artificial lift methods
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GAS LIFTSUCKER ROD PUMP
ELECTRIC SUBMERSIBLE PUMPOTHERS
Artificial Lift Methods
1
PENDAHULUAN (1)
Pwf
Pwh Psep
Pwf
PwhPsep
Pwf=Psep+dPf+dPt
Pwf<Psep+dPf+dPt
Flowing Well No - Flow Well
2
PENDAHULUAN (2)
Untuk mengangkat fluida sumur:
Menurunkan gradien aliran dalam tubing
Memberikan energy tambahan di dalam sumur untuk mendorong fluida sumur ke permukaan
Pwf
PwhPsep
No - Flow Well
Energy ?
3
Gradien ?
PENDAHULUAN (3)
Figure 1
Gas Lift Well ESP Well Sucker Rod Pump Well
4
PENDAHULUAN GAS LIFT (1)
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Persamaan Umum Pressure Loss
Pengurangan gradien aliran dengan menurunkan densitas fluida
dZ
L
dZ
dv
g
v
g
g
dZ
dp w
cc
dg2
vf)
dL
dp(
c
2
f
Pwf
PwhPsep
PENDAHULUAN GAS LIFT (2)
Densitas Campuran
Gradient Elevasi Gradient Friksi
Gradient Akselerasi
?
?
6
vd
N Re
PENDAHULUAN GAS LIFT (3)
Pwf
PwhPsepPwf<Psep+dPf+dPt
7
Pwf>Psep+(dPf+dPt)
Berkurang
GAS LIFT (1)
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Gas lift technology increases oil production rate by injection of compressed gas into the lower section of tubing through the casing–tubing annulus and an orifice installed in the tubing string.
Upon entering the tubing, the compressed gas affects liquid flow in two ways:
(a) the energy of expansion propels (pushes) the oil to the surface and
(b) the gas aerates the oil so that the effective density of the fluid is less and, thus, easier to get to the surface.
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SURFACE COMPONENTS
SUB-SURFACE COMPONENTS
RESERVOIR COMPONENTS
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Detail Gas Lift Surface Operation
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InjectedGas
Res. Fluid +Inj. Gas
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Sistem Sumur Gas Lift
Gas Injection Line
Pt
Pc
Compressor Subsystem• intake system• outlet system• choke • pressure gauge• injection rate metering
Flow Line
Separator
Wellhead Subsystem :• Production subsystem
• wellhead• production choke• pressure gauge
• Injection subsystem• injection choke
ValveSubsystem
Wellbore Subsystem:• perforation interval• tubing shoe• packer
Separator Subsystem:• separator• manifold• pressure gauges• flow metering
Unloading Gas Lift Mandrells
Gas Injection Valve
13
Compressor Sub-System
DPgas
Compressor
Wellhead
Separator
Pintake Pdischarge
Horse PowerCompressor
Pinjection@wellhead
Pinjection@wellhead=Pdischarge - DP
QgasQgas
Wellhead
14
Wellhead Sub-System
ProductionChoke
InjectionChoke
Surface InjectionPressure
WellheadPressure
Gas Injection
Production Fluid
15
Gas Lift Valve Sub-System
Pt
Pc
Pc
Pt
GasInjeksi
FluidaProduksi
Pc = Pt
16
Gas Lift Valve
GasInjection
TubingPressure
Close condition Open condition
Kriteria Operasi Sumur Gas Lift
17
There are four categories of wells in which a gas lift can be considered:
High productivity index (PI), high bottom-hole pressure wells
High PI, low bottom-hole pressure wells
Low PI, high bottom-hole pressure wells
Low PI, low bottom-hole pressure wells
• Wells having a PI of 0.50 or less are classified as low productivity wells.
• Wells having a PI greater than 0.50 are classified as high productivity wells.
• High bottom-hole pressures will support a fluid column equal to 70% of the well depth.
• Low bottom-hole pressures will support a fluid column less than 40% of the well depth.
Continuous Gas Lift Intermittent Gas Lift
• A continuous gas lift operation is a steady-state flow of the aerated fluid from the bottom (or near bottom) of the well to the surface.
• Continuous gas lift method is used in wells with a high PI (0:5 stb=day=psi) and a reasonably high reservoir pressure relative to well depth.
• Intermittent gas lift operation is characterized by a start-and-stop flow from the bottom (or near bottom) of the well to the surface. This is unsteady state flow.
