New EOR Technology: Simultaneous Gas Alternating Gas (SGAG) injection
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IOP Conference Series: Earth and Environmental Science
PAPER • OPEN ACCESS
New EOR Technology: Simultaneous Gas Alternating Gas (SGAG)
injection
To cite this article: Mvomo N. Edouard et al 2021 IOP Conf. Ser.: Earth Environ. Sci. 814 012006
View the article online for updates and enhancements.
This content was downloaded from IP address 46.4.80.155 on 19/09/2021 at 13:11
2021 5th International Conference on Sustainable Energy Engineering (ICSEE 2021) IOP Publishing
IOP Conf. Series: Earth and Environmental Science 814 (2021) 012006 doi:10.1088/1755-1315/814/1/012006
New EOR Technology: Simultaneous Gas Alternating Gas
(SGAG) injection
Mvomo N. Edouard a, 1, Pingchuan Dong b, 2, Chinedu J. Okere a
a
College of Petroleum Engineering, China University of Petroleum (Beijing), Beijing, 102249,
China.
b State Key Laboratory of Petroleum Resources and Prospecting, China University of
Petroleum (Beijing), Beijing 102249, China.
*
corresponding author e-mail: 2019390101@student.cup.edu.cn;dpcfem@163.com
Abstract. A new oil recovery method known as Simultaneous Gas Alternating Gas (SGAG)
injection that is based on the principle of the conventional Simultaneous Water Alternating Gas
(SWAG) injection has been proposed in this study. The performance was observed via a
simulation process based on data from an oil field of a shale oil reservoir. The effectiveness of
SGAG was evaluated through a sensitivity analysis, and by observing its effect on oil recovery
factor and ultimate oil recovery. The results of the sensitivity analysis show that (1) SGAG
technique will improve the ultimate recovery factor compared to continuous gas injection; (2)
Based on gravity segregation between two gases, oil recovery is enhanced; and (3) Because the
produced CH4 can be reinjected and based on the availability of CO2, the possible SGAG
combination of (CH4 + CO2) is more economically and feasible for a tank of Shale Oil reserve.
This study provides a reliable basis for minimizing operating costs per unit CO2 injection
volume and insight into cost-effectively enhanced oil recovery (EOR) technique.
1. Introduction
Enhanced oil recovery (EOR) refers to the recovery of the quantities of oil left after the primary and
secondary recoveries, by improving the efficiency of oil displacement and volumetric sweeping. EOR
techniques are numerous and require a significant investment in terms of capital and are associated
with risks (Figure1) [1].
Each method has its considerations which are generally based on the objective of maximizing oil
and gas production. Many effective EOR techniques have been introduced with tremendous success in
field application. In 2019, a new method Gas Alternating Gas (GAG) injection technique was
introduced by Mohammed et al (2019). the results revealed that the GAG method was economical
even though the gas injection scheme was continuous and time-consuming.
Since 2018, the price of CO2 has continued to increase as shown in Figure 2, necessary due to the
supply mechanism for this gas whose stages are capture; sequestration, storage, transport, injection,
and the potential of CO2-EOR will perhaps be a great contribution to the reduction of CO2 emissions
from greenhouse gases in the world [2]. This leads engineers to reflect on new technologies as
efficient as and less expensive that can allow structures to save money to the maximum.
In this study, we propose a new technique of EOR Simultaneous Gas Alternating Gas (SGAG)
injection, via a simultaneous injection scheme. The feasibility of this method was validated by CMG
simulation using input parameters from a shale oil reservoir.
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution
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Published under licence by IOP Publishing Ltd 1
2021 5th International Conference on Sustainable Energy Engineering (ICSEE 2021) IOP Publishing
IOP Conf. Series: Earth and Environmental Science 814 (2021) 012006 doi:10.1088/1755-1315/814/1/012006
Figure 1. Flow sheet for EOR methods
Figure 2. The spot price of CO2 emissions in €/EEA (European Emission Allowance) [3].
2. Simultaneous Gas Alternating Gas (SGAG) injection
The new technique of tertiary recovery of oil, known as Simultaneous Gas Alternating Gas (SGAG)
injection is an Enhanced Oil Recovery process in which gas is mixed with another gas and the
mixtures are then injected as a two-phase mixture in the well to get better oil recovery (Figure3) [4].
The SGAG mechanism of oil recovery, which is miscibility, gravity segregation, mobility control, IFT
reduction, and classification among the cyclic methods like those of SWAG and WAG.
SGAG can be in two ways:
• Mixing the two gas at the wellhead and then injecting it into the reservoir through to single
injection well;
• Simultaneously injecting the two gas using different horizontal wells or one well at the same
time [5].
