Evaluation of Wax Deposition and Its Control During Production of Alaska North Slope Oils

Evaluation of Wax Deposition and Its Control During Production of Alaska North Slope OilsAnnual Report Jan Dec, 2006

University of Alaska FairbanksKansas UniversityConocoPhilips 22 January 2007

Project ObjectivesEvaluate the mechanisms and environments leading to wax deposition during ANS oil productionDevelop predictive models and give guidance for potential wax-free productionEvaluate methods and techniques to prevent and control wax deposition during production

Wax Deposition DiagramPressureTemperatureCritical PointInitial Reservoir ConditionWax EnvelopeGasLiquidLiquid + GasP-T Path

To Achieve Wax-Free ProductionP-T path for production must stay outside of the wax envelopeRequires in-depth understanding ofThermodynamic properties of crude oilHeat transfer characteristics of production string and the influence of permafrostWax deposition under dynamic conditions

Work DoneDensity determination of all tank oil samples as function of temperatureMolecular weight determination of crude oil using Cryette A for all 28 tank oil samplesDetermination of tank oil WATs by cross polar microscope (CPM) (12 samples) and viscometer (28 samples)Composition analysis of crude oil using GC-MSSelection of suitable thermodynamic model for wax precipitation Bubble point curve prediction program

Work Done (Cont.)Development of program for plus fraction splitting into suitable number of componentsAlgorithm development for prediction of WAT of the oilDevelopment of analytical solution for wellbore geometry (by KU)Development of numerical solution for wellbore geometry (by KU)Development of computer program for solid-liquid flash problem (by KU)

Density MeasurementDensity measured using ANTON-PAAR density-meterDensity as a function of temperature is determined for modeling purpose

Density Measurement Results (Cont.)Sample density at 15 0C

Density Measurement Results (Cont.)Density of all samples as a function of temperature

Sheet1

0.125CF

744.6

0.25846.4

0.1250.04908738521559

0.012271846315.55559.999

2475.2

3595

0.12560140

80176

90194

210012631.5100212

10006015.75642.8

1006541

439.2

337.4

80.439181056844111.2

133.8

0.613631.889.24

10.055102470420.368.54

41.2106.16

36.297.16

30.286.36

90194

Login: 3132355337.4

New Password: 474512732

WAT

deg Cdeg F

531.889.24

430.286.36

620.368.54

2441.2106.16

2536.297.16

Sheet2

Density Meter CalDensity Meter Cal

TeperatureTaTwwater dengas denABTeperatureTaTwwater dengas denAB

deg Cdeg C

356.16437.98640.994030.001145819525.968779618137.9688389563356.16518.00490.994030.001145819526.2568337.9783724225cgi

306.16598.00580.995650.001164759926.21910288837.9877838495306.16598.00580.995650.001164759926.21910288837.9877838495

256.16758.01030.997040.001184337126.235578922438.0069844812256.16758.01030.997040.001184337126.235578922438.0069844812

236.16818.01180.997540.001192353426.239316889538.0141710701236.16818.01180.997540.001192353426.239316889538.0141710701

206.16928.01450.99820.001204583626.252058112438.0274058422206.16928.01450.99820.001204583626.252058112438.0274058422

186.178.01610.998590.001212877326.257830277638.0370524731186.178.01610.998590.001212877326.257830277638.0370524731

166.17058.01760.998940.001221286126.266761507438.0429910198166.17058.01760.998940.001221286126.266761507438.0429910198

156.17128.01830.99910.001225534326.265253147438.0515204705156.17128.01830.99910.001225534326.265253147438.0515204705

146.18068.01880.999240.001229812226.153377390638.1676526162

126.18138.01980.99950.001238458326.154190319238.176078816

106.18188.02080.99970.001247226826.15905539138.1820249656

Chart1

0.825

0.8243

0.8224

0.8208

0.8184

0.8166

0.8125

0.8062

Temperature (deg C)

Density (g/cc)

Sample 28

Chart2

0.825

0.8243

0.8224

0.8208

0.8184

0.8166

0.8125

0.8062

15

16

16

18

20

23

25

30

35

Temperature / deg C

Density

Sample 28

Sample28

0.825

0.8243

0.8224

0.8208

0.8184

0.8166

0.8125

0.8062

15

16

18

20

23

25

30

35

DENSITY(g/cc)

Temperature / deg C

Sample 28

15deg

0.7877

0.7841

0.7827

0.8251

0.8424

0.8161

0.7838

0.8333

0.7534

0.8727

0.7481

0.7578

0.8611

0.874

0.9114

0.91

0.7654

0.7581

0.7602

0.7644

0.7603

0.8268

0.8252

0.8258

0.8267

0.8279

0.825

density/g/cc

Sample number

Density at 15 deg C.