• Intermittent gas lift method is suitable to wells with (1) high PI and low reservoir pressure or (2) low PI and low reservoir pressure.
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2 Types of Gas Lift Operation
Materi Perencanaan Sumur Gas Lift
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This chapter covers basic system engineering design fundamentals for gas lift operations. Relevant topics include the following:
1. Liquid flow analysis for evaluation of gas lift potential2. Gas flow analysis for determination of lift gas compression
requirements3. Unloading process analysis for spacing subsurface valves4. Valve characteristics analysis for subsurface valve selection5. Installation design for continuous and intermittent lift
systems.
Evaluation of Gas Lift Potential
20
Evaluation of gas lift potential requires system analyses to determine well operating points for various lift gas availabilities.
The principle is based on the fact that there is only one pressure at a given point (node) in any system; no matter, the pressure is estimated based on the information from upstream (inflow) or downstream (outflow).
The node of analysis is usually chosen to be the gas injection point inside the tubing, although bottom hole is often used as a solution node.
Gas Injection Rates
21
Four gas injection rates are significant in the operation of gas lift installations:
1. Injection rates of gas that result in no liquid (oil or water) flow up the tubing. The gas amount is insufficient to lift the liquid. If the gas enters the tubing at an extremely low rate, it will rise to the surface in small semi-spheres (bubbly flow).
2. Injection rates of maximum efficiency where a minimum volume of gas is required to lift a given amount of liquid.
3. Injection rate for maximum liquid flow rate at the ‘‘optimum GLR.’’4. Injection rate of no liquid flow because of excessive gas injection.
This occurs when the friction (pipe) produced by the gas prevents liquid from entering the tubing
THE GAS IS INJECTED CONTINUOUSLY TO ANNULUS
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CONTINUOUS GAS LIFT
Continuous Gas Lift Operation
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The tubing is filled with reservoir fluid below the injection point and with the mixture of reservoir fluid and injected gas above the injection point. The pressure relationship is shown in Fig. 13.4.
Gas Lift OperationPressure vs Depth
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Parameter Design
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• Jumlah gas injeksi yang tersedia• Jumlah gas injeksi yang dibutuhkan• Tekanan Gas Injeksi yang dibutuhkan di setiap
sumur• Tekanan Kompresor yang dibutuhkan
GAS LIFT PERFORMANCE CURVE
26
GAS INJEKSI YANG DIPERLUKAN
Unlimited amount of liftgas Limited amount of gas
• In a field-scale valuation, if an unlimited amount of lift gas is available for a given gas lift project, the injection rate of gas to individual wells should be optimized to maximize oil production of each well.
• If only a limited amount of gas is available for the gas lift, the gas should be distributed to individual wells based on predicted well lifting performance, that is, the wells that will produce oil at higher rates at a given amount of lift gas are preferably chosen to receive more lift gas.
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Availability amount of Gas Injection
Kebutuhan Gas Injeksi (1)
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• Nodal Analysis:– IPR Curve– Tubing Performance
Curve– GLR formasi
• Variasi GLR– GLR-total (assume)– Qg-inj = Qtotal – Qq-f
• Plot Qg-inj vs Qliquid
0
500
1000
1500
2000
2500
0 200 400 600 800 1000
Laju Produksi, stb/d
Tek
anan
Alir
Das
ar S
umu
r, p
si
IPR
200 scf/stb
400 scf/stb
600 scf/stb
800 scf/stb
1000 scf/stb
1200 scf/stb
Kebutuhan Gas Injeksi (2)
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• Qg-inj >> maka Qliq >>
• Pertambahan Qliq makin kecil dengan makin meningkatnya Qg-inj
• Sampai suatu saat dengan pertambahan Qg-inj, Qliq berkurang
• Titik puncak dimana Qliq maksimum disebut sebagai Qoptimum
0
100
200
300
400
500
600
700
0 200 400 600 800 1000 1200 1400
Perbandingan Gas-Cairan, scf/stb
Laj
u P
rodu
ksi,
stb
Unlimited Gas Injection Case
30
If an unlimited amount of gas lift gas is available for a well, the well should receive a lift gas injection rate that yields the optimum GLR in the tubing so that the flowing bottom-hole pressure is minimized, and thus, oil production is maximized.
