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Data from analysis of oils and condensates can contribute to the effective development and management of petroleum fields. These data also can be essential for equity studies and for environmental or pollution cases. Table 1 provides a quick reference to common questions that can be answered with the use of oil and condensate analyses. However, chemical analysis data, such as provided by gas chromatography, must be integrated with geological, engineering, and wellsite information to make these interpretations ([[:file:oil-and-condensate-analysis_fig1.png|Figure 1]]).
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Data from analysis of oils and condensates can contribute to the effective development and management of [[petroleum]] fields. These data also can be essential for equity studies and for environmental or pollution cases. Table 1 provides a quick reference to common questions that can be answered with the use of oil and condensate analyses. However, chemical analysis data, such as provided by [[gas chromatography]], must be integrated with geological, engineering, and wellsite information to make these interpretations ([[:file:oil-and-condensate-analysis_fig1.png|Figure 1]]).
    
{| class = "wikitable"
 
{| class = "wikitable"
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|-
 
|-
 
| Poor production test flow rates
 
| Poor production test flow rates
| Low viscosity (due to oil source or biodegradation) or high wax paraffinic
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| Low [[viscosity]] (due to oil source or [[biodegradation]]) or high wax paraffinic
 
| Bulk properties, GC, and HPLC
 
| Bulk properties, GC, and HPLC
 
|-
 
|-
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|-
 
|-
 
| Reservoir continuity
 
| Reservoir continuity
| Lateral or vertical continuity
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| [[Lateral]] or vertical continuity
 
| GC
 
| GC
 
|-
 
|-
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[[file:oil-and-condensate-analysis_fig1.png|thumb|{{figure number|1}}Flow diagram showing the basic steps followed in oil-oil correlations using gas chromatography.]]
 
[[file:oil-and-condensate-analysis_fig1.png|thumb|{{figure number|1}}Flow diagram showing the basic steps followed in oil-oil correlations using gas chromatography.]]
   −
The key to useful data depends on proper sampling. Provisions for proper sampling of oils and condensates should be included in all well proposals, tests, completions, and workover programs. The following list gives when to sample wells for oils:
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The key to useful data depends on proper sampling. Provisions for proper sampling of oils and condensates should be included in all well proposals, tests, completions, and [[workover]] programs. The following list gives when to sample wells for oils:
    
* When FTs or DSTs recover oil and/or water
 
* When FTs or DSTs recover oil and/or water
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* Pertinent neighboring wells, if sampling is permitted
 
* Pertinent neighboring wells, if sampling is permitted
   −
The expected character of the petroleum (such as API gravity and gas to oil ratio) and reservoir conditions (such as pressure and temperature) must be considered so that representative samples can be obtained. Changes in pressure and flow rate during well testing can alter petroleum composition and physical properties. In addition, samples of drilling mud, load and kill fluids, drilling additives, and wellsite fuel oils and lubricants should be kept until petroleum analyses are completed. If contamination is discovered or suspected, these samples can be analyzed and compared to recovered “petroleum.”
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The expected character of the petroleum (such as [[API gravity]] and gas to oil ratio) and reservoir conditions (such as pressure and temperature) must be considered so that representative samples can be obtained. Changes in pressure and flow rate during well testing can alter petroleum composition and physical properties. In addition, samples of drilling mud, load and kill fluids, drilling additives, and wellsite fuel oils and lubricants should be kept until petroleum analyses are completed. If contamination is discovered or suspected, these samples can be analyzed and compared to recovered “petroleum.”
    
For drilling wells, all recovered fluids should be sampled, including shows, oil on the pits, DSTs, and formation tests. Drill cuttings and core samples may be solvent extracted to obtain liquid samples. For completed wells, each zone test should be sampled before, during, and after [[workovers]], and prior to abandonment. For reservoir continuity studies or production allocation, samples should be collected as necessary.
 
