Production technology solutions to enhance heavy oil recovery of marginal fields, offshore Vietnam
PETROVIETNAM
PETROVIETNAM JOURNAL
Volume 10/2020, p. 41 - 48
ISSN 2615-9902
PRODUCTION TECHNOLOGY SOLUTIONS TO ENHANCE HEAVY
OIL RECOVERY OF MARGINAL FIELDS, OFFSHORE VIETNAM
Tran Quoc Viet, Vu Viet Hung, Nguyen Hai An
PetroVietnam Exploration Production Corporation (PVEP)
Email: viettq@pvep.com.vn
Summary
The finding of heavy oil at Dong Do field of Cuu Long basin is a success in exploration. It could be considered as a large heavy oil field
offshore Vietnam. Maximising reserve is a challenge to the operator when they think of a suitable development strategy to efficiently
and economically exploit the field. Over the past decades, production technology application in heavy oil production has been widely
developed in the industry. Apart from the thermal method, pumping technology makes remarkable advances by enlarging the draw-
down created over the conventional gas lift in several heavy oil projects.
This paper presents all the production technology solutions that apply to the marginal heavy oil field offshore Vietnam. One of the
major solutions is the electric submersible pump (ESP) and gas-lift (GL) combination method to enhance the wellbore lifting efficiency. In
doing so, a series of solutions to improve heavy oil recovery have been conducted from design to pilot test whilst optimising the economic
yield over the field life. Among them, the application of ESP and GL combination plays as the key driver to reinforce good production
performance.
As a result, the design includes an electrical pump system coupled with GL back-up, all integrated with one to boost production and
prolong well life. Beside that, closely monitoring and optimising is one factor to give the pump a longer life.
Key words: Heavy oil, enhanced oil recovery, ESP, diesel injection, Dong Do field.
1. Introduction
Heavy oil and bitumen (referred to as heavy oil) are
important sources of energy. With an assessed potential
of more than 4,000 billion barrels globally, heavy oil is a
much larger resource than conventional oil.
- Type A: Medium heavy oil; density and viscosity in
the range of 18 - 25o API, 10 - 100 cP, respectively; flow in
reservoir condition.
- Type B: Heavy/extra-heavy oil; density and viscosity
in the range of 7 - 20o API, 100 - 10,000 cP, respectively;
flow in reservoir condition.
At UNITAR 1982 conference in Venezuela, a basic
heavy oil definition had been agreed upon as follows:
heavy oil is the oil which has a viscosity (at reservoir
- Type C: bitumen; density and viscosity in the range
of 7 - 12o API, and >10,000 cP, respectively; no flow in
reservoir condition.
º
condition) from 100 to >10,000 cP, and density at 15.6 C
from 943 to 1,000 kg/m3 or <10 - 20o API.
In March 2010, Dong Do field was discovered by
appraisal well DD-3X drilled in the central part of BII.2.20
reservoir. Based on the oil type classification, hydrocarbon
in Dong Do field is near a heavy oil zone, which has 20o API
gravity and 17 cP viscosity. The question how to develop
this heavy oil at maximum recovery rate and lowest cost
was raised from early. Using the ESP lift system to produce
heavy oil from only one formation is a preferable concept
for this marginal field development with high challenges.
Heavy oil is identified based on viscosity and density,
or density only if viscosity data are not available. Heavy
oil contains about 3% or more sulfur, and 2,000 ppm
vanadium. Nickel and molybdenum are also common.
Heavy oil classification: [1]
Date of receipt: 8/10/2020. Date of review and editing: 8 - 30/10/2020.
Date of approval: 30/10/2020.
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PETROLEUM EXPLORATION & PRODUCTION
The application of ESP has been
common in the industry but still
less in Vietnam. Operators from the
neighbouring field employed ESP as
an alternative in the case of gas lift
system unavailability. But application
in this project is to enhance artificial lift
efficiency in heavy oil production. This
paper introduces a systematic approach
to design an efficient dual artificial lift
system with ESP and GL combination to
enhance the production of the heavy oil
reservoir.
