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Recognition and differentiation of gas condensates and other oil types using microthermometry of petroleum inclusions
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JOURNAL OF
SCIENCE~DIRECT e ELSEVIER
GEOCHEMICAL EXPLORATION
Journal of Geochemical Exploration 78-79 (2003) 367-371
www.elsevier.com/locate/jgeoexp
Abstract
Recognition and differentiation of gas condensates and other oil types using microthermometry of petroleum inclusions J6rg O.W. Grimmer a'*, Jacques Pironon a, St@hane Teinturier a, Jerome Mutterer b aCREGU-CNRS UMR G2R, B.P 23, Vandoeuvre-lOs-Naney 54501, France bIBMP, 12 rue du gdndral Zimmeg Strasbourg 67084, France
Abstract Microthermometrical observations are a powerful tool to determine the oil type in oil-bearing fluid inclusions, Five different oil types (gas condensates, wet gas, light, volatile and black oil) and their different phase transitions are presented, and Fourier Transform InfraRed (FT-IR), Confocal Scanning Laser Microscopy (CSLM) and PIT modelling validate these results. © 2003 Elsevier Science B.V. All rights reserved. Keywords: Gas condensates; Microthermometry;Petroleum inclusions; Phase transition
1. Introduction, methods and materials Petroleum inclusions are one interesting member o f the fluid inclusion family. Because most o f the petroleum inclusions have characteristic fluorescence behaviour under UV excitation, they can easily be separated from other inclusions. This so-called UV fluorescence o f the petroleum inclusion has been used to determine API gravity and type o f the oil trapped in the inclusion versus their fluorescence colour index. However, even without a fluorescence microscope, estimations of the trapped oil type can be done only with microthermometry. Some petroleum inclusions show during microthermometric measurements a special relief, before they homogenise depending on their oil composition. As petroleum inclusions do not have a
* Corresponding author. Tel.: +33-3-83-68-47-32;fax: +33-383-68-47-01. E-mail address: [email protected] (J.O.W. Grimmer). URL: http://www.petroleuminclusion.uhp-nancy.fr.
eutectic or a final ice melting temperature, therefore, microthermometry is mainly used to determine the homogenisation temperature. Phase transitions are rarely observed below 23 °C. Especially below 23 °C, some oil inclusions show important phase transitions. The aim o f this short review is to show that the oil type o f petroleum inclusions can be estimated from microthermometric measurements at low temperatures. Possible phase transitions or the optical relief change for some inclusions before their bulk homogenisation can be noticed. All microthermometric observations and measurements were done on double-polished thick sections of natural quartz chips on a Linkam ® stage coupled with an Olympus ® microscope at the CREGU laboratory in Nancy. Confocal Scanning Laser Microscopy (CSLM) analyses were performed to measure the volume o f the inclusions and to calculate precisely the liquidvapour ratio (Fv%) at the Institut de Biologie Mol6culaire des Plantes in Strasbourg with a Zeiss® LSM510 apparatus. Consecutive (overlapping) 0.9-gm-thick
0375-6742/03/$ - see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0375-6742(03)00137-7
368
Abstract
optical z-sections were collected at 0.5-gm intervals with a xy pixel size of 0.1 gm. Volume calculations have been made by using Igor software after thresholding of the images in 256 gray levels (Pironon et al., 1998). The microthermometric (homogenisation temperature = Th) and CSLM (Fv) values are the input data for the PIT modelling (CREGU software) to calculate the isochores and isopleths of the observed oil system. The validation of the microthermometric and the estimation of the petroleum type were performed by Fourier Transform InfraRed (FT-IR) microspectroscopy at the Laboratoire Environnement-Min6ralurgie (LEM), Nancy, with a Bruker® Equinox spectrometer (Pironon et al., 2001). All FT-IR spectra acquired at constant temperatures were interpreted using the Opus ® software (Bruker®).
2. Results
After cooling a petroleum inclusion from Quebec (sample Que14/16 in Fig. 1) up to - 1 2 0 °C, two liquid phases and one vapour phase can be observed
(LLV). The phase transition from three to two phases happens at - 6 0 . 2 °C (LLV~LV=Thl). This is the typical behaviour of a gas condensate with a high methane content (Table 1), which is as well described for samples of the North Sea (Teinturier et al., 2002). The inclusion homogenises finally into the liquid domain at +52 °C (Th2). The final homogenisation of gas condensates is always close to the critical point. Therefore, all three phase transitions can be observed, into the liquid and gas domain as well a critical homogenisation is possible (Grimmer et al., 2002). The phase transition of a monophase petroleum inclusion (Fv 100% at 23 °C) containing wet gas (sample Quel2, Table 1) can only be observed after cooling. The cooled two-phase inclusion homogenises at - 2 °C into the vapour phase (L+V=*V). The homogenisation of wet and dry gases (Teinturier et al., 2002) is generally into the gas phase for petroleum environments. Light oils (sample Vonol7 from Czech Republic) are in the two-phase domain at 23 °C and have solids in the liquid phase below 20 °C. While heating the cooled sample, light oils indicate a change of viscosity of the liquid phase, which can be observed in slight
Fig. 1. Typical phase changes of a petroleum inclusion filled with a gas condensate (sample Quel4/16) from - 120 to + 53 °C. Thl is the phase transition from the three-phase (L + L + V) into the two-phase domain (L + V) at - 60 °C. Th2 is the bulk homogenisation into the liquid domain at +52 °C.
Abstract
369
Table 1 FT-IR analysed composition, PIT-modelled composition, microthermometric data (homogenisation: L= into liquid, G = into gas) and Fv of petroleum inclusions containing different oil types Oil type sample
Component
FT-IR (mol%)
CH4 CO2 Alkanes CH2/CH3 CO2 C1 C2 C3 iC4 nC4 iC5 nC5 nC6 nC7 nC8 nC9 nC10 Cnl Cn2 API (°) Thl (°C) Th (°C) Fv (%) at 23 °C
PIT (mol%)
Microth. CSLM
Black oil Encan(a8) 20.6 14.5 64.9 8.0 14.5 18.1 3.6 4.4 1.1 2.6 1.9 3.0 4.4 4.7 4.4 4.1 3.9 22.0 7.2 16.8 111.0 L 9.8
movements of particles in the liquid phase and form changes of the vapour bubble. However, the most important observation on light oils in comparison to condensates is the presence of a maximum of two phases and without phase transitions. Many light oils homogenise into the liquid domain, like Vonol7 at +52.3 °C. When a critical homogenisation is observed, the light oil is a volatile critical oil as it is described for the Alwyn area in the North Sea (Table 1, sample Alwyl). Black oils (Encan(aS) from Mexico) show no reactions at low temperatures and they always homogenise into the liquid domain. In sample Encan(a8), the vapour bubble disappears at + 111 °C. This homogenisation is accompanied by a high contrast of the refractive index between the bubble and the liquid in the inclusion, which is typical for black oil inclusions. FT-IR analyses of the petroleum inclusions show an increase from 20.6 mol % CH4 (black oil, Encan(a8)) to 74.4 mol % CH4 (wet gas, Quel2). Obtaining similar C H 4 c o n t e n t ( C 1 in Table 1) and
Lightoil Vono 17
Volatile Alwy 1
Condensate • Que 14/16
37.3 1.1 61.6 2.4 1.1 44.7 8.4 6.7 1.4 3.1 2.0 3.2 3.5 3.7 3.3 2.9 2.5 11.5 2.0 24.9
49.0 1.5 49.5 1.0 52.0 9,0 6.5 1.3 3.0 1.8 2.7 2.8 3.0 2.6 2.3 2.0 1.8 1.4 25.0
52.3 L 7.1
94.7 L 20.0
69.1 1.7 24.1 2.9 3.0 66.0 8.3 5.2 2.2 1.2 1.2 0.6 0.7 1.5 1.3 1.1 1.8 0.7 1.2 31.9 - 60.2 53.8 L 37.0
Wetgas Que 12 74.4 1.5 24.1 1.1 4.8 88.0 4.0 1.5 1.1 0.2 0.2 0.1 0.1 0.0 0.0 0.0 0.0 0.0 0.0 35.6 -2.0 G 100.0
increasing API gravity from 16.8 ° (black oil) to 35.6 ° (wet gas) validates PIT modelling.
3. Discussion and conclusion
Fig. 2 represents three phase envelopes modelled by PIT in thep-Tdiagram: a black oil with 21 mol % CH4, a gas condensate with 69 tool % CH4 and a wet gas with 74 mol % CH4. The black oil has the highest cricondentherm and the gas condensate has the highest cricondenbar. At low temperatures, gas condensates, dry and wet gases have the same behaviour as described by Luks et al. (1983) for synthetic hydrocarbon mixtures. In fact, the phase envelopes of the synthetic hydrocarbon mixtures estimate the three-phase domain (L + L + V). In the case of Que14/16, the Thl is at - 60.2 °C and Th2 is at + 52 °C, while the evolution of the bubble follows the isochore. The three-phase domain for natural petroleum inclusions is still not adapted to
370
Abstract
Pressure (bar)
Critical isochore
Isochore of Que14/16
Liquid
;ritical point
Vapour L+L+V L+V % b~,~,~, ~
Thl -60
"
• wet gas I 74% CH4
black oil 21% CH4
Th2 /" +52
Temperature (°C)
Fig. 2. Phase diagram of the calculated isochores and isopleths of a gas condensate with 69 mol% CH4 (sample Quel4/16). The isopleths of a wet gas with 74 mol% CH4 and a black oil with 21 mol% CH 4 are added to show the evolution of the isopleths in the p - T diagram.
the real oil complex composition, but observations in the three- or more phase domain are helpful and should always be taken in account to determine in a first step the present oil type. If the L + L + V domain can be thermodynamically calculated, the Thi would give the precise composition of the present oil type in the inclusion. Therefore, thermodynamic modelling should be improved for petroleum inclusions. However, not only the low temperature range is interesting. In the first place, observations of the thermal behaviour near the homogenisation are very informative. The change of refractive index of the liquid and the vapour phase is directly related to the temperature difference (AT) to the critical temperature. De facto, a critical homogenisation is marked by the progressive disappearance of the contours of the vapour phase. A homogenisation far from the critical temperature does not show any modification of the refractive index of the vapour and liquid phase. The second important observation is the volumetric change of the vapour phase, which can be another good indicator of the oil composition. In the case of critical homogenisation, the vapour bubble volume remains unchanged. In contrast, for example, the homogenisation of a black oil is marked by a slight regular decrease of the vapour volume with increasing temperature. Close to the critical point, the bubble
disappears very rapidly, e.g. gas condensates, instead of a constant decrease of the vapour bubble when homogenisation is reached far away from the critical point, e.g. black oil. In conclusion, the careful observation of the thermal behaviour of petroleum inclusions can help to classify the oil trapped in the diagenetic mineral cement and can help to develop an adequate and analytical modelling procedure.
Acknowledgements
We appreciate the valuable comments of D. Leythaeuser and an anonymous reviewer. We are also grateful to G. Beaudoin and D. Kirkwood from Laval University (Quebec), E. Gonzalez-Partida (UNAM Mexico), E Dobes (Czech Geological Survey) and TotalFinaElf, which provided us with the samples.
References Grimmer, J.O.W., Pironon, J,, Such~, V., Dobes, E, 2002. Petroleum inclusions in the Barrandian Palaeozoic Basin, Czech Republic: P,T,X modelling. PACROFI VIII, Abstracts, pp. 32-34. Luks, K.D., Merrill, R.C., Kohn, J.P., 1983. Partial miscibility behavior in cryogenic natural gas systems. Fluid Phase Equilibria 14, 193 201.
Abstract
Pironon, J., Canals, M., Dubessy, J., Walgenwitz, F., LaplaceBuilhe, C., 1998. Volumetric reconstruction of individual oil inclusions by confocal scanning laser microscopy. European Journal of Mineralogy 10, 1143-1150. Pironon, J., Thirry, R., Ayt Ougougdal, M., Teinturier, S., Beaudoin, G., Walgenwitz, F., 2001. FT-IR measurements of petro-
371 leum fluid inclusions: methane, n-alkanes and carbon dioxide quantitative analysis. Geofluids 1, 2 10. Teinturier, S., Pironon, J., Walgenwitz, F., 2002. Fluid inclusions and PVTX modelling examples from the Gain Formation in well 6507/2-2, Haltenbanken, Mid-Norway. Marine and Petroleum Geology 19 (6), 755-765.
JOURNAL OF
SCIENCE~DIRECT e ELSEVIER
GEOCHEMICAL EXPLORATION
Journal of Geochemical Exploration 78-79 (2003) 367-371
www.elsevier.com/locate/jgeoexp
Abstract
Recognition and differentiation of gas condensates and other oil types using microthermometry of petroleum inclusions J6rg O.W. Grimmer a'*, Jacques Pironon a, St@hane Teinturier a, Jerome Mutterer b aCREGU-CNRS UMR G2R, B.P 23, Vandoeuvre-lOs-Naney 54501, France bIBMP, 12 rue du gdndral Zimmeg Strasbourg 67084, France
Abstract Microthermometrical observations are a powerful tool to determine the oil type in oil-bearing fluid inclusions, Five different oil types (gas condensates, wet gas, light, volatile and black oil) and their different phase transitions are presented, and Fourier Transform InfraRed (FT-IR), Confocal Scanning Laser Microscopy (CSLM) and PIT modelling validate these results. © 2003 Elsevier Science B.V. All rights reserved. Keywords: Gas condensates; Microthermometry;Petroleum inclusions; Phase transition
1. Introduction, methods and materials Petroleum inclusions are one interesting member o f the fluid inclusion family. Because most o f the petroleum inclusions have characteristic fluorescence behaviour under UV excitation, they can easily be separated from other inclusions. This so-called UV fluorescence o f the petroleum inclusion has been used to determine API gravity and type o f the oil trapped in the inclusion versus their fluorescence colour index. However, even without a fluorescence microscope, estimations of the trapped oil type can be done only with microthermometry. Some petroleum inclusions show during microthermometric measurements a special relief, before they homogenise depending on their oil composition. As petroleum inclusions do not have a
* Corresponding author. Tel.: +33-3-83-68-47-32;fax: +33-383-68-47-01. E-mail address: [email protected] (J.O.W. Grimmer). URL: http://www.petroleuminclusion.uhp-nancy.fr.
eutectic or a final ice melting temperature, therefore, microthermometry is mainly used to determine the homogenisation temperature. Phase transitions are rarely observed below 23 °C. Especially below 23 °C, some oil inclusions show important phase transitions. The aim o f this short review is to show that the oil type o f petroleum inclusions can be estimated from microthermometric measurements at low temperatures. Possible phase transitions or the optical relief change for some inclusions before their bulk homogenisation can be noticed. All microthermometric observations and measurements were done on double-polished thick sections of natural quartz chips on a Linkam ® stage coupled with an Olympus ® microscope at the CREGU laboratory in Nancy. Confocal Scanning Laser Microscopy (CSLM) analyses were performed to measure the volume o f the inclusions and to calculate precisely the liquidvapour ratio (Fv%) at the Institut de Biologie Mol6culaire des Plantes in Strasbourg with a Zeiss® LSM510 apparatus. Consecutive (overlapping) 0.9-gm-thick
0375-6742/03/$ - see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0375-6742(03)00137-7
368
Abstract
optical z-sections were collected at 0.5-gm intervals with a xy pixel size of 0.1 gm. Volume calculations have been made by using Igor software after thresholding of the images in 256 gray levels (Pironon et al., 1998). The microthermometric (homogenisation temperature = Th) and CSLM (Fv) values are the input data for the PIT modelling (CREGU software) to calculate the isochores and isopleths of the observed oil system. The validation of the microthermometric and the estimation of the petroleum type were performed by Fourier Transform InfraRed (FT-IR) microspectroscopy at the Laboratoire Environnement-Min6ralurgie (LEM), Nancy, with a Bruker® Equinox spectrometer (Pironon et al., 2001). All FT-IR spectra acquired at constant temperatures were interpreted using the Opus ® software (Bruker®).
2. Results
After cooling a petroleum inclusion from Quebec (sample Que14/16 in Fig. 1) up to - 1 2 0 °C, two liquid phases and one vapour phase can be observed
(LLV). The phase transition from three to two phases happens at - 6 0 . 2 °C (LLV~LV=Thl). This is the typical behaviour of a gas condensate with a high methane content (Table 1), which is as well described for samples of the North Sea (Teinturier et al., 2002). The inclusion homogenises finally into the liquid domain at +52 °C (Th2). The final homogenisation of gas condensates is always close to the critical point. Therefore, all three phase transitions can be observed, into the liquid and gas domain as well a critical homogenisation is possible (Grimmer et al., 2002). The phase transition of a monophase petroleum inclusion (Fv 100% at 23 °C) containing wet gas (sample Quel2, Table 1) can only be observed after cooling. The cooled two-phase inclusion homogenises at - 2 °C into the vapour phase (L+V=*V). The homogenisation of wet and dry gases (Teinturier et al., 2002) is generally into the gas phase for petroleum environments. Light oils (sample Vonol7 from Czech Republic) are in the two-phase domain at 23 °C and have solids in the liquid phase below 20 °C. While heating the cooled sample, light oils indicate a change of viscosity of the liquid phase, which can be observed in slight
Fig. 1. Typical phase changes of a petroleum inclusion filled with a gas condensate (sample Quel4/16) from - 120 to + 53 °C. Thl is the phase transition from the three-phase (L + L + V) into the two-phase domain (L + V) at - 60 °C. Th2 is the bulk homogenisation into the liquid domain at +52 °C.
Abstract
369
Table 1 FT-IR analysed composition, PIT-modelled composition, microthermometric data (homogenisation: L= into liquid, G = into gas) and Fv of petroleum inclusions containing different oil types Oil type sample
Component
FT-IR (mol%)
CH4 CO2 Alkanes CH2/CH3 CO2 C1 C2 C3 iC4 nC4 iC5 nC5 nC6 nC7 nC8 nC9 nC10 Cnl Cn2 API (°) Thl (°C) Th (°C) Fv (%) at 23 °C
PIT (mol%)
Microth. CSLM
Black oil Encan(a8) 20.6 14.5 64.9 8.0 14.5 18.1 3.6 4.4 1.1 2.6 1.9 3.0 4.4 4.7 4.4 4.1 3.9 22.0 7.2 16.8 111.0 L 9.8
movements of particles in the liquid phase and form changes of the vapour bubble. However, the most important observation on light oils in comparison to condensates is the presence of a maximum of two phases and without phase transitions. Many light oils homogenise into the liquid domain, like Vonol7 at +52.3 °C. When a critical homogenisation is observed, the light oil is a volatile critical oil as it is described for the Alwyn area in the North Sea (Table 1, sample Alwyl). Black oils (Encan(aS) from Mexico) show no reactions at low temperatures and they always homogenise into the liquid domain. In sample Encan(a8), the vapour bubble disappears at + 111 °C. This homogenisation is accompanied by a high contrast of the refractive index between the bubble and the liquid in the inclusion, which is typical for black oil inclusions. FT-IR analyses of the petroleum inclusions show an increase from 20.6 mol % CH4 (black oil, Encan(a8)) to 74.4 mol % CH4 (wet gas, Quel2). Obtaining similar C H 4 c o n t e n t ( C 1 in Table 1) and
Lightoil Vono 17
Volatile Alwy 1
Condensate • Que 14/16
37.3 1.1 61.6 2.4 1.1 44.7 8.4 6.7 1.4 3.1 2.0 3.2 3.5 3.7 3.3 2.9 2.5 11.5 2.0 24.9
49.0 1.5 49.5 1.0 52.0 9,0 6.5 1.3 3.0 1.8 2.7 2.8 3.0 2.6 2.3 2.0 1.8 1.4 25.0
52.3 L 7.1
94.7 L 20.0
69.1 1.7 24.1 2.9 3.0 66.0 8.3 5.2 2.2 1.2 1.2 0.6 0.7 1.5 1.3 1.1 1.8 0.7 1.2 31.9 - 60.2 53.8 L 37.0
Wetgas Que 12 74.4 1.5 24.1 1.1 4.8 88.0 4.0 1.5 1.1 0.2 0.2 0.1 0.1 0.0 0.0 0.0 0.0 0.0 0.0 35.6 -2.0 G 100.0
increasing API gravity from 16.8 ° (black oil) to 35.6 ° (wet gas) validates PIT modelling.
