energiesArticleHuff-n-Puff Experimental Studies of CO2

energies
Article
Huff-n-Puff Experimental Studies of CO2 with
Heavy Oil
Evgeny Shilov 1,*,† , Alexey Cheremisin 1 , Kirill Maksakov 2
and Sergey Kharlanov 3
1 Center for Hydrocarbon Recovery, Skolkovo Institute of
Science and Technology, Moscow 121205, Russia;
[email protected]
2 Department of Technology Development for High Viscosity
and Heavy Oils, LUKOIL-Engineering LCC,
Moscow 109028, Russia; [email protected]
3 Management Department of Scientific and Technical Projects,
RITEK JSC, Moscow 115035, Russia;
[email protected]
* Correspondence: [email protected]
† Current address: Skolkovo Innovation Center, Bolshoy Bulvar
30-1, Moscow 121205, Russia.
Received: 30 September 2019; Accepted: 6 November 2019;
Published: 12 November 2019 ��
Abstract: This work is devoted to CO2 Huff-n-Puff studies on
heavy oil. Oil recovery for heavy oil
reservoirs is sufficiently small in comparison with conventional
reservoirs, and, due to the physical
limitation of oil flow through porous media, a strong need for
better understanding of tertiary

recovery mechanisms of heavy oil exists. Notwithstanding that
the idea of Huff-n-Puff gas injection
technology for enhanced oil recovery has existed for dozens of
years, there is still no any precise
methodology for evaluating the applicability and efficiency of
this technology in heavy oil reservoirs.
Oil recovery factor is a question of vital importance for heavy
oil reservoirs. In this work, we repeated
Huff-n-Puff tests more than three times at five distinct pressure
points to evaluate the applicability
and efficiency of CO2 Huff-n-Puff injection to the heavy oil
reservoirs. Additionally, the most critical
factor that affects oil recovery in gas injection operation is the
condition of miscibility. Experimental
data allowed to distinguish the mixing zone of the light
fractions of studied heavy oil samples.
The experimental results showed that the pressure increase in
the Huff-n-Puff injection process does
not affect the oil recovery when the injection pressure stays
between miscibility pressure of light
components of oil and minimum miscibility pressure. It was
detected that permeability decreases
after Huff-n-Puff CO2 tests.
Keywords: enhanced oil recovery; CO2 injection; heavy oil;
Huff-n-Puff; miscibility evaluation;
permeability reduction
1. Introduction
The continuous increase in energy consumption [1] enhances the
total demand for every type of
hydrocarbon resource [2,3]. Despite the very challenging
production of oil from heavy oil reservoirs,
heavy oil is becoming a very prospective and valuable source of
energy these days. Combined with

the facts that (1) oil production from conventional reservoirs is
decreasing [4], (2) tremendous heavy
reserves are more than 3 times bigger than conventional oil
reserves [5], and (3) tertiary oil recovery
techniques are advancing each year [6,7], we predict that more
and more studies about heavy oil will
be published in the upcoming years.
This work is devoted to the experimental studies of CO2
applicability, efficiency, and miscibility
with heavy oil by Huff-n-Puff tests. Oil recovery in heavy oil
reservoirs is sufficiently small in
comparison with oil recovery from conventional reservoirs due
to the physical limitation of the oil flow
through the porous media. As heavy oil reservoirs do not
effectively respond to secondary recovery
Energies 2019, 12, 4308; doi:10.3390/en12224308
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Energies 2019, 12, 4308 2 of 15
methods, the tertiary enhanced oil recovery techniques are the
only practical and possible options.
Therefore, a need for better understanding of tertiary recovery
mechanisms for heavy oil reservoirs

exists nowadays. Notwithstanding that the idea of gas injection
technology for enhanced oil recovery
operations, either in flooding or the Huff-n-Puff regime, was
developed long time ago [8], and the
first experimental studies of CO2 applicability in heavy oil
reservoirs were conducted in the 1980s
and 1990s [9,10], there is no precise methodology for the
evaluation of applicability and efficiency of
Huff-n-Puff gas injection technology in heavy oil reservoirs
[11].
Huff-n-puff CO2 injection is an enhanced oil recovery
technique that is widely used for
conventional oil reservoirs [12] and is known as cyclic injection
of CO2. The Huff-n-Puff injection is
presented by three divided stages: (1) the injection stage, (2)
the soaking stage, and (3) the production
stage [9]; all three stages will be experimentally modeled. Oil
recovery factor is a question of vital
importance that petroleum companies have about hard to
recover resources. The most critical factor
that affects oil recovery in any gas injection operation is the
condition of miscibility [13]. The injected
gas can be either in the miscible or immiscible regime.
Commonly, gas injection over minimum
miscibility pressure (MMP) is considered as the most favorable
regime with the highest possible
oil recovery [14]. Miscibility depends on the number of
parameters like oil composition, swelling
coefficient, diffusion, solubility, and mainly on pressure, which
is above MMP [15]. MMP is an
indication of pressure, temperature, or gas composition when
gas and oil are completely miscible in
any proportions [16].
Regarding the light oil of conventional reservoirs, the

determination of MMP is not very
challenging: MMP of CO2 and oil can be predicted by empirical
correlations, numerical simulations,
and rapid experimental techniques. Most of the empirical
correlations were made with the help of
experimental data obtained from experiments performed with
light oil. Therefore, they are hardly
applicable to heavy oil [17]. For the proper numerical
simulation, the composition of the oil is needed.
However, the composition of heavy oil is very hard to precisely
determine, and it is sufficiently different
in its behavior from field to field. Due to the high
compositional differences of heavy oil, it tends to
have two distinct miscibility pressures at which we can reach
miscibility, with light components of oil
first, and only then with heavy components of oil. In the most
cases related to heavy oil reservoirs,
researches assume that heavy oil is not miscible because MMP
in heavy oil reservoir is usually much
higher than the reservoir pressure [18–20]. However, it also
coincides with another problem—MMP
determination for heavy oil is very challenging. Traditionally,
MMP for the light oil can be determined
by such conventional methods as the slim tube, Vanishing
Interfacial Tension (VIT), and Rising Bubble
Apparatus (RBA) tests. However, these techniques fail when
dealing with high viscosity oil. The
industrially accepted method, the slim tube test, is not
physically affordable for high viscosity oil [21].
To evaluate heavy oil recovery by Huff-n-Puff CO2 injection
and evaluate the miscibility conditions
of CO2 and heavy oil, we implement the Huff-n-Puff gas
injection tests. The studied pressure range was
restricted to the field injection limitations. Obtaining oil
recovery factors after five Huff-n-Puff cycles of

five different pressure points expanded our knowledge on the
Huff-n-Puff process and its efficiency for
heavy oil reserves. Forty Huff-n-Puff gas injection tests were
conducted in total. Experiments coincide
with other studies where heavy oil is mainly extracted by the
first three cycles of CO2 Huff-n-Puff
injection [11,22]. Then, the received data allowed to distinguish
the mixing zone for the light fractions
of studied oil samples with CO2, proving that it is applicable
for possible miscibility evaluation.
Experiments shown no difference for oil recovery when
injection pressure is between miscibility
pressure of light components and MMP. Additionally, the
change of oil composition after Huff-n-Puff
tests was analyzed. Permeability reduction was observed by
running core flood experiments with
different solvents.
2. Materials
In this study, wellhead oil samples from heavy oilfields #1 and
#2 were provided by
LUKOIL-Engineering; the oil samples were free from gas.
Reservoir properties are presented in Table 1.
Energies 2019, 12, 4308 3 of 15
As some part of the experimental procedure is meant to be
conducted under atmospheric pressure,
there was no need to make recombined oil samples. Berea
Sandstone core plugs were used for these
Huff-n-Puff tests. The main properties of dead oil samples were
measured by PVT 3000-L (Chandler
Engineering, Tulsa, OK, USA) and are presented in Table 2.

The compositions of the oil samples
were measured by gas chromatography/mass spectrometry and
presented in Table 3. The initial
water content of the oilfield #1 and oilfield #2 oil samples was
over 20%. Therefore, the samples
were dewatered by (1) thermostabilization at 90 ◦C for 72 h and
(2) the centrifuge, PrO-ASTM BC
(Centurion Scientific Ltd., Chichester, UK), at 75 ◦C for 80
min. Every core sample was drilled from
one homogeneous block of Berea sandstone. Core diameters,
lengths, and helium permeability are
presented in Table 4. The volume difference of used samples
does not exceed 20%, the porosity is
~20%, and permeability ranges from 154 to 175 mD. The
injection gas in these Huff-n-Puff tests is CO2
with purity greater than 99.99%.
Table 1. Reservoir properties.
Reservoir Oilfield #1 Oilfield #2
Temperature ( ◦C) 27.4 21.6
Pressure (MPa) 13.8 10.9
Table 2. Measured properties of dead oil samples from oilfield
#1 and oilfield #2.
Dead Oil Sample Oilfield #1 Oilfield #2
Dead oil density at 20.0 ◦C (kg m3) 1006.70 931.03
Dead oil viscosity at 25.0 ◦C (mPa s) 1116.00 421.8
Dead oil molecular weight (g mol−1) 346.74 499.51
Dead oil compressibility (1/MPa) 4.45 × 10−4 6.29 × 10−4
Water content after dewatering (%) 0.78 0.33
Paraffin crystallization temperature at 0.2 MPa ( ◦C) 30.4 33.1

Table 3. Results of compisitional analysis of the dead oil
samples from oilfield #1 and oilfield #2.
Component
Oilfield #1 Oilfield #2
Component
Oilfield #1 Oilfield #2
wt.% mol.% wt.% mol.% wt.% mol.% wt.% mol.%
H 0 0.0003 0 0 C17 0.0784 0.1651 0.3508 0.5132
H2S 0.0012 0.0170 0 0 C18 0.0993 0.1975 0.3914 0.5407
CO2 0.0135 0.1532 0.0005 0.0040 C19 0.0726 0.1378 0.2503
0.3299
N2 0.2919 5.2056 0.0188 0.2330 C20 0.0636 0.1156 0.2486
0.3134
C1 0.0207 0.6442 0.0139 0.2996 C21 0.0577 0.0991 0.2079
0.2477
C2 0.0266 0.4413 0.0460 0.5304 C22 0.0431 0.0706 0.1984
0.2256
C3 0.0310 0.3511 0.4608 3.6235 C23 0.0399 0.0627 0.1891
0.2062
iC4 0.0128 0.1104 0.0442 0.2639 C24 0.0358 0.0541 0.1687
0.1768
nC4 0.0349 0.2997 0.7141 4.2601 C25 0.0322 0.0466 0.1425
0.1432
iC5 0.0281 0.1948 0.2672 1.2843 C26 0.0314 0.0436 0.1360
0.1313
nC5 0.0266 0.1844 0.5736 2.7567 C27 0.0251 0.0335 0.1050
0.0973
C6 0.1033 0.6143 1.5685 6.4746 C28 0.0219 0.0282 0.0856
0.0765
C7 0.1189 0.6185 1.5188 5.4856 C29 0.0188 0.0234 0.0640
0.0552
C8 0.1040 0.4857 0.8171 2.6479 C30 0.0162 0.0195 0.0493

0.0411
C9 0.0453 0.1870 0.2532 0.7256 C31 0.0144 0.0168 0.0459
0.0370
C10 0.0465 0.1733 0.2283 0.5907 C32 0.0138 0.0156 0.0352
0.0275
C11 0.0484 0.1644 0.2064 0.4869 C33 0.0122 0.0134 0.0147
0.0111
C12 0.0495 0.1535 0.2478 0.5336 C34 0.0087 0.0092 0.0108
0.0079
C13 0.0467 0.1333 0.2829 0.5606 C35 0.0066 0.0068 0.0081
0.0058
C14 0.0666 0.1751 0.2864 0.5227 C36+ 98.0613 88.229 89.2027
64.6417
C15 0.0661 0.1603 0.2775 0.4671 Total 100 100 100 100
C16 0.0643 0.1447 0.2689 0.4201
Energies 2019, 12, 4308 4 of 15
Table 4. Summary of physical properties of the cores applied in
this study.
Sample No.
Length Diameter Volume Surface Area/Volume Porosity
Permeability
cm cm cm3 m2/cm3 % mD
1 4.819 2.940 32.72 1.64 20.14 153.5
2 4.760 2.941 32.34 1.65 20.21 157.6
3 4.764 2.941 32.36 1.65 20.16 153.2
4 4.725 2.938 32.03 1.65 20.16 156.4
5 4.698 2.943 31.96 1.65 20.15 156.5
6 4.503 2.941 30.58 1.66 20.35 168.3
7 4.375 2.940 29.71 1.67 20.40 173.7

8 4.371 2.940 29.68 1.67 20.42 174.9
9 4.282 2.941 29.08 1.68 20.42 171.4
10 3.892 2.937 26.36 1.71 20.63 174.8
3. Experimental Setup
The assemblies used in saturation operations and Huff-n-Puff
tests are presented in Figures 1 and
2, respectively. The assemblies are presented by two piston
vessels, a climate chamber, vacuum pump,
and the pump. The pump, Quizix QX (Chandler Engineering,
Tulsa, OK, USA), is a piston pump with
two cylinders that works in the regime of continuous delivery
and receiving; it pushes the piston of
the cylinder filled by oil or gas and replaces the liquid into
high-pressure stainless steel container 1,
which is filled by the vertically placed rock samples. The
samples are placed on the piston inside the
annulus of container 1, and they are free from any sleeves. The
piston is adjusted on the desired level
by water on the bottom side of container 1. The pump allowed
to inject the gas at the pressure up to
24 MPa. The climate chamber, MK 240 (Binder GmbH,
Tuttlingen, Germany), maintained the reservoir
temperature with fluctuations up to 0.5 ◦C.
Version October 28, 2019 submitted to Energies 4 of 16
Table 4. Summary of physical properties of the cores applied in
this study.
Sample no. Length Diameter Volume Surface Area/Volume
Porosity Permeabilitycm cm cm3 m2∕cm3 % mD
1 4.819 2.940 32.72 1.64 20.14 153.5
2 4.760 2.941 32.34 1.65 20.21 157.6
3 4.764 2.941 32.36 1.65 20.16 153.2

4 4.725 2.938 32.03 1.65 20.16 156.4
5 4.698 2.943 31.96 1.65 20.15 156.5
6 4.503 2.941 30.58 1.66 20.35 168.3
7 4.375 2.940 29.71 1.67 20.40 173.7
8 4.371 2.940 29.68 1.67 20.42 174.9
9 4.282 2.941 29.08 1.68 20.42 171.4
10 3.892 2.937 26.36 1.71 20.63 174.8
Climate
Chamber
Co
nta
ine
r1
Co
nta
ine
r2
Pump
Vacuum
PumpOil
WaterWater
Figure 1. Schematic of experimental setup used for saturation.
3. Experimental setup81
The assemblies used in saturation operations and Huff-n-Puff
tests are presented on fig. 1 and fig. 282

respectively. The assemblies are presented by two piston
vessels, climate chamber, vacuum pump, and the pump.83
The pump, Quizix QX (Chandler Engineering), is a piston pump
with two cylinders that can work in the regime84
of continuous delivery and receiving; it pushes the piston of the
cylinder filled by oil or gas and replaces the85
liquid into high-pressure stainless steel container 1 filled by the
rock samples placed vertically. The samples are86
placed on the piston inside the annulus of container 1; and they
are free from any sleeves. The piston is adjusted87
on the desired level by water on the bottom side of container 1.
The pump allowed to inject the gas at the pressure88
up to 24 MPa. Climate chamber, MK 240 (Binder), allowed to
keep the reservoir temperature with fluctuation up89
to 0.5 ◦C.90
4. Experimental procedures91
The experimental procedure [23] was adopted in this work to
the experiments with heavy oil. In the original92
procedure, the Huff-n-Puff injection of gas happens at each
pressure regimes with every shale core sample.93
Despite the real rock samples had moderately high porosity-
permeability, it was decided to work with highly94
homogeneous samples of Berea sandstone to speed up the
original procedure of CO2 Huff-n-Puff injection at95
different pressure regimes. The experimental procedure is
presented by the step of core saturation (1) and by the96
part of Huff-n-Puff gas injection tests (2).97
Figure 1. Schematic of experimental setup used for saturation.
Energies 2019, 12, 4308 5 of 15Version October 28, 2019
submitted to Energies 5 of 16

Climate
Chamber
Co
nta
ine
r1
Co
nta
ine
r2
CO2
Pump
WaterWater
Figure 2. Schematic of experimental setup for the CO2 Huff-n-
Puff test.
4.1. Saturation Step98
In order to saturate the samples, the collection of samples was
extracted by kerosen and then dried in the99
oven under 120 ◦C during 24 hours. The weight (Wd) of dried
core samples was measured. Then the samples100
were placed in the container 1 (fig. A2a) and vacuumed in the
container during 6 hours. The saturation process101
was conducted at the temperature two times bigger than the
temperature of paraffin crystallization (table 2). At102
the next stage Quizix QX pump pushed the piston of container 2
and oil filled container 1 with samples with the103

speed of 5 ml/min and restored the reservoir pressure. The
pressure of container 2 was maintained for at least104
24 hours (section A). Then the core samples were taken out,
cleaned by cleaning paper and the weight of each105
sample was measured and registered as Ws. Then the samples
were stored in desiccator to keep the oil in the106
samples. The core samples were saturated by 100% with oil
without connate water.107
4.2. Huff-n-Puff gas injection procedure108
Part of Huff-n-Puff gas injection tests is presented on fig. 2 and
should simulate the Huff-n-Puff injection of109
CO2 in the oil field. Initially, the air in the container 1 is blown
off by multiple reinjections of CO2 from external110
gas cylinder under 0.25 MPa. Then the lines between the
containers are vacuumed by a vacuum pump. Then the111
CO2 in injected from container 2 to container 1 during 30
minutes, and then the pressure should be raised to the112
experimental pressure by piston pump if it is needed. The
soaking time is equal to 6 hours. After the soaking113
period, the pressure should be released with depletion rate of
0.5 MPa/min to the atmospheric pressure. Then the114
production period is equal to 6 hours. So in the end, the the
samples are taken out from the vessel (fig. A2b) and115
cleaned (fig. A3). Then weight of the core samples is measured
(Wi). The next injection cycle starts immediately116
after weight measuring. The same procedure is repeated for all
subsequent cycles after the first cycle of injection.117
The weight measurements are done to estimate oil recovery
using the following eq. (1). But the eq. (1) does not118
estimate the density of original oil is similar to the remaining
oils at different stages.119
Oil Recovery in cycle i =
Wi − Wd
Ws − Wd

× 100% (1)
In the original procedure developed for the shale samples, each
sample should go through all the injection120
pressure regimes. However, in our case, homogeneous Berea
sandstone samples were used. Despite high121
similarities in sizes, porosity and permeability among the
samples, oil recovery of each sample should be122
normalized according to their surface area and volume using eq.
(2). The first injection cycle yielded the highest123
incremental oil recovery from 20.70% to 27.67% for different
injection pressure regimes. The porosity has not124
been used in this normalizing factor since it is taken into
account in the oil recovery values itself.125
Oil Recoverynormalized =
Oil Recoverycycle i
Surface Area
V olume
×
Mean Surface Area
Mean Volume (2)
Figure 2. Schematic of experimental setup for the CO2 Huff-n-
Puff test.
4. Experimental Procedures
The experimental procedure used in this work [23] was adapted
to the experiments with heavy
oil. In the original procedure, the Huff-n-Puff injection of gas
occurs at each pressure regime with

every shale core sample. Despite the real rock samples having
moderately high porosity–permeability,
we decided to use highly homogeneous samples of Berea
sandstone to speed up the original procedure
of CO2 Huff-n-Puff injection at different pressure regimes. The
experimental procedure presented has
two steps: (1) core saturation and (2) the Huff-n-Puff gas
injection tests.
4.1. Saturation Step
To saturate the samples, the collection of samples was extracted
by kerosene and then dried
in the oven under 120 ◦C during 24 h. The weight (Wd) of the
dried core samples was measured.
Then, the samples were placed in the container 1 (Appendix A)
and vacuumed in the container for
6 h. The saturation process was conducted at a temperature two
times greater than the temperature
of paraffin crystallization (Table 2). At the next stage, the
Quizix QX pump pushed the pistons of
container 2 and oil-filled container 1 with samples at a speed of
5 mL/min and restored the reservoir
pressure. The pressure of container 2 was maintained for at least
24 h (Appendix B). Then, the core
samples were taken out, cleaned by cleaning paper, and the
weight of each sample was measured and
registered as Ws. Then, the samples were stored in desiccator to
keep the oil in the samples between
the experiments. The core samples were saturated to 100% with
oil without connate water.
4.2. Huff-n-Puff Gas Injection Procedure
Part of the Huff-n-Puff gas injection tests is presented in Figure
2 and should simulate the

Huff-n-Puff injection of CO2 in the oil field. Initially, the air in
container 1 is blown off by multiple
reinjections of CO2 from the external gas cylinder under 0.25
MPa. Then, the lines between the
containers are vacuumed by a vacuum pump. Then, the CO2 is
injected from container 2 to container
1 for 30 min, and then the pressure should be raised to the
experimental pressure by piston pump
if it is needed. The soaking time is 6 h. After the soaking
period, the pressure should be released
with depletion rate of 0.5 MPa/min to the atmospheric pressure.
Then, the production period is 6 h.
Therefore, finally, the samples are taken out from the vessel
(Figure A1b) and cleaned (Figure A2).
Then, the core samples are weighed (Wi). The next injection
cycle starts immediately after weighing.
Energies 2019, 12, 4308 6 of 15
The same procedure is repeated for all subsequent cycles after
the first cycle of injection. The weight
measurements are done to estimate oil recovery using Equation
(1). However, Equation (1) does not
estimate the density of the original oil as being similar to the
remaining oils at different stages.
Oil Recovery in cycle i =
Wi − Wd
Ws − Wd
× 100% (1)
In the original procedure developed for the shale samples, each
sample should go through all of

the injection pressure regimes. However, in our case,
homogeneous Berea sandstone samples were
used. Despite the high similarity in size, porosity, and
permeability among the samples, oil recovery
of each sample should be normalized according to their surface
area and volume using Equation (2).
The first injection cycle yielded the highest incremental oil
recovery from 20.70% to 27.67% for different
injection pressure regimes. The porosity has not been used in
this normalizing factor as it is taken into
account in the oil recovery values itself.
Oil Recoverynormalized =
Oil Recoverycycle i
Surface Area
Volume
×
Mean Surface Area
Mean Volume (2)
5. Results and Discussion
5.1. Effect of Cycle Number
Each subsequent cycle of the Huff-n-Puff CO2 injection gives
less incremental oil recovery than
the previous cycle. Experiments with oil from oilfield #1 was
conducted earlier than experiment with
oil from oilfield #2. The biggest amount of oil from oilfield #1
is extracted during the first three cycles
of injection, and then just a small volume of oil can be
produced. This is why we only use three cycles
of injection instead of six cycles in the experiments with oil

from oilfield #2. Incremental oil recovery
for each injection cycle is shown in Tables 5 and 6 for both
reservoirs. The decrease of subsequent
incremental oil recovery occurs because of the reduction of the
contact area of CO2 and oil inside the
pore space, which caused the remaining oil to become heavier
and more viscous (2) and the heavy oil
deposits to be destabilized, and they caused a decrease of
permeability of the core samples (3). The first
two cycles can give an incremental recovery factor above 35%.
After these cycles, the incremental oil
recovery does not usually exceed 3% in one cycle. Raw
experimental data was previously published
by Maksakov and Cheremisin [24].
Table 5. Incremental oil recovery at each cycle of Huff-n-Puff
CO2 injection for experiments with oil
from oilfield #1.
Sample No.
Pressure Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 5 Cycle 6
MPa % % % % % %
3 6 20.70 10.62 1.06 1.08 0.37 0.44
4 6 20.63 11.27 0.64 0.35 0.60 0.69
7 10 26.70 9.37 3.41 1.66 1.57 1.15
9 10 26.12 8.98 2.70 1.63 1.67 0.40
2 14 27.20 9.49 2.54 0.65 1.10 1.35
1 14 27.67 8.36 2.68 1.57 0.85 0.39
5 19 21.48 15.88 2.43 1.51 1.05 1.51
6 19 21.57 15.84 1.86 1.08 1.30 0.81
8 24 23.99 12.41 1.67 1.26 1.78 1.32
10 24 26.06 10.40 1.84 1.61 1.71 0.83

Energies 2019, 12, 4308 7 of 15
Table 6. Incremental oil recovery at each cycle of Huff-n-Puff
CO2 injection for experiments with oil
from oilfield #2.
Sample No.
Pressure Cycle 1 Cycle 2 Cycle 3
MPa % % %
1 5 23.92 16.33 0.56
6 5 29.56 7.05 0.57
2 7.5 21.39 13.84 5.02
3 12 31.56 5.75 3.25
4 18 30.81 4.66 3.06
5 24 28.27 7.92 3.16
5.2. Cumulative Oil Recovery
The graphical representation of cumulative oil recovery for both
oil reservoirs is presented in
Figure 3. Clearly, three cycles is not high enough for the
experiments with oilfield #2, as shown
in Figure 3b, if the experiments continued cumulative oil
recovery for different pressure regimes
would be equalized. According to the company’s prerequisite,
the range of injection pressure of CO2
was predetermined by the limitation of the surface injection
pumps and reservoir fracture pressure.
The cumulative heavy oil recovery can be over 40% after a
number of Huff-n-Puff CO2 injection cycles.Version October
28, 2019 submitted to Energies 7 of 16
1 2 3 4 5 6

20
25
30
35
40
45
Cycle Number
Cu
mu
lat
ive
Oi
lR
eco
ve
ry,
%
Sample 3 (6 MPa) Sample 4 (6 MPa)
(a) Oil from Oilfield #1

1 2 3
20
25
30
35
40
Cycle Number
Cu
mu
lat
ive
Oi
lR
eco
ve
ry,
%
Sample 2 (7.5 MPa) Sample 3 (12 MPa)
(b) Oil from Oilfield #2
Figure 3. Pressure effect on CO2 Huff-n-Puff performance.

equalised. According to the company’s prerequisite, the range
of injection pressure of CO2 was predetermined by146
the limitation of the surface injection pumps and reservoir
fracture pressure.147
5.3. Miscibility Studies148
In order to evaluate the miscibility of oil samples with CO2,
vast Huff-n-Puff injection experiments were149
conducted at five different pressure regimes for both oil heavy
samples. Each oil recovery was normalized150
according to the volume and surface area of used samples, and
the mean value was taken if more than one samples151
were used in the Huff-n-Puff injection test. Normalized oil
recovery for oil samples from oilfield #1 and oilfield152
#2 are presented on fig. 4 and fig. 5. For the normalized oil
recovery studies (Oilfield #1) on figs. 4b to 4f two153
straight lines can be drawn. Since there is not a clear
intersection of these lines, the miscibility pressure cannot154
be determined. However, taking into account the results of
special PVT studies it is possible to conclude that155
the mixing zone of CO2 with light oil components of oil from
oilfield #1, when CO2 becomes miscible with156
light components of oil, lies in the interval from 6 MPa to 10
MPa as it is shown on fig. 4f. The mixing zone of157
CO2 and light oil components of oil from oilfield #2 lies below
5 MPa as it is shown on fig. 5c. Therefore, the158
assumption is the following: when the miscibility pressure of
CO2 with light components is achieved, the oil159
recovery remained the same until it reaches miscibility pressure
with heavy components.160
5.4. Effect of CO2 injection on oil and rock properties161
The Huff-n-Puff injection of CO2 leads to the extraction of
light components first and can accelerate heavy162
oil depositions. In order to prove the idea that light components
of oil yield first, the extracted oil sample was163