100000000
1000000
Canada
US
Venezla/Colombia
China
100000
10000
Bitumen
India/Indonesia
US
Extra Heavy
Canada
1000
100
Heavy
0
1
0.1
0
5
10
15 20
25
30
35
40
45
50
API Gravity
Figure 1. Heavy oil type classification [1].
2. The heavy oil development concept
2.1. Heavy oil global and Vietnam
resource
1 Gb
10 Gb
100 Gb
1000 Gb
Heavy oil reserves are widely
distributed around the world. According
to the Barrels in Place statistics of heavy
oil, its spread are mainly in North-South
America, Russia, Europe, the Middle East,
and China as shown in Figure 2.
In Vietnam, there are currently
two fields, namely Dong Do and Kinh
Ngu Vang, where heavy oil has been
discovered. Table 1 shows the heavy oil
resource of Dong Do and Kinh Ngu Vang
fields, and BII.2.20 is presently the largest
heavy oil reservoir offshore Vietnam.
Figure 2. Heavy oil resources [1].
Table 1. Heavy oil in place of Dong Do and Kinh Ngu Vang fields
ꢈIIꢉꢊꢉꢋꢌ
ꢍꢃiꢂꢂion ꢆtꢄndꢄrd
ꢀiꢁꢂd ꢀorꢃꢄtion ꢅꢁꢆꢁrꢇoir
ꢅꢁꢃꢄrꢐꢆ
ꢎꢄrrꢁꢂꢆꢏ
ꢑꢉ
8.2
1ꢉ
ꢒꢉ
8.2
1.6
BIII sand
BII.2.10
BII.2.20
BII.2.30
Development reserves,
not yet produced
2.2. Heavy oil production technology
1.6
Duetothecharacteristicsofheavyoil
with high viscosity and low dissolved gas
content, traditional recovery methods
are often less applicable. Recovery in the
primary stage is usually very low with an
average rate of approximately 5% only.
The assisted recovery methods applied
include the thermal and non-thermal
methods (Figure 3).
Dong
Do
101.5 101.5 101.5
Development reserves,
in production
Miocene
24.4
24.4
24.4
Development reserves,
not yet produced
BI.2.30
3.2
4.3
BII.1.10
BII.1.20
Intra BI.1 15.1
24.3
27.5
9.9
21.4
27.5
9.9
21.4
Kinh
Ngu
Vang
Reserves, not yet
developed
Miocene
Total
165.3 197.7 198.6
Production processes
2.3. Heavy oil recovery factor
Thermal
Primary
Non-Thermal
The heavy oil production methods
as shown in Figure 4 have been applied
in many parts of the world, bringing
positive results with recovery factor up
to more than 30%.
Steam-Based
Combustion
- Fire flooding
- THAI
- Water flooding
- CO2 & gas injection
- Chemical injection
- VAPEX
- Cold production
- CHOPS
- CSS
- Flooding
- SAGD
Figure 3. Heavy oil production technology [2].
- Top down
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SPE-113132 - Table 2
60
50
40
30
20
Rf (% OOIP)
EUR (% OOIP)
10
0
Figure 4. Heavy oil recovery factor [2].
Upper - Lower Con Son formations
(BII.2.20, BII.2.30 and BII.1.10) in
wildcat wells A, B and C as stacked
channel sandstones trapped. Each
gross sandstone package is about 30
- 40 m thick, capped above by 10 - 30
m of shale/clay stones.
DD-3P, Clean-up
(1387 - 1393.5mTVDSS, 1398.5
- 1410.8 mTVDSS) Oil flow: 1300
bopd (Choke: 36/64’’, ESP)
DD-2X, DST#3
(1398.2 - 1421.7 mTVDSS)
Recovered 60 bbls oil (15 API)
DD-4P, DST#1 Clean-up
(1383.5 - 1408 mTVDSS) Oil flow:
1804 bopd (30/64’’choke, ESP)
The diversity of fluid properties
(20o API) made it difficult to select the
production technology method to
enhance wellbore lifting efficiency.
