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Bromine as an indicator of oil migration in northern Iraqi oil fields
GeochimicaetCoamochimica Acts.1074.Vol.38,pp.1303to1306. Pergamon Preaa.Printed inNorthern Ireland
NOTES
Bromine as an indicator of oil migration in northern Iraqi oil fields H. AL-SHAHRISTANI Department of Physics, University of Mosul, Mosul, Iraq
and A. G. HANNA Nuclear Research Institute, Baghdad, Iraq (Receivd 10 October 1973; acwpted in rev&edforna 12 February 1974) Abstract-The Br content of oil varies systematically along the paths of oil migration in northern Iraqi oil fields, indicating that this element may be used &8 an indicator of oil movement. The variation in Br parallels that of V and Ni, and like these two elements it is concentrated in the asphaltene fraction of petroleum.
report by AL-SHAHRISTANI and An-Arm (1972), the vertical migration of oil in the northern Iraqi oil fields was discussed in detail and it was shown that oil in these fields has migrated vertically from Middle/Upper Cretaceoua reservoirs to the overlying Tertiary reservoirs. It was further shown that vertical migration of oil in the Ain Zalah oil field in the north of Iraq is taking place through fractures even at the present time. The paths of oil migration were traced by studying the variation of the V and Ni contents of oil. Vanadium and nickel are introduced into crude oil quite early in its history of formation (CORWIN, 1959) and are generally associated with porphyrins and other high-molecular-weight compounds (BONHAM, 1956; ERDMAN, 1965; BLUMER and SNYDER, 1967; HODGSON et al., 1969). During the course of oil movement through porous rocks these high-molecular-weight compounds tend to move slower than the light non-polar fractions (HODGSON and BAKER, 1959). This differential movement of oil components results in a concentration gradient along the line of migration and features of this gradient oan be used to study oil movement. In this paper the variation of the Br content along the established lines of oil migration in the northern Iraqi oil fields are studied. IN A RECENT
RESULTS AND DISCUSSION
Instrumental neutron activation analysis techniques were used to determine the trace element composition of samples of crude oil obtained from all the producing formations in the northern Iraqi oil fields. Several distillation fractions of these 1303
Notes
1304
crude oils were also analyzed. Great care was taken to asmm that the oil samples were free from any solid or liquid suspension. A total of 29 trace elements were determined in these oils (AL-SHAHRISTANI and AL-ATYIA, 1973). Among all the trace elements studied only the Br content was found to vary systematically, and in a pattern similar to that of V and Ni. Bromine content in samples of crude oil together with pertinent strati~aphic i~ormation and oil densities are given in Table 1. Table 1. Contents of bromine, vanadium and nickel in oils from the northern Iraqi oil fields Oil field Kirkuk
D0m.3
I&T?1
Khurmala
First
AVfUl8b
First
E&be
First
Well no.
Density [g/cm3 (2O”C)l
&fiddle Eocenej Lower Miocene Middle Eocenef Lower Miocene Middle Eocene/ Lower Miocene
K-113 K-123 K-166 K-172 K-165 K-140 K-129 K-145 K-142 K-175 K-130 K-109 BH-23 BH-18 BH-13
0.877 0‘877 0.868 0*867 0.872 0+360 0.869 0.876 0.871 0.897 0.888 0+392 0.86 0.871 0.892
Jrt-5
0.832
< 0.01
AZ-20 AZ-26 AZ-Ii AZ-28
0.876 0.872 0.89 0.89
O*ll O-25 0.25
76 70 102 109
Bm-11
0.878
0.11
35
Second
UPPer Cretsceoua
First
MiddIe Eocene1 Lower Mioce& Middle
Second
Jambur
Age
First
&fiddle Eoaene/ Lower Miocene
Ain Z&h
Butma
First
UPPer Cretaceow
Br cono. V cona. (ppm) (PPm) 0.070 0.23 0*061 0.059 o*os9 0.040 0.052 0.062 0*064 0.27 O-42 0.39 0.10 0.11 0‘25
26.9 34.0 28.3 25-5 25.0 25.7 26.0 26.5 47.0 43.0 44.0 26.5 29.0 48.0
9.0
Ni cow. (PPm) 19-O 16.6 15.3 13,s 15.9 16.7 17.0 18.0 16.8 22.9 20.0 20.3 17.2 14.5 --
20 24.6 26
19.5