This technique combines two recovery techniques, namely gas injection and gas flooding, which
involves the alternating injection of CO2 with N2; CH4; H2S and Air. A physical model describing the
recovery process in-situ condition is shown in Figure 3.
2
2021 5th International Conference on Sustainable Energy Engineering (ICSEE 2021) IOP Publishing
IOP Conf. Series: Earth and Environmental Science 814 (2021) 012006 doi:10.1088/1755-1315/814/1/012006
Figure 3. Schematic of Simultaneous Gas-Alternating-Gas (SGAG) injection
3. Simulation
A field-scale simulation model was built to investigate the enhanced shale oil recovery performance of
SGAG.
The simulation work was conducted by using CMG-2012(computer management group ltd,
Calgary, Canada). The compositional model was built by the CMG-GEM model. The CMG-
WINPROP module was used for oil component lumping, according to the fluid properties of the target
reservoir. To speed up the numerical simulation and ensure the accuracy of the calculation results, we
divided the crude oil of pseudo-components are listed in table1 [6].
Table 1. Component composition
Component Composition
CO2 0.2600052
N2-CH4 25.056501
C2H6 11.868237
C3H8 9.7581952
IC4-NC4 6.399128
IC5-NC5 4.0290806
C6 3.3790676
C7-C10 18.346367
C11-C13 7.8721574
C14-C17 6.0911218
C18-C21 3.2440649
C22+ 3.6960739
Sum 100
3
2021 5th International Conference on Sustainable Energy Engineering (ICSEE 2021) IOP Publishing
IOP Conf. Series: Earth and Environmental Science 814 (2021) 012006 doi:10.1088/1755-1315/814/1/012006
Based on the reservoir characteristics and properties, a model using the number of 30×15×5 grid
blocks with dimensions of 200×400×35 ft. The depth of the reservoir is about 8500-9000 ft and the
pay thickness is 35-50ft, the lithology is mainly an average porosity of 9%, and permeability range
from 0.0272-0.1445mD [7]. The shale oil density of 49-60lb/ft3, the Gas-Oil-Ratio of 28-2000scf/bbl
is medium crude oil. The viscosity of crude oil is 0.3-45cp (at the temperature of 200c and the pressure
of 14.5psi). The bubble point pressure of the crude oil is 2500psi. Formation fluids are difficult to flow
due to the poor reservoir physical properties, but formation overpressure can provide energy for
flowing. Initial oil saturation averages 0.6 [8].
Table 2. Reservoir Properties
Variable Name Value
Reservoir depth (ft) 8500-9000
Pay thickness (ft) 30-50
Average porosity (%) 9
Average permeability (mD) 0.0272-0.1445
Bottom hole pressure of production (psi) 1000-8700
Production rate (bbl/d) 200-500
Water saturation 0.4
Initial oil saturation 0.6
Figure 4. Three-dimensional finite differences grid
3.1. Simulation Period
The simulation time run for 10 years. The first three years were used for natural depletion, after the
first three years, the injection will start for all the scenarios. The SGAG cycle was fixed for 7 years;
this means the production constrains will be as the following:
• SGAG = zero slug size;
• 0 to 10 years gas slug plus production.
Several simulations have been done to compare different EOR mechanisms: Air, H2S, N2, CO2,
SGAG (CO2+Air); SGAG (CO2+H2S); SGAG (CO2+N2), and SGAG (CO2+CH4) [9].
4. Results and discussions
4.1. Sensitivity analysis for different Gas types
4
2021 5th International Conference on Sustainable Energy Engineering (ICSEE 2021) IOP Publishing
IOP Conf. Series: Earth and Environmental Science 814 (2021) 012006 doi:10.1088/1755-1315/814/1/012006
Figure 5. Sensitivity analysis for different gas type (Oil recovery factor)
As Figure 5 shows, the SGAG technique (CH4+CO2) gave a higher oil recovery factor compared with
other EOR methods, the recovery factor for SGAG (CH4+CO2) was between 35-40%. During the H2S
injection, the recovery factor was lower but after the CO2 injection, the oil recovery factor increased
because gravity segregation intensifies with an increasing density difference of the displacing fluid.
CO2 is heavier than the H2S and will result in improving the efficiency of the surface sweeping, hence
the recovery factor will increase [9-10].
The SGAG (Air + CO2) gives an increased recovery factor after the injection of CO2; this was due
to the obvious effect of CO2 as the injection of Air was as low as 5-10%. This implies that, if the
parameters of SGAG are optimized we can obtain about 21% improvements, this analogy was also
applied for SGAG (N2+CO2), where the recovery factor increased after CO2 injection [9].