16deg

0.7868

0.7835

0.7819

0.8241

0.8416

0.815

0.7831

0.8328

0.7527

0.8718

0.7474

0.7569

0.8603

0.8732

0.9105

0.9091

0.7645

0.7574

0.7592

0.7635

0.7595

0.8259

0.8242

0.825

0.8258

0.8271

0.8243

density/g/cc

Sample number


18deg

0.7854

0.7815

0.7796

0.8222

0.84

0.813

0.7813

0.8313

0.7507

0.8702

0.7451

0.755

0.8585

0.8712

0.9083

0.9077

0.7623

0.7557

0.7573

0.7615

0.758

0.8244

0.8224

0.823

0.8238

0.8251

0.8224

density/g/cc

Sample number


20deg

0.7836

0.7795

0.7776

0.8205

0.8383

0.8114

0.7795

0.8298

0.7488

0.8686

0.743

0.7531

0.8567

0.869

0.9064

0.9061

0.7602

0.7541

0.7553

0.759

0.7557

0.8226

0.8202

0.821

0.8218

0.823

0.8208

density/g/cc

Sample number


23deg

0.7799

0.7773

0.7747

0.8177

0.8355

0.8082

0.7768

0.8271

0.7459

0.8662

0.7402

0.7501

0.8542

0.8669

0.9039

0.9036

0.7569

0.7514

0.7524

0.7557

0.752

0.8202

0.8174

0.8181

0.8189

0.8203

0.8184

density/g/cc

Sample number


25deg

0.7778

0.7751

0.7727

0.8157

0.8336

0.8052

0.7748

0.8253

0.7438

0.8644

0.738

0.7482

0.8522

0.8648

0.9019

0.9018

0.7545

0.7494

0.7503

0.7534

0.7492

0.8185

0.8152

0.8161

0.8168

0.8183

0.8166

density/g/cc

Sample number


30deg

0.7732

0.7705

0.7678

0.8112

0.8293

0.8016

0.7702

0.8212

0.739

0.8604

0.733

0.7434

0.848

0.8608

0.898

0.8977

0.7493

0.7447

0.7457

0.7484

0.7446

0.8144

0.8107

0.8114

0.812

0.8138

0.8125

density/g/cc

Sample number


35deg

0.7666

0.7638

0.7613

0.8046

0.8228

0.7946

0.7634

0.8148

0.7324

0.8544

0.7255

0.7368

0.8417

0.8545

0.8914

0.8912

0.7424

0.7381

0.739

0.7413

0.7375

0.8081

0.8041

0.8045

0.8049

0.807

0.8062

density/g/cc

Sample number


Chart3

0.8251

0.8241

0.8222

0.8205

0.8177

0.8157

0.8112

0.8046

Temperature (deg C)

Density (g/cc)

Sample 04

Chart4

0.7877

0.7868

0.7854

0.7836

0.7799

0.7778

0.7732

0.7666

Temperature (deg C)

Density (g/cc)

Sample 01

Chart5

0.8161

0.815

0.813

0.8114

0.8082

0.8052

0.8016

0.7946

Temperature (deg C)

Density (g/cc)

Sample 06

Chart6

0.9114

0.9105

0.9083

0.9064

0.9039

0.9019

0.898

0.8914

Temperature (deg C)

Density (g/cc)

Sample 16

Chart7

0.78770.78410.78270.82510.84240.81610.78380.83330.75340.87270.74810.75780.86110.8740.91140.910.76540.75810.76020.76440.76030.82680.82520.82580.82670.82790.825

0.78680.78350.78190.82410.84160.8150.78310.83280.75270.87180.74740.75690.86030.87320.91050.90910.76450.75740.75920.76350.75950.82590.82420.8250.82580.82710.8243

0.78540.78150.77960.82220.840.8130.78130.83130.75070.87020.74510.7550.85850.87120.90830.90770.76230.75570.75730.76150.7580.82440.82240.8230.82380.82510.8224

0.78360.77950.77760.82050.83830.81140.77950.82980.74880.86860.7430.75310.85670.8690.90640.90610.76020.75410.75530.7590.75570.82260.82020.8210.82180.8230.8208

0.77990.77730.77470.81770.83550.80820.77680.82710.74590.86620.74020.75010.85420.86690.90390.90360.75690.75140.75240.75570.7520.82020.81740.81810.81890.82030.8184

0.77780.77510.77270.81570.83360.80520.77480.82530.74380.86440.7380.74820.85220.86480.90190.90180.75450.74940.75030.75340.74920.81850.81520.81610.81680.81830.8166

0.77320.77050.76780.81120.82930.80160.77020.82120.7390.86040.7330.74340.8480.86080.8980.89770.74930.74470.74570.74840.74460.81440.81070.81140.8120.81380.8125

0.76660.76380.76130.80460.82280.79460.76340.81480.73240.85440.72550.73680.84170.85450.89140.89120.74240.73810.7390.74130.73750.80810.80410.80450.80490.8070.8062

Sample1

Sample2

Sample3

Sample4

Sample5

Sample6

Sample7

Sample8

Sample9

Sample10

Sample11

Sample12

Sample13

Sample14

Sample16

Sample17

Sample18

Sample19

Sample20

Sample21

Sample22

Sample23

Sample24

Sample25

Sample26

Sample27

Sample28

Temperature (deg C)

Density (g/cc)

Sample Densities

Chart8

0.7877

0.7841

0.7827

0.8251

0.8424

0.8161

0.7838

0.8333

0.7534

0.8727

0.7481

0.7578

0.8611

0.874

0.9114

0.91

0.7654

0.7581

0.7602

0.7644

0.7603

0.8268

0.8252

0.8258

0.8267

0.8279

0.825

Sample no

Density (g/cc)

15 deg Celcius

Sheet3

DENSITY MEASUREMENTS

TEMPERATURE deg CDensity in pounds per cubic feet

15161820232530355960.864.46873.4778695T/deg F

SAMPLEKg/m3lb/ft3lb/gal

10.78770.78680.78540.78360.77990.77780.77320.766649.1524849.0963249.0089648.8966448.6657648.5347248.2476847.83584773.248.26930928446.4526681933

20.78410.78350.78150.77950.77730.77510.77050.763848.9278448.890448.765648.640848.5035248.3662448.079247.66112770.548.10075375546.4301355962

30.78270.78190.77960.77760.77470.77270.76780.761348.8404848.7905648.6470448.5222448.3412848.2164847.9107247.50512767.847.93219822636.407602999

40.82510.82410.82220.82050.81770.81570.81120.804651.4862451.4238451.3052851.199251.0244850.8996850.6188850.20704811.250.6415722866.7697936348

50.84240.84160.840.83830.83550.83360.82930.822852.5657652.5158452.41652.3099252.135252.0166451.7483251.34272829.351.77151861046.9208454898

60.81610.8150.8130.81140.80820.80520.80160.794650.9246450.85650.731250.6313650.4316850.2444850.0198449.58304801.650.04226373826.6896777338

70.78380.78310.78130.77950.77680.77480.77020.763448.9091248.8654448.7531248.640848.4723248.3475248.0604847.63616770.248.08202536326.4276319743

80.83330.83280.83130.82980.82710.82530.82120.814851.9979251.9667251.8731251.7795251.6110451.4987251.2428850.84352821.251.26585202326.8532476983

90.75340.75270.75070.74880.74590.74380.7390.732447.0121646.9684846.8436846.7251246.5441646.4131246.113645.7017673946.1342725836.167255296

100.87270.87180.87020.86860.86620.86440.86040.854454.4564854.4003254.3004854.2006454.0508853.9385653.6889653.31456860.453.71302859337.1803876274

110.74810.74740.74510.7430.74020.7380.7330.725546.6814446.6377646.4942446.363246.1884846.051245.739245.271273345.75970474076.1171828579

120.75780.75690.7550.75310.75010.74820.74340.736847.2867247.2305647.11246.9934446.8062446.6876846.3881645.97632743.446.40895566746.203975084

130.86110.86030.85850.85670.85420.85220.8480.841753.7326453.6827253.570453.4580853.3020853.1772852.915252.5220884852.93892171917.0769045886

140.8740.87320.87120.8690.86690.86480.86080.854554.537654.4876854.3628854.225654.0945653.9635253.7139253.3208860.853.73799978287.18372579

1500000000000

160.91140.91050.90830.90640.90390.90190.8980.891456.8713656.815256.6779256.5593656.4033656.2785656.035255.6233689856.06032040537.4941749064

170.910.90910.90770.90610.90360.90180.89770.891256.78456.7278456.6404856.5406456.3846456.2723256.0164855.61088897.756.04159201327.4916712845

180.76540.76450.76230.76020.75690.75450.74930.742447.7609647.704847.5675247.4364847.2305647.080846.7563246.32576749.346.77728071246.2532129814

190.75810.75740.75570.75410.75140.74940.74470.738147.3054447.2617647.1556847.0558446.8873646.7625646.4692846.05744744.746.49011203326.2148241122

200.76020.75920.75730.75530.75240.75030.74570.73947.4364847.3740847.2555247.1307246.9497646.8187246.5316846.1136745.746.5525400076.2231695186

210.76440.76350.76150.7590.75570.75340.74840.741347.6985647.642447.517647.361647.1556847.0121646.7001646.25712748.446.7210955366.2457021157

220.76030.75950.7580.75570.7520.74920.74460.737547.4427247.392847.299247.1556846.924846.7500846.4630446.02744.646.48386923596.2139895716

230.82680.82590.82440.82260.82020.81850.81440.808151.5923251.5361651.4425651.3302451.1804851.074450.8185650.42544814.450.84134180196.7964989351

240.82520.82420.82240.82020.81740.81520.81070.804151.4924851.4300851.3177651.1804851.0057650.8684850.5876850.17584810.750.61035829916.7656209316

250.82580.8250.8230.8210.81810.81610.81140.804551.5299251.4851.355251.230451.0494450.9246450.6313650.2008811.450.65405788076.7714627161

260.82670.82580.82380.82180.81890.81680.8120.804951.5860851.5299251.4051251.2803251.0993650.9683250.668850.2257681250.6915146656.7764699599

270.82790.82710.82510.8230.82030.81830.81380.80751.6609651.6110451.4862451.355251.1867251.0619250.7811250.3568813.850.80388501776.7914916913

280.8250.82430.82240.82080.81840.81660.81250.806251.4851.4363251.3177651.2179251.0681650.9558450.750.30688812.550.72272865186.7806426631

00000000

Density values in gram per cubic centimeter (g/cc)

1516182023253035

SAMPLE

120.75780.75690.7550.75310.75010.74820.74340.7368

190.75810.75740.75570.75410.75140.74940.74470.7381

200.76020.75920.75730.75530.75240.75030.74570.739

150.825230.82680.82590.82440.82260.82020.81850.81440.8081

160.8243280.8250.82430.82240.82080.81840.81660.81250.8062

180.8224

200.8208

230.8184

250.8166

300.8125

350.8062Density values in gram per cubic centimeter (g/cc)

