- Email: [email protected]
Naturally occurring radioactive materials (NORM) and petroleum origin
Appl. Radiat. lsot. Vol. 48, No. 1(~12,pp. 1391-1396,1997
~
Pergamon PII: S0969-8043(97)00134-6
© 1997ElsevierScienceLtd. All rights reserved Printed in Great Britain 0969-8043/97 $17.00+ 0.00
Naturally Occurring Radioactive Materials (NORM) and Petroleum Origin A N S E L M O S. P A S C H O A *l Pontificia Universidade Cat61ica do Rio de Janeiro, Depto. de Fisica, C.P. 38071, Rio de Janeiro, RJ 22452-970, Brazil The presence of natural radioactivity in crude oil has been known since the beginning of this century. In the first half of the century, severaltheories proposed that alpha particles would play a role in petroleum origin. There are data available in the literature indicating 226Ra and 228Ra activity concentrations in radioactive scales in the order of 1.0 x 10 3 kBq/kg. It is reasonable to assume that these radionuclides had been concentrated about 100 times in the radioactive scales, taking into account the concentration factors typical of the fossilizedorganisms that originate the scales. Such data are consistent with petroleum formed some 25 million years ago. The implications of the activity concentrations of NORM found in oil fields to the validation of a new version of the alpha radiation theory of petroleum origin is examined. ~, 1997 Elsevier Science Ltd. All rights reserved
Introduction Definitive evidence that petroleum hydrocarbons are formed in nature from the conversion of organic matter into hydrocarbons, with a full account of the energy necessary and the time elapsed for the transformation to occur, has proved elusive thus far. The uncertainties associated with petroleum formation in nature have been clearly summarized (Krauskopf, 1967). Some authors have suggested thermal processes as the most important mechanisms for the conversion of organic matter into petroleum (Hoering and Abelson, 1963; Philippi, 1965, 1975, 1977). Geologists generally consider as separate events the origin, migration, and accumulation of petroleum into pools. The role of continental drift in the cyclic variation of the Earth's climate (Fischer and Arthur, 1977), and in the deposition and preservation of hydrocarbon source material to produce oil and natural gas (Tarling, 1973) deserves to be more carefully examined to provide an understanding of the migration and accumulation of petroleum into pools (Kerr, 1979). The present work, however, deals only with one possible source of energy associated with petroleum genesis, because the nature of the energy involved in the transformations of organic matter into petroleum hydrocarbons is still largely debatable even today. This paper will show how long term natural alpha radioactivity can be a strong candidate as one of the sources of energy associated with petroleum formation, and will call attention to the implications that the existing activity concentrations of naturally *Fax: (55 21) 259 9397.
occurring radioactive materials (NORM) in oil fields and wastes of oil production may have to the validation of this new version of the alpha radiation theory of petroleum origin.
The AlphaRadiationTheoryof Petroleum Genesis The presence of natural radioactivity in crude petroleum was detected as early as 1904 (Burton, 1904). In 1908, it was suggested that the relatively high radium concentrations found at the bottom of the oceans were due to the continuous supply of radium enriched organic materials falling from above (Joly, 1908). It was not until 20 years later that the hypothesis that the alpha radiation emitted by naturally occurring radionuclides could play a role in petroleum origin was raised (Lind, 1928). The basis for the alpha radiation hypothesis of petroleum origin was the observation that under the influence of alpha particles emitted by radon in a mixture of ethane (CH3CH3), propane (CH3CH2CH3) or butane (CH3CH2CH2CH3), each condenses, eliminating hydrogen (H2) and methane (CH4) to give place to higher hydrocarbons (Lind, 1931). The idea that the alpha radiation emitted by natural radionuclides could play a role in petroleum genesis was discarded almost immediately (Brooks, 1931) and not much later abandoned by the author himself (Lind, 1938), because he could not answer at that time some of the objections raised by his opponents. One of the main objections was the lack of helium in most petroleum pools (Brooks, 1931). By 1940, some other objections were partially erased by radioactive surveys on
1391
1392
A.S. Paschoa
sedimentary rocks associated with petroleum (Bell
et al., 1940). A differential equation describing the conversion rate, dM/dt, of organic matter into petroleum was proposed in 1944 (Sheppard, 1944): dM dM dt - ~ C x I
(1)
where d M / d N is the ratio of molecules converted to ion-pairs produced, specific to each chemical reaction under consideration; C is the relative concentration of organic material (in grams per gram of sediment); and I is the total number of ion-pairs produced per second per alpha particle per gram of sediment. Here one must bear in mind that only ions produced within a matrix of organic material are effective to convert molecules. In such a case, the rate of ion-pairs formed by means of alpha particle bombardment dN/dt can be expressed as: dN d~ = C × I
(2)
It was pointed out that the conversion efficiency would be higher if the radioactive materials were closely associated with the organic constituents of sediments (Sheppard, 1944). Thus, based upon data on radium concentration in sediments and marine organisms (Evans et al., 1938), and taking into account the 1.6 x 103 years half-life of 226Ra, it was estimated that only about 0.01 ~g of organic material would be converted per gram of sediment in 100 centuries (Sheppard, 1944). This conversion rate was much too low to be seriously considered for petroleum genesis, because the remaining activity of radium could not sustain the conversion of organic matter into petroleum for a time period longer than 104 years (Sheppard, 1944). By 1948, the idea of any connection between the energy of alpha particles and petroleum formation was discredited and called 'the physicist's point of view' on petroleum genesis (Brooks, 1948). Data on the concentrations of 238U and 232Th in plankton, organic matter and petroleum were largely unavailable in the 1940s and 1950s, when the old theory of alpha radiation of petroleum origin was recognized as a failure (Brooks, 1948; Whitehead, 1954). To the best of my knowledge, it was then a long time before any association was again made between natural alpha radioactivity and petroleum genesis in the literature. The one exception was a classical textbook on geochemistry, which mentioned that bombardment of fatty-acid molecules with alpha particles from natural radioactive decay could be a possible process to produce hydrocarbons (Krauskopf, 1967). At the time the alpha radiation theory of petroleum was discarded there was no evidence available that the organic segment of organic-rich sediments, like sapropel, apparently a result of 'polytaxic-mode' of long-term variation of ocean temperatures (Fischer and Arthur, 1977), might itself have had high
uranium and thorium content. For many years there were no other attempts to revive the alpha radiation theory for petroleum genesis. However, relevant multidisciplinary data started to become available in the 1960s and 1970s. Such data were applied to evaluate the feasibility of new ideas concerning alpha radiation and petroleum origin (Paschoa, 1981a). It was then pointed out that most of the objections raised earlier (Brooks, 1931, 1948) were becoming meaningless (Paschoa, 1981a). In the last decade or so, a number of papers, either published or in the process of being published, deal with NORM in association with operations used in the petroleum industry. Such papers report a wide variety of concentrations of natural radionuclides in scales and sludge (Kolb and Wojcik, 1985; Hartley, 1993; Heaton and Lambley, 1995; Paschoa and Tranjan Filho, 1995; Paschoa and MacDowell, 1996; MacDowell, 1996). In addition, concentration levels of 226Ra in the order of 1 x 103 kBq/kg have been reported (Kolb and Wojcik, 1985), and 300 kBq 228Ra/kg is not an uncommon concentration (Kvasnicka, 1996). Concentrations of 232U and 232Th in plankton and other organic materials known to be associated with petroleum origin are compatible with the alpha energy estimated to be needed for petroleum production (Paschoa, 198 la). Taking into account current information on NORM, it seems reasonable to hypothesize that there is an association between NORM in the petroleum industry and the alpha radiation theory of petroleum origin.
Age of Petroleum and Alpha Radiation Energy According to current ideas, kerogen is the organic constituent of sedimentary materials that is associated with petroleum formation (Tissot and WeRe, 1978; Ujfie, 1978). Thus, it is interesting to note that the percent composition of kerogen, asphalt, petroleum and urano-organic substances have a similar pattern as far as carbon, hydrogen and oxygen are concerned, which suggests a genetic association of these substances (Paschoa, 1981a). Kerogen is considered by petroleum geologists as being of two different varieties: humic kerogen associated with poor oil sources affected by dry-land conditions and sapropelic kerogen, related to subaqueous sediments deposited under conditions of isolation from land areas and associated with rich oil sources (Markovskii, 1978, Tissot and WeRe, 1978). It is worth mentioning here that sapropel is formed when blooming plankton secretes a poisonous substance that kills most marine organisms, in a restricted area of the ocean, which thus fall to the bottom. Relying on the hypothesis that the climate of the Earth behaves cyclically, it has been suggested that most global petroleum reserves have been formed as a result of sapropelic episodes, favorable
NORM and petroleum origin to the accumulation of petroleum source beds, that have occurred in the last 200 million years (Fischer and Arthur, 1977). However, the petroleum source beds might have resulted from high phytoplanktonic productivity associated with six sapropelic episodes (polytaxic) that occurred in the Early Jurassic, Late Jurassic, Mid-Cretaceous, Late Cretaceous, Eocene and Miocene periods (Fischer and Arthur, 1977). These sapropelic episodes are indeed associated with the geological age distribution of the known petroleum reserves (Paschoa, 1981a). Sapropelic episodes might have resulted in black shales with a uranium content higher than that of sedimentary rocks (Getseva, 1958; Wedepohl, 1978). It has been reported that a sapropel found at a depth of 100 m in the Black Sea, estimated to have been deposited some 5000 years ago, had a uranium concentration of about 40 ppm (0.5 kBq 238U/kg), mostly associated with planktonic matter rather than with land-derived organic debris (Deggens et al., 1977). In addition, studies on the form of occurrence of uranium in petroleum deposits associated with organic matter confirmed that uranium-bearing substances were genetically associated with petroleum (Vassiliou, 1980). Table 1 summarizes the thorium and uranium contents of some black shales throughout the world. Although the maximum reported value for thorium is only 0.05 Bq 232Th/g (12 ppm), uranium levels are as high as 15 Bq 238U/g (1244 ppm). Stagnant marine conditions are known to prevail in the formation of marine black shales which also have a high organic matter content, favored by high phytoplanktonic productivity in surface waters (Goldhaber, 1978). Activity concentrations of natural thorium and uranium in the Caribbean Sea have been reported to be in the order of 10 3 Bq/g, while 226Ra and 2t°po concentrations are enhanced by factors of 102 and 103, respectively (Kharkar et al., 1976). In several other places the uranium and thorium concentrations in plankton are between 10 4 and 10 2 Bq/g, and the enhancement factors for 226Ra and 21°po a r e similar to those found in the Caribbean (Paschoa et al., 1981b). Such values, however, cannot be considered as representative of the thorium and uranium concentrations in marine plankton in general.
Table 1. Thorium and uranium concentrations in black shales from selected sites. Adapted from Paschoa (1981a) Concentrations in Bq/g (ppm) :32Th n.r.* 0.002 (0.6)~).008 (1.9) n.r. n.r. n.r. 0.05 *Not reported. 'Range.
2s8U 0.04 (3)-15 (1244)* 0.24 (20)-2.4 (200) 0.04 (3)-3.0 (250) 0.16 (13)-0.5 (42) 0.6 (50)--1.2 (100) 0.6 (50)
1393
The uranium content of some oil field brines has been reported to be 2.4 Bq 238U/kg in association with helium in accumulations of petroleum and natural gas (Pierce et al., 1955). The distribution of helium concentrations in gas pools, gas-oil fields, gas-oil and oil pools from the Volga-Urals region, Central Asia (Nicanov, 1969; Tverdova and Fedina, 1974), Canada and the United States (Pierce et al., 1955; Anderson and Hinson, 1951; Boone, 1958) leads us to the conclusion that the relationship of helium to oil and to petroleum hydrocarbons had implications in the formation of these materials, which have yet to be understood. As a matter of fact, helium can be expected to accumulate in small amounts during the formation processes of petroleum and natural gas, as a result of the alpha decay of uranium and thorium and their alpha emitting progenies also present in black shales. As mentioned above, one of the main objections that discredited the original alpha radiation theory of petroleum genesis in the late 1930s was the lack of observation of helium in oil fields at that time. The alpha energy available for deposition per disintegration of 238U plus daughter products can be between 18.5 and 43 MeV, corresponding to total or no radon loss, respectively (Paschoa and Baptista, 1978). For the 23-'Th series the lower and upper limits for the alpha energy available for deposition per disintegration of the parent atom are 15.1 MeV (with total thoron loss) and 36 MeV (with no loss of thoron) (Paschoa and Baptista, 1978). If there is any excess activity of daughter products in the organic segment of sediments in relation to either 238U or 232Th, due to direct accumulation of 226Ra, 228Ra or 224Ra, the alpha energy limits presented above will tend to be higher. The subsequent estimates are made under the following restrictive assumptions (Paschoa, 1981a). 1. The mean alpha energy available due to the disintegration of 238U plus progeny up to 226Ra is totally deposited in the organic segment of sapropel, taking into account that the 238U in sapropel is essentially bound to planktonic matter (Deggens et al., 1977). 2. Although the alpha energy available for deposition per disintegration of 238U plus daughter products lies between 18.5 and 43 MeV, the individual alpha particles emitted by 23su and progeny up to 226Ra have energies below 5 MeV, with typical ranges in organic matter being less than 40 ~tm (Paschoa et al., 1979). 3. The contribution of radon plus daughters to the alpha energy available for deposition per disintegration will not be taken into account, because atoms of radon and its daughter products may disintegrate far from the initial position of the 238U parent atom.