For drilling wells, all recovered fluids should be sampled, including shows, oil on the pits, DSTs, and formation tests. Drill cuttings and core samples may be solvent extracted to obtain liquid samples. For completed wells, each zone test should be sampled before, during, and after [[workovers]], and prior to abandonment. For reservoir continuity studies or production allocation, samples should be collected as necessary.
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The most commonly run analyses performed on bulk samples are
 
The most commonly run analyses performed on bulk samples are
   −
* API gravity
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* [[API gravity]]
 
* Viscosity
 
* Viscosity
 
* Pour point
 
* Pour point
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Bulk properties should be measured on all test samples and measured (or estimated) on shows. They are essential for calculation of fluid properties, reserves, and economic value. They also are critical to the design of production methods and refinery processes. (For more on oil and condensate properties, see [[Petroleum reservoir fluid properties]]).
 
Bulk properties should be measured on all test samples and measured (or estimated) on shows. They are essential for calculation of fluid properties, reserves, and economic value. They also are critical to the design of production methods and refinery processes. (For more on oil and condensate properties, see [[Petroleum reservoir fluid properties]]).
   −
Variations in these properties can be used to test exploration models and evaluate development strategies. All of the basic bulk properties are affected by geological mechanisms that produce variations in oil composition (Table 2<ref name=pt05r154>Tissot, B. P., Weite, W. H., 1978, Petroleum Formation and Occurrence: New York, Springer-Verlag, 538 p.</ref><ref name=pt05r81>Hunt, J. M., 1979, Petroleum Geochemistry and Geology: San Francisco, CA, W. H. Freeman, 617 p.</ref>).
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Variations in these properties can be used to test exploration models and evaluate development strategies. All of the basic bulk properties are affected by geological mechanisms that produce variations in oil composition (Table 2<ref name=pt05r154>Tissot, B. P., and W. H. Weite, 1978, Petroleum Formation and Occurrence: New York, Springer-Verlag, 538 p.</ref><ref name=pt05r81>Hunt, J. M., 1979, Petroleum Geochemistry and Geology: San Francisco, CA, W. H. Freeman, 617 p.</ref>).
    
{| class = "wikitable"
 
{| class = "wikitable"
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! Mechanism
 
! Mechanism
 
|-
 
|-
| Before accumulation
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| Before [[accumulation]]
 
|
 
|
*  Source input and diagenesis
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*  Source input and [[diagenesis]]
*  Maturation processes
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[[Maturation]] processes
 
** Time
 
** Time
 
** Temperature
 
** Temperature
 
** Pressure
 
** Pressure
 
** Lithology
 
** Lithology
*  Primary migration
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[[Primary migration]]
 
|-
 
|-
 
| After accumulation
 
| After accumulation
 
|
 
|
*  Secondary migration  
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[[Secondary migration]]
 
*  Maturation processes  
 
*  Maturation processes  
 
*  Alteration processes
 
*  Alteration processes
** Biodegradation
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** [http://www.oiltracers.com/services/exploration-geochemistry/oil-biodegradation.aspx Biodegradation]
 
** Water washing
 
** Water washing
** Asphaltene precipitation
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** [[Asphaltenes|Asphaltene]] precipitation
 
** Weathering
 
** Weathering
 
|}
 
|}
    
===Molecular composition===
 
===Molecular composition===
<gallery>
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<gallery mode=packed heights=300px widths=300px>
file:oil-and-condensate-analysis_fig2.png|{{figure number|2}}Gas chromatograms of a “normal” 35° API gravity oil and a biodegraded oil showing the lose of aliphatics (n-paraffins and isoprenoids) due to biodegradation.
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file:oil-and-condensate-analysis_fig2.png|{{figure number|2}}Gas chromatograms of a “normal” 35° ]]API gravity]] oil and a biodegraded oil showing the lose of aliphatics (n-paraffins and isoprenoids) due to biodegradation.
 
file:oil-and-condensate-analysis_fig3.png|{{figure number|3}}Gas chromatography can be used to determine geological processes experienced by an oil.
 
file:oil-and-condensate-analysis_fig3.png|{{figure number|3}}Gas chromatography can be used to determine geological processes experienced by an oil.
 
