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Tracers are used in [[ | Tracers are used in [[Well_to_well_tracer_tests|well to well tests]] to gather data about the movement and saturation of fluids and hydrocarbons in the subsurface. Radioactive tracers can be used to gather data about [[Radioactive_water_tracers|water]] or gas. This article discusses some of the commonly used radioactive gas tracers. | ||
==Application== | == Application == | ||
<gallery widths=300px heights=200px> | Several authors report the use of radioactive gas tracers in oilfield applications. The tracers most frequently applied have been tritiated methane, tritiated ethane, and <sup>85</sup>Kr. <ref name="r1">_</ref><ref name="r2">_</ref><ref name="r3">_</ref> In addition, the use of tritiated butane, <sup>127</sup>Xe, <sup>133</sup>Xe, and tritiated hydrogen gas (HT) has been reported. '''Table 1''' lists the most widely applied radioactive tracers. | ||
<gallery widths="300px" heights="200px"> | |||
File:Vol5 Page 0657 Image 0001.png|'''Table 1''' | File:Vol5 Page 0657 Image 0001.png|'''Table 1''' | ||
</gallery> | </gallery> | ||
The tritium-labeled compounds may be measured directly in the gas phase by proportional counter techniques. To obtain the low detection limit normally required in well-to-well tracer studies, it is normal to convert the gas to water by combustion. The produced water then is counted by a liquid scintillation technique. The detection limit of the water produced from this process depends on the instrumentation but can be less than 1 Bq/L. Typically, approximately 5 to 10 mL of water must be produced to obtain the low detection limits. The water, mixed with a liquid scintillator, is counted for a few hours. The same technique can be applied for the different tritium-labeled hydrocarbon gases. If several tritium-labeled compounds are present in the same sample, it will be necessary to perform a chemical separation of the compounds before oxidation to produce the water. This separation complicates the analysis considerably; therefore, it is not common to use several of these tritiated compounds in the same reservoir segment. | The tritium-labeled compounds may be measured directly in the gas phase by proportional counter techniques. To obtain the low detection limit normally required in well-to-well tracer studies, it is normal to convert the gas to water by combustion. The produced water then is counted by a liquid scintillation technique. The detection limit of the water produced from this process depends on the instrumentation but can be less than 1 Bq/L. Typically, approximately 5 to 10 mL of water must be produced to obtain the low detection limits. The water, mixed with a liquid scintillator, is counted for a few hours. The same technique can be applied for the different tritium-labeled hydrocarbon gases. If several tritium-labeled compounds are present in the same sample, it will be necessary to perform a chemical separation of the compounds before oxidation to produce the water. This separation complicates the analysis considerably; therefore, it is not common to use several of these tritiated compounds in the same reservoir segment. | ||
The chemical properties of tritium-labeled hydrocarbon compounds are equal to their nonlabeled homologues in almost all practical situations, which means that their behavior in the reservoir will be the same as the nonlabeled hydrocarbons. The partition coefficients of these compounds, therefore, can be found by ordinary pressure-volume-temperature (PVT) packages like those applied in phase-equilibria calculations. The partition coefficient will influence the residence time in the reservoir and the concentration of the tracer in the production line. It is important to take into account partitioning both in the evaluation of flow behavior in the reservoir and in the understanding of sampling quality. Because of partitioning to the oil phase, some of the tracers will be in the oil phase at the sampling point. Calculation of total recovery of the tracer then requires partition coefficient and gas/oil ratio (GOR) at sampling conditions. This problem will be more significant for heavier hydrocarbons than for the lighter ones. | The chemical properties of tritium-labeled hydrocarbon compounds are equal to their nonlabeled homologues in almost all practical situations, which means that their behavior in the reservoir will be the same as the nonlabeled hydrocarbons. The partition coefficients of these compounds, therefore, can be found by ordinary pressure-volume-temperature (PVT) packages like those applied in phase-equilibria calculations. The partition coefficient will influence the residence time in the reservoir and the concentration of the tracer in the production line. It is important to take into account partitioning both in the evaluation of flow behavior in the reservoir and in the understanding of sampling quality. Because of partitioning to the oil phase, some of the tracers will be in the oil phase at the sampling point. Calculation of total recovery of the tracer then requires partition coefficient and gas/oil ratio (GOR) at sampling conditions. This problem will be more significant for heavier hydrocarbons than for the lighter ones. | ||
All the hydrocarbons that are labeled with tritium can also be labeled with <sup>14</sup>C. These molecules are, in general, more expensive and their analyses are more complicated. From a general demand for reducing the application of long-lived radioactive tracers, the <sup>14</sup>C-labeled compounds are less attractive than the tritium-labeled compound. | All the hydrocarbons that are labeled with tritium can also be labeled with <sup>14</sup>C. These molecules are, in general, more expensive and their analyses are more complicated. From a general demand for reducing the application of long-lived radioactive tracers, the <sup>14</sup>C-labeled compounds are less attractive than the tritium-labeled compound. | ||