1516182023253035

SAMPLE

10.78770.78680.78540.78360.77990.77780.77320.7666

20.78410.78350.78150.77950.77730.77510.77050.7638

30.78270.78190.77960.77760.77470.77270.76780.7613

40.82510.82410.82220.82050.81770.81570.81120.8046

50.84240.84160.840.83830.83550.83360.82930.8228

60.81610.8150.8130.81140.80820.80520.80160.7946

70.78380.78310.78130.77950.77680.77480.77020.7634

80.83330.83280.83130.82980.82710.82530.82120.8148

90.75340.75270.75070.74880.74590.74380.7390.7324

100.87270.87180.87020.86860.86620.86440.86040.8544

110.74810.74740.74510.7430.74020.7380.7330.7255

120.75780.75690.7550.75310.75010.74820.74340.7368

130.86110.86030.85850.85670.85420.85220.8480.8417

140.8740.87320.87120.8690.86690.86480.86080.8545

160.91140.91050.90830.90640.90390.90190.8980.8914

170.910.90910.90770.90610.90360.90180.89770.8912

180.76540.76450.76230.76020.75690.75450.74930.7424

190.75810.75740.75570.75410.75140.74940.74470.7381

200.76020.75920.75730.75530.75240.75030.74570.739

210.76440.76350.76150.7590.75570.75340.74840.7413

220.76030.75950.7580.75570.7520.74920.74460.7375

230.82680.82590.82440.82260.82020.81850.81440.8081

240.82520.82420.82240.82020.81740.81520.81070.8041

250.82580.8250.8230.8210.81810.81610.81140.8045

260.82670.82580.82380.82180.81890.81680.8120.8049

270.82790.82710.82510.8230.82030.81830.81380.807

280.8250.82430.82240.82080.81840.81660.81250.8062

Molecular Weight MeasurementNeed for measurement of molecular weightUsed for calculating critical properties of fractions which are required for modelingInstrument- Cryette AMeasures depletion in freezing point and relates it to the concentration of solvent (benzene) and hence to the molecular weight of the solute

Kf = 5.120C/mole, FP= Meter Reading

Cryette A apparatus

Molecular Weight Measurement Results

Wax Appearance Temperature (WAT) measurementDead oil WAT measurement using Brookfield Programmable viscometer, Model LVDV-II+Sudden increase in viscosity is used as indication of sign of wax appearanceDead oil WAT measurement using Cross Polar Microscope (CPM)Polar light makes the wax crystals shine as soon as they appear

WAT measurement by ViscometryBrookfield viscometerData gathering PC Programmable LVDV-II+ ViscometerHeating/Refrigerating bath

WAT By CPM(for dead oil)

WAT by ViscometrySpindle: SC4-21RPM: 200Temp range: 50 to 0oCWAT = 20.3oCWAT plot of sample 06

WAT Results by Viscometry

Oil Sample slides using CPM at T=60oC (T>WAT)

Oil Sample slides using CPM at T=31.8oC(T=WAT)

Oil Sample slides using CPM at T=28.8oC(T

WAT measurement by CPM

Sample noWAT (CPM)deg Cdeg F12780.6227.982.22325.778.26431.889.24540.6105.08633.892.8482984.2142882.42331.588.7243696.82533.692.482634.293.56

Comparison of WAT by Viscometry and CPM

Chart1

28.127

3027.9

43.125.7

3031.8

36.140.6

29.133.8

43.229

46.228

3631.5

44.236

36.133.6

3234.2

WAT by Viscometry

WAT by CPM

Sample No.

WAT (0C)

Comparison of WAT by Viscometry and by CPM

Sheet1

Sample noWAT(Viscometery)WAT (CPM)

128.127

23027.9

343.125.7

43031.8

536.140.6

629.133.8

843.229

1446.228

233631.5

2444.236

2536.133.6

263234.2

Sheet1

WAT by Viscometry

WAT by CPM

Sample No.

WAT (0C)

Comparison of WAT by Viscometry and by CPM

Sheet2

Sheet3

Composition AnalysisNeed for composition analysisUsed for identifying the type of crudeRequired for modeling phase equilibrium and properties of hydrocarbon mixturesMethod of analysisGC-MSFlame Ionization Detector

Composition Analysis Results for Sample 13

Procedure For Bubble Point Prediction

Bubble Point Prediction Results

Plus Fraction SplittingNeed for plus fraction splittingNot well defined composition gives gross information and make EOS models behave poorlyExtended composition distribution gives better resultsPedersens method used for splitting plus fraction into suitable number of componentsProgram flexible to consider splitting upto desired carbon number depending on the requirement

Plus Fraction Splitting ResultsNorth Sea Crude Oil sample

Work Done at University of Kansas (KU)Thermodynamic ModelHeat-Transfer ModelDynamic Wax Deposition Model

Heat-Transfer ModelObjective:Establish temperature profiles in production string.Approach:Model heat exchanges between producing fluids, production string, insulation materials and formation rock/permafrost using total system energy balance.Generate system temperature profiles by solving total-system- energy-balance equation numerically using finite-difference method.