file:oil-and-condensate-analysis_fig4.png|{{figure number|4}}Gas chromatogram showing drilling mud contamination to a biodegraded oil.
 
file:oil-and-condensate-analysis_fig4.png|{{figure number|4}}Gas chromatogram showing drilling mud contamination to a biodegraded oil.
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</gallery>
 
</gallery>
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The most common analyses done to determine molecular composition are as follows (see <ref name=pt05r1>Altgelt, K. W., Gouw, T. H., 1979, Chromatography in Petroleum Analysis: New York, Marcel Dekker.</ref>, and <ref name=pt05r154 />, for a description of these analyses and their applications):
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The most common analyses done to determine molecular composition are as follows (see Altgelt and Gouw<ref name=pt05r1>Altgelt, K. W., and T. H. Gouw, 1979, Chromatography in Petroleum Analysis: New York, Marcel Dekker.</ref> and Tissot and Weite<ref name=pt05r154 /> for a description of these analyses and their applications):
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* Gas chromatography (GC)
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* [[Gas chromatography]] (GC)
* High performance liquid chromatography (HPLC)
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* High performance liquid [[chromatography]] (HPLC)
 
* Porphyrin distribution
 
* Porphyrin distribution
 
* Gas chromatography-mass spectroscopy (GCMS)
 
* Gas chromatography-mass spectroscopy (GCMS)
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Molecular compositions can be used to categorize oils (such as waxy or paraffinic and aromatic) and to determine the effects of geological processes (such as biodegraded, water washed, or immature). Bulk properties such as API gravity can sometimes be predicted from molecular composition data.<ref name=pt05r94>Kennicutt, M. C., Brooks, J. M., 1988, Surface geochemical exploration studies predict API gravity off California: Oil and Gas Journal: Sept. 12, p. 101–106.</ref> Chromatographic methods are typically used to determine these characteristics.
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Molecular compositions can be used to categorize oils (such as waxy or paraffinic and aromatic) and to determine the effects of geological processes (such as [http://www.oiltracers.com/services/exploration-geochemistry/oil-biodegradation.aspx biodegraded], water washed, or immature). Bulk properties such as API gravity can sometimes be predicted from molecular composition data.<ref name=pt05r94>Kennicutt, M. C., and J. M. Brooks, 1988, Surface geochemical exploration studies predict API gravity off California: Oil and Gas Journal: Sept. 12, p. 101–106.</ref> Chromatographic methods are typically used to determine these characteristics.
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Gas chromatography (GC) data can indicate the geological mechanisms responsible for changes in composition of an oil. For example, during biodegradation, bacteria preferentially remove the ''n''-paraffins that are prominent features in most chromatograms ([[:file:oil-and-condensate-analysis_fig2.png|Figure 2]]). Therefore the decrease or absence of n-paraffins is a strong indication that an oil is biodegraded. Other geological processes recognizable from chromatograms are thermal immaturity (odd-even predominance of the ''n''-paraffins), water washing (depletion of light aromatics), leaky reservoir seals (loss of light ends), and source characteristics (biomarkers) ([[:file:oil-and-condensate-analysis_fig3.png|Figure 3]]). Drilling additives and contaminants can also be identified by chromatography ([[:file:oil-and-condensate-analysis_fig4.png|Figure 4]]).
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Gas chromatography (GC) data can indicate the geological mechanisms responsible for changes in composition of an oil. For example, during [[biodegradation]], bacteria preferentially remove the ''n''-paraffins that are prominent features in most chromatograms ([[:file:oil-and-condensate-analysis_fig2.png|Figure 2]]). Therefore the decrease or absence of n-paraffins is a strong indication that an oil is biodegraded. Other geological processes recognizable from chromatograms are thermal immaturity (odd-even predominance of the ''n''-paraffins), water washing (depletion of light aromatics), leaky reservoir seals (loss of light ends), and source characteristics (biomarkers) ([[:file:oil-and-condensate-analysis_fig3.png|Figure 3]]). Drilling additives and contaminants can also be identified by chromatography ([[:file:oil-and-condensate-analysis_fig4.png|Figure 4]]).
   −
If proper standardized procedures are followed, chromatograms can provide reproducible “fingerprints” of oils. These oil fingerprints can then be used to compare and correlate oils. This technique of molecular characterization is more discriminating than bulk property data.<ref name=pt05r88>Kaufman, R. L., Ahmed, A. S., Elsinger, R. J., 1990, Gas chromatography as a development and production tool, in Geochemistry of Gulf Coast Oils and Gases: Proceedings of the 9th Annual Research Conference, Gulf Coast Section, Society of Economic Paleontologists and Mineralogists, p. 263–282.</ref> For ease in interpretation, chromatographic data can also be displayed as polar or star plots of hydrocarbon peak ratios ([[:file:oil-and-condensate-analysis_fig5.png|Figure 5]]).
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If proper standardized procedures are followed, chromatograms can provide reproducible “fingerprints” of oils. These oil fingerprints can then be used to compare and correlate oils. This technique of molecular characterization is more discriminating than bulk property data.<ref name=pt05r88>Kaufman, R. L., A. S. Ahmed, and R. J. Elsinger, 1990, Gas chromatography as a development and production tool, in Geochemistry of Gulf Coast Oils and Gases: Proceedings of the 9th Annual Research Conference, Gulf Coast Section, Society of Economic Paleontologists and Mineralogists, p. 263–282.</ref> For ease in interpretation, chromatographic data can also be displayed as polar or star plots of hydrocarbon peak ratios ([[:file:oil-and-condensate-analysis_fig5.png|Figure 5]]).
    