DD-1X, DST#3 add-on
(1409 - 1415 mTVDSS) 10% total flow
(total 2428 bopd) Indicated from PLT
DD-6P, DST#1 Clean-up
(1392.4 – 1412.5 mTVDSS) Oil flow:
1730 bopd (50/64’’choke, Gas lift)
3.2. Designing submersible electric
pump and gas-lift in Dong Do field [3]
DD-3X, DST#2
(1384.8 - 1389.4 mTVDSS, 1398.6 -
1410.9 mTVDSS) Main flow: 540 bopd,
22 API (24/64’’choke)
Similar data to simulate the
submersible electric pump mining
(ESP) model are calculated based on
well parameters, fluid parameters,
and referring to the seam test results
with N2-lift-gas support. The results
show that ESP's performance is
better than that of N2-lift-gas with
the stable flow reaching 1,500 barrels
per day. ESP can work well with the
water cut increase to 80 - 90% and
lower critical pressure and creates
Depth
-1330
Legend
DD-2P, DST#1 Clean-up
-1370
-1410
-1450
-1490
-1530
-1570
Proven (P1)
(1375.8 - 1385.4 mTVDSS, 1397.9 -
1407.7 mTVDSS) Oil flow: 1640 bopd
(10/64’’choke, ESP)
Figure 5. Dong Do heavy oil top reservoir map.
3. Designing heavy oil production technology for marginal fields offshore
Vietnam
3.1 Dong Do heavy oil reservoir
Dong Do field is located in the northwest of Block 02/97 in the northeast
area of Cuu Long basin.Three pay zones were discovered in the Middle Miocene
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PETROLEUM EXPLORATION & PRODUCTION
Junction box
Control panel
Electrical feed through/
Wellhead penetrator
Transformers
Wellhead
Safety valve (optional)
Packer penetrator
(optional)
Tubing
Casing
Tubing drain (optional)
Tubing check
valve (optional)
Gas-lift valves
Power cable
Cable splice(s)
Cable bands
Pump discharge head
Pump(s)
Motor lead extension
ESP system
Intake or gas
separator
Seal(s)/Protector(s)
Motor(s)
ESP system
Auxiliary
equipment (e.g.,
Instrumentation)
Note: Component in italics are outside the
system boundary for ESP's
Figure 6. Single ESP system [3].
Figure 7. ESP and GL combination system schematic.
a larger drawdown. This will help the recovery factor to
be higher than the GL method. ESP adds energy to the
well, increasing the well-productivity. The equipment
has a huge advantage over the GL method in extracting
heavy oil with a small oil-gas ratio. This method helps
improve the extraction rate to compensate for the
decrease in oil flow and increase the flow of exploitation
water. To optimise the production capacity of the well, the
submersible electric pump will be applied to the Middle
Miocene reservoir of Dong Do field (BII.2.20 and BII.2.30).
The production wells will then be completed with a
submersible electric pump combined with a backup gas
system from the beginning. The submersible electric
pump will be placed at the appropriate depth in the well
completion equipment to optimise the extraction flow
and be able to work in harsh environments (sand, H2S).
The schematic diagram of the well equipment using the
basic submersible electric pump is illustrated in Figure 6.
3.3. Improving heavy oil recovery solutions
Many solutions to improve heavy oil production
have been conducted by simulation model, such as infill
wells, water/gas injection, polymer, and diesel injection.
The results of the simulations also indicate the difficulty
of enhancing heavy oil recovery. Most of them showed
reverse recovery factors, except infill wells with the densely
well pattern and diesel injection. Thus, diesel injection has
been conducted in reality with positive results, and infill
well is proposed in the next phase as a major solution to
enhance heavy oil recovery in BII.2.20 Dong Do field.
3.3.1. Infill with the dense well pattern
Based on the research results of the reservoir
simulation model, the infill well cases were evaluated,
then the optimal number, position, and trajectory were
selected for BII.2.20 reservoir. The results showed that one
infill well for each reservoir is the optimal case. The results
are shown in Figure 8.
