17.08.2015   IAEA RADIATION TECHNOLOGY SERIES No

Selection of conditionally qualified tracers

For unambiguous, single phase tracing of water in secondary or tertiary recovery schemes, the following practical tracer selection criteria apply to passive tracers:

• Insignificant degradation, reservoir and production conditions (i. e. high stability against thermal, chemical, physical and microbial degradation and a suitable half-life for radiotracers);

• Insignificant phase partitioning;

• Insignificant sorption on reservoir minerals;

• Insignificant natural occurrence in involved fluids (low background);

• Detectable in very low concentrations in reservoir fluid samples;

• Toxicity and radiotoxicity at acceptable levels;

• Non-problematic preparations, handling and logistics;

• Adequate commercial availability of components for preparation of tracer mixture;

• Acceptable cost.

For geothermal tracers, all of the above criteria apply except for the second item. For the tracing of H2O movement, in many reservoirs it will be advantageous to apply simultaneously selective tracers for the condensed water phase, selective tracers for the vapour phase and tracers for both phases.

Tables 1 and 2 list some water radiotracers which have been conditionally qualified for water tracing in oilfield operations and in geothermal operations, respectively, conditionally because each one has certain limitations to be observed.

Tables 3 and 4 list examples of corresponding non-radioactive tracers used in oilfields and geothermal fields, respectively.

Water tracer compound

Half-life

Main radiation characteristics

Comments

НТО

12.32 у

P (18 keV)

Generally applicable

CH2TOHa

12.32 у

P (18 keV)

Caution at temperatures >100°C (partition into gas phase)

CHjCHTOH b

12.32 у

P (18 keV)

Caution at temperatures >100°C (partition into gas phase), some biodegradation below 70-80°C

CH3CTOHCH3

12.32 у

P (18 keV)

Reasonably general application

S14CN-

5730 у

PH156keV)

For T< 90-100°C, long term experiments

35SCN~

87 d

p-(167keV)

For T< 90-100°C, medium term experiments

36cr

3 х 105 у

PH709keV)

High temperature reservoirs, long term, EMS analysis

125j-

60 d

у (35.5 keV)

Reducing chemical conditions, medium term

131I-

8 d

p-(606 keV),y (364.5 keV)

Reducing chemical conditions, short term (fracture detection)

[56Co(CN)6]3-

77.7 d

P+ (1459 keV),

Y (846.8 keV, 1238.3 keV)

Use with caution at T< 90°C, medium term

[57Co(CN)6]3-

271.8 d

Y (122.1 keV, 136.5 keV)

Use with caution at T< 90°C, medium to long term

[58Co(CN)6]3-

70.9 d

P+ (470 keV),Y (810.8 keV)

Use with caution at T< 90°C, medium term

Water tracer compound

Half-life

Main radiation characteristics

Comments

[60Co(CN)6]3-

5.27 у

P“ (317.9 keV), у (1173.2 keV, 1332.4 keV)

Use with caution at T< 90°C, long term

[Co(14CN)(CN)5]3-

5730 у

PA156keV)

Use with caution at T< 90°C, long term

22Na+

2.6 у

P+ (545 keV),y (1274.5 keV)

High temperature tracer in saline reservoirs, long term, slight reversible sorption

a The alcohol tracers may also be labelled with 14C.

b Position of the tritium in the alcohol compounds heavier than methanol may vary.

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Water tracer compound

Half-life

Main radiation characteristics

Conmients

НТО

12.32 у

P (18 keV)

Generally applicable, tracer for condensed and vapour phases

CH2TOHa

12.32 у

P (18 keV)

Tracer for condensed and vapour phases

CH3CHTOHb

12.32 у

P (18 keV)

Some biodegradation below 70-80°C, tracer for condensed and vapour phases

CH3CTOHCH3

12.32 у

P (18 keV)

Reasonably general application, tracer for condensed and vapour phases

125j-

60 d

у (35.5 keV)

Reducing chemical conditions, medium term, tracer for condensed phase

шг

8 d

p — (606 keV),y (364.5 keV)

Reducing chemical conditions, short term (fracture detection), tracer for condensed phase

a The alcohol tracers may also be labelled with 14C.

b Position of tlie tritium in the alcohol compounds heavier than methanol may vary.

 

Tracer

Тетрегайте limitations Remarks

Inorganic molecules

d2o

None

Limit in use: Natural content of deuterium in waters

SCN-

<90°C

If oxygen scavenger is absent: ~100°C

[Co(CN)6]3-

<90°C

Limit in use: ‘Natural’ cobalt in waters and equipment for handling samples

Organic molecules

Tliree monofluoro benzoic acids: 2-FBA, 3-FBA, 4-FBA

<130°C

Some of the monofluorinated benzoic acids may experience some biodegradation at Г < ~70°C

Six diiluoro benzoic acids: 2,3-DFBA, 2,4-DFBA, 2,5-DFBA, 2,6-DFBA, 3,4-DFBA, 3,5-DFBA

<120°C

Six triiluoro benzoic acids:

2.3.4-TriFBA, 2,3,5-TriFBA, 2,3,6-TriFBA, 2,4,6-TriFBA,

3.4.5-TriFBA, 3,4,6-TriFBA

<120°C

Stable against biodegradation

Two tetrailuoro benzoic acids: 2,3,4,5-TFBA, 2,3,5,6-TFBA

<100°C

Stable against biodegradation

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Tracer

Temperature limitations

Remarks

Sodium benzoate

Generally applicable to water dominated reservoirs Dyes

Rhodamine WT

<160°Ca

Ref. [12]

Fluorescine

<200°Ca

Ref. [12]

Naphtalene sulphonates

1-NS

<320°Ca

Ref. [13], tracer for condensed phase

2-NS

<320°Ca

Ref. [13], tracer for condensed phase

1,5-NDS

<280°Ca

Ref. [12], tracer for condensed phase

2,6-NDS

<320°Ca

Ref. [13], tracer for condensed phase

2,7-NDS

<320°Ca

Ref. [13], tracer for condensed phase

1,3,6-NTS

<290°Ca

Ref. [12], some biodegradation below 70-80°C, tracer for condensed phase

l,3,6,8-PTSAb

<260°Ca

Ref. [12], tracer for condensed phase

Tracer

Temperature limitations

Remarks

Hydrofluorocarbons + SF6

Freon R-134a, (CF3CH2F)

<5% degraded in 50 d at 225°C

Ref. [14], tracer for vapour phase

Freon R-23,CHF3

Thennally stable

Ref. [14] , tracer for vapour phase

SF6

No degradation in 14 d at 300°C

Ref. [15], tracer for vapour phase, 10% degraded in 14 d at 330°C

Cyclic perfluorinated hydrocarbons

PFC family

T> 300°C

Tracers for the gas (vapour) phase

Alcohols

Methanol (CHjOH)

No degradation in 14 d at 320°C

Refs [15-17], tracer for both condensed and vapour phases

Ethanol (CH3CH2OH)

8% degradation in 7 d at 300°C

Refs [15-17], tracer for both condensed and vapour phases

n-propanol (CH3CH3CH2OH)

19% degradation in 14 d at 280°C

Refs [15-17], tracer for both condensed and vapour phases

a L/2 (>400 d) here defined as the time needed at the indicated temperature to reduce the concentration by thermal breakdown to half of its original value. b Pyrene tetrasulphonate.

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