Gas chromatography should never be used alone to make these interpretations. Supporting analytical data and geological information should be obtained as well. A combination of several processes (that is, multiple sources for oils and/or different thermal maturities) can make interpretation complex.
 
Gas chromatography should never be used alone to make these interpretations. Supporting analytical data and geological information should be obtained as well. A combination of several processes (that is, multiple sources for oils and/or different thermal maturities) can make interpretation complex.
  −
[[file:oil-and-condensate-analysis_fig6.png|thumb|{{figure number|6}}Gas chromatographic data can be used to determine oil reservoir continuity in conjunction with other methods such as pressure-depth plots. Diagram on right shows a graphical comparison of chromatographic data.]]
      
==Applications==
 
==Applications==
 
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<gallery mode=packed heights=200px widths=200px>
[[file:oil-and-condensate-analysis_fig7.png|left|thumb|{{figure number|7}}A binary mixing diagram showing how the relative proportions of an unknown oil can be determined using the two end-member oils (separate zones) and laboratory mixtures.]]
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oil-and-condensate-analysis_fig6.png|{{figure number|6}}Gas chromatographic data can be used to determine oil reservoir continuity in conjunction with other methods such as pressure-depth plots. Diagram on right shows a graphical comparison of chromatographic data.
 +
oil-and-condensate-analysis_fig7.png|{{figure number|7}}A binary mixing diagram showing how the relative proportions of an unknown oil can be determined using the two end-member oils (separate zones) and laboratory mixtures.
 +
</gallery>
    
Correlation of recovered fluids to other oils or source rock extracts can verify exploration models for development of new plays<ref name=pt05r154 /><ref name=pt05r81 />
 