collected after Huff-n-Puff CO2 injection tests and analyzed
using GC/MS. Oil sample from oilfield #1 was164
collected after the 1st cycle of injection at 14 MPa, and oil
sample from oilfield #2 was collected after the 1st165
cycle of injection at 5 MPa. Figure 6 presents the difference of
composition of the original oil, extracted oil and166
the oil remained in the samples after yield. The composition of
remained oil was calculated using compositions167
of initial and extracted oil, and the masses of oil before and
after the experiments. This investigation of the change168
of oil composition after Huff-n-Puff injection of CO2 tests
proved that the extracted oil from the samples is much169
lighter that the remained in the samples. However, it is an
opened question about heavy oil deposits.170
Figure 3. Pressure effect on CO2 Huff-n-Puff performance.
5.3. Miscibility Studies
To evaluate the miscibility of oil samples with CO2, vast Huff-
n-Puff injection experiments were
conducted at five different pressure regimes for both oil heavy
samples. Each oil recovery was
normalized according to the volume and surface area of the used
samples, and the mean value was
taken if more than one samples were used in the Huff-n-Puff
injection test. Normalized oil recovery
for oil samples from oilfield #1 and oilfield #2 are presented in
Figures 4 and 5. For the normalized
oil recovery studies (Oilfield #1) shown in Figure 4b–f, two
straight lines can be drawn. As there is
not a clear intersection of these lines, the miscibility pressure
cannot be determined. According to the
special PVT studies of oil samples from oilfield #1 and oilfield
#2, these oil samples tended to form
two-phase systems under reservoir conditions when the

concentration of CO2 was higher than 70%
mole (Appendix C). These two-phase systems formed by the
phase of CO2 and light oil components
Energies 2019, 12, 4308 8 of 15
and by the phase of heavy oil components. Taking into account
the results of special PVT studies,
it is possible to define the mixing zone, when CO2 becomes
miscible with light components of oil.
The mixing zone of CO2 with light oil components of oil from
oilfield #1 lies in the interval from 6
MPa to 10 MPa, as shown in Figure 4f. The mixing zone of CO2
and light oil components of oil from
oilfield #2 is below 5 MPa, as it is shown in Figure 5c. Oil
samples from oilfield #1 and oilfield #2
tended to split into the two-phase mixture over 10 MPa and 5
MPa accordingly. Therefore, we made
the following assumption: when the miscibility pressure of CO2
with light components is achieved,
the oil recovery remained the same until it reaches miscibility
pressure with heavy components.
0 5 10 15 20 25 30
20
22
24
26

28
30
6 MPa
10 MPa
14 MPa
19 MPa
24 MPa
Pressure, MPa
No
rm
ali
zed
Oi
lR
eco
ve
ry,
%
(a) Cycle #1
0 5 10 15 20 25 30
30

32
34
36
38
40
6 MPa
10 MPa
14 MPa
19 MPa
24 MPa
Pressure, MPa
No
rm
ali
zed
Oi
lR
eco
ve
ry,
%

0.8582x + 26.723
-0.0965x + 38.515
(b) Cycle #2
0 5 10 15 20 25 30
30
35
40
45
6 MPa
10 MPa
14 MPa 19 MPa
24 MPa
Pressure, MPa
No
rm
ali
zed
Oi
lR
eco
ve
ry,

%
1.4017x + 24.315
-0.1884x + 42.433
(c) Cycle #3
0 5 10 15 20 25 30
30
35
40
45
6 MPa
10 MPa
14 MPa
19 MPa
24 MPa
Pressure, MPa
No
rm
ali
zed
Oi
lR

eco
ve
ry,
%
1.629x + 23.674
-0.0981x + 41.877
(d) Cycle #4
0 5 10 15 20 25 30
30
35
40
45
6 MPa
10 MPa 14 MPa
19 MPa
24 MPa
Pressure, MPa
No
rm
ali
zed

Oi
lR
eco
ve
ry,
%
1.9091x + 22.482
-0.0759x + 42.842
(e) Cycle #5
0 5 10 15 20 25 30
30
35
40
45
6 MPa
10 MPa 14 MPa
19 MPa
24 MPa
Pressure, MPa
No
rm
ali

zed
Oi
lR
eco
ve
ry,
%
mixing zone for CO2 with light components of oil
1.9587x + 22.756
-0.0533x + 43.44
(f) Cycle #6
Figure 4. Effect of pressure on normalized oil recovery at
different cycles of huff-n-puff CO2 injection with oil
from oilfield #1.Figure 4. Effect of pressure on normalized oil
recovery at different cycles of Huff-n-Puff CO2 injection
with oil from oilfield #1.
Energies 2019, 12, 4308 9 of 15
0 5 10 15 20 25 30
20
25
30

35
5 MPa
7.5 MPa
12 MPa
18 MPa
24 MPa
Pressure, MPa
No
rm
ali
zed
Oi
lR
eco
ve
ry,
%
(a) Cycle #1
0 5 10 15 20 25 30
36
38

40
42
44
5 MPa
7.5 MPa
12 MPa
18 MPa
24 MPa
Pressure, MPa
No
rm
ali
zed
Oi
lR
eco
ve
ry,
%
(b) Cycle #2
0 5 10 15 20 25 30

36
38
40
42
44
5 MPa
7.5 MPa 12 MPa
18 MPa
24 MPa
Pressure, MPa
No
rm
ali
zed
Oi
lR
eco
ve
ry,
%
mixing zone of CO2 with light components of oil

(c) Cycle #3
Figure 5. Effect of pressure on normalized oil recovery at
different cycles of huff-n-puff CO2 injection with oil
from oilfield #2.Figure 5. Effect of pressure on normalized oil
recovery at different cycles of Huff-n-Puff CO2 injection
with oil from oilfield #2.
5.4. Effect of CO2 Injection on Oil and Rock Properties
The Huff-n-Puff injection of CO2 leads to the extraction of
light components first and can accelerate
heavy oil depositions. To prove the idea that light components
of oil yield first, the extracted oil sample
was collected after Huff-n-Puff CO2 injection tests and
analyzed using gas chromatography–mass
spectrometry (GC-MS). The oil sample from oilfield #1 was
collected after the 1st cycle of injection
at 14 MPa, and the oil sample from oilfield #2 was collected
after the 1st cycle of injection at 5 MPa.
Figure 6 presents the difference of composition of the original
oil, extracted oil, and the remaining
oil in the samples after yield. The composition of remained oil
was calculated using compositions of
initial and extracted oil, and the masses of oil before and after
the experiments. This investigation of
the change of oil composition after Huff-n-Puff injection of
CO2 tests proved that the extracted oil from
the samples is much lighter that the oil that remained in the
samples. However, it represents an open
question about heavy oil deposits.
Energies 2019, 12, 4308 10 of 15

