GAS LIFT

1
Artificial Lift Methods

• GAS LIFT
• SUCKER ROD PUMP
• ELECTRIC SUBMERSIBLE PUMP
• OTHERS

2
PENDAHULUAN (1)
PwfltPsepdPfdPt
Flowing Well
No - Flow Well
PwfPsepdPfdPt
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PENDAHULUAN (2)

• Untuk mengangkat fluida sumur
• Menurunkan gradien aliran dalam tubing
• Memberikan energy tambahan di dalam sumur untuk
  mendorong fluida sumur ke permukaan

Gradien ?
No - Flow Well
Energy ?
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PENDAHULUAN (3)
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PENDAHULUAN GAS LIFT (1)

• Persamaan Umum Pressure Loss
• Pengurangan gradien aliran dengan menurunkan
  densitas fluida

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PENDAHULUAN GAS LIFT (2)
?
Gradient Elevasi
Gradient Friksi
Densitas Campuran
?
Gradient Akselerasi
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PENDAHULUAN GAS LIFT (3)
PwfltPsepdPfdPt
PwfgtPsep(dPfdPt)
Berkurang
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GAS LIFT (1)

• Gas lift technology increases oil production rate
  by injection of compressed gas into the lower
  section of tubing through the casingtubing
  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
Injected Gas
Res. Fluid Inj. Gas
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Sistem Sumur Gas Lift
Separator
Flow Line
Gas Injection Line

• Wellhead Subsystem
• Production subsystem
• wellhead
• production choke
• pressure gauge
• Injection subsystem
• injection choke

• Separator Subsystem
• separator
• manifold
• pressure gauges
• flow metering

• Compressor Subsystem
• intake system
• outlet system
• choke
• pressure gauge
• injection rate metering

Unloading Gas Lift Mandrells
Gas Injection Valve
Valve Subsystem

• Wellbore Subsystem
• perforation interval
• tubing shoe
• packer

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Compressor Sub-System
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Wellhead Sub-System
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Gas Lift Valve Sub-System
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Gas Lift Valve
Gas Injection
Tubing Pressure
Close condition
Open condition
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Kriteria Operasi Sumur Gas Lift

• 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.

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2 Types of Gas Lift Operation

• 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 (05 stbdaypsi) 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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Materi Perencanaan Sumur Gas Lift

• This chapter covers basic system engineering
  design fundamentals for gas lift operations.
• Relevant topics include the following
• Liquid flow analysis for evaluation of gas lift
  potential
• Gas flow analysis for determination of lift gas
  compression requirements
• Unloading process analysis for spacing subsurface
  valves
• Valve characteristics analysis for subsurface
  valve selection
• Installation design for continuous and
  intermittent lift systems.

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Evaluation of Gas Lift Potential

• 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.

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Gas Injection Rates

• Four gas injection rates are significant in the
  operation of gas lift installations
• 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).
• Injection rates of maximum efficiency where a
  minimum volume of gas is required to lift a given
  amount of liquid.
• Injection rate for maximum liquid flow rate at
  the optimum GLR.
• 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

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CONTINUOUS GAS LIFT

• THE GAS IS INJECTED CONTINUOUSLY TO ANNULUS

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Continuous Gas Lift Operation

• 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.

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Gas Lift OperationPressure vs Depth
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Parameter Design

• Jumlah gas injeksi yang tersedia
• Jumlah gas injeksi yang dibutuhkan
• Tekanan Gas Injeksi yang dibutuhkan di setiap
  sumur
• Tekanan Kompresor yang dibutuhkan

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Gas Injeksi yang diperlukan

• GAS LIFT PERFORMANCE CURVE

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Availability amount of Gas Injection

• Unlimited amount of lift
• gas

• 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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Kebutuhan Gas Injeksi (1)

• Nodal Analysis
• IPR Curve
• Tubing Performance Curve
• GLR formasi
• Variasi GLR
• GLR-total (assume)
• Qg-inj Qtotal Qq-f
• Plot Qg-inj vs Qliquid

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Kebutuhan Gas Injeksi (2)

• Qg-inj gtgt maka Qliq gtgt
• 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

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Unlimited Gas Injection Case

• 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).

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Unlimited Gas Injection Case

• 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

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Limited amount of gas injection

• If a limited amount of gas lift gas is available
  for a well, the well potential should be
  estimated based on GLR expressed as

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Gas Flow Rate Requirement

• 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,

where qg total output gas flow rate of the
compression station, scf/day Sf safety factor,
1.05 or higher Nw number of wells
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Point of Injection
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Output Gas Pressure Requirement (1)

• 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.

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Output Gas Pressure Requirement (2)

• 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

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COMPRESSOR
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Output Gas Pressure Requirement (3)

• 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

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Tekanan Tubing _at_ Valve Gas Lift
Dp _at_ tubing
Pwf
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Output Gas Pressure Requirement (4)

• 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)

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Up-Stream Choke / Injection Choke

• 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

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Gas Lift Injection Parameters
Compressor Pressure
Pwf
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Point of Injection
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Point of Balanced
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Unloading Valves Design

• Unloading ProcessGas Lift Wells

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Persiapan Operasi Sumur Gas Lift
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TAHAP O
Choke Tutup

• Katup Unloading sudah dipasang.
• Sumur masih diisi killing fluid
• Fluida produksi masih belum mengalir ke dalam
  tubing

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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.