The Br content of crude oil although very small (never exceeding O-5ppm} was positively correlated tith the V and Ni contents. The Br content of oils taken from different wells in the same producing formation remained fairly constant. In the Kirkuk field the Br content of oil in eight wells (K-113, 166, 172, 155, 140, 129, 145, 142) producing from the Tertiary rocks ranged from 0*04 to 0.07 ppm compared with 25-26-g ppm V and 13%19.0 ppm Ni. The only exception was well K-123 where the Br content was 0.23 ppm. This increase in Br content was accompanied by a similar increase in the V content (34 ppm V). The abnormality may be explained by the fact that well K-123 is structurally lower than the other wells producing from this level (AL-SHAHRIST~I and AL-AT=, 1972, Fig. 2). The Br content in oils produced from the Upper Gretaceous reservoir of Baba dome in the same oil field, Kirk& ranged from 0.27 to 0.42 ppm while the V and Xi contenm ranged from 34 to 47 ppm and 20.0 to 22.9 ppm, respectively. It is
Notes
1305
interesting to note that the Br content of oil decreases about 7-fold along the axis of migration from the Upper Cretaceous reservoir to the overlying Tertiary reservoir, compared to a decrease of less than 2-fold in the V and Ni contents. In addition to the Kirkuk oil field, there are two other fields in this area: Bai Hassan and Jambur. In the Bai Hassan oil field a similar pattern of variation in the Br content was observed. Oils from the Tertiary reservoir contained about O-1 ppm Br while an oil from Middle Cretaceous contained 0.25 ppm Br. In the Jambur oil field the Br content was below the detection level of 0.01 ppm. Here the concentration of V was only 9-Oppm compared to the average value of 26 ppm for the other Tertiary reservoirs. This relationship is perhaps due to the fact that the Jambur reservoir is structurally much higher than the other Tertiary reservoirs in the area. In the Mosul area there are two oil fields: Ain Zalah and Butma. Ain Zalah oil field produces from two levels, the higher is of Late Cretaceous age and the lower of Middle Cretaceous age. The two levels are separated b7 about 2000 ft of impermeable limestone. However, there are fractures in this layer and oil can be drawn from these fractures (well AZ-11). Oil produced from the fracture contains 0.25 ppm Br compared to O-11ppm Br in oils of the first level and 0.25 ppm Br in oils of the second level. This observation suggests that oil from the fracture is being continuously replaced by the vertical migration of oil from the second level. This phenomenon was also indicated by the vanadium content in these oils. The second oil field in this area, Butma, produces from one level of Late Cretaceous age. The Br content of oil produced from this field is 0.11 ppm which compares well with the Br content of oil from the Upper Cretaceous reservoir of Ain Zalah. The results presented in Table 1 indicate that the Br concentration in oil varies systematically along the established path of oil migration from the Upper Cretaceous to the overlying Tertiary reservoir in the Kirkuk area oil fields and from the Middle Cretaceous to the Upper Cretaceous reservoir in the Ain Zalah oil field. The same pattern of variation was observed by AL-SHA~RISTANI and AL-ATYIA (1972) in the V and Ni contents of these oils. Since V and Ni are associated with the porphyrins and other high-molecular-weight compounds (CORWEN,1959; HODWON and BAKER, 1959) and are generally found in the heavier fractions of petroleum, it was expected that Br may also be concentrated in these heavy fractions. In general, the higher the Br, V and Ni contents the denser the oil (see Table 1). Oil samples from the Kirkuk area were fractioned in a two-stage vacuum distillation unit into several fractions, and the Br and V contents of each fraction were determined separately. No Br or V was detected in any of the distillation fractions. All the Br and V was concentrated in the vacuum residue. The vacuum residue was treated with propane to separate the asphaltene and deasphalted oil fractions. The Br and V contents in the deasphalted oil were less than 0.1 ppm and less than 0.6 ppm, respectively, while the asphaltene fraction contained O-6ppm Br and 186 ppm V. Hence, almost all the Br and V are concentrated in the asphaltene fraction. A plot of the Br vs V contents in crude oils of the Kirkuk field is shown in Fig. 1. There is a correlation between the Br and V contents. The correlation coefficient is 0.9. However, the least square fit does not pass through the origin but intercepts the V content axis at 21.6 ppm. Hence, as the V content increases from 21.5 to
Notes
1306
V.
rwm
Fig. 1. Correlationbetween Br and V contents in oils from northernIraqi oil fields.