C 4 C 8 C 12 C 16 C 20 C 24 C 28 C 32 C 36 C 40
0
0.5
1
1.5
Compounds
Am
ou
nt
in
Oi
l,%
ma
ss
Composition of Original Oil
Composition of Extracted Oil
Composition of Remained Oil
(a) Oil from Oilfield #1
C 4 C 8 C 12 C 16 C 20 C 24 C 28 C 32 C 36 C 40
0
0.5
1

1.5
2
Compounds
Am
ou
nt
in
Oi
l,%
ma
ss
Composition of Original Oil
Composition of Extracted Oil
Composition of Remained Oil
(b) Oil from Oilfield #2
Figure 6. Difference in oil composition after CO2 huff-n-puff
injection.
Table 7. Permeability Change due to the Huff-n-Puff CO2
injection.
Sample no. Reservoir
Helium
permeability
N-pentane
permeability

Helium
permeability
Toluene
permeability
before experiments after experiments after experiments after
experiments
mD mD mD mD
7 (10 MPa) Oilfield #1 173 13 159 77
2 (7.5 MPa) Oilfield #2 147 8 144 39
Compositional change of heavy oil due to injection CO2 can
lead to destabilization of asphaltenes, resin,171
and paraffin deposits [25]. Since the fact that this process can
cause the precipitation and deposition of asphaltene172
particles in the pore space of the samples [26], it was a need to
evaluate the change of permeability after173
Huff-n-Puff CO2 injection. In order to evaluate the permeability
sample #7 from experiments with oil from174
oilfield #1 and sample #2 from experiments with oil from
oilfield #2 were taken. Flood experiments were175
conducted and permeability was measured by N-pentane with
both samples. Permeability was measured in the176
presence of asphaltenes because N-pentane does not dissolve
precipitated heavy oil deposits [27,28]. Then the177
samples were dried, and permeability by helium was measured
in order to compare it with the initial permeability178
before Huff-n-Puff tests. So in the end, another core flood
experiments were conducted using toluene. Toluene179
dissolves all heavy deposits, that is why true liquid permeability
was measured. The injection pressure was equal180
to reservoir pressure. The confining pressure was 30% higher
than the injection pressure. The injection speed181

was 0.5 ml/min in flood experiments with solvents. These
permeability tests proved that the injection of CO2182
decreased the permeability of the rock sample due to the heavy
oil deposits, and all the permeability values are183
presented in table 7.184
These tests indicated the permeability decrease after huff-n-puff
injection tests, but the damage from heavy185
oil deposits depends on the specific oil composition, amount of
heavy oil deposits of the specific oil, reservoir186
pressure and temperature, gas injection rate, and oil depletion
rate. An universal strategy could not exist due to187
the high amount of variables.188
Figure 6. Difference in oil composition after CO2 Huff-n-Puff
injection.
Compositional change of heavy oil due to injection CO2 can
lead to destabilization of asphaltenes,
resin, and paraffin deposits [25]. As this process can cause the
precipitation and deposition of
asphaltene particles in the pore space of the samples [26], we
needed to evaluate the change of
permeability after Huff-n-Puff CO2 injection. To evaluate the
permeability, sample #7 from experiments
with oil from oilfield #1 and sample #2 from experiments with
oil from oilfield #2 were taken. Flood
experiments were conducted, and permeability was measured by
N-pentane with both samples.
Permeability was measured in the presence of asphaltenes
because N-pentane does not dissolve
precipitated heavy oil deposits [27,28]. Then, the samples were
dried, and permeability by helium was
measured so as to compare it with the initial permeability
before the Huff-n-Puff tests. Therefore, in
the end, further core flood experiments were conducted using

toluene. Toluene dissolves all heavy
deposits, which is why true liquid permeability was measured.
The injection pressure was equal to
reservoir pressure. The confining pressure was 30% higher than
the injection pressure. The injection
speed was 0.5 mL/min in flood experiments with solvents.
These permeability tests proved that the
injection of CO2 decreased the permeability of the rock sample
due to the heavy oil deposits, and all
the permeability values are presented in Table 7.
These tests indicated the permeability decrease after Huff-n-
Puff injection tests, but the damage
from heavy oil deposits depends on the specific oil composition,
amount of heavy oil deposits of the
specific oil, reservoir pressure and temperature, gas injection
rate, and oil depletion rate. A universal
strategy could not exist due to the high amount of variables.
Table 7. Permeability change due to the Huff-n-Puff CO2
injection.
Sample No. Reservoir
Helium Permeability N-Pentane Permeability Helium
Permeability Toluene Permeability
before Experiments after Experiments after Experiments after
Experiments
mD mD mD mD
7 (10 MPa) Oilfield #1 173 13 159 77
2 (7.5 MPa) Oilfield #2 147 8 144 39
Energies 2019, 12, 4308 11 of 15

6. Conclusions
In this study, CO2 Huff-n-Puff tests with two heavy oil samples
were conducted using Berea
sandstone samples. The determination of oil miscibility with
CO2 by Huff-n-Puff tests was proved.
From this study, some conclusions can be drawn:
1. The recovery of heavy oil obtained from CO2 injection
experiments was as high as 43%. This result
shows that CO2 Huff-n-Puff injection can be an efficient
approach to enhance heavy oil recovery.
However, it was not to possible to differentiate the oil recovery
as a result of solution gas drive
(gas nucleation, gas expansion) during the pressure drop mode.
2. The major amount of oil is extracted by the first three cycles
of CO2 injection. The subsequent
cycles of CO2 injection do not cause a considerable change in
oil recovery.
3. CO2 injection in heavy oil causes heavy oil deposition and
decreases permeability. Permeability
measured by gas, n-pentane, and toluene showed the difference
of permeability of the core plugs
in the presence and the absence of heavy oil deposits.
4. Huff-n-puff tests can be applied for miscibility studies of
heavy oil with gas. However, MMP for
heavy oil is very high should be taken into consideration.
5. When miscibility of CO2 with light oil components of heavy
oil is achieved, the subsequent
pressure increase under MMP does not affect oil recovery at the
core scale experiments. However,

it would be conjecture to presume that the higher injection
pressure of gas leads to the higher rate
of oil heavy deposits and more severe porosity and permeability
damage.
Author Contributions: Conceptualization, E.S., A.C., K.M., and
S.K.; Methodology, E.S.; Formal Analysis, E.S.;
Investigation, E.S.; Resources, K.M. and A.K.; Data Curation,
E.S.; Writing—Original Draft Preparation, E.S.;
Writing—Review & Editing, E.S. and A.C.; Visualization, E.S.;
Supervision, A.C.
Funding: This research is based on the results of the industrial
project funded by LUKOIL-Engineering LCC.
Acknowledgments: This research was funded by LUKOIL-
Engineering LCC and Ritek JSC. We thank our
colleagues from industry for providing the resources for
experimental studies. We would also like to show
our gratefulness to Pavel Zobov, Denis Bakulin, and Sergey
Antonov for their technical assistance in the
presented experiments.
Conflicts of Interest: The authors declare no conflicts of
interest.
Abbreviations
The following abbreviations are used in this manuscript.
Wd dry core sample weight, g
Ws saturated core sample weight, g
Wi core sample weight after Huff-n-Puff injection cycle, g
AS/V surface-to-volume ratio, cm2/cm3

