Artificial Lift Methods

GAS LIFTSUCKER ROD PUMP

ELECTRIC SUBMERSIBLE PUMPOTHERS

Artificial Lift Methods1

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)5

Persamaan Umum Pressure Loss

Pengurangan gradien aliran dengan menurunkan densitas fluida Pwf

PwhPsep

PENDAHULUAN GAS LIFT (2)

Densitas Campuran

Gradient Elevasi Gradient Friksi

Gradient Akselerasi

?

?

6

vdN Re

PENDAHULUAN GAS LIFT (3)

Pwf

PwhPsepPwf<Psep+dPf+dPt

7

Pwf>Psep+(dPf+dPt)

Berkurang

GAS LIFT (1)8

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.

9

SURFACE COMPONENTS

SUB-SURFACE COMPONENTS

RESERVOIR COMPONENTS

10

Detail Gas Lift Surface Operation 11

InjectedGas

Res. Fluid +Inj. Gas

12

Sistem Sumur Gas Lift Sistem Sumur Gas Lift

Gas Injection Line

PtPc

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

Pgas

Compressor

Wellhead

Separator

Pintake Pdischarge

Horse PowerCompressor

Pinjection@wellhead

Pinjection@wellhead=Pdischarge - P

Qgas Qgas

Wellhead

14

Wellhead Sub-System

ProductionChokeInjection

Choke

Surface InjectionPressure

WellheadPressure

Gas Injection

Production Fluid

15

Gas Lift Valve Sub-System

PtPc

Pc

Pt

GasInjeksi

FluidaProduksi

Pc = Pt

16

Gas Lift Valve

GasInjection

TubingPressure

Close condition Open condition

Kriteria Operasi Sumur Gas Lift17

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.

18

2 Types of Gas Lift Operation

Materi Perencanaan Sumur Gas Lift19

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 Potential20

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

22

CONTINUOUS GAS LIFT

Continuous Gas Lift Operation23

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

24

Parameter Design25

Jumlah gas injeksi yang tersediaJumlah gas injeksi yang dibutuhkanTekanan Gas Injeksi yang dibutuhkan di

setiap sumurTekanan 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.

27

Availability amount of Gas Injection

Kebutuhan Gas Injeksi (1)28

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

Teka

nan

Alir

Das

ar S

umur

, psi

IPR200 scf/stb400 scf/stb600 scf/stb800 scf/stb1000 scf/stb1200 scf/stb

Kebutuhan Gas Injeksi (2)29

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

Laju

Pro

duks

i, st

b

Unlimited Gas Injection Case30

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


Laju

Pro

duks

i, st

b

Unlimited Gas Injection Case31

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 injection32

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


Laju

Pro

duks

i, st

b

Gas Flow Rate Requirement33

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)35

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.


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

Pgas

Compressor

Wellhead

Separator

Pintake Pdischarge

Horse PowerCompressor

Pinjection@wellhead

Pinjection@wellhead=Pdischarge - P

Qgas Qgas

Wellhead

COMPRESSOR37


The injection pressure at valve depth in the casing side can be expressed as:

It is a common practice to use pv = 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 ,,

PtPc

Pc

Pt

GasInjeksi

FluidaProduksi

Pc = Pt

Tekanan Tubing @ Valve Gas Lift39

Pwfp @ tubing


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)


Choke


WellheadPressure

Gas Injection

Production Fluid

Up-Stream Choke / Injection Choke41

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


Choke


WellheadPressure

Gas Injection

Production Fluid

Gas Lift Injection Parameters42

Compressor Pressure

Pwf

Point of Injection43

vvfvc PPP ,

Point of Balanced44

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


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


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.


PermukaanFluida Res.

Valve 1 : Tertutup

Valve 2 : Tertutup

Valve 3 : Tertutup

Valve 4 : Terbuka

TAHAP IV51

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 Valve54

Gas Lift Valve55

56

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 Valve57

PtPc

Pc

Pt

GasInjeksi

FluidaProduksi

Pc = Pt

Penampang Gas Lift Valve58

Jenis Gas Lift Valves59

Gas Lift Valve60

GasInjection

TubingPressure

Close condition Open condition

MEKANIKA VALVE

CLOSING & OPENING PRESSURE

61

Valve Mechanics

Mekanika Valve (Membuka+Menutup)

62

Dome berisi gas Nitrogen yang mempunyai tekanan tertentu.

Gas Nitrogen ini menekan bagian dasar dome, Pd, pada luas penampang bellow, Ab

Port terbuka untuk dilalui gas masuk kedalam tubing, jika ujung stem tidak menempel pada port.

Jika gaya membuka sedikit lebih besar dari gaya menutup.

Posisi Valve Tertutup

Gas Lift - Design

63 Perkalian antara tekanan

dalam dome, Pd, dengan luas penampang bellow, Ab, menghasilkan gaya kebawah yang mendorong stem dan ujung stem kebawah, sehingga menutup port. Gaya ini disebut sebagai gaya menutup.

