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SPE European Artificial Lift Forum 2008Artificial Lift Selection for Waxy Crude Production

Authors : Dale Chenery, Murat Kece, and

Rosaura Heath

Date : 27/02/2008

Introduction

Topics

• Field and Reservoir

• Flow Assurance Challenges

• Artificial Lift Selection

• Conclusions

• Future Plans

Project Location and Topography

Structure Map on Z4 Unit

General Reservoir Characteristics

• High porosity & permeability sands

• PI’s (from DST’s) of 18 – 27 m3/bar (8 – 12 bpd/psi)

• Porosity 24 – 30 %

• Shallow depth

• Less than 1000 m tvd (3200 ft tvd)

• Low reservoir energy

• No aquifer or gas cap detected

• GOR 35 – 45 m3/m3 (200 – 250 SCF/STB)

• Initial rates of 190 m3/day (1200bpd), but rapidly declining

• Initial Reservoir Pressure 75 – 90 bar (1100 - 1300 psi)

• Static Reservoir Temperature 53 - 60 OC (112 - 140OF)

Oil Characteristics

• API Gravity 31 – 38 O

• Wax 35 weight %

• Resins 13 weight %

• Asphaltenes 0.15 weight %

• Upper Pour Point 39.0 OC

• Lower Pour Point 36.0 OC

• Wax Appearance Temperature 61.0 OC (First Appearance)

53.0 OC (Bulk Crystallisation)

• Wax Dissolution Temperature 59.0 OC (Commencement)

64.0 OC (Complete)

Oil Viscosity

Comparison with Other Waxy Crudes

Waxy Crude Database(Viscosity)

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 10 20 30 40 50 60 70 80

Temperature (OC)

Vis

co

sit

y (

cp

)

NZ India Vietnam E Africa China This Study

Wax Deposition

Emulsion Tendencies at 60 OC

10

100

1000

0.1 1.0 10.0 100.0Shear Rate (sec-1)

Vis

cosity (cp)

M-01 20% M-01 40% M-03 20%M-03 40% M-04 20% M-04 40%

Points = Measured

Lines = Fit

Sucker Rod Pump (SRP)

Jet Pump

1. Nozzle to convert

pressure to velocity

2. Intake to direct

produced fluids into jet

3. Throat where power

fluid and produced fluid

mix

4. Diffuser where velocity

is converted back to

pressure

Progressive Cavity Pump (PCP)

Hydraulic Submersible Pump

Artificial Lift Challenges

• Flow Assurance Issues.

• Potential sand production due to shallow,

relatively weak rock

• High wax content in crude

• High pour point temperature

• Emulsions

Artificial Lift Ranking Matrix

FairExcellentFair/GoodFair/GoodWorkover/Interventions

PoorPoorGood/ExcellentExcellentPower Requirements

Fair/Poor: typically designed for flow rates >1200 bpd

Fair: > 200 B/D from 4000ft.Excellent for <100 B/D

shallow wells that do not pump off

Excellent: most commonly used methods for wells producing < 100 B/D.

Low Volume Lift Capabilities

ExcellentGoodPoor/FairPoor / FairHigh Volume Lift Capabilities

Poor/FairPoorGoodGoodEmulsification

FairGood/excellentExcellentGoodHigh Viscosity Fluid Handling Capabilities

ExcellentExcellentFairExcellentTemperature Limitation

FairFairExcellentFairSolids/Sand Handling Ability

Good/ExcellentGood/excellentFairFair/goodParaffin Handling Capability

FairFairGoodGoodCorrosion/Scale Handling Ability

HSPJPPCPSRPAttribute

Hydraulic Submersible Pumps

• HSP’s were eliminated due to:

• Currently recommended only for high flow rates (above 1200 bpd).

• Limited oilfield implementation.

• But also have the limitations of:

• The high cost and complexity of the surface equipment required for

cleaning, conditioning and pressurising the power fluid.

• The high cost and added complexity of the equipment required for surface

separation of the return fluids.

• The generation of stable emulsions due to the mixing of the power fluid

and produced oil.

• High power requirements

Normalised CAPEX and OPEX Comparison

• High level comparison based on UK Prices

• Normalized to lowest cost in each category

• Jet Pump costs are a direct result of surface pumping equipment,

heated water for power fluid, and high pressure pipe lines.

Lift Capex OpexMethod $/bbl

PCP 1.00 1.00

SRP 2.54 1.26JP 5.11 4.18

Jet Pumps

• Jet pumps were not recommended due to:

• The high cost and complexity of the surface equipment required for

cleaning, conditioning and pressurizing the power fluid.

• The high cost and added complexity of the equipment required for surface

separation of the return fluids.

• Limited solids handling capability due to erosion in the jet impingement

area.

• The generation of stable emulsions due to the mixing of the power fluid

and produced oil at high shear rates.

• Low efficiency (high power requirements)

Sucker Rod Pumps

• Sucker Rods pumps were not recommended due to:

• High profile surface unit in wildlife refuge.

• Limited rate capacity without using large unit.

• Limited sand handling capability.

Progressive Cavity Pumps

• PCP’s were recommended as the artificial lift method due to:

• Operational flexibility.

• High tolerance to solids.

• Low shear through pump.

• Simple and reliable.

• Lowest Capex and Opex.

Heat Tracing System

Tubing Heat Up Curves

Conclusions

• No “One Best” artificial lift system

• Hydraulic pumps, due to heated power fluids, provide the best

flow assurance, but:

• Introduce emulsion, and fluid handling problems

• Poor efficiency means high energy costs

• PCP’s offer most flexible and lowest cost solution

• Require heat tracing for flow assurance

Future Plans

• Possible trial of Hollow Tubing Rods as they will allow

circulation and simplify down hole chemical injection

• Perform Sand Influx Tests

• Wax Studies

• Pour point depressants and/or diluents

• Demulsifier testing

• Development of life cycle intervention / reservoir management

strategy and plan