3. Discussion and conclusion
Fig. 2 represents three phase envelopes modelled by PIT in thep-Tdiagram: a black oil with 21 mol % CH4, a gas condensate with 69 tool % CH4 and a wet gas with 74 mol % CH4. The black oil has the highest cricondentherm and the gas condensate has the highest cricondenbar. At low temperatures, gas condensates, dry and wet gases have the same behaviour as described by Luks et al. (1983) for synthetic hydrocarbon mixtures. In fact, the phase envelopes of the synthetic hydrocarbon mixtures estimate the three-phase domain (L + L + V). In the case of Que14/16, the Thl is at - 60.2 °C and Th2 is at + 52 °C, while the evolution of the bubble follows the isochore. The three-phase domain for natural petroleum inclusions is still not adapted to
370
Abstract
Pressure (bar)
Critical isochore
Isochore of Que14/16
Liquid
;ritical point
Vapour L+L+V L+V % b~,~,~, ~
Thl -60
"
• wet gas I 74% CH4
black oil 21% CH4
Th2 /" +52
Temperature (°C)
Fig. 2. Phase diagram of the calculated isochores and isopleths of a gas condensate with 69 mol% CH4 (sample Quel4/16). The isopleths of a wet gas with 74 mol% CH4 and a black oil with 21 mol% CH 4 are added to show the evolution of the isopleths in the p - T diagram.
the real oil complex composition, but observations in the three- or more phase domain are helpful and should always be taken in account to determine in a first step the present oil type. If the L + L + V domain can be thermodynamically calculated, the Thi would give the precise composition of the present oil type in the inclusion. Therefore, thermodynamic modelling should be improved for petroleum inclusions. However, not only the low temperature range is interesting. In the first place, observations of the thermal behaviour near the homogenisation are very informative. The change of refractive index of the liquid and the vapour phase is directly related to the temperature difference (AT) to the critical temperature. De facto, a critical homogenisation is marked by the progressive disappearance of the contours of the vapour phase. A homogenisation far from the critical temperature does not show any modification of the refractive index of the vapour and liquid phase. The second important observation is the volumetric change of the vapour phase, which can be another good indicator of the oil composition. In the case of critical homogenisation, the vapour bubble volume remains unchanged. In contrast, for example, the homogenisation of a black oil is marked by a slight regular decrease of the vapour volume with increasing temperature. Close to the critical point, the bubble
disappears very rapidly, e.g. gas condensates, instead of a constant decrease of the vapour bubble when homogenisation is reached far away from the critical point, e.g. black oil. In conclusion, the careful observation of the thermal behaviour of petroleum inclusions can help to classify the oil trapped in the diagenetic mineral cement and can help to develop an adequate and analytical modelling procedure.
Acknowledgements
We appreciate the valuable comments of D. Leythaeuser and an anonymous reviewer. We are also grateful to G. Beaudoin and D. Kirkwood from Laval University (Quebec), E. Gonzalez-Partida (UNAM Mexico), E Dobes (Czech Geological Survey) and TotalFinaElf, which provided us with the samples.
References Grimmer, J.O.W., Pironon, J,, Such~, V., Dobes, E, 2002. Petroleum inclusions in the Barrandian Palaeozoic Basin, Czech Republic: P,T,X modelling. PACROFI VIII, Abstracts, pp. 32-34. Luks, K.D., Merrill, R.C., Kohn, J.P., 1983. Partial miscibility behavior in cryogenic natural gas systems. Fluid Phase Equilibria 14, 193 201.
Abstract
Pironon, J., Canals, M., Dubessy, J., Walgenwitz, F., LaplaceBuilhe, C., 1998. Volumetric reconstruction of individual oil inclusions by confocal scanning laser microscopy. European Journal of Mineralogy 10, 1143-1150. Pironon, J., Thirry, R., Ayt Ougougdal, M., Teinturier, S., Beaudoin, G., Walgenwitz, F., 2001. FT-IR measurements of petro-
371 leum fluid inclusions: methane, n-alkanes and carbon dioxide quantitative analysis. Geofluids 1, 2 10. Teinturier, S., Pironon, J., Walgenwitz, F., 2002. Fluid inclusions and PVTX modelling examples from the Gain Formation in well 6507/2-2, Haltenbanken, Mid-Norway. Marine and Petroleum Geology 19 (6), 755-765.