Gaya menutup= Fc = Pd Ab

Posisi Valve Terbuka

Gas Lift - Design

64 Gaya membuka ini berasal

dari tekanan gas injeksi dari anulus, Pc yang menekan bellow ke atas, pada luas penampang efektif sebesar (Ab-Ap) serta tekanan fluida dari tubing, Pt (melalui port) yang menekan ujung stem keatas.

Gaya membuka = Pc (Ab - Ap) + Pt Ap

Keseimbangan Gaya Membuka dan Menutup

Gas Lift - Design

65

Dalam keadaan seimbang, yaitu sesaat katup akan membuka, gaya membuka sama dengan gaya menutup, hal ini dapat dinyatakan sebagai berikut:

Untuk tekanan tubing, Pt tertentu, gas akan mengalir kedalam katup apabila:

Jika persamaan (2) dibagi dengan Ab, maka diperoleh persamaan berikut:

bdptpbinj APAPAAP )(

P A A P A P Ac b p d b t p( )

PA

AP P

A

Acp

bd t

p

b( )1

Penentuan Tekanan Injeksi Katup Terbuka/Tertutup

Gas Lift - Design

66

Apabila R = Ap/Ab, maka

Harga tekanan injeksi, Pc, dapat ditentukan dengan persamaan berikut :

Persamaan diatas dapat digunakan untuk menentukan tekanan gas injeksi yang dibutuhkan untuk membuka katup dibawah kondisi operasi.

RPPRP tdinj )1(

RRPPP td

inj

1

Contoh Soal

Gas Lift - Design

67

Katup sembur buatan ditempatkan di kedalaman 6000 ft. Tekanan dome dan tekanan tubing di kedalaman tersebut

masing-masing sebesar 700 psi dan 500 psi. Apabila Ab katup sebesar 1.0 in2 dan Ap = 0.1 in2, tentukan tekanan gas di annulus yang diperlukan untuk membuka katup.

Perhitungan:R = Ap/Ab = 0.1/1.0 = 0.1Pd = 700 psiPt = 500 psi

Dengan menggunakan persamaan (5), tekanan gas injeksi yang diperlukan untuk membuka katup sebesar:Pc = (700 - 500(0.1) / (1.0-0.1) = 722 psi

Penentuan Tekanan Dome

Gas Lift - Design

68

RRPPP td

inj

1

Pd = ?

Pada TemperatureDi kedalaman Valve

Diubah menjadi Tekananpada Temperatur Bengkel

Test RackOpeningPressure

DOME PADA GAS LIFT VALVE

Gas Lift - Design

69

Dome pada Gas Lift Valve, diisi gas Nitrogen sejumlah mole tertentu, sehingga dapat memberikan tekanan tutup valve yang sesuai.

Sesuai dengan

P V=Z n R T P-dome

Vol. domeTemperatur di sekitardome

70

Gas Lift - Design

Penentuan Tekanan Dome

Tekanan dome @ TD = Pd Tekanan casing @ D = Pc

Test Rack (di Bengkel)Tekanan dome @ TD convertTekanan dome @ 60 oF (Tabel 5-3)Tekanan buka valve, pvo

RpRpp tcd )1(

@TD

dtFdPCP o

60@

Tabel 5-3

Gradien gas injeksi

Gradien Aliran @ tubing

R

PP Fdvo

o

160@

Temperatur pada Valve

Gas Lift - Design

71

-8000

-7000

-6000

-5000

-4000

-3000

-2000

-1000

00 200 400 600 800 1000 1200 1400 1600

Pressure, psia

Depth,ft

T-surface

T-bottom

GradientGeothermal

(oF/ft)

Gradient TemperaturAliran

Retreivable valve

Non-Retreivablevalve

72

Penentuan Opening/ClosingPressure di Bengkel

Penentuan Test Rack Opening Pressure

Gas Lift - Design

73

P1 = Pc

P2 = 0

Ptro (1)

Gas Lift - Design

74

Keseimbangan Gaya Buka dan Gaya Tutup, pada Pt = Patm :

Dimana Pvc = tekanan tutup di bengkel

Jika R = Ap/Ab, maka

Maka P-dome di bengkel :

P A P A Ad b vc b p ( )

R1

PP dTvo

)R1(PP vod

Ptro (2)

Gas Lift - Design

75

Gaya Buka hanya dipengaruhi oleh Pvc, yaitu:

Pd di set pada temperatur bengkel (60oF)

Perlu dilakukan koreksi terhadap temperatur pada kedalaman valve

P A P A A P Ad b vc b p vc p ( )

P A P A atau P Pd b vc b d vc :

oF Ct oF Ct oF Ct oF Ct oF Ct oF Ct

61 .998 101 .919 141 .852 181 .794 221 .743 261 .698 62 .996 102 .917 142 .850 182 .792 222 .742 262 .697 63 .994 103 .915 143 .849 183 .791 223 .740 263 .696 64 .991 104 .914 144 .847 184 .790 224 .739 264 .695 65 .989 105 .912 145 .845 185 .789 225 .738 265 .694 66 .987 106 .910 146 .844 186 .787 226 .737 266 .693 67 .985 107 .908 147 .842 187 .786 227 .736 267 .692 68 .983 108 .906 148 .841 188 .784 228 .735 268 691 69 .981 109 .905 149 .839 189 .783 229 .733 269 .690 70 .979 110 .903 150 .838 190 .782 230 .732 270 .689 71 .977 111 .901 151 .836 191 .780 231 .731 271 688 72 .975 112 .899 152 .835 192 .779 232 .730 272 .687 73 .973 113 .898 153 .833 193 .778 233 .729 273 .686 74 .971 114 .896 154 .832 194 .776 234 .728 274 .685 75 .969 115 .894 155 .830 195 .775 235 .727 275 .684 76 .967 116 .893 156 .829 196 .774 236 .725 276 .683 77 .965 117 .891 157 .827 197 .772 237 .724 277 .682 78 .963 118 .889 158 .826 198 .771 238 .723 278 .681 79 .961 119 .887 159 .825 199 .770 239 .722 279 .680 80 .959 120 .886 160 .823 200 .769 240 .721 280 .679 81 .957 121 .884 161 .822 201 .767 241 .720 281 .678 82 .955 122 .882 162 .820 202 .766 242 .719 282 .677 83 .953 123 .881 163 .819 203 .765 243 .718 283 .676 84 .951 124 .879 164 .817 204 .764 244 .717 284 .675 85 .949 125 .877 165 .816 205 .762 245 .715 285 .674 86 .947 126 .876 166 .814 206 .761 246 .714 286 .673 87 .945 127 .874 167 .813 207 .760 247 .713 287 .672 88 .943 128 .872 168 .812 208 .759 248 .712 288 .671 89 .941 129 .871 169 .810 209 .757 249 .711 289 .670 90 .939 130 .869 170 .809 210 .756 250 .710 290 .669 91 .938 131 .868 171 .807 211 .755 251 .709 291 .668 92 .936 132 .866 172 .806 212 .754 252 .708 292 .667 93 .934 133 .864 173 .805 213 .752 253 .707 293 .666 94 .932 134 .863 174 .803 214 .751 254 .706 294 .665 95 .930 135 .861 175 .802 215 .750 255 .705 295 .664 96 .928 136 .860 176 .800 216 .749 256 .704 296 .663 97 .926 137 .858 177 .799 217 .748 257 .702 297 .662

76Gas Lift -

Design

Faktor Koreksi Tekanan Gas Nitrogen Dalam Dome (pada Temperatur Bengkel 60 oF)

PV = ZnRT @ Tv

PV = ZnRT @ 60 oF

77

Gas Lift - Desig

n

Perhitungan Tekanan @ Bellow secara Analitis

P(x) = tekanan rata-rata yang bekerja pada bellowPvi = P(x) yang diperlukan untuk membuka katupz = pergerakan stem dari posisi

tertutupk = cp/cvAb = luas permukaan bellowPdi = tekanan dome awalPd(x)=tekanan dome jika stem bergerak sejauh x

P x P

kA

x dPvib

dP

P x

di

d

( )( )

78

Gas Lift - Desig

n

Penentuan Ukuran Port ValveQ = laju alir gas, MCF/dCd= discharge coefficientAp= luas penampang portPu = tekanan injeksi gas dalam annulus, psiak = cp/cvR = perbandingan antara tekanan upstream

dengan downstream

T = temperatur alirang = specific gravity gas

Q

C A P gk R R

T

d p u

g

kk

k

1555 2

2 1.

( )

Atau dengan menggunakanGrafik, yang dibuat pada kondisi

Laju Alir pada kondisi kritik :

Specific Gravity gas = 0.65Temperatur alir = 60 oFTekanan dasar = 14.65 psiak = cp/cv = 1.27Discharge coeficient = 0.865

79

Gas Lift - Design

Penentuan Ukuran Port : R

Berdasarkan rate injeksi (di permukaan – Mscf/d), qgi, sc tentukan rate injeksi @ TD

Berdasarkan Pt dan Pc, gunakan Gambar 5-22, untuk menentukan ukuran Port

Pt = downstream pressPc = upstream press

520)460T(q

q vsc,ggi

PENEMPATAN VALVE UNLOADING

VALVE SPACING

80

Unloading Valve Design

81

Various methods are being used in the industry for designing depths of valves of different types. They are the universal design method, the API-recommended method, the fallback method, and the percent load method.

However, the basic objective should be the same:1. To be able to open unloading valves with kickoff and

injection operating pressures2. To ensure single-point injection during unloading and

normal operating conditions3. To inject gas as deep as possible

82

No matter which method is used, the following principles apply:

The design tubing pressure at valve depth is between gas injection pressure (loaded condition) and the minimum tubing pressure (fully unloaded condition).

Depth of the first valve is designed on the basis of kickoff pressure from a special compressor for well kickoff operations.

Depths of other valves are designed on the basis of injection operating pressure.

Kickoff casing pressure margin, injection operating casing pressure margin, and tubing transfer pressure margin are used to consider the following effects:

Pressure drop across the valve Tubing pressure effect of the upper valve Nonlinearity of the tubing flow gradient curve.

83

84

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Artificial Lift Methods