No flow

Permukaan Killing fluid
Valve 1 Terbuka
Valve 2 Terbuka
Valve 3 Terbuka
Valve 4 Terbuka
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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 1 Tertutup
Permukaan Killing fluid
Valve 2 Terbuka
Valve 3 Terbuka
Valve 4 Terbuka
Permukaan Fluida Res.
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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.

Valve 1 Tertutup
Permukaan Fluida Res.
Valve 2 Tertutup
Valve 3 Tertutup
Valve 4 Terbuka
Permukaan Killing fluid
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TAHAP IV

• 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.

Fluida Produksi
Valve 1 Tertutup
Valve 2 Tertutup
Valve 3 Tertutup
Valve 4 Terbuka
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Unloading Valves Design

• gas lift Valve
• gas lift Valve Mechanics

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Gas Lift Valve
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Gas Lift Valve
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Contoh Penampang Sumur Gas Lift

Gas Lift Mandrell Gas Lift Valves

• Gas Lift Valves
• Mandrell Dummy Valves
• Mandrell Valves

• Valves Operating Conditions
• Casing pressure
• Test Rack Opening Pressure
• Port Size
• Temperature _at_ Lab.
• Jenis Valves

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Gas Lift Valve
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Penampang Gas Lift Valve
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Jenis Gas Lift Valves
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Gas Lift Valve
Gas Injection
Tubing Pressure
Close condition
Open condition
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Valve Mechanics

• Mekanika valve
• Closing opening pressure

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Mekanika Valve (MembukaMenutup)

• 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.

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Posisi Valve Tertutup

• 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

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Posisi Valve Terbuka

• 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

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Keseimbangan Gaya Membuka dan Menutup

• 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

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Penentuan Tekanan Injeksi Katup Terbuka/Tertutup

• 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.

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Contoh Soal

• 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 0.1
• Pd 700 psi
• Pt 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

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Penentuan Tekanan Dome
Pd ?
Pada Temperature Di kedalaman Valve
Test Rack Opening Pressure
Diubah menjadi Tekanan pada Temperatur Bengkel
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DOME PADA GAS LIFT VALVE

• Dome pada Gas Lift Valve, diisi gas Nitrogen
  sejumlah mole tertentu, sehingga dapat memberikan
  tekanan tutup valve yang sesuai.
• Sesuai dengan
• P VZ n R T

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Penentuan Tekanan Dome

• Tekanan dome _at_ TD Pd
• Tekanan casing _at_ D Pc
• Test Rack (di Bengkel)
• Tekanan dome _at_ TD
• convert
• Tekanan dome _at_ 60 oF
• (Tabel 5-3)
• Tekanan buka valve, pvo

Gradien Aliran _at_ tubing
_at_TD
Gradien gas injeksi
Tabel 5-3
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Temperatur pada Valve
T-surface
Gradient Temperatur Aliran
Gradient Geothermal (oF/ft)
Retreivable valve
Non-Retreivable valve
T-bottom
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Penentuan Opening/ClosingPressure di Bengkel
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Penentuan Test Rack Opening Pressure
P1 Pc P2 0
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Ptro (1)

• 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

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Ptro (2)

• Gaya Buka hanya dipengaruhi oleh Pvc, yaitu
• Pd di set pada temperatur bengkel (60oF)
• Perlu dilakukan koreksi terhadap temperatur pada
  kedalaman valve

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Faktor Koreksi Tekanan Gas Nitrogen Dalam Dome
(pada Temperatur Bengkel 60 oF)
PV ZnRT _at_ Tv PV ZnRT _at_ 60 oF
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Perhitungan Tekanan _at_ Bellow secara Analitis

• P(x) tekanan rata-rata yang bekerja
• pada bellow
• Pvi P(x) yang diperlukan untuk
• membuka katup
• z pergerakan stem dari posisi tertutup
• k cp/cv
• Ab luas permukaan bellow
• Pdi tekanan dome awal
• Pd(x)tekanan dome jika stem bergerak
• sejauh x

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Penentuan Ukuran Port Valve

• Q laju alir gas, MCF/d
• Cd discharge coefficient
• Ap luas penampang port
• Pu tekanan injeksi gas dalam
• annulus, psia
• k cp/cv
• R perbandingan antara
• tekanan upstream dengan
• downstream
• T temperatur aliran
• gg specific gravity gas

Laju Alir pada kondisi kritik
Atau dengan menggunakan Grafik, yang dibuat pada
kondisi
Specific Gravity gas 0.65 Temperatur alir 60
oF Tekanan dasar 14.65 psia k cp/cv
1.27 Discharge coeficient 0.865
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Penentuan Ukuran Port R

• Berdasarkan rate injeksi (di permukaan Mscf/d),
  qgi, sc tentukan rate injeksi _at_ TD
• Berdasarkan Pt dan Pc, gunakan Gambar 5-22, untuk
  menentukan ukuran Port
• Pt downstream press
• Pc upstream press

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Unloading Valve Design

• Penempatan valve unloading
• Valve spacing

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• 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 pressures
• 2. To ensure single-point injection during
  unloading and normal operating conditions
• 3. To inject gas as deep as possible

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• 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.

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Test II Kamis, 26 Februari 2009
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