Therefore, the SGAG method is optimized during the injection of CO2 and the availability of CO2 gas
will make the SGAG method an economical choice.
4.2. The Effect of the SGAG cycle size on the oil recovery factor
The SGAG can be understood as the timing of the switch from gas to gas during simultaneous gas
alternating gas injection in a large field simulation. After the SGAG (CH4+CO2), injection gave a
higher recovery factor, we decided to run a cycle sensitivity analysis for the best case that has been
obtained and observe the effect of the SGAG cycle on the oil recovery as studied by. The SGAG cycle
included 1 month, 2 months, and 3 months [9, 11].
Figure 6 shows the case 3 months best because when the cycle time of injection increases, the
recovery factor increases. Thus, the choice of the cycle will depend on the decisions and politics of the
company.
5
2021 5th International Conference on Sustainable Energy Engineering (ICSEE 2021) IOP Publishing
IOP Conf. Series: Earth and Environmental Science 814 (2021) 012006 doi:10.1088/1755-1315/814/1/012006
Figure 6. Effect of the SGAG cycle on the oil recovery.
4.3. The Effect of the SGAG ratio on the oil recovery
The SGAG ratio is a function of the volume of first slug gas between volumes of second slug gas with
cycle length. These parameters are critical for the optimal design of the SGAG process.
As Figure 7 indicates, the SGAG ratio 1:3 gave higher oil recovery compared with other SGAG
ratios, and the SGAG ratio 1:1 gave the same oil recovery with SGAG ratio 1:2. This implies that a
ratio of 1:3 is the best choice for optimal SGAG operation [9, 12].
Figure 7. Effect of SGAG ratio on the oil recovery
4.4. Reverse of slug volume
This part includes the best run for the SGAG ratio sensitivity analysis and best cycle sensitivity
analysis and best run for Gas injection. Figure 8 shows the first slug CO2 while the CH4 slug was
injected as the second slug higher than gas flooding. When we combined the best ratio and cycle, the
recovery factor becomes higher, and this is one of the major advantages of SGAG [9,13].
62021 5th International Conference on Sustainable Energy Engineering (ICSEE 2021) IOP Publishing
IOP Conf. Series: Earth and Environmental Science 814 (2021) 012006 doi:10.1088/1755-1315/814/1/012006
Figure 8. Effect of the reverse of slug volume
5. Conclusion and future work
1. In this paper, we introduced a new method of EOR and we compared against some other EOR
method. This new method is a combination of two favorable commercial methods, gas injection Air,
N2, CO2, H2S and Simultaneous Gas Alternating Gas SGAG(CO2+Air), SGAG(CO2+CH4),
SGAG(CO2+N2), SGAG(CO2+H2S). Where SGAG shows significant-good performance in terms of
hydrocarbon recovery. Besides, the effect of segregation by gravity had a positive impact on the
mobility ratio.
2. SGAG has proven to be an economical method involving the simultaneous continuous injection.
Especially when we use SGAG (CO2 + CH4) because the CH4 produced here is immediately reinjected
into the well to optimize production.
3. The SGAG report is a useful tool that gives an economic prediction of the gas injection volume
as well as the GAG.
Base on the limitation of the simulation process, there are still areas that are relevant for future
research work:
1. We can talk about the mechanism of SGAG in the shale oil reservoir and other tight formation
reservoirs;
2. We can use the field data to validate the simulation result;
3. Immiscible SGAG;
4. The future collapse should study the feasibility economic of use new method Simultaneous
Water Alternating Gas Alternating Gas (SWAGAG) injection;
5. The future collapse should study the feasibility economic of using a new method of
Simultaneous Gas Alternating Gas Alternating Gas (SGAGAG) injection.
Nomenclatures
€ Euro
EEA European Emission Allowance
EOR Enhanced Oil recovery
GAG Gas Alternating Gas
IFT Interfacial Tension
SGAG Simultaneous Gas Alternating Gas
SGAGAG Simultaneous Gas Alternating Gas Alternating Gas
SWAG Simultaneous Water Alternating Gas
SWAGAG Simultaneous Water Alternating Gas Alternating Gas
WAG Water Alternating Gas.
72021 5th International Conference on Sustainable Energy Engineering (ICSEE 2021) IOP Publishing
IOP Conf. Series: Earth and Environmental Science 814 (2021) 012006 doi:10.1088/1755-1315/814/1/012006
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Acknowledgments
We appreciate the scholarship from the Cameroon-China Scholarship council (2019DFJ000912,
2019ZFY020452), Special thanks to my mother Ndomo Agathe for her profound support.
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