Figure 7 shows the equipment string where GL system
is placed above ESP packer to provide a backup system
as well as optimisation capability in case of simultaneous
production by both ESP and GL [3, 4].
The application of commingling wells has been
evaluated. However, the results showed that it is
ineffective for this case.
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3.3.2. Water injection
6000
5000
4000
3000
2000
1000
0
8
7
6
5
4
3
2
1
0
No infill
× 106
Infill 2 wells
According to the results
of research based on reservoir
simulation, due to the relatively
heavy oil fluid nature, water
injection is not an effective solution
for maintaining reservoir pressure.
The results are shown in Figure 9.
Besides that, the case of
combinedinjectioninbothreservoirs
has been evaluated. However, this
also results in poor recovery.
1/1/15 1/1/16 1/1/17 1/1/18 1/1/19 1/1/20 1/1/21 1/1/22 1/1/23 1/1/24 1/1/25 1/1/26 1/1/27
Date
3.3.3. Gas injection
Figure 8. Oil recovery in case of infill well into BII.2.20 reservoir.
Both cases of converting
producers which have low oil rate
(< 100 standard barrels per day) to
the gas injector and drilling new gas
injectors have been evaluated. The
results show that gas injection is
ineffective in the case of converting
producers to injectors. In contrast,
in the case of infill two producers
and two injectors, the gas injection
is effective, however, the oil
incremental is insignificant. The
results are shown in Figure 10.
6000
8
7
× 106
No water injection
Water injection
5000
6
5
4
3
2
1
0
4000
3000
2000
1000
3.3.4. Water alternating gas
0
1/1/15 1/1/16 1/1/17 1/1/18 1/1/19 1/1/20 1/1/21 1/1/22 1/1/23 1/1/24 1/1/25 1/1/26 1/1/27
Similartothegasinjectioncases,
evaluationofthecaseofmaintaining
reservoir pressure to improve the oil
recovery factor by water alternating
gas injection (WAG) showed that it
is insignificantly efficient for BII.2.20
heavy oil reservoir. The results are
shown in Figure 11.
Date
Figure 9. Oil recovery in case of water injection into BII.2.20 reservoir.
9
8
7
6
5
4
6000
×106
No gas injection
Gas injection
5000
4000
3000
2000
1000
0
3.3.5. Polymer injection
The cases of polymer injection
have been studied. However, it is
also ineffective in improving oil
recovery. The results are shown in
Figure 12.
3
2
1
0
3.3.6. Diesel injection
1/1/15 1/1/16 1/1/17 1/1/18 1/1/19 1/1/20 1/1/21 1/1/22 1/1/23 1/1/24 1/1/25 1/1/26 1/1/27
Date
In the case of shutting-in high
Figure 10. Oil recovery in case of gas injection into BII.2.20.
water cut production wells, the
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PETROLEUM EXPLORATION & PRODUCTION
water volume will settle down near
the wellbore. After re-opening,
the oil rate will be reduced, and
the water cut is higher than before
shutting-in. This phenomenon
is caused by the effect of
hysteresis that reduces oil relative
permeability. The application of
this hysteresis phenomenon can
maintain production for high water
cut wells after the shut-in stage by
injecting non-wetting fluid (diesel).
The re-starting of wells after the
long shut-in period is easy and the
oil production increases by about
20 - 30%. Figure 13 shows the actual
oil rate jumps up and the water cut
drops down with diesel injection [5].
6000
5000
8
7
× 106
No WAG injection
WAG injection
6
5
4
3
2
1
0
4000
3000
2000
1000
0
1/1/15 1/1/16 1/1/17 1/1/18 1/1/19 1/1/20 1/1/21 1/1/22 1/1/23 1/1/24 1/1/25 1/1/26 1/1/27
Date
Figure 11. Oil recovery in case of water alternating gas injection into BII.2.20 and BII.2.30.
6000
8
7
× 106
No polymer injection
Polymer injection
5000
4. Application results
6
5
4
3
2
1
0
Up to now, there have been four
production wells drilled into BII.2.20
reservoir (DD-2P, DD-3P, DD-4P, and
DD-6P), and one well into BII.2.30
reservoir (DD-7P). All of the wells are
completed with ESPs that operate
at the designed flow rate of about
1,500 bbl/day [4]. The flow range
operates at a higher efficiency than
the initial design. The ESPs have
been operating for more than 5
years beyond the manufacturer's
recommended replacement time
limit (2.5 - 3.0 years) as shown in
Figure 14.
4000
3000
2000
1000
0
1/1/15 1/1/16 1/1/17 1/1/18 1/1/19 1/1/20 1/1/21 1/1/22 1/1/23 1/1/24 1/1/25 1/1/26 1/1/27
Date
Figure 12. Oil recovery in case of polymer injection into BII.2.20 reservoir.
Without hysteresis
The actual pump life longer than
recommended by the manufacturer
revealed the optimal production
Water cut
No hysteresis
With hysteresis
With hysteresis
technology
from
design
to
operation. In summary, the success
of ESP application in the heavy oil
Dong Do field could come from the
following:
Diesel injection
BHP
- Exact evaluation of the rock
- fluid, and reservoir performance
(low temperature and pressure, low
dissolved gas).
Oil rate
1/10/17
1/11/17
1/12/17
1/1/18
Date
Figure 13. Simulation results of diesel injection application for ESP well.
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PETROVIETNAM
One of the important solutions
actually applied is ESP and GL
combination. Figure 15 shows
the production performance with
primary ESP and dual artificial lift
system in the pilot test period (Dec-
2015).
2014
2015
2019 2020
June August
May June July
December September
DD-3P
DD-6P
DD-7P
DD-2P
DD-4P
1,200 - 1,600 barrels/day
1,500 - 1,800 barrels/day
1,800 barrels/day
1,600 barrels/day
Operating ~ 2,211 days
~ 1,136 days (*)
~ 1,892 days
~ 1,873 days
Varied injection gas-lift rate
is tested to analyse the behaviour
of ESP when supported by GL
technique. Table 2 summarised the
production performance and ESP
action with and without GL (given
the same choke size and frequency).
1,600 barrels/day ~ 1,851 days
(*) ESP failure due to scale since November 2017
Figure 14. Current ESP’s life in Dong Do field.
Three flow test points were
systematically examined with:
(A) only ESP, (B) ESP and GL 0.2
MMscfd, and (C) ESP and GL 0.28
MMscf as illustrated in Table 2. The
incremental liquid between Test
A and Test B is quite considerable
around 30% and continues rising
with more gas injected. It is noted
that the power consumption also
slightly reduces by 2% as a result
of a lighter fluid column above the
pump created by gas-lift injection.
Reducing power consumption is
one of the crucial factors helping
ESP have a longer life.
2500
100
Liquid rate
2250
2000
1750
1500
Oil rate
GOR
90
80
70
60
50
40
30
20
10
0
WHFP
1250
1000
750
500
250
0
Figure 15. Well production performance with ESP & gas-lift combination.
One of the solutions improving
heavy oil recovery is diesel injection
which has been applied in reality.
DD-3P in BII.2.20 has selected diesel
injection to the wellbore. Before
shut-in, DD-3P produced with high
water cut, up to 89%, and oil rate
at 185 standard barrels per day.
After applying diesel injection,
the results showed that the well
restarted quickly and reached 350
standard barrels per day (except the
amount of diesel injection). The oil
rate was higher, about 165 standard
barrels per day (+ 85%); water cut
decreased from 89% to 76% [5].