1394
A.S. Paschoa
The above assumptions may need to be slightly modified for more precise estimates, because of the following: • only part of the alpha energy available may be deposited in the organic part of sapropel, due to the fact that the mean diameter of the organic constituents of sapropel (mostly phytoplankton) is likely to be somewhat less than 40 ~tm; • the natural alpha emitters may be selectively located in the border layers between the organic and inorganic segments of sapropel; • to the best of my knowledge, there are no conclusive data available on the fraction of radon loss from the organic segment of sapropel. The simple calculations made to estimate the time necessary to convert organic matter (sapropel) with a concentration Z ( = 1 Bq 23SU/g, for example) into petroleum can be summarized as follows. 1. By definition, 1 Bq 238U = 1 disintegration 238U/s = 3.15 × 107 dis. 238U/y. 2. The mean ionization energy for complex organic matter (as sapropel) can be considered as T ~ 60 eV/ion-pair, which is a conservative value compared with 27 eV/ion-pair or 56 eV/ion-pair (Sheppard, 1944). 3. The number of ion-pairs produced per year per gram of sapropel, due to 1 Bq 238U, Z, can then be estimated by substituting the proper values in Z = 1 Bq 238U/g (sapropel) = 3.15 × 107 (s/y)Odis. 238U/sOg of sapropelOl8.5 x 106 (eV/dis. 238U)O1/ 60 (ion-pair/eV) -- 0.98 × 10~3 (ion-pairs produced/g ofsapropelOy) ~ 1 × I0 ~3(ion-pairs produced/yOg of sapropel). 4. In addition, one can state that for complex organic matter, V = 6.02 x 1023 molecules/250 g/ mol = 2.4 × 102~ molecules/g of sapropel. 5. Taking into account the values of Z and V given in (3) and (4), respectively, the quotient V~ Z = 2.4 x 108 y can be interpreted as the time needed for 1 Bq 238U/g of sapropel to be converted into petroleum hydrocarbons, in accordance with the original ideas of the alpha radiation theory of petroleum genesis. Figure 1 represents in a graph the length of time needed to convert organic matter into petroleum hydrocarbons as a function of the 238Uconcentration in sapropel (in Bq/g). Data for Fig. 1 were obtained by using the rationale presented in (5) above. As an interesting application one can consider that the 238U concentration of 0.52 Bq/g in a Black Sea sapropel (Deggens et al., 1977) implies a rate of deposition of alpha energy of approximately 10 MeV/sOg, assuming total radon loss. Now, using the hypothesis (Sheppard, 1944) that 'one molecule of hydrocarbon is produced by 56 eV expended by alpha particles', one can adopt 60 eV/ion-pair formed as the ionization energy for complex organic material of sapropelic sediment, with 250 as the mean
109
10a
10 7
I"
10~
10s
104
........ .
0 1
.
.
.
.
.
.
.
~
........
i
. . . . . . . .
1
t
.
i
. . . . . . . .
10
.
.
.
.
.
.
.
I
........
i
. . . . . . . .
1 O0
,
........
i
. . . . . . . .
1000
i
10000
238U ( Bqlg ) Fig. 1. Length of time (in y) needed to convert organic matter into petroleum hydrocarbons as a function of the initial :ssU concentration (in Bq/g) in sapropel.
molecular weight. Thus, using the reasoning explained above, 5.2 × 1012 ion-pairs/yOg would be produced in the Black Sea sapropel. Furthermore, taking into account the value of V given in (4) above, one can estimate that the length of time needed to convert the Black Sea sapropel into petroleum hydrocarbon is 4.6 × l0 s years.
N O R M and Petroleum Genesis The problem of NORM in the petroleum industry has been recognized to the extent that the American Petroleum Institute (AP1) proposed options for disposal of NORM wastes produced in the oil and gas industries (API, 1992). In addition, radioactive scales have been known to be a potential problem for the petroleum industry for some time. Concentrations of 226Ra as high as 1 × 103 Bk/g and slightly less for 22SRa in radioactive scales in oilfield tubulars have been reported (Kolb and Wojcik, 1985; Heaton and Lambley, 1995; Kvasnicka, 1996; Paschoa and MacDowell, 1996). The association between NORM in the petroleum industry and petroleum genesis has apparently escaped the attention of most investigators, with one exception (Paschoa, 1981a). As an illustration of the potential relation between NORM and petroleum origin, the high uranium concentration in a sample of sludge taken from a petroleum pit associated with a salt dome in Louisiana was considered to be an indication that the uranium concentration in the initial organic matter was about 7.2 Bq/g (Paschoa, 1981a). Applying this concentration to the graph shown in Fig. 1, one could observe that the length of time needed to convert the initial organic material into petroleum would be of the order of 30 million years. Here it is interesting to observe that the petroleum found in the reservoirs of the Louisiana salt domes were usually associated with Pliocene-Miocene (i.e. 10-27 million year old; Krauskopf, 1967) lenticular sands.
NORM and petroleum origin The alpha theory of petroleum genesis, as presented here, suggests that the time necessary for the conversion of organic matter into petroleum is a function of the initial concentrations of :38U and 232Th in sapropel. In this case, the contribution of the 23~Th series to the alpha energy available for deposition in the organic matter should also have been taken into account in the calculations made earlier. However, this correction would probably not cause the orders of magnitude to change significantly. The age distribution of known petroleum reserves ranges from the Tertiary (10-70 million years ago; Krauskopf, 1967) to the Paleozoic (260-570 million years ago; Krauskopf, 1967), with more than 50% being from the former. Taking into account such data and the version of the alpha radiation theory of petroleum genesis presented here, one could estimate that the initial 23~U concentrations in sapropel would have to be between 0.8 and 12 Bq/g. Such range is narrow enough to be properly estimated from current data on radioactivity concentrations in N O R M associated with petroleum. Thus, the alpha radiation hypothesis of petroleum origin is worth re-examining. Concluding remarks 1. The alpha radiation theory of petroleum origin was re-examined, taking into account information gathered in recent decades. 2. The geological ages accepted for the formation of most known petroleum reserves are within a time span that makes natural alpha radiation energy a strong candidate as one of the energy sources for the production of petroleum hydrocarbons. 3. Future research should include the following: 1. systematic studies on 238U and 232Th concentrations in sapropel and other organic materials known to be associated with petroleum genesis; 2. knowledge of the microdistribution of long lived natural alpha emitters in the organic segment of sapropel; 3. determination of the fractions of radon and thoron that escape from the organic part of the sediments; 4. determination of the mean diameter of the organic constituents of sapropel; 5. correlations between the age of the petroleum and the concentrations of 238U and 232Th in sapropel and N O R M . Acknowledgements--Discussions with Professors M. Eisenbud and K.B. Krauskopf during a period of many years encouraged the author to proceed with his line of thinking. The author is indebted to the following Brazilian sponsoring agencies: FINEP, CNPq, CAPES and FAPERJ.
References Anderson, C. C. and Hinson, H. H. (1951) Bureau Mines Bull. 486.
1395
API (1992) Bulletin on the management of naturally occurring radioactive materials (NORM) in oil and gas production. American Petroleum Institute, Washington, D.C. Bell K. G., Goodman C. and Whitehead W. L. (1940). Am. Assoc. Petrol. Geol. Bull. 24, 1529. Boone, J. (1958) Bureau Mines Bull. 576. Brooks B. T. (1931). Amer. Assoc. Petrol. Geol. Bull. 15, 611. Brooks B. T. (1948). Amer. Assoc. Petrol. Geol. Bull. 32, 2269. Burton E. F. (1904). Philosophical Magazine g, 498. Deggens E. T., Khoo F. and Michaelis W. (1977). Nature 269, 566-569. Evans R. D., Kipp A. F. and Moberg E. C. (1938). American Journal of Science 36, 241. Fischer, A. G. and Arthur, M. A. (1977) In Deep-Water Carbonate Environments, ed. H.E. Cook and P. Enos, Society of Economic Paleontologists and Mineralogists (SEPM), Special Publication No. 25, pp. 19-50. Getseva, R. V. (1958) In The Geology of Uranium, Suppl. No. 6 of the Soviet Journal of Atomic Energy, Atomic Press, Moskow, 1957 (translated from Russian by Consultants Bureau, New York), p. 14. Goldhaber, M. (1978) In The Encyclopedia of Sedimentology, ed. R. W. Fairbridge and J. Bourgeois, Dowdenm Hutchinson and Ross, Inc., pp. 29~299. Hartley B. M. (1993) Disposal of radioactive waste from mining and processing of mineral sands. Radiation Petroleum in Australia 11, 53 59. Hassib, G. M. (1996) Radiation safety aspects in the oil and gas production facilities in Egypt. In Proceedings of the 1996 International Congress on Radiation Protection (1RPA9), 4, 4-624. Heaton B. and Lambley J. (1995) TENORM in the oil, gas and mineral mining industry. Applied Radiation and Isotopes 46, 577-581. Hoering, T. C. and Abelson, P. H. (1963) Geophysics Laboratory Annual Report 1962-63, pp. 229-234. Joly J. (1908). Philosophical Magazine 16, 190. Kharkar D. P., Thomson J., Turekian K. K. and Forster W. O. (1976) Uranium and thorium decay series nuclides in plankton from the Caribbean. Limnology and Oceanography 21, 294. Kerr R. A. (1979). Science 204, 1067-1072. Kolb W. A. and Wojcik M. (1985) Enhanced radioactivity due to natural oil and gas production and related radiological problems. The Science of the Total Environment 45, 77-84. Krauskopf, K. (1967) Introduction to Geochemistry, McGraw-Hill. Kvasnicka, J. (1996) Radiation protection in the offshore petroleum industry, Proceedings of the 1996 International Congress on Radiation Protection (IRPA9), 4, 4-625-4627. Lind, S. C. (1928) The Chemical Catalogue Company, New York. Lind S. C. (1931). Science 73, 19 22. Lind, S. C. (1938) The Science of Petroleum, Oxford University Press, Vol. I, p. 39. MacDowell, P. (1996) Use of naturally occurring radioactive material as shielding medium. Environmental International, in press. Markovskii, N. 1. (1978) In Paleogeographic Principles of Oil and Gas Prospecting (translated from Russian by R. Tateruk-Schneider, ed. R. Amoils). John Wiley and Sons, New York. Nicanov, V. F. (1969) Geochemistry, 199, (translated from Doklady Akad. Nauk. SSSR, 188, 1148). Paschoa A. S. and Baptista G. B. (1978). Health Physics 35, 404-405. Paschoa A. S., Wrenn M. E. and Eisenbud M. (1979). Radioproteetion 14, 99 115.
1396
A.S. Paschoa
Paschoa, A. S. (1981a) Old and new versions of the alpha radiation theory of petroleum origin. In Natural Radiation Environment, ed. K. G. Vohra, U. C. Mishra, K. C. Pillai and S. Sadasivan, pp. 651-657. Paschoa, A. S., Baptista, G. B., Wrenn, M. E. and Eisenbud, M. (1981b) Dosimetry of natural and man-made alpha emitters in plankton. In Impacts of Radionuclide Releases into the Marine Environment, International Atomic Energy Agency, Vienna, IAEA-SM-248/125, pp. 695-716. Paschoa A. S. and Tranjan Filho A. (1995) Radioactive waste management in developing and newly industrialized countries. Applied Radiation and Isotopes 46, 707-715. Paschoa, A. S. and MacDowell, P. (1996) Radiation protection and the naturally occurring radioactive materials (NORM), Proceedings of the 1996 International Congress on Radiation Protection (IRPA9), 4, 4-611-4-613. Philippi G. T. (1965). Geochimica Cosmochimica Acta 29, 1021-1049. Philippi G. T. (1975). Geochimica Cosmochimica Acta 39, 1353-1373.
Philippi G. T. (1977). Geochirnica Cosmochimiea Acta 41, 33-52. Pierce, A. P., Mytton, J. W. and Gott, G. B. (1955) In Geology of Uranium and Thorium; an International Conference, pp. 527-532. Sheppard C. W. (1944). Amer. Assoc. Petrol. Geol. Bull. 28, 924-952. Tarling D. H. (1973). Nature 243, 277 279. Tverdova, R. A. and Fedina, V. V. (1974) Geochemistry International, 722, 1974 (translated into English from Geokhimiya, 7, 1045). Tissot, B. P. and Welte, D. H. (1978) Petroleum Formation and Occurrence: A New Approach to Oil and Gas Exploration. Springer, Berlin. UjlJe Y. (1978). Nature 272, 438. Vassiliou A. H. (1980). Economic Geology 75, 609. Wedepohl, K. H. (Ed.) (1978) Handbook of Geochemistry, Vol. II/5. Elements La(57) to U(92). 92-K-1 and 92-K-2, Springer. Whitehead, W. L. (1954) Nuclear Geology, ed. Henry Faul. John Wiley & Sons, pp. 195-218.