Other alternatives are the noble gases. The noble gases are virtually inert against chemical reaction. <sup>85</sup>Kr has a half-life of 10.76 years and is a beta emitter with an energy of 687 keV. The two xenon isotopes, <sup>127</sup>Xe and <sup>133</sup>Xe, are also inert noble gases that may be applied in special situations in which rapid response is expected. The half-lives are 36.4 and 5.25 days, respectively. | Other alternatives are the noble gases. The noble gases are virtually inert against chemical reaction. <sup>85</sup>Kr has a half-life of 10.76 years and is a beta emitter with an energy of 687 keV. The two xenon isotopes, <sup>127</sup>Xe and <sup>133</sup>Xe, are also inert noble gases that may be applied in special situations in which rapid response is expected. The half-lives are 36.4 and 5.25 days, respectively. | ||
For CO<sub>2</sub> as injection gas, <sup>14</sup>CO<sub>2</sub> will be an ideal tracer. CO<sub>2</sub> will interact with the formation water, which must be considered when <sup>14</sup>CO<sub>2</sub> is used as a tracer. A few papers have reported application of HT.9 Hydrogen gas is reactive, and the tracer is lost in the reservoir. | For CO<sub>2</sub> as injection gas, <sup>14</sup>CO<sub>2</sub> will be an ideal tracer. CO<sub>2</sub> will interact with the formation water, which must be considered when <sup>14</sup>CO<sub>2</sub> is used as a tracer. A few papers have reported application of HT.9 Hydrogen gas is reactive, and the tracer is lost in the reservoir. | ||
==References== | == References == | ||
< | <references /> | ||
== Noteworthy papers in OnePetro == | |||
Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read | Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read | ||
==External links== | == External links == | ||
Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro | Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro | ||
==See also== | == See also == | ||
[[Chemical gas tracers]] | |||
[[Chemical_gas_tracers|Chemical gas tracers]] | |||
[[Radioactive_water_tracers|Radioactive water tracers]] | |||
[[ | [[Well_to_well_tracer_tests|Well to well tracer tests]] | ||
[[Well | [[PEH:Well-To-Well_Tracer_Tests]] | ||
[[ | [[Category:5.6.5 Tracer test analysis]] | ||
Revision as of 10:40, 4 June 2015
Tracers are used in well to well tests to gather data about the movement and saturation of fluids and hydrocarbons in the subsurface. Radioactive tracers can be used to gather data about water or gas. This article discusses some of the commonly used radioactive gas tracers.
Application
Several authors report the use of radioactive gas tracers in oilfield applications. The tracers most frequently applied have been tritiated methane, tritiated ethane, and 85Kr. [1][2][3] In addition, the use of tritiated butane, 127Xe, 133Xe, and tritiated hydrogen gas (HT) has been reported. Table 1 lists the most widely applied radioactive tracers.
Table 1
The tritium-labeled compounds may be measured directly in the gas phase by proportional counter techniques. To obtain the low detection limit normally required in well-to-well tracer studies, it is normal to convert the gas to water by combustion. The produced water then is counted by a liquid scintillation technique. The detection limit of the water produced from this process depends on the instrumentation but can be less than 1 Bq/L. Typically, approximately 5 to 10 mL of water must be produced to obtain the low detection limits. The water, mixed with a liquid scintillator, is counted for a few hours. The same technique can be applied for the different tritium-labeled hydrocarbon gases. If several tritium-labeled compounds are present in the same sample, it will be necessary to perform a chemical separation of the compounds before oxidation to produce the water. This separation complicates the analysis considerably; therefore, it is not common to use several of these tritiated compounds in the same reservoir segment.
The chemical properties of tritium-labeled hydrocarbon compounds are equal to their nonlabeled homologues in almost all practical situations, which means that their behavior in the reservoir will be the same as the nonlabeled hydrocarbons. The partition coefficients of these compounds, therefore, can be found by ordinary pressure-volume-temperature (PVT) packages like those applied in phase-equilibria calculations. The partition coefficient will influence the residence time in the reservoir and the concentration of the tracer in the production line. It is important to take into account partitioning both in the evaluation of flow behavior in the reservoir and in the understanding of sampling quality. Because of partitioning to the oil phase, some of the tracers will be in the oil phase at the sampling point. Calculation of total recovery of the tracer then requires partition coefficient and gas/oil ratio (GOR) at sampling conditions. This problem will be more significant for heavier hydrocarbons than for the lighter ones.
All the hydrocarbons that are labeled with tritium can also be labeled with 14C. These molecules are, in general, more expensive and their analyses are more complicated. From a general demand for reducing the application of long-lived radioactive tracers, the 14C-labeled compounds are less attractive than the tritium-labeled compound.
Other alternatives are the noble gases. The noble gases are virtually inert against chemical reaction. 85Kr has a half-life of 10.76 years and is a beta emitter with an energy of 687 keV. The two xenon isotopes, 127Xe and 133Xe, are also inert noble gases that may be applied in special situations in which rapid response is expected. The half-lives are 36.4 and 5.25 days, respectively.
For CO2 as injection gas, 14CO2 will be an ideal tracer. CO2 will interact with the formation water, which must be considered when 14CO2 is used as a tracer. A few papers have reported application of HT.9 Hydrogen gas is reactive, and the tracer is lost in the reservoir.
References
Noteworthy papers in OnePetro
Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read
External links
Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro