
Fig. 3), and the wettability of No. 7 was neutral (wetting angle 88.9○ ).
It can be seen from this figure that compared with the T 2 spectrum
after 0.32 MPa displacement, the T 2 spectrum variations after the
5.12 MPa displacement of both the hydrophilic and neutral cores are
significantly different. The relatively larger relaxation time part of
the two cores has a certain degree of reduction, indicating that there
is a certain volume of residual oil in the large pores that has been
driven out; the residual oil of this type can be divided into two categories: one is the crude oil in large pores controlled by small throats
(as this part of throats is very small and 0.32 MPa is not enough to
start the displacement, the crude oil in which cannot be produced
until the displacement pressure value has increased to a certain
extent) and the other type is the oil droplets controlled by large pore
throats (due to the Jiamin effect, 0.32 MPa is not enough to overcome the seepage resistance caused by the Jiamin effect, resulting in
the residual oil being distributed in the large pores after 0.32 MPa
displacement until the displacement pressure is increased to a certain extent before being produced). The relatively small relaxation
time part of the two cores also has a certain degree of reduction, but
the neutral wetting cores have a greater reduction. For the studied
AIP Advances 10, 015042 (2020); doi: 10.1063/1.5131775
© Author(s) 2020
tight cores in this essay, the displacement at 0.32 MPa for 5 PV takes
a long time (all over 10 days) and the core static imbibition experiment shows that the core imbibition mainly occurs in the initial
stage of imbibition, and the oil recovery from imbibition becomes
little after 72 h. Therefore, the oil recovery effect of imbibition has
been fully utilized in the 0.32 MPa displacement experiment. When
the displacement pressure is increased from 0.32 MPa to 5.12 MPa,
the effect of imbibition recovery is very small and the improvement
of oil recovery depends mainly on other functions. After increasing the displacement pressure, some part of the oil controlled in the
small pore throats can be produced; on the other hand, part of the
boundary layer oil film in the neutral wetting cores became thinner,
which increases the oil recovery ratio (the influence of this mechanism is minimal as the portion of the hydrophilic core boundary
layer oil is little). After increasing the displacement pressure, the
common point for the oil recovery mechanism through water flooding of both the hydrophilic and the neutral wetting cores reached
that both types started the oil controlled by the small throats and
the residual oil droplets trapped in the large pores; the discrepancy
FIG. 5. Relative oil content statistics of different T 2 interval pores.
10, 015042-5
AIP Advances
ARTICLE
scitation.org/journal/adv
is that the oil recovery ratio of the neutral wetting cores improved
due to the thinning of the oil film in the boundary layer, while this
kind of oil recovery mechanism influences the hydrophilic cores
little.
C. Comparison of microscopic action mechanism
of water flooding of different wettability cores
The results of water flooding of 8 tight cores were compared
according to wettability (Figs. 5–7). The relatively large pores in
saturated oil under irreducible water state of cores with a different
wettability have a relatively high oil content (Fig. 5). The neutral
and weak hydrophilic cores are higher than the hydrophilic ones,
indicating that the crude oil in the large pores of the neutral and
weak hydrophilic cores has been fully injected, while the filling of
the crude oil in the large pores of the hydrophilic cores is not completely full. After 0.32 MPa displacement, the recovery ratios of the
crude oil in the larger pores of cores with a different wettability
are higher; the hydrophilic and weak hydrophilic cores have higher
production in the pore space below 10 ms (6 cores range from 7.5%
to 17.7% with an average of 11.8%), while the producing degree of
such pores in the neutral wetted cores is relatively low (2 cores range
from 0.5% to 3.8% with an average of 2.1%) (Fig. 6, Table I); this
indicates that the hydrophilic and weakly hydrophilic cores have
stronger denudation and imbibition under low displacement pressure, while the neutral wetting cores have weaker denudation and
imbibition under low displacement pressure. From Fig. 6, it can be
further seen that the relative recovery of oil below 10 ms in waterwet cores can reach 41.8%, while that of neutral cores is only about
7.5%. This indicates that water-wet reservoirs more easily play the
role of imbibition in oil recovery. After 5.12 MPa displacement,
the crude oil recovery ratio of pores in different wettability cores
in different T 2 intervals all increased to some extent; the recovery ratios of crude oil in the pore space below 10 ms in neutral
wetting cores are significantly higher than that in hydrophilic and
weakly hydrophilic cores. It shows that after increasing the displacement pressure, part of the boundary layer oil film has been
activated in the neutral wetting cores, which has increased the oil
recovery.
FIG. 6. Oil recovery degree of different T 2 interval pores of cores with a different
wettability after 0.32 MPa displacement.
FIG. 7. Increased amount of oil recovery degree of different T2 interval pores after
5.12 MPa displacement.
The microscopic mechanisms of water flooding in 8 tight
cores have been quantitatively calculated (Fig. 8, Table I). The oil
recovery mechanism of hydrophilic cores mainly includes flooding, imbibition, and denudation, producing oil controlled by small
FIG. 8. Micromechanism of water flooding in different wetting cores.
AIP Advances 10, 015042 (2020); doi: 10.1063/1.5131775
© Author(s) 2020
10, 015042-6
AIP Advances
pore throats, and by large pores controlled by small pore throats.
The percentage of produced oil is 14.7%, 11.8%, 2.2%, and 4.3%,
respectively, with flooding, imbibition, and denudation being dominant. The oil recovery mechanism of neutral wetting cores, mainly
including flooding, imbibition, and denudation, starts producing oil
controlled by small pore throats and boundary layers, and large
pores controlled by small pore throats. The recovery ratios are
24.5%, 2.1%, 5.8%, and 3.3%, respectively, with flooding production
being dominant.
ARTICLE
scitation.org/journal/adv
and the residual oil droplets trapped in the large pores; the discrepancy is that the oil film of the neutral wetting core boundary layer
became thinner and the oil recovery degree was improved, while
these kinds of the oil recovery mechanisms have less effect on the
hydrophilic cores (the oil produced by the hydrophilic and neutral
wetting cores increased by 6.4% and 9.1%, respectively, and the neutral wetting cores was slightly higher, indicating that the increased
displacement pressure might convert some crude oil in the boundary
layer into producing volume).
D. Oilfield application and limitations
In order to improve the development effect of tight reservoirs
in the Ordos Basin of China, field tests, such as synchronous injection and production of horizontal wells, asynchronous injection and
production of horizontal wells, and asynchronous injection and production of staggered fracture distribution, were carried out in the
oilfield. The energy supplement mode of cyclic water injection and
wheel-injection production in the mixed injection-production pattern of directional wells and horizontal wells is attempted. In typical
tight oil areas of China, tests of imbibition production and supplementary energy by fracturing fluid in “artificial reservoirs” have also
been carried out. The purpose of these technologies is to increase
formation energy, reduce displacement distance, and give full play
to displacement and imbibition. This is consistent with the technical thinking and development mechanism proposed in this study.
Moreover, the method of this study can quantitatively give oil production of each mechanism and provide support for development
decision-making of oilfields.
Nevertheless, there are some limitations in this study. In this
study, core experiments cannot take into account the impact of large
natural fractures in the actual formation. In addition, the wettability
of actual reservoir is more complex, and this study can only carry
out experiments on specific wettability cores.
VI. CONCLUSION
Combining water flooding experiments under different pressures with nuclear magnetic resonance, a quantitative analysis
approach for oil recovery from different microscopic actions has
been established and the microscopic mechanisms of water flooding
in tight oil cores have been quantitatively studied. The production
mechanism of hydrophilic cores and neutral wetting cores under
low displacement pressure is analyzed quantitatively, and the main
mechanism is clarified: The oil recovery mechanism of hydrophilic
cores mainly includes flooding, imbibition, denudation, and other
mechanisms (the oil recovery ratio in hydrophilic cores with flooding and imbibition and denudation was 14.7% and 11.8%, respectively, which are the main mechanisms of water flooding); the mechanism of neutral wetting cores recovery mainly includes flooding
and imbibition (the oil recovery ratio in neutral wetting cores with
flooding is 24.5%, which is the main oil recovery mechanism of water
flooding). The mechanism of improving water displacement recovery of hydrophilic core and neutral wetting core after increasing the
displacement pressure is analyzed quantitatively, and the similarities and differences between them are analyzed. Both the hydrophilic
cores and the neutral wetting cores have a certain increase in oil
recovery; the common point of the two producing mechanisms is
that both of them activated the oil controlled small throat control
AIP Advances 10, 015042 (2020); doi: 10.1063/1.5131775
© Author(s) 2020
ACKNOWLEDGMENTS
We gratefully acknowledge financial support from the National
Science and Technology Major Project (Grant Nos. 2017ZX05013001, 2017ZX05069003, and 2017ZX05049005-004) and the Ministry
of Science and Technology of PetroChina (Grant Nos. 2017E-1514
and 2018E-11-05).
REFERENCES
Bai, B., Zhu, R., Wu, S. et al., “Multi-scale method of nano(Micro)-CT study on
microscopic pore structure of tight sandstone of Yanchang formation, Ordos
basin,” Pet. Explor. Dev. 40(3), 354 (2013).
Chen, C. Y. and Yan, P. Y., “A diffuse interface approach to injection-driven flow
of different miscibility in heterogeneous porous media,”Phys. Fluids 27(8),
083101 (2015).
Datta, S. S., Ramakrishnan, T. S., and Weitz, D. A., “Mobilization of a trapped nonwetting fluid from a three-dimensional porous medium,” Phys. Fluids 26(2),
022002 (2014).