The optimum GLR is liquid flow rate dependent and can be found from traditional gradient curves such as those generated by Gilbert (Gilbert, 1954).
0
100
200
300
400
500
600
700
0 200 400 600 800 1000 1200 1400
Perbandingan Gas-Cairan, scf/stb
Laj
u P
rodu
ksi,
stb
Unlimited Gas Injection Case
31
• After the system analysis is completed with the optimum GLRs in the tubing above the injection point, the expected liquid production rate (well potential) is known.
• The required injection GLR to the well can be calculated by
Limited amount of gas injection
32
• If a limited amount of gas lift gas is available for a well, the well potential should be estimated based on GLR expressed as
0
100
200
300
400
500
600
700
0 200 400 600 800 1000 1200 1400
Perbandingan Gas-Cairan, scf/stb
Laj
u P
rodu
ksi,
stb
Gas Flow Rate Requirement
33
• The total gas flow rate of the compression station should be designed on the basis of gas lift at peak operating condition for all the wells with a safety factor for system leak consideration, that is,
whereqg = total output gas flow rate of the compression station, scf/daySf = safety factor, 1.05 or higherNw = number of wells
34
POINT OF INJECTION
Output Gas Pressure Requirement (1)
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Kickoff of a dead well (non-natural flowing) requires much higher compressor output pressures than the ultimate goal of steady production (either by continuous gas lift or by intermittent gas lift operations).Mobil compressor trailers are used for the kickoff operations.
Output Gas Pressure Requirement (2)
36
• The output pressure of the compression station should be designed on the basis of the gas distribution pressure under normal flow conditions, not the kickoff conditions. It can be expressed as
L
fout P
SP
DPgas
Compressor
Wellhead
Separator
Pintake Pdischarge
Horse PowerCompressor
Pinjection@wellhead
Pinjection@wellhead=Pdischarge - DP
QgasQgas
Wellhead
COMPRESSOR
37
Output Gas Pressure Requirement (3)
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• The injection pressure at valve depth in the casing side can be expressed as:
• It is a common practice to use Dpv = 100 psi. The required size of the orifice can be determined using the choke-flow equations presented in Subsection 13.4.2.3
vvtvc PPP ,,
Pt
Pc
Pc
Pt
GasInjeksi
FluidaProduksi
Pc = Pt
Tekanan Tubing @ Valve Gas Lift
39
Pwf
Dp @ tubing
Output Gas Pressure Requirement (4)
40
• Accurate determination of the surface injection pressure pc,s requires rigorous methods such as the Cullender and Smith method (Katz et al., 1959).
• However, because of the large cross-sectional area of the annular space, the frictional pressure losses are often negligible.
• Then the average temperature and compressibility factor model degenerates to (Economides et al., 1994)
ProductionChoke
InjectionChoke
Surface InjectionPressure
WellheadPressure
Gas Injection
Production Fluid
Up-Stream Choke / Injection Choke
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• The pressure upstream of the injection choke depends on flow condition at the choke, that is, sonic or subsonic flow.
• Whether a sonic flow exists depends on a downstream-toupstream pressure ratio. If this pressure ratio is less than a critical pressure ratio, sonic (critical) flow exists.
• If this pressure ratio is greater than or equal to the critical pressure ratio, subsonic (subcritical) flow exists. The critical pressure ratio through chokes is expressed as
ProductionChoke
InjectionChoke
Surface InjectionPressure
WellheadPressure
Gas Injection
Production Fluid
Gas Lift Injection Parameters
42
Compressor Pressure
Pwf
Point of Injection
43
vvfvc PPP ,
Point of Balanced
44
vvfvc PPP ,
Unloading ProcessGas Lift Wells
45
UNLOADING VALVES DESIGN
Persiapan Operasi Sumur Gas Lift
46
47
• Katup Unloading sudah dipasang.
• Sumur masih diisi killing fluid
• Fluida produksi masih belum mengalir ke dalam tubing
Valve 1 : Terbuka
Valve 2 : Terbuka
Valve 3 : Terbuka
Valve 4 : Terbuka
PermukaanKilling fluid
No flowChokeTutup
TAHAP O
48
Tahap I
• Pada Gambar 1 ditunjukkan penampang sumur yang siap dilakukan proses pengosongan (unloading). Pada tubing telah dipasang empat katup, yang terdiri dari 3 katup, yaitu katup (1), (2) dan (3), yang akan berfungsi sebagai katup unloading. Sedangkan katup (4) akan berfungsi sebagai katup operasi. Sebelum dilakukan injeksi semua katup dalam keadaan terbuka.