Correlation of recovered fluids to other oils or source rock extracts can verify exploration models for development of new plays<ref name=pt05r154 /><ref name=pt05r81 />
   −
Correlation techniques, especially gas chromatography, have also been used for the following development applications:
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Correlation techniques, especially [[gas chromatography]], have also been used for the following development applications:
   −
* Reservoir continuity studies<ref name=pt05r148>Slentz, L. W., 1981, Geochemistry of reservoir fluids as a unique approach to optimum reservoir management: Middle East Oil Technical Conference of the Society of Petroleum Engineers, Manama, Baharain, SPE 9582.</ref><ref name=pt05r137>Ross, L. M., Ames, R. L., 1988, Stratification of oils in Columbus Basin off Trinidad: Oil and Gas Journal, Sept. 26, p. 72–76.</ref>
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* Reservoir continuity studies<ref name=pt05r148>Slentz, L. W., 1981, Geochemistry of reservoir fluids as a unique approach to optimum reservoir management: Middle East Oil Technical Conference of the Society of Petroleum Engineers, Manama, Baharain, SPE 9582.</ref><ref name=pt05r137>Ross, L. M., and R. L. Ames, 1988, Stratification of oils in Columbus Basin off Trinidad: Oil and Gas Journal, Sept. 26, p. 72–76.</ref>
* Identification of producing and nonproducing zones<ref name=pt05r109>Maness, M., Price, J. G. W., 1977, Well formation characterization by residual hydrocarbon analysis: Annual Meeting of the Society of Petroleum Engineers, Denver, CO, Oct. 9–12, SPE 6860.</ref>
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* Identification of producing and nonproducing zones<ref name=pt05r109>Maness, M., and J. G. W. Price, 1977, Well formation characterization by residual hydrocarbon analysis: Annual Meeting of the Society of Petroleum Engineers, Denver, CO, Oct. 9–12, SPE 6860.</ref>
 
* Identification and localization of [[production problems]]<ref name=pt05r88 />
 
* Identification and localization of [[production problems]]<ref name=pt05r88 />
* Allocation of production to specific intervals when production is commingled<ref name=pt05r87>Kaufman, R. L., Ahmed, A. S., Hempkins, W. B., 1987, A new technique for the analysis of commingled oils and its application to production allocation calculations: 16th Annual Convention Proceedings of the Indonesian Petroleum Association, p. 247–268.</ref>
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* Allocation of production to specific intervals when production is commingled<ref name=pt05r87>Kaufman, R. L., A. S. Ahmed, and W. B. Hempkins, 1987, A new technique for the analysis of commingled oils and its application to production allocation calculations: 16th Annual Convention Proceedings of the Indonesian Petroleum Association, p. 247–268.</ref>
    
For example, in a formation that has a continuous oil reservoir, the fingerprint of that oil does not change, in other words, a change in a fingerprint reflects a discontinuous reservoir. Therefore, by sampling reservoirs vertically and laterally, it is possible to determine reservoir continuity. [[:file:oil-and-condensate-analysis_fig6.png|Figure 6]] shows a schematic drawing of two reservoir sands that actually define three separate reservoirs. Although geologically equivalent, sands A and B are discontinuous and should be produced as separate reservoirs. Sand C is laterally continuous but vertically discontinuous from both sands A and B. The star diagram shows a representation of the different oil fingerprints. If production from sands A and C in well 1 is commingled, production could be allocated to the individual sands by using the fingerprint differences with a binary mixing model.<ref name=pt05r87 /> [[:file:oil-and-condensate-analysis_fig7.png|Figure 7]] illustrates this with a simple mixing diagram.
 
For example, in a formation that has a continuous oil reservoir, the fingerprint of that oil does not change, in other words, a change in a fingerprint reflects a discontinuous reservoir. Therefore, by sampling reservoirs vertically and laterally, it is possible to determine reservoir continuity. [[:file:oil-and-condensate-analysis_fig6.png|Figure 6]] shows a schematic drawing of two reservoir sands that actually define three separate reservoirs. Although geologically equivalent, sands A and B are discontinuous and should be produced as separate reservoirs. Sand C is laterally continuous but vertically discontinuous from both sands A and B. The star diagram shows a representation of the different oil fingerprints. If production from sands A and C in well 1 is commingled, production could be allocated to the individual sands by using the fingerprint differences with a binary mixing model.<ref name=pt05r87 /> [[:file:oil-and-condensate-analysis_fig7.png|Figure 7]] illustrates this with a simple mixing diagram.
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==See also==
 
==See also==
* [[Introduction to laboratory methods]]
   
* [[Wettability]]
 
* [[Wettability]]
 
* [[Oilfield water analysis]]
 
* [[Oilfield water analysis]]
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[[Category:Laboratory methods]]
 
[[Category:Laboratory methods]]
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[[Category:Methods in Exploration 10]]

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