Dejam, M., Hassanzadeh, H., and Chen, Z., “Pre-Darcy flow in porous media,”
Water Resour. Res. 53(10), 8187–8210 (2017a).
Dejam, M., Hassanzadeh, H., and Chen, Z., “Pre-Darcy flow in tight and shale
formations,” in 70th Annual Meeting of the APS Division of Fluid Dynamics
(American Physical Society, Denver, Colorado, USA, 2017b).
Dejam, M., Hassanzadeh, H., and Chen, Z., “Semi-analytical solution for pressure
transient analysis of a hydraulically fractured vertical well in a bounded dualporosity reservoir,” J. Hydrol. 565, 289–301 (2018).
De Paoli, M., Zonta, F., and Soldati, A., “Influence of anisotropic permeability on
convection in porous media: Implications for geological CO2 sequestration,”
Phys. Fluids 28(5), 056601 (2016).
Ghanizadeh, A., Clarkson, C. R., Aquino, S. et al., “Petrophysical and
geomechanical characteristics of Canadian tight oil and liquid-rich gas
reservoirs: II. Geomechanical property estimation,” Fuel 153(1), 682–691
(2015).
Gu, X., Chunsheng, P. U., Huang, H. et al., “Micro-influencing mechanism of permeability on spontaneous imbibition recovery for tight sandstone reservoirs,”
Pet. Explor. Dev. 44(6), 1003–1009 (2017).
Guo, S., Huang, Y., Zhou, J. et al. Porous Flow with Physico-Chemical Processes—
Microscopic Study (Science China Press, 1990).
Guo, Y., Song, Y., Pang, X., et al., “Characteristics and genetic mechanism of near
source accumulated accumulation for continuous type tight sand gas,” Earth
Sci., 41(03), 433–440 (2016).
Huang, Y., Percolation Mechanism of Low-Permeability Reservoirs (Petroleum
Industry Press, 1999).
Jia, C., Caineng, Z., Jianzhong, L. et al., “Assessment criteria, main types, basic
features and resource prospects of the tight oil in China,” Acta Pet. Sin. 33(3),
343–350 (2012).
Jianming, F., Chong, W., Xuefeng, Q. et al., “Development and practice of water
flooding huff-puff in tight oil horizontal well, Ordos Basin: A case study of
Yanchang Formation Chang 7 oil layer,” Acta Pet. Sin. 40(6), 706 (2019).
Law, B. E. and Curtis, J. B., “Introduction to unconventional petroleum systems,”
AAPG Bull. 86(11), 1851–1852 (2002).
10, 015042-7
AIP Advances
Li, D., Wenshu, Z., Shufeng, L. et al., “Pressure transient analysis of low permeability reservoir with pseudo threshold pressure gradient,” J. Pet. Sci. Eng. 147,
308–316 (2016).
Li, Z., He, S., Yang, W. et al., “Physical simulation experiment of water driving by
micro-model and fractal features of residual oil distribution,” J China Univ.
Pet. 30(3), 68–71 (2006).
Loucks, R. G., Read, R. M., Ruppel, S. C. et al., “Morphology, genesis, and distribution of nanometer-scale pores in siliceous mudstones of the Mississippian
Barnett shale,” J. Sediment. Res. 79, 848–861 (2009).
Mullen, J., “Petrophysical characterization of the eagle ford shale in south Texas,”
Report No. SPE-138145, 2010.
Pan, W. Y., Lang, D. J., Lun, Z. M. et al., “Experimental study of effective displacement characteristics of different displacing methods in tight oil reservoir,”
Comput. Tomogr. Theory Appl. 25(6), 647–652 (2016).
Qu, X., Fan, J., Chong, W. et al., “Impact of fractures on water flooding seepage
features of Chang 7 tight cores in Longdong area, Ordos basin,” J. Xian Shiyou
Univ. 32(5), 55–60 (2017).
Qu, X., Lei, Q., Gao, W. et al., “Experimental study on imbibition of Chang 7 tight
oil cores in Erdos basin,” J. China Univ. Pet. 42(2), 102–109 (2018).
Quan, H., Zhu, Y., Zhang, H. et al., “Reservoir pore structure and micro
flow characteristics of water flooding: A case study from Chang 6 reservoir of Wangyao block in Ansai oilfield,” Oil Gas Geol. 32(54), 952–956,
https://doi.org/10.11743/ogg20110620 (2011).
Suleimanov, B. A., Abbasov, E. M., and Sisenbayeva, M. R., “Mechanism of gas
saturated oil viscosity anomaly near to phase transition point,” Phys. Fluids
29(1), 012106 (2017).
Wang, R., Shen, P., Ziqi, S. et al., “Characteristics of micropore throat in ultralow
permeability sandstone reservoir,” Acta Pet. Sin. 30(4), 560–563 (2009).
Wang, R. and Sun, W., “Main controls for oil displacement efficiency by the
micro-model water flooding experiment in ultra-low permeability sandstone
reservoir,” Pet. Geol. Exp. 32(1), 93–97 (2010).
Wang, Y. D., Yang, Y. S., Liu, K. Y. et al., “Quantitative and multi-scale characterization of pore connections in tight reservoirs with micro-CT and DCM,”
Bull. Mineral., Petrol. Geochem. 34, 86 (2015).
Wei, Q., Li, Z., Wang, X. et al., “Mechanism and influence factors of imbibition
in fractured tight sandstone reservoir:An example from Chang8 reservoir of
Wuqi area in Ordos basin,” Pet. Geol. Recovery Effic. 32(5), 103–107 (2016).
Wei, X., Ok, J. T., Feng, X., et al., “Effect of pore geometry and interfacial tension on water-oil displacement efficiency in oil-wet microfluidic porous media
analogs,” Phys. Fluids 26(9), 1–68 (2014).
Wu, G., Fang, H., Han, Z. et al., “Growth features of measured oil initially in place
and gas initially in place during the 12th five-year plan and its outlook for the
13th five-year plan in China,” Acta Pet. Sin. 37(9), 1145–1151 (2016).
AIP Advances 10, 015042 (2020); doi: 10.1063/1.5131775
© Author(s) 2020
ARTICLE
scitation.org/journal/adv
Wu, S., Zou, C., Zhu, R. et al., “Reservoir quality characterization of upper triassic Chang 7 shale in Ordos basin,” Earth Sci.-J. China Univ. Geosci. 11,
1810–1823 (2015).
Xueling, Z., Weiyao, Z., Qiang, C. et al., “Compressible liquid flow in nanoor micro-sized circular tubes considering wall–liquid Lifshitz–van der Waals
interaction,” Phys. Fluids 30(6), 062002 (2018).
Yang, H., Li, S., and Liu, X., “Characteristics and resource prospects of
tight oil and shall oil in Ordos basin,” Acta Pet. Sin. 34(1), 1–11
(2013).
Yang, W., Zhu, Y., Chen, S. et al., “Characteristics of the nanoscale pore structure in Northwestern hunan shale gas reservoirs using field emission scanning
electron microscopy, high-pressure mercury intrusion, and gas adsorption,”
Energy Fuels 28(2), 945–955 (2014).
Yang, X., Zhao, W., Zou, C. et al., “Origin of low permeability reservoir and distribution of favorable reservoir,” Acta Pet. Sin. 28(4), 57–61
(2007).
Yang, Y., Birmingham, T., and Kremer, A., “From hydraulic fracturing, what can
we learn about reservoir properties of tight sand at the Wattenberg field in the
Denver-Julesburg basin,” Report No. SPE 123031, 2009.
Yang, Z., Guo, H., Liu, X. et al., Characteristic Experimental Technology of an
Extra-ultra Low Permeability Reservoir (Petroleum Industry Press, Beijing,
2012), pp. 135–155.
Yao, J., Deng, X., Zhao, Y. et al., “Characteristics of tight oil in triassic Yanchang formation, Ordos basin,” Pet. Explor. Dev. 40(2), 161
(2013).
Yu, B., Luo, X., Qiao, X. et al., “Influential factor and characteristics of Shan-2
member of shanxi formation in Yanchang oil-gas field, Ordos basin,” J. Cent.
South Univ. 43(10), 3931–3937 (2012).
Zhao, H., Ning, Z., Wang, Q. et al., “Petrophysical characterization of tight
oil reservoirs using pressure-controlled porosimetry combined with ratecontrolled porosimetry,” Fuel 154, 233–242 (2015).
Zhang, L., Kou, Z., Wang, H., Zhao, Y. et al., “Performance analysis for a model
of a multi-wing hydraulically fractured vertical well in a coalbed methane gas
reservoir,” J. Pet. Sci. Eng. 166, 104–120 (2018).
Zhang, X. S., Wang, H. J., Ma, F. et al., “Classifcation and characteristics of tight
oil plays,” Pet. Sci. 13(1), 18–33 (2016).
Zhong, D., Zhou, L., Sun, H. et al., “Influences of petrologic features on diagenesis and pore development: An example from the triassic Yanchang
formation in Longdong area, Ordos basin,” Oil Gas Geol. 33(6), 890–895
(2012).
Zou, C., Zhu, R., Wu, S. et al., “Types, characteristics, genesis and prospects of
conventional and unconventional hydrocarbon accumulation: Taking tight oil
and tight gas in China as an instance,” Acta Pet. Sin. 33(2), 173–187 (2012).
10, 015042-8