Physical Model

Total System Energy BalanceHeat loss into the formation = Total heat flow from center of well to cement/formation interface

Newtons Law of Cooling:

Where A: crossectional-area T: temperature Ut: overall heat-transfer coefficientEquating Eqs. (1) and (2) yields

Overall Energy Balance of Heat Transfer Into Formation Rock

where

: formation thermal conductivity , Btu/hr-ft-F;

r : radial distance for the center of the wellbore, ft;

: outside cement radius (drilled hole radius), ft;

: outside tubing radius, ft;

t : time, hr;

T : temperature, F;

: tubing fluid temperature, F;

: overall heat-transfer coefficient, Btu/hr-sq ft-F;

Z : vertical depth, ft.

_1187869780.unknown

_1200518623.unknown

_1213126414.unknown

_1199511021.unknown

_1187867230.unknown

Overall Energy Balance of Heat Transfer Into Formation RockAssumptions:Physical properties of system components independent of temperature.Steady-state heat flow in the formation rock.Radial heat flow from wellbore into formation rock.Heat transfer from center of wellbore to cement/formation interface (0 rh) represented by an overall heat transfer coefficient, Ut.

Overall Energy Balance of Heat Transfer Into Formation RockBoundary Conditions:

= Constant

= Constant

where

a: geothermal gradient, F/ft;

b: surface temperature, F;

: tubing fluid temperature, F;

: undisturbed formation temperature, F.

_1213119718.unknown

_1230584410.unknown

_1230584454.unknown

_1230584394.unknown

_1199511021.unknown

Numerical ModelFinite Difference Approximation:

r

r

e

r

h

T/z=0

z

z

i

-

1,j

T

air

T

e

=az+b

r

i

i,j

-

1

i

+

1,j

i,j

+1

i,j

r

i

+1

Simulation of Heat Loss from Cement/Formation Interface into Formation RockSteam Injection Example Well

Depth= 5,000 ft, Ke = 1.0 Btu/hr-ft-F, ce = 0.21 Btu/lb-F, cf = 1.0 Btu/lb-F, Tf = 600 F, Te = 80 F, Ut = 3.4274 Btu/hr-sq ft-F, = 167 lb/ft3, rto = 0.146 ft, rh = 0.5 ft.

Analytical SolutionsAnalytical solutions of heat conduction in an infinite circular cylinder bounded by a surface can be used to calculate cement/formation temperature change vs. time (Willhite, 1967).

wheref(t): transient heat conduction function solved analytically

Validation of Numerical Model with Analytical SolutionsEq. (3) can be rearranged as

Eq. (4) can be used to calculate f(t) using temperature data from numerical model.

Numerical model can be validated by comparing f(t)analytical vs. f(t)numerical

Analytical vs. Numerical SolutionsSteam Injection Example Well

During first 200 hours of steam injection, cement/formation interface temperatures calculated using Numerical model match analytical solutions well.

TD=

Time, hr

Numerical Solution

Analytical Solution in Willhites article

Error, %

Th(F)

f(t)

f(t)

0.1

0.9

152.48

0.324

0.323

0.3

0.2

1.7

172.06

0.430

0.439

-2.0

0.5

4.4

206.18

0.641

0.644

-0.5

1

8.7

232.96

0.833

0.842

-1.0

2

17.5

260.87

1.067

1.08

-1.2

5

43.7

295.79

1.419

1.44

-1.5

10

87.4

319.79

1.711

1.73

-1.1

20

174.8

341.22

2.019

2.05

-1.5

_1224570889.unknown

Phase Composition in Solid-Liquid Equilibrium (Experimental data from Dauphin et al. 1999)Predictions from our thermodynamic model match experimental data well.Thermodynamic Model

Future WorkMeasure WAT of remaining tank oil and live oil samples by CPMComplete GC-MS characterizationConduct PVT AnalysisComplete GC-FID analysisDevelop program to predict WATDevelopment of the thermodynamic model to predict cloud point

AcknowledgementWe gratefully acknowledge the financial support from AEDTL/NETL/DOE

ThanksandQuestions?

Evaluation of Wax Deposition and Its Control During Production of Alaska North Slope Oils

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