~
Pergamon PII: S0969-8043(97)00134-6
© 1997ElsevierScienceLtd. All rights reserved Printed in Great Britain 0969-8043/97 $17.00+ 0.00
Naturally Occurring Radioactive Materials (NORM) and Petroleum Origin A N S E L M O S. P A S C H O A *l Pontificia Universidade Cat61ica do Rio de Janeiro, Depto. de Fisica, C.P. 38071, Rio de Janeiro, RJ 22452-970, Brazil The presence of natural radioactivity in crude oil has been known since the beginning of this century. In the first half of the century, severaltheories proposed that alpha particles would play a role in petroleum origin. There are data available in the literature indicating 226Ra and 228Ra activity concentrations in radioactive scales in the order of 1.0 x 10 3 kBq/kg. It is reasonable to assume that these radionuclides had been concentrated about 100 times in the radioactive scales, taking into account the concentration factors typical of the fossilizedorganisms that originate the scales. Such data are consistent with petroleum formed some 25 million years ago. The implications of the activity concentrations of NORM found in oil fields to the validation of a new version of the alpha radiation theory of petroleum origin is examined. ~, 1997 Elsevier Science Ltd. All rights reserved
Introduction Definitive evidence that petroleum hydrocarbons are formed in nature from the conversion of organic matter into hydrocarbons, with a full account of the energy necessary and the time elapsed for the transformation to occur, has proved elusive thus far. The uncertainties associated with petroleum formation in nature have been clearly summarized (Krauskopf, 1967). Some authors have suggested thermal processes as the most important mechanisms for the conversion of organic matter into petroleum (Hoering and Abelson, 1963; Philippi, 1965, 1975, 1977). Geologists generally consider as separate events the origin, migration, and accumulation of petroleum into pools. The role of continental drift in the cyclic variation of the Earth's climate (Fischer and Arthur, 1977), and in the deposition and preservation of hydrocarbon source material to produce oil and natural gas (Tarling, 1973) deserves to be more carefully examined to provide an understanding of the migration and accumulation of petroleum into pools (Kerr, 1979). The present work, however, deals only with one possible source of energy associated with petroleum genesis, because the nature of the energy involved in the transformations of organic matter into petroleum hydrocarbons is still largely debatable even today. This paper will show how long term natural alpha radioactivity can be a strong candidate as one of the sources of energy associated with petroleum formation, and will call attention to the implications that the existing activity concentrations of naturally *Fax: (55 21) 259 9397.
occurring radioactive materials (NORM) in oil fields and wastes of oil production may have to the validation of this new version of the alpha radiation theory of petroleum origin.
The AlphaRadiationTheoryof Petroleum Genesis The presence of natural radioactivity in crude petroleum was detected as early as 1904 (Burton, 1904). In 1908, it was suggested that the relatively high radium concentrations found at the bottom of the oceans were due to the continuous supply of radium enriched organic materials falling from above (Joly, 1908). It was not until 20 years later that the hypothesis that the alpha radiation emitted by naturally occurring radionuclides could play a role in petroleum origin was raised (Lind, 1928). The basis for the alpha radiation hypothesis of petroleum origin was the observation that under the influence of alpha particles emitted by radon in a mixture of ethane (CH3CH3), propane (CH3CH2CH3) or butane (CH3CH2CH2CH3), each condenses, eliminating hydrogen (H2) and methane (CH4) to give place to higher hydrocarbons (Lind, 1931). The idea that the alpha radiation emitted by natural radionuclides could play a role in petroleum genesis was discarded almost immediately (Brooks, 1931) and not much later abandoned by the author himself (Lind, 1938), because he could not answer at that time some of the objections raised by his opponents. One of the main objections was the lack of helium in most petroleum pools (Brooks, 1931). By 1940, some other objections were partially erased by radioactive surveys on
1391
1392
A.S. Paschoa
sedimentary rocks associated with petroleum (Bell
et al., 1940). A differential equation describing the conversion rate, dM/dt, of organic matter into petroleum was proposed in 1944 (Sheppard, 1944): dM dM dt - ~ C x I
(1)
where d M / d N is the ratio of molecules converted to ion-pairs produced, specific to each chemical reaction under consideration; C is the relative concentration of organic material (in grams per gram of sediment); and I is the total number of ion-pairs produced per second per alpha particle per gram of sediment. Here one must bear in mind that only ions produced within a matrix of organic material are effective to convert molecules. In such a case, the rate of ion-pairs formed by means of alpha particle bombardment dN/dt can be expressed as: dN d~ = C × I
(2)
It was pointed out that the conversion efficiency would be higher if the radioactive materials were closely associated with the organic constituents of sediments (Sheppard, 1944). Thus, based upon data on radium concentration in sediments and marine organisms (Evans et al., 1938), and taking into account the 1.6 x 103 years half-life of 226Ra, it was estimated that only about 0.01 ~g of organic material would be converted per gram of sediment in 100 centuries (Sheppard, 1944). This conversion rate was much too low to be seriously considered for petroleum genesis, because the remaining activity of radium could not sustain the conversion of organic matter into petroleum for a time period longer than 104 years (Sheppard, 1944). By 1948, the idea of any connection between the energy of alpha particles and petroleum formation was discredited and called 'the physicist's point of view' on petroleum genesis (Brooks, 1948). Data on the concentrations of 238U and 232Th in plankton, organic matter and petroleum were largely unavailable in the 1940s and 1950s, when the old theory of alpha radiation of petroleum origin was recognized as a failure (Brooks, 1948; Whitehead, 1954). To the best of my knowledge, it was then a long time before any association was again made between natural alpha radioactivity and petroleum genesis in the literature. The one exception was a classical textbook on geochemistry, which mentioned that bombardment of fatty-acid molecules with alpha particles from natural radioactive decay could be a possible process to produce hydrocarbons (Krauskopf, 1967). At the time the alpha radiation theory of petroleum was discarded there was no evidence available that the organic segment of organic-rich sediments, like sapropel, apparently a result of 'polytaxic-mode' of long-term variation of ocean temperatures (Fischer and Arthur, 1977), might itself have had high
uranium and thorium content. For many years there were no other attempts to revive the alpha radiation theory for petroleum genesis. However, relevant multidisciplinary data started to become available in the 1960s and 1970s. Such data were applied to evaluate the feasibility of new ideas concerning alpha radiation and petroleum origin (Paschoa, 1981a). It was then pointed out that most of the objections raised earlier (Brooks, 1931, 1948) were becoming meaningless (Paschoa, 1981a). In the last decade or so, a number of papers, either published or in the process of being published, deal with NORM in association with operations used in the petroleum industry. Such papers report a wide variety of concentrations of natural radionuclides in scales and sludge (Kolb and Wojcik, 1985; Hartley, 1993; Heaton and Lambley, 1995; Paschoa and Tranjan Filho, 1995; Paschoa and MacDowell, 1996; MacDowell, 1996). In addition, concentration levels of 226Ra in the order of 1 x 103 kBq/kg have been reported (Kolb and Wojcik, 1985), and 300 kBq 228Ra/kg is not an uncommon concentration (Kvasnicka, 1996). Concentrations of 232U and 232Th in plankton and other organic materials known to be associated with petroleum origin are compatible with the alpha energy estimated to be needed for petroleum production (Paschoa, 198 la). Taking into account current information on NORM, it seems reasonable to hypothesize that there is an association between NORM in the petroleum industry and the alpha radiation theory of petroleum origin.