• Sumur berisi cairan work-over, ditunjukkan dengan warna biru, dan puncak cairan berada diatas katup unloading (1).
• Gas mulai diinjeksikan, maka gas akan menekan permukaan cairan work over kebawah, dan penurunan permukaan cairan ini akan mencapai katup unloading (1). Pada saat ini gas akan mengalir dalam tubing melalui katup (1) yang terbuka.
Valve 1 : Terbuka
Valve 2 : Terbuka
Valve 3 : Terbuka
Valve 4 : Terbuka
PermukaanKilling fluid
No flow
49
Tahap II
• Pada Gambar 2 gas injeksi mendorong permukaan cairan work-over, dan telah me-lampaui katup unloading (1) dan mencapai katup unloading (2). Pada saat ini katup unloading (1) tertutup dan gas injeksi mendorong permukaan cairan kebawah.
• Bagian bawah tubing yang semula berisi cairan work-over ditempati oleh fluida for-masi.
• Pada saat ini gas akan masuk kedalam tubing, melalui katup unloading (2) yang terbuka. Dengan masuknya gas injeksi tersebut kedalam tubing maka kolom cairan dalam tubing akan lebih ringan dan aliran cairan work over ke permukaan akan berlanjut.
Valve 2 : Terbuka
Valve 3 : Terbuka
Valve 4 : Terbuka
Valve 1 : Tertutup
PermukaanKilling fluid
PermukaanFluida Res.
50
Tahap III
• Pada Gambar 3 gas injeksi mendorong permukaan cairan work-over, sampai me-lampaui katup unloading (1), (2) dan (3). Setiap saat permukaan kolom cairan work-over mencapai katup unloading, maka gas injeksi akan mengalir masuk kedalam tubing dan aliran cairan work-over dalam tubing akan tetap berlangsung. Jika per-mukaan kolom cairan work-over mencapai katup unlaoding (3), maka katup unloading (2) akan tertutup, dan gas injeksi akan masuk melalui katup unloading (3).
• Selama ini pula permukaan cairan formasi akan bergerak ke permukaan. Pada saat cairan work-over mencapai katup terakhir, yaitu katup operasi (4), maka katup unloading (3) akan tertutup dan seluruh cairan work-over telah terangkat semua ke permukaan, dan hanya katup operasi yang terbuka.
PermukaanKilling fluid
PermukaanFluida Res.
Valve 1 : Tertutup
Valve 2 : Tertutup
Valve 3 : Tertutup
Valve 4 : Terbuka
TAHAP IV
51
• Pada Gambar 4 ditunjukkan bahwa semua cairan work-over telah terangkat dan sumur berproduksi secara sembur buatan.
• Katup operasi (4) akan tetap terbuka, sebagai jalan masuk gas injeksi kedalam tubing. Katup ini diharapkan dapat bekerja dalam waktu yang lama. Dimasa mendatang akan terjadi perubahan perbandingan gas-cairan dari formasi, yang cenderung menurun serta peningkatan produksi air, maka jumlah gas injeksi dapat ditingkatkan dan diharapkan katup injeksi dapat menampung peningkatan laju injeksi gas tersebut. Dengan demikian pemilihan ukuran katup injeksi perlu direncanakan dengan baik.
FluidaProduksi
Valve 1 : Tertutup
Valve 2 : Tertutup
Valve 3 : Tertutup
Valve 4 : Terbuka
52
gas lift Valve
gas lift Valve Mechanics
53
UNLOADING VALVES DESIGN
Gas Lift Valve
54
Gas Lift Valve
55
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Contoh Penampang Sumur Gas Lift
}Gas Lift MandrellGas Lift Valves
Gas Lift Valves:• Mandrell + Dummy Valves• Mandrell + Valves
Valves Operating Conditions:• Casing pressure• Test Rack Opening Pressure• Port Size• Temperature @ Lab.• Jenis Valves
Gas Lift Valve
57
Pt
Pc
Pc
Pt
GasInjeksi
FluidaProduksi
Pc = Pt
Penampang Gas Lift Valve
58
Jenis Gas Lift Valves
59
Gas Lift Valve
60
GasInjection
TubingPressure
Close condition Open condition
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