This better production condition
Table 2. Summary well test points for ESP + GL system analysis
ꢀꢁrꢁꢂꢃtꢃrꢄ ꢅꢃꢄt ꢆ ꢅꢃꢄt ꢇ
ꢅꢃꢄt ꢈ
1ꢉꢊꢋꢌ
ꢍꢎ
Liquid rates (standard barrel per day)
1,340
1,740
Water cut (%)
WHP (psi)
72
72
294
0
2,140
1,670
49
441
0.2
2,060
1,650
49
ꢏꢏꢊ
Gas-lift rate (MMscfd)
Pump discharge pressure (psi)
Pump intake pressure (psi)
Frequency (Hz)
ꢌ.ꢎꢊ
ꢎꢉꢌꢐꢎ
1ꢉꢑꢑꢏ
ꢏꢒ
HP (KVA)
31.8
31.2
ꢋ1
- Good design for lower and upper completion (with sand-screen to avoid
the sand production).
- Suitable selection of production technology with ESP and gas-lift back up.
- Continuously monitoring and optimising ESP.
- Studying new solution to improve ESP performance and enhance heavy
oil recovery.
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PETROLEUM EXPLORATION & PRODUCTION
References
[1] Abha Dwivedy, “Steam generation
by solar and natural gas generators for
thermal enhanced oil recovery”, Master
Science Thesis, West Virginia University,
USA.
DD- 7P Daily Production Plot
3000
2700
2400
2100
1800
1500
1200
900
100
90
80
70
60
50
40
30
20
10
0
Diesel injection
Water cut drop down
Oil rate jump up
[2] Dennis Beliveau, “Waterflooding
viscous oil reservoirs”, SPE Reservoir
Evaluation & Engineering, Vol. 12, No. 5, pp.
689 - 701, 2009. DOI: 10.2118/113132-PA.
600
300
[3] S.T. Tran, H.V. Vu, V.M. Le, T.N.
Nguyen, L.H. Nguyen, P. Prajunla, and
H.M.H. Dong, “Hybrid system of ESP and
gas lift application from conceptual
design, pilot test to system analysis”, SPE
Middle East Artificial Lift Conference and
Exhibition held in Manama, Kingdom of
Bahrain, 30 November - 1 December, 2016.
DOI: 10.2118/184215-MS.
0
Figure 16. Diesel injection solution applied to Dong Do heavy oil reservoir [5].
maintained for 1 month, then the well returned to the previous conditions
as before diesel injection.
Up to date, ESP in Dong Do heavy oil reservoir has been operating
in good performance (excluding 1 ESP failure due to scale). To achieve
the success, selecting suitable production technology (hereby ESP and
GL backup) is the priority. Moreover, solutions to improve heavy oil
production have been studied and commenced with the best results,
respectively as diesel injection.
[4] Vu Viet Hung and Tran Thai Son,
“Production technology designed for
heavy oil recovery of a marginal field
offshore Vietnam”, Science and Technology
Development Journal, Vol. 19, No.1, pp. 190
- 202, 2016. DOI: 10.32508/stdj.v19i1.516.
5. Conclusion and recommendation
[5] Lê Minh Vũ, Nguyễn Đức Đông,
Cao Hữu Bình và Vũ Việt Hưng, “Duy trì
khai thác dầu cho giếng có hàm lượng
nước cao sau quá trình đóng giếng bằng
phương pháp bơm diesel”, Tạp chí Dầu
khí, Số 1, trang 20 - 29, 2020.
Heavy oil discovery in a marginal field in Cuu Long basin, offshore
Vietnam is an exploration success and puts forward challenges for field
development. Selecting suitable production technology in cost-effective
and high-efficiency concepts is the key factor to maximise heavy oil
recovery in Dong Do field.
Prudent study of solutions to improve heavy oil production is
essential. Dual artificial lift systems (ESP supported by GL) help reduce
pump workload downtime and provide the flexible capacity to ramp
up production when necessary. The combination of ESP and GL system
allows the pump to operate beyond its designed frequency/flow rates
which ultimately results in a cost-saving of replacing the new pump and
improving oil recovery factor.
Diesel injection is a good solution to improve oil production which
has been proved by actual results. This solution should be recommended
to other operators when the production flows with high water cut.
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