Age of Petroleum and Alpha Radiation Energy According to current ideas, kerogen is the organic constituent of sedimentary materials that is associated with petroleum formation (Tissot and WeRe, 1978; Ujfie, 1978). Thus, it is interesting to note that the percent composition of kerogen, asphalt, petroleum and urano-organic substances have a similar pattern as far as carbon, hydrogen and oxygen are concerned, which suggests a genetic association of these substances (Paschoa, 1981a). Kerogen is considered by petroleum geologists as being of two different varieties: humic kerogen associated with poor oil sources affected by dry-land conditions and sapropelic kerogen, related to subaqueous sediments deposited under conditions of isolation from land areas and associated with rich oil sources (Markovskii, 1978, Tissot and WeRe, 1978). It is worth mentioning here that sapropel is formed when blooming plankton secretes a poisonous substance that kills most marine organisms, in a restricted area of the ocean, which thus fall to the bottom. Relying on the hypothesis that the climate of the Earth behaves cyclically, it has been suggested that most global petroleum reserves have been formed as a result of sapropelic episodes, favorable
NORM and petroleum origin to the accumulation of petroleum source beds, that have occurred in the last 200 million years (Fischer and Arthur, 1977). However, the petroleum source beds might have resulted from high phytoplanktonic productivity associated with six sapropelic episodes (polytaxic) that occurred in the Early Jurassic, Late Jurassic, Mid-Cretaceous, Late Cretaceous, Eocene and Miocene periods (Fischer and Arthur, 1977). These sapropelic episodes are indeed associated with the geological age distribution of the known petroleum reserves (Paschoa, 1981a). Sapropelic episodes might have resulted in black shales with a uranium content higher than that of sedimentary rocks (Getseva, 1958; Wedepohl, 1978). It has been reported that a sapropel found at a depth of 100 m in the Black Sea, estimated to have been deposited some 5000 years ago, had a uranium concentration of about 40 ppm (0.5 kBq 238U/kg), mostly associated with planktonic matter rather than with land-derived organic debris (Deggens et al., 1977). In addition, studies on the form of occurrence of uranium in petroleum deposits associated with organic matter confirmed that uranium-bearing substances were genetically associated with petroleum (Vassiliou, 1980). Table 1 summarizes the thorium and uranium contents of some black shales throughout the world. Although the maximum reported value for thorium is only 0.05 Bq 232Th/g (12 ppm), uranium levels are as high as 15 Bq 238U/g (1244 ppm). Stagnant marine conditions are known to prevail in the formation of marine black shales which also have a high organic matter content, favored by high phytoplanktonic productivity in surface waters (Goldhaber, 1978). Activity concentrations of natural thorium and uranium in the Caribbean Sea have been reported to be in the order of 10 3 Bq/g, while 226Ra and 2t°po concentrations are enhanced by factors of 102 and 103, respectively (Kharkar et al., 1976). In several other places the uranium and thorium concentrations in plankton are between 10 4 and 10 2 Bq/g, and the enhancement factors for 226Ra and 21°po a r e similar to those found in the Caribbean (Paschoa et al., 1981b). Such values, however, cannot be considered as representative of the thorium and uranium concentrations in marine plankton in general.
Table 1. Thorium and uranium concentrations in black shales from selected sites. Adapted from Paschoa (1981a) Concentrations in Bq/g (ppm) :32Th n.r.* 0.002 (0.6)~).008 (1.9) n.r. n.r. n.r. 0.05 *Not reported. 'Range.
2s8U 0.04 (3)-15 (1244)* 0.24 (20)-2.4 (200) 0.04 (3)-3.0 (250) 0.16 (13)-0.5 (42) 0.6 (50)--1.2 (100) 0.6 (50)
1393
The uranium content of some oil field brines has been reported to be 2.4 Bq 238U/kg in association with helium in accumulations of petroleum and natural gas (Pierce et al., 1955). The distribution of helium concentrations in gas pools, gas-oil fields, gas-oil and oil pools from the Volga-Urals region, Central Asia (Nicanov, 1969; Tverdova and Fedina, 1974), Canada and the United States (Pierce et al., 1955; Anderson and Hinson, 1951; Boone, 1958) leads us to the conclusion that the relationship of helium to oil and to petroleum hydrocarbons had implications in the formation of these materials, which have yet to be understood. As a matter of fact, helium can be expected to accumulate in small amounts during the formation processes of petroleum and natural gas, as a result of the alpha decay of uranium and thorium and their alpha emitting progenies also present in black shales. As mentioned above, one of the main objections that discredited the original alpha radiation theory of petroleum genesis in the late 1930s was the lack of observation of helium in oil fields at that time. The alpha energy available for deposition per disintegration of 238U plus daughter products can be between 18.5 and 43 MeV, corresponding to total or no radon loss, respectively (Paschoa and Baptista, 1978). For the 23-'Th series the lower and upper limits for the alpha energy available for deposition per disintegration of the parent atom are 15.1 MeV (with total thoron loss) and 36 MeV (with no loss of thoron) (Paschoa and Baptista, 1978). If there is any excess activity of daughter products in the organic segment of sediments in relation to either 238U or 232Th, due to direct accumulation of 226Ra, 228Ra or 224Ra, the alpha energy limits presented above will tend to be higher. The subsequent estimates are made under the following restrictive assumptions (Paschoa, 1981a). 1. The mean alpha energy available due to the disintegration of 238U plus progeny up to 226Ra is totally deposited in the organic segment of sapropel, taking into account that the 238U in sapropel is essentially bound to planktonic matter (Deggens et al., 1977). 2. Although the alpha energy available for deposition per disintegration of 238U plus daughter products lies between 18.5 and 43 MeV, the individual alpha particles emitted by 23su and progeny up to 226Ra have energies below 5 MeV, with typical ranges in organic matter being less than 40 ~tm (Paschoa et al., 1979). 3. The contribution of radon plus daughters to the alpha energy available for deposition per disintegration will not be taken into account, because atoms of radon and its daughter products may disintegrate far from the initial position of the 238U parent atom.