43 ppm, the Br content increases from
REFERENCES H. and AL-ATYIA M. J. (1972) Vertical migration of oil in Iraqi oil fields: evidence based on vanadium and nickel concentrations. Geochim. Coemochim. Acta 36, 929-938. AL-SHAHXISTAN-I H. and AL-ATYIA M. J. (1973) Determination and geochemical significanceof trace elements in Iraqi crude oils using instrumental neutron activation analysis. J. Rudioad. Chem. 14, 401-413. BONH~ML. C. (1956) Geochemicctlinvestigation of crude oils. Bull. Amer. Assoc. Petrol. Geol. 40, 897-908. BLUMERM. and SNYDERW. D. (1967) Porphyrins of high molecular weight in a Triassic oil shale: evidence by gel permeation chromatography. Chsm. Geol. 2, 35-45. CORWINA. H. (1969) Petroporphyrins. Proc. 5th World Petrol. Cong. V, pp. 119-129. ERDMANJ. G. (1966) The molecular complex comprising heavy petroleum fractions. Hydrocarbon Analysis ASTM STP 389, 259-300. HODQSONG. W. and B-a B. L. (1959) Geochemical aspects of petroleum migration in Pembina, Red Water, Jaffre end Lloyd-Minster oil fields of Alberta and Saskatchewan, Canada. Bull. Amer. ABBOC.Petrol. Geol. 43, 331-328. HODQSONG. W., FLO~ES J. and BARER B. L. (1969) The origin of petroleum porphyrins: preliminary evidence for protein fragments associated with porphyrins. Ueochim. oosmochim. Aota 88, 632-636. AL-SHAHRISTANI
NOTES
Bromine as an indicator of oil migration in northern Iraqi oil fields H. AL-SHAHRISTANI Department of Physics, University of Mosul, Mosul, Iraq
and A. G. HANNA Nuclear Research Institute, Baghdad, Iraq (Receivd 10 October 1973; acwpted in rev&edforna 12 February 1974) Abstract-The Br content of oil varies systematically along the paths of oil migration in northern Iraqi oil fields, indicating that this element may be used &8 an indicator of oil movement. The variation in Br parallels that of V and Ni, and like these two elements it is concentrated in the asphaltene fraction of petroleum.
report by AL-SHAHRISTANI and An-Arm (1972), the vertical migration of oil in the northern Iraqi oil fields was discussed in detail and it was shown that oil in these fields has migrated vertically from Middle/Upper Cretaceoua reservoirs to the overlying Tertiary reservoirs. It was further shown that vertical migration of oil in the Ain Zalah oil field in the north of Iraq is taking place through fractures even at the present time. The paths of oil migration were traced by studying the variation of the V and Ni contents of oil. Vanadium and nickel are introduced into crude oil quite early in its history of formation (CORWIN, 1959) and are generally associated with porphyrins and other high-molecular-weight compounds (BONHAM, 1956; ERDMAN, 1965; BLUMER and SNYDER, 1967; HODGSON et al., 1969). During the course of oil movement through porous rocks these high-molecular-weight compounds tend to move slower than the light non-polar fractions (HODGSON and BAKER, 1959). This differential movement of oil components results in a concentration gradient along the line of migration and features of this gradient oan be used to study oil movement. In this paper the variation of the Br content along the established lines of oil migration in the northern Iraqi oil fields are studied. IN A RECENT
RESULTS AND DISCUSSION
Instrumental neutron activation analysis techniques were used to determine the trace element composition of samples of crude oil obtained from all the producing formations in the northern Iraqi oil fields. Several distillation fractions of these 1303
Notes
1304
crude oils were also analyzed. Great care was taken to asmm that the oil samples were free from any solid or liquid suspension. A total of 29 trace elements were determined in these oils (AL-SHAHRISTANI and AL-ATYIA, 1973). Among all the trace elements studied only the Br content was found to vary systematically, and in a pattern similar to that of V and Ni. Bromine content in samples of crude oil together with pertinent strati~aphic i~ormation and oil densities are given in Table 1. Table 1. Contents of bromine, vanadium and nickel in oils from the northern Iraqi oil fields Oil field Kirkuk
D0m.3
I&T?1
Khurmala
First
AVfUl8b
First
E&be
First
Well no.
Density [g/cm3 (2O”C)l
&fiddle Eocenej Lower Miocene Middle Eocenef Lower Miocene Middle Eocene/ Lower Miocene
K-113 K-123 K-166 K-172 K-165 K-140 K-129 K-145 K-142 K-175 K-130 K-109 BH-23 BH-18 BH-13
0.877 0‘877 0.868 0*867 0.872 0+360 0.869 0.876 0.871 0.897 0.888 0+392 0.86 0.871 0.892
Jrt-5
0.832
< 0.01
AZ-20 AZ-26 AZ-Ii AZ-28
0.876 0.872 0.89 0.89
O*ll O-25 0.25
76 70 102 109
Bm-11
0.878
0.11
35
Second
UPPer Cretsceoua
First
MiddIe Eocene1 Lower Mioce& Middle
Second
Jambur
Age
First
&fiddle Eoaene/ Lower Miocene
Ain Z&h
Butma
First
UPPer Cretaceow
Br cono. V cona. (ppm) (PPm) 0.070 0.23 0*061 0.059 o*os9 0.040 0.052 0.062 0*064 0.27 O-42 0.39 0.10 0.11 0‘25
26.9 34.0 28.3 25-5 25.0 25.7 26.0 26.5 47.0 43.0 44.0 26.5 29.0 48.0
9.0
Ni cow. (PPm) 19-O 16.6 15.3 13,s 15.9 16.7 17.0 18.0 16.8 22.9 20.0 20.3 17.2 14.5 --
20 24.6 26
19.5
The Br content of crude oil although very small (never exceeding O-5ppm} was positively correlated tith the V and Ni contents. The Br content of oils taken from different wells in the same producing formation remained fairly constant. In the Kirkuk field the Br content of oil in eight wells (K-113, 166, 172, 155, 140, 129, 145, 142) producing from the Tertiary rocks ranged from 0*04 to 0.07 ppm compared with 25-26-g ppm V and 13%19.0 ppm Ni. The only exception was well K-123 where the Br content was 0.23 ppm. This increase in Br content was accompanied by a similar increase in the V content (34 ppm V). The abnormality may be explained by the fact that well K-123 is structurally lower than the other wells producing from this level (AL-SHAHRIST~I and AL-AT=, 1972, Fig. 2). The Br content in oils produced from the Upper Gretaceous reservoir of Baba dome in the same oil field, Kirk& ranged from 0.27 to 0.42 ppm while the V and Xi contenm ranged from 34 to 47 ppm and 20.0 to 22.9 ppm, respectively. It is
Notes
1305
interesting to note that the Br content of oil decreases about 7-fold along the axis of migration from the Upper Cretaceous reservoir to the overlying Tertiary reservoir, compared to a decrease of less than 2-fold in the V and Ni contents. In addition to the Kirkuk oil field, there are two other fields in this area: Bai Hassan and Jambur. In the Bai Hassan oil field a similar pattern of variation in the Br content was observed. Oils from the Tertiary reservoir contained about O-1 ppm Br while an oil from Middle Cretaceous contained 0.25 ppm Br. In the Jambur oil field the Br content was below the detection level of 0.01 ppm. Here the concentration of V was only 9-Oppm compared to the average value of 26 ppm for the other Tertiary reservoirs. This relationship is perhaps due to the fact that the Jambur reservoir is structurally much higher than the other Tertiary reservoirs in the area. In the Mosul area there are two oil fields: Ain Zalah and Butma. Ain Zalah oil field produces from two levels, the higher is of Late Cretaceous age and the lower of Middle Cretaceous age. The two levels are separated b7 about 2000 ft of impermeable limestone. However, there are fractures in this layer and oil can be drawn from these fractures (well AZ-11). Oil produced from the fracture contains 0.25 ppm Br compared to O-11ppm Br in oils of the first level and 0.25 ppm Br in oils of the second level. This observation suggests that oil from the fracture is being continuously replaced by the vertical migration of oil from the second level. This phenomenon was also indicated by the vanadium content in these oils. The second oil field in this area, Butma, produces from one level of Late Cretaceous age. The Br content of oil produced from this field is 0.11 ppm which compares well with the Br content of oil from the Upper Cretaceous reservoir of Ain Zalah. The results presented in Table 1 indicate that the Br concentration in oil varies systematically along the established path of oil migration from the Upper Cretaceous to the overlying Tertiary reservoir in the Kirkuk area oil fields and from the Middle Cretaceous to the Upper Cretaceous reservoir in the Ain Zalah oil field. The same pattern of variation was observed by AL-SHA~RISTANI and AL-ATYIA (1972) in the V and Ni contents of these oils. Since V and Ni are associated with the porphyrins and other high-molecular-weight compounds (CORWEN,1959; HODWON and BAKER, 1959) and are generally found in the heavier fractions of petroleum, it was expected that Br may also be concentrated in these heavy fractions. In general, the higher the Br, V and Ni contents the denser the oil (see Table 1). Oil samples from the Kirkuk area were fractioned in a two-stage vacuum distillation unit into several fractions, and the Br and V contents of each fraction were determined separately. No Br or V was detected in any of the distillation fractions. All the Br and V was concentrated in the vacuum residue. The vacuum residue was treated with propane to separate the asphaltene and deasphalted oil fractions. The Br and V contents in the deasphalted oil were less than 0.1 ppm and less than 0.6 ppm, respectively, while the asphaltene fraction contained O-6ppm Br and 186 ppm V. Hence, almost all the Br and V are concentrated in the asphaltene fraction. A plot of the Br vs V contents in crude oils of the Kirkuk field is shown in Fig. 1. There is a correlation between the Br and V contents. The correlation coefficient is 0.9. However, the least square fit does not pass through the origin but intercepts the V content axis at 21.6 ppm. Hence, as the V content increases from 21.5 to
Notes
1306
V.
rwm
Fig. 1. Correlationbetween Br and V contents in oils from northernIraqi oil fields.
43 ppm, the Br content increases from
REFERENCES H. and AL-ATYIA M. J. (1972) Vertical migration of oil in Iraqi oil fields: evidence based on vanadium and nickel concentrations. Geochim. Coemochim. Acta 36, 929-938. AL-SHAHXISTAN-I H. and AL-ATYIA M. J. (1973) Determination and geochemical significanceof trace elements in Iraqi crude oils using instrumental neutron activation analysis. J. Rudioad. Chem. 14, 401-413. BONH~ML. C. (1956) Geochemicctlinvestigation of crude oils. Bull. Amer. Assoc. Petrol. Geol. 40, 897-908. BLUMERM. and SNYDERW. D. (1967) Porphyrins of high molecular weight in a Triassic oil shale: evidence by gel permeation chromatography. Chsm. Geol. 2, 35-45. CORWINA. H. (1969) Petroporphyrins. Proc. 5th World Petrol. Cong. V, pp. 119-129. ERDMANJ. G. (1966) The molecular complex comprising heavy petroleum fractions. Hydrocarbon Analysis ASTM STP 389, 259-300. HODQSONG. W. and B-a B. L. (1959) Geochemical aspects of petroleum migration in Pembina, Red Water, Jaffre end Lloyd-Minster oil fields of Alberta and Saskatchewan, Canada. Bull. Amer. ABBOC.Petrol. Geol. 43, 331-328. HODQSONG. W., FLO~ES J. and BARER B. L. (1969) The origin of petroleum porphyrins: preliminary evidence for protein fragments associated with porphyrins. Ueochim. oosmochim. Aota 88, 632-636. AL-SHAHRISTANI