Energies 2019, 12, 4308 12 of 15
Appendix A. Example Photos
0 20 40 60
0
5
10
15
Time, Hours
Pre
ssu
re,
M
Pa
Pressure
0
200
400
600

Tr
an
sfe
rre
dO
il,
cm
3
Pressure Cumulative Volume
(a) Sample Saturation of Oilfield #1
0 20 40 60
0
2
4
6
8
10
Time, Hours
Pre
ssu
re,
M

Pa
Pressure
0
50
100
150
200
Tr
an
sfe
rre
dO
il,
cm
3
(b) Sample Saturation of Oilfield #2
Figure A1. Saturation Logs.
Appendix B. Example Photos231
(a) Extracted samples inside the vessel before the
saturation.

(b) Sample inside the opened container after
Huff-n-Puff injection cycle.
Figure A2. Example of Experimental Operations.
Figure A1. Example of experimental operations.Version October
28, 2019 submitted to Energies 13 of 16
(a) Oily Sample after Huff-n-Puff CO2 Injection
Cycle.
(b) Cleaned Sample for Weighting.
Figure A3. Photos of Sample after Huff-n-Puff Injection Cycle .
Appendix C. Viscosity Measurements from Special PVT
Test232
According to the special PVT studies, if the concentration of
CO2 is over 70%, the oils from both oilfields233
split to unmixed light and heavy phases. The special PVT
studies were done with recombined oil samples, which234
are less viscous than the dead oil samples used in the Huff-n-
Puff experiments. The light phase is presented235
mainly by CO2, and the heavy phase is mainly presented by
oil.236
0 20 40 60 80 100
200
400
600
800
1,000

CO2 concentration, % mole
Vi
sco
sit
y,
m
Pa
s
(a) Oilfield #1
0 20 40 60 80 100
100
200
300
Vi
sco
sit
y,
m
Pa
s
(b) Oilfield #2

Figure A4. Viscosity of heavy phase depending on amount CO2
mole concentration for recombined oil.
References237
1. U.S. EIA. Annual Energy Outlook 2017 with projections to
2050. Technical Report 8, 2017.238
2. Atkinson, N.; Barret, C.; Packey, P.; Bosoni, T.; Petrosyan,
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Conventional Oil Production Impacts on Oil Price - Lessons242
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Figure A2. Photos of sample after Huff-n-Puff injection cycle.
Appendix B. Saturation Logs
As the samples were placed to the stainless steel container 1
(Figure A1a), the oil should fill
the empty volume of the container first and only then the porous
media of the samples. Figure A3a
shows the saturation process of the samples by the oil sample
from Oilfield #1; during this saturation

operation, an oil leakage between the transfer vessel filled with
oil and the vessel filled with samples
occurred; that is why the amount of transferred oil is bigger
than in the next saturation operation.
Figure A3b shows the saturation process of the samples by the
oil sample from Oilfield #2; after
transferring of 209 mL of oil, the pressure was rapidly increased
to the reservoir pressure of 10.3 MPa.
Energies 2019, 12, 4308 13 of 15Version October 28, 2019
submitted to Energies 12 of 16
0 20 40 60
0
5
10
15
Time, Hours
Pre
ssu
re,
M
Pa
Pressure
0

200
400
600
Tr
an
sfe
rre
dO
il,
cm
3
(a) Sample Saturation of Oilfield #1
0 20 40 60
0
2
4
6
8
10

Time, Hours
Pre
ssu
re,
M
Pa
Pressure
0
50
100
150
200
Tr
an
sfe
rre
dO
il,
cm
3
(b) Sample Saturation of Oilfield #2

Figure A1. Saturation Logs.
Appendix B. Example Photos231
(a) Extracted samples inside the vessel before the
saturation.
(b) Sample inside the opened container after
Huff-n-Puff injection cycle.
Figure A2. Example of Experimental Operations.
Figure A3. Saturation logs.
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CO2 is over 70%, the oils from both
oilfields split to unmixed light and heavy phases; it is reflected
by viscosity increase on the Figure A4.
The special PVT studies were done with recombined oil
samples, which are less viscous than the dead
oil samples used in the Huff-n-Puff experiments. The light
phase is presented mainly by CO2, and the
heavy phase is mainly presented by oil.
(a) Oily Sample after Huff-n-Puff CO2 Injection
Cycle.
(b) Cleaned Sample for Weighting.
Figure A3. Photos of Sample after Huff-n-Puff Injection Cycle .
Appendix C. Viscosity Measurements from Special PVT
Test232

CO2 is over 70%, the oils from both oilfields233
split to unmixed light and heavy phases. The special PVT
studies were done with recombined oil samples, which234
are less viscous than the dead oil samples used in the Huff-n-
Puff experiments. The light phase is presented235
mainly by CO2, and the heavy phase is mainly presented by
oil.236
0 20 40 60 80 100
200
400
600
800
1,000
Vi
sco
sit
y,
m
Pa
s
(a) Oilfield #1

0 20 40 60 80 100
100
200
300
Vi
sco
sit
y,
m
Pa
s
(b) Oilfield #2
References237
1. U.S. EIA. Annual Energy Outlook 2017 with projections to
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Report December, 2018. doi:10.1787/weo-2018-en.240
2019. Technical report, London, UK, 2019.241
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Learnt with Glance to the Future. Journal of Global Economics
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K.; Beshry, M.; Krawchuk, P.; Brown, G.; Calvo, R.; Triana,
J.a.C.; Hathcock, R.; Koerner, K.; Hughes, T.; Kundu,245
D.; De Cárdenas, J.L.; West, C. Highlighting Heavy Oil.
Oilfield Review 2006, 18, 34–53.246
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Engineering Conference, Port-of-Spain,
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21. Shilov, E.; Cheremisin, A. The CO2 Huff-n-Puff Test For
Minimum Miscibility Pressure Determination
for Heavy Oil. In Proceedings of the 5th CO2 Geological
Storage Workshop, Utrecht, The Netherlands,
21–23 November 2018; pp. 1–5. [CrossRef]
22. Qazvini Firouz, A.; Torabi, F. Feasibility Study of Solvent-
Based Huff-n-Puff Method (Cyclic Solvent Injection)
To Enhance Heavy Oil Recovery. In Proceedings of the SPE
Heavy Oil Conference Canada, Calgary, AB,
Canada, 12–14 June 2012. [CrossRef]
23. Li, L.; Sheng, J.J. Experimental study of core size effect on
CH4 Huff-n-Puff enhanced oil recovery in
liquid-rich shale reservoirs. J. Nat. Gas Sci. Eng. 2016, 34,
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http://dx.doi.org/10.1016/j.fuel.2017.09.047
http://dx.doi.org/10.3390/en20300714
http://dx.doi.org/10.1016/B978-1-933762-03-6.50010-1
http://dx.doi.org/10.1021/acs.energyfuels.7b00031
http://dx.doi.org/10.2118/06-07-02
http://dx.doi.org/10.2118/184407-PA
http://dx.doi.org/10.3997/2214-4609.201802977
http://dx.doi.org/10.2118/157853-ms
http://dx.doi.org/10.1016/j.jngse.2016.08.028
Energies 2019, 12, 4308 15 of 15
24. Nekrasov, A.; Maksakov, K.; Usachev, G.; Karpov, V.;
Cheremisin, A. Optimization of the Technological
Efficiency Of CO2 Injection in Extra-Viscous Oil Deposits
Using Laboratory Studies and Numerical Modeling.
In Geology, Geophysics and Development of Oil and Gas
Fields; All-Russian Scientific Research Institute of
Organization, Management and Economy of the Oil and Gas
Industry: Moscow, Russia, 2019; pp. 81–86.
[CrossRef]
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review of the CO2 huff ‘n’ puff process for
enhanced heavy oil recovery. Fuel 2018, 215, 813–824.
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26. Abedini, A.; Torabi, F. Oil Recovery Performance of
Immiscible and Miscible CO2 Huff-and- Puff Processes.
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27. Speight, J.G. The Chemistry and Technology of Petroleum,
5th ed.; Chemical Industries; CRC Press: Boca Raton,
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c© 2019 by the authors. Licensee MDPI, Basel, Switzerland.
This article is an open access
article distributed under the terms and conditions of the
Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/ ).
http://dx.doi.org/10.30713/2413-5011-2019-8(332)-81-86
http://dx.doi.org/10.1016/j.fuel.2017.11.092
http://dx.doi.org/10.1021/ef401363b
http://dx.doi.org/10.1016/S0920-4105(96)00059-9
http://creativecommons.org/
http://creativecommons.org/licenses/by/4.0/.IntroductionMateria
lsExperimental SetupExperimental ProceduresSaturation
StepHuff-n-Puff Gas Injection ProcedureResults and
DiscussionEffect of Cycle NumberCumulative Oil
RecoveryMiscibility StudiesEffect of CO2 Injection on Oil and
Rock PropertiesConclusionsExample PhotosSaturation
LogsViscosity Measurements from Special PVT TestReferences
Name
Period

English 8 Final Exam—2021
Dr. Nohrden
Instructions: Type your name and period number in the upper
left corner of this document where indicated. Read the prompts
carefully and write your responses in the spaces provided. Give
deep thought to your responses, and give a thorough explanation
using a academic writing (formal: no first person, no
contractions, etc.). Your responses must be 200-300 words
each. Each prompt/response is worth 25 points for a total of
100 points (for example, these instructions are 131 words).
This test is worth 20% of your grade for this semester. When
you are finished, save your completed test to your computer and
upload it to Turnitin.com. All responses must be uploaded no
later than 3:00 p.m. on June 8, 2021. The information you may
need for Turnitin.com is as follows:
Period 4—
Class I.D.: 26203122
Enrollment Key: NohrdenP4
Period 5—
Class I.D.: 26203146
Period 6—
Class I.D.26203159
Type your response in the space immediately below each
prompt. Type your responses in black.
1
Choose one of the following prompts:

a. Compare the character of Iago in Othello with Mr. Collins in
Pride and Prejudice.
b. Compare the character Emilia in Othello with Charlotte Lucas
in Pride and Prejudice.
c. Compare the character Othello in Othello with Mr. Hyde in
Dr. Jekyll and Mr. Hyde.
2
Read the following poem, then explicate it in two paragraphs.
You answer must include one paragraph explaining its hidden
meaning as well as a paragraph that discusses the poems
metaphors and other figurative language, imagery, and
structure.
Santa’s Not Coming
By Michael Murray
Santa’s not coming
this year
I saw him
hung from a tree
by his neck
like a sacrifice
to Odin.
But no eight-legged
horse will carry
him to his grave
because no one
remembers
the old ways.
But he won’t be missed.

At yule’s dawn
we’ll don Santa masks
to hide our thoughts
that bite
each other
like the Fenrir-wolf
who devours
the sun and the moon
How Loki-Lucifer
will laugh.
3
Choose one of these topics and write one paragraph in favor of
the topic and one paragraph against the topic. Use at least one
piece of evidence from the internet for each paragraph.
1. Teaching critical race theory in public schools
2. Requiring all students be vaccinated for COVID-19 before
returning to school in the fall
3. Making hate speech a crime
4. Allowing biological males who identify as female compete as
women in high school or college sports
4
How has COVID-19 affected you this year? Include comments
on whether you learned more or learned less due to the hybrid
protocols or full distance learning you experienced.

Rubric for each prompt
25 points: Fully and adequately answers the prompt without
major errors in English conventions
20 points: Partially answers the prompt or has major errors in
English conventions
15 points: Partially answers the prompt and has major err ors in
English conventions
10 points: Attempts to answer the prompt but the response is
nowhere close to being on point, or the response is woefully
under the 100 word minimum
5 points: Does not come close to answering the prompt
The final exam for Dr. Nohrden’s English 8 classes will likely
cover the following areas:
Poetry:
You will be tested on general understanding of poetry. This
includes knowing the following terms:
verse
stanza
quatrain
triplet

cinquain
rhyme and rhyme schemes
meter
iambic pentameter
sonnet
haiku
tanka
ballad
villanelle
free verse
You should also know the difference between various poetic
devices, including, but not limited to, metaphor, simile,
apostrophe, and personification. You should also be ready to
write a short essay about a poem and to explicate it.
Novel Study:
You should understand how a novel is created, including the
development of conflict, setting, theme, point of view, and
especially characterization.
Shakespeare:
You should understand how Shakespeare created his plays with
an emphasis on tragedy and plot development. Just as
important, you must understand the differences in the characters
as shown by Othello and how they contribute to the conflict and

how theyrelate to characters in other stories. Review the play at
home and be familiar with various parts of the play, the names
of the characters, and various aspects of setting, theme, plot,
point of view, and characterization. Be ready to write about
Othello.
Writing Techniques:
By the time of the final exam, we will have learned and
practiced thesis-based writing. You should be certain that you
understand how to create a thesis, the mechanics of essay
writing, the importance of a thesis statement and other elements
of an essay (such as a dynamic opener or “hook”). You will
also be required to know how to reduce the excessive number of
linking verbs (helping verbs) and to include imagery in your
writing.
Debate:
You should be to understand the value of debate and to be able
to write convincingly about both sides of a controversial topic
based upon your own research.
EXTREMELY HELPFUL STUDY HINT: Review all prior tests
and quizzes. This will help you become familiar with what you
don’t know. Also, go over prior writing assignments and read
the teacher’s notes. This can be particularly enlightening if you
are making the same mistakes from assignment to assignment.

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