1394
A.S. Paschoa
The above assumptions may need to be slightly modified for more precise estimates, because of the following: • only part of the alpha energy available may be deposited in the organic part of sapropel, due to the fact that the mean diameter of the organic constituents of sapropel (mostly phytoplankton) is likely to be somewhat less than 40 ~tm; • the natural alpha emitters may be selectively located in the border layers between the organic and inorganic segments of sapropel; • to the best of my knowledge, there are no conclusive data available on the fraction of radon loss from the organic segment of sapropel. The simple calculations made to estimate the time necessary to convert organic matter (sapropel) with a concentration Z ( = 1 Bq 23SU/g, for example) into petroleum can be summarized as follows. 1. By definition, 1 Bq 238U = 1 disintegration 238U/s = 3.15 × 107 dis. 238U/y. 2. The mean ionization energy for complex organic matter (as sapropel) can be considered as T ~ 60 eV/ion-pair, which is a conservative value compared with 27 eV/ion-pair or 56 eV/ion-pair (Sheppard, 1944). 3. The number of ion-pairs produced per year per gram of sapropel, due to 1 Bq 238U, Z, can then be estimated by substituting the proper values in Z = 1 Bq 238U/g (sapropel) = 3.15 × 107 (s/y)Odis. 238U/sOg of sapropelOl8.5 x 106 (eV/dis. 238U)O1/ 60 (ion-pair/eV) -- 0.98 × 10~3 (ion-pairs produced/g ofsapropelOy) ~ 1 × I0 ~3(ion-pairs produced/yOg of sapropel). 4. In addition, one can state that for complex organic matter, V = 6.02 x 1023 molecules/250 g/ mol = 2.4 × 102~ molecules/g of sapropel. 5. Taking into account the values of Z and V given in (3) and (4), respectively, the quotient V~ Z = 2.4 x 108 y can be interpreted as the time needed for 1 Bq 238U/g of sapropel to be converted into petroleum hydrocarbons, in accordance with the original ideas of the alpha radiation theory of petroleum genesis. Figure 1 represents in a graph the length of time needed to convert organic matter into petroleum hydrocarbons as a function of the 238Uconcentration in sapropel (in Bq/g). Data for Fig. 1 were obtained by using the rationale presented in (5) above. As an interesting application one can consider that the 238U concentration of 0.52 Bq/g in a Black Sea sapropel (Deggens et al., 1977) implies a rate of deposition of alpha energy of approximately 10 MeV/sOg, assuming total radon loss. Now, using the hypothesis (Sheppard, 1944) that 'one molecule of hydrocarbon is produced by 56 eV expended by alpha particles', one can adopt 60 eV/ion-pair formed as the ionization energy for complex organic material of sapropelic sediment, with 250 as the mean
109
10a
10 7
I"
10~
10s
104
........ .
0 1
.
.
.
.
.
.
.
~
........
i
. . . . . . . .
1
t
.
i
. . . . . . . .
10
.
.
.
.
.
.
.
I
........
i
. . . . . . . .
1 O0
,
........
i
. . . . . . . .
1000
i
10000
238U ( Bqlg ) Fig. 1. Length of time (in y) needed to convert organic matter into petroleum hydrocarbons as a function of the initial :ssU concentration (in Bq/g) in sapropel.
molecular weight. Thus, using the reasoning explained above, 5.2 × 1012 ion-pairs/yOg would be produced in the Black Sea sapropel. Furthermore, taking into account the value of V given in (4) above, one can estimate that the length of time needed to convert the Black Sea sapropel into petroleum hydrocarbon is 4.6 × l0 s years.
N O R M and Petroleum Genesis The problem of NORM in the petroleum industry has been recognized to the extent that the American Petroleum Institute (AP1) proposed options for disposal of NORM wastes produced in the oil and gas industries (API, 1992). In addition, radioactive scales have been known to be a potential problem for the petroleum industry for some time. Concentrations of 226Ra as high as 1 × 103 Bk/g and slightly less for 22SRa in radioactive scales in oilfield tubulars have been reported (Kolb and Wojcik, 1985; Heaton and Lambley, 1995; Kvasnicka, 1996; Paschoa and MacDowell, 1996). The association between NORM in the petroleum industry and petroleum genesis has apparently escaped the attention of most investigators, with one exception (Paschoa, 1981a). As an illustration of the potential relation between NORM and petroleum origin, the high uranium concentration in a sample of sludge taken from a petroleum pit associated with a salt dome in Louisiana was considered to be an indication that the uranium concentration in the initial organic matter was about 7.2 Bq/g (Paschoa, 1981a). Applying this concentration to the graph shown in Fig. 1, one could observe that the length of time needed to convert the initial organic material into petroleum would be of the order of 30 million years. Here it is interesting to observe that the petroleum found in the reservoirs of the Louisiana salt domes were usually associated with Pliocene-Miocene (i.e. 10-27 million year old; Krauskopf, 1967) lenticular sands.
NORM and petroleum origin The alpha theory of petroleum genesis, as presented here, suggests that the time necessary for the conversion of organic matter into petroleum is a function of the initial concentrations of :38U and 232Th in sapropel. In this case, the contribution of the 23~Th series to the alpha energy available for deposition in the organic matter should also have been taken into account in the calculations made earlier. However, this correction would probably not cause the orders of magnitude to change significantly. The age distribution of known petroleum reserves ranges from the Tertiary (10-70 million years ago; Krauskopf, 1967) to the Paleozoic (260-570 million years ago; Krauskopf, 1967), with more than 50% being from the former. Taking into account such data and the version of the alpha radiation theory of petroleum genesis presented here, one could estimate that the initial 23~U concentrations in sapropel would have to be between 0.8 and 12 Bq/g. Such range is narrow enough to be properly estimated from current data on radioactivity concentrations in N O R M associated with petroleum. Thus, the alpha radiation hypothesis of petroleum origin is worth re-examining. Concluding remarks 1. The alpha radiation theory of petroleum origin was re-examined, taking into account information gathered in recent decades. 2. The geological ages accepted for the formation of most known petroleum reserves are within a time span that makes natural alpha radiation energy a strong candidate as one of the energy sources for the production of petroleum hydrocarbons. 3. Future research should include the following: 1. systematic studies on 238U and 232Th concentrations in sapropel and other organic materials known to be associated with petroleum genesis; 2. knowledge of the microdistribution of long lived natural alpha emitters in the organic segment of sapropel; 3. determination of the fractions of radon and thoron that escape from the organic part of the sediments; 4. determination of the mean diameter of the organic constituents of sapropel; 5. correlations between the age of the petroleum and the concentrations of 238U and 232Th in sapropel and N O R M . Acknowledgements--Discussions with Professors M. Eisenbud and K.B. Krauskopf during a period of many years encouraged the author to proceed with his line of thinking. The author is indebted to the following Brazilian sponsoring agencies: FINEP, CNPq, CAPES and FAPERJ.
References Anderson, C. C. and Hinson, H. H. (1951) Bureau Mines Bull. 486.
1395
API (1992) Bulletin on the management of naturally occurring radioactive materials (NORM) in oil and gas production. American Petroleum Institute, Washington, D.C. Bell K. G., Goodman C. and Whitehead W. L. (1940). Am. Assoc. Petrol. Geol. Bull. 24, 1529. Boone, J. (1958) Bureau Mines Bull. 576. Brooks B. T. (1931). Amer. Assoc. Petrol. Geol. Bull. 15, 611. Brooks B. T. (1948). Amer. Assoc. Petrol. Geol. Bull. 32, 2269. Burton E. F. (1904). Philosophical Magazine g, 498. Deggens E. T., Khoo F. and Michaelis W. (1977). Nature 269, 566-569. Evans R. D., Kipp A. F. and Moberg E. C. (1938). American Journal of Science 36, 241. Fischer, A. G. and Arthur, M. A. (1977) In Deep-Water Carbonate Environments, ed. H.E. Cook and P. Enos, Society of Economic Paleontologists and Mineralogists (SEPM), Special Publication No. 25, pp. 19-50. Getseva, R. V. (1958) In The Geology of Uranium, Suppl. No. 6 of the Soviet Journal of Atomic Energy, Atomic Press, Moskow, 1957 (translated from Russian by Consultants Bureau, New York), p. 14. Goldhaber, M. (1978) In The Encyclopedia of Sedimentology, ed. R. W. Fairbridge and J. Bourgeois, Dowdenm Hutchinson and Ross, Inc., pp. 29~299. Hartley B. M. (1993) Disposal of radioactive waste from mining and processing of mineral sands. Radiation Petroleum in Australia 11, 53 59. Hassib, G. M. (1996) Radiation safety aspects in the oil and gas production facilities in Egypt. In Proceedings of the 1996 International Congress on Radiation Protection (1RPA9), 4, 4-624. Heaton B. and Lambley J. (1995) TENORM in the oil, gas and mineral mining industry. Applied Radiation and Isotopes 46, 577-581. Hoering, T. C. and Abelson, P. H. (1963) Geophysics Laboratory Annual Report 1962-63, pp. 229-234. Joly J. (1908). Philosophical Magazine 16, 190. Kharkar D. P., Thomson J., Turekian K. K. and Forster W. O. (1976) Uranium and thorium decay series nuclides in plankton from the Caribbean. Limnology and Oceanography 21, 294. Kerr R. A. (1979). Science 204, 1067-1072. Kolb W. A. and Wojcik M. (1985) Enhanced radioactivity due to natural oil and gas production and related radiological problems. The Science of the Total Environment 45, 77-84. Krauskopf, K. (1967) Introduction to Geochemistry, McGraw-Hill. Kvasnicka, J. (1996) Radiation protection in the offshore petroleum industry, Proceedings of the 1996 International Congress on Radiation Protection (IRPA9), 4, 4-625-4627. Lind, S. C. (1928) The Chemical Catalogue Company, New York. Lind S. C. (1931). Science 73, 19 22. Lind, S. C. (1938) The Science of Petroleum, Oxford University Press, Vol. I, p. 39. MacDowell, P. (1996) Use of naturally occurring radioactive material as shielding medium. Environmental International, in press. Markovskii, N. 1. (1978) In Paleogeographic Principles of Oil and Gas Prospecting (translated from Russian by R. Tateruk-Schneider, ed. R. Amoils). John Wiley and Sons, New York. Nicanov, V. F. (1969) Geochemistry, 199, (translated from Doklady Akad. Nauk. SSSR, 188, 1148). Paschoa A. S. and Baptista G. B. (1978). Health Physics 35, 404-405. Paschoa A. S., Wrenn M. E. and Eisenbud M. (1979). Radioproteetion 14, 99 115.
1396
A.S. Paschoa
Paschoa, A. S. (1981a) Old and new versions of the alpha radiation theory of petroleum origin. In Natural Radiation Environment, ed. K. G. Vohra, U. C. Mishra, K. C. Pillai and S. Sadasivan, pp. 651-657. Paschoa, A. S., Baptista, G. B., Wrenn, M. E. and Eisenbud, M. (1981b) Dosimetry of natural and man-made alpha emitters in plankton. In Impacts of Radionuclide Releases into the Marine Environment, International Atomic Energy Agency, Vienna, IAEA-SM-248/125, pp. 695-716. Paschoa A. S. and Tranjan Filho A. (1995) Radioactive waste management in developing and newly industrialized countries. Applied Radiation and Isotopes 46, 707-715. Paschoa, A. S. and MacDowell, P. (1996) Radiation protection and the naturally occurring radioactive materials (NORM), Proceedings of the 1996 International Congress on Radiation Protection (IRPA9), 4, 4-611-4-613. Philippi G. T. (1965). Geochimica Cosmochimica Acta 29, 1021-1049. Philippi G. T. (1975). Geochimica Cosmochimica Acta 39, 1353-1373.
Philippi G. T. (1977). Geochirnica Cosmochimiea Acta 41, 33-52. Pierce, A. P., Mytton, J. W. and Gott, G. B. (1955) In Geology of Uranium and Thorium; an International Conference, pp. 527-532. Sheppard C. W. (1944). Amer. Assoc. Petrol. Geol. Bull. 28, 924-952. Tarling D. H. (1973). Nature 243, 277 279. Tverdova, R. A. and Fedina, V. V. (1974) Geochemistry International, 722, 1974 (translated into English from Geokhimiya, 7, 1045). Tissot, B. P. and Welte, D. H. (1978) Petroleum Formation and Occurrence: A New Approach to Oil and Gas Exploration. Springer, Berlin. UjlJe Y. (1978). Nature 272, 438. Vassiliou A. H. (1980). Economic Geology 75, 609. Wedepohl, K. H. (Ed.) (1978) Handbook of Geochemistry, Vol. II/5. Elements La(57) to U(92). 92-K-1 and 92-K-2, Springer. Whitehead, W. L. (1954) Nuclear Geology, ed. Henry Faul. John Wiley & Sons, pp. 195-218.