Advancement in Application of Diamondoids on Organic Geochemistry*

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Journal of Natural Gas Geoscience 1 (2016) 257e265 http://www.keaipublishing.com/jnggs Original research paper Advancement in application of diamondoids on organic geochemistry*

Anlai Ma

Exploration & Production Research Institute, SINOPEC, Beijing 100083, China

Received 19 July 2016; revised 10 August 2016 Available online 27 September 2016

Abstract

Diamondoids occur in all kinds of fossil fuels. Due to peculiar cage molecular structures, diamondoids have been widely used in the maturity assessment of high mature to over-mature oils as well as source rocks since the 1990s. New advancements in maturity, oil-cracking, oil mixing, oil biodegradation, organic facies, TSR, gas washing, migration, and oil spill identiﬁcation using diamondoids during the 21st century will be further discussed in this paper; the origin and possible forming mechanisms of diamondoids are also explained. Owing to the vagueness of the origin of diamondoid, the results of the maturity and oil cracking among researchers brought about great differences. It is suggested that the research of the evolution of diamondoid in different type oils and source rocks are beneﬁcial when applied in organic geochemistry, especially for the depth limits for the deep reservoirs. Copyright © 2016, Lanzhou Literature and Information Center, Chinese Academy of Sciences AND Langfang Branch of Research Institute of Petroleum Exploration and Development, PetroChina. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Keywords: Diamondoids; Adamantane; Diamantane; Maturity; Oil-cracking; Biodegraded; Organic facies; Thermochemical sulfate reduction (TSR)

1. Introduction diamondoids only contain one isomer, while polymantanes contain 4, 5, and 6 repeated units, the isomer numbers are 3, 6, Diamondoids, a cage hydrocarbon with a molecular for- and 17, respectively [3]. mula of C4nþ6H4nþ12, widely occur in fossil fuels [1]. The Diamondoids play a vital role by applying it in the field of basic repeated unit of diamondoids is adamantane [2,3] petroleum geochemistry, medicine, chemistry, and nanometer (Fig. 1), a four ring cage system containing 10 carbons. The new material [3] since Landa et al. [1] discovered adamantane scientific name of adamantane is tricyclo [3,3,1,1,(3,7)] in the oil from Hodonin oilfield within Czechoslovakia. Lin decane, which can be regarded as composed by three rigidly et al. [4] reported higher diamondoids namely tetramantane, fused cyclohexane rings in an all-chair configuration. The pentamantane, and hexamantane in the condensate oil pro- polyhomologous members of adamantanes include dia- duced from the Jurassic Norphlet Formation sandstone in its mantanes, triamantanes, tetramantanes, pentamantanes, and depth of 6800 m within the U.S. Gulf of Mexico. Using hexamantanes, in which adamantanes, diamantane, and tri- reversed-phased high-performance liquid chromatography amantanes belong to lower diamondoids, whereas repeated (HPLC), Dahl et al. [5,6] isolated the crystal of hexamantane units reaching over 4 belong to higher diamondoids. Lower or cyclohexamantane from distillate fractions from oil and determined the structure of C26H30 by means of X-ray diffusion, and GCeMS, 1H, 13C NMR methods.

* In fossil fuels, the abundance of adamantanes is the highest This is English translational work of an article originally published in Natural Gas Geoscience (in Chinese).The original article can be found at:10. sequence. Assuming that the abundance of adamantanes is 11764/j.issn.1672-1926.2016.05.0851. 100, the concentration of diamantanes, triadamantanes, tetra- E-mail address: [email protected]. mantanes, pentamantanes, and hexamantanes are 50, 15, 5, 1, Peer review under responsibility of Editorial Ofﬁce of Journal of Natural Gas and 0.1, respectively [4]. Geoscience. http://dx.doi.org/10.1016/j.jnggs.2016.09.001 2468-256X/Copyright © 2016, Lanzhou Literature and Information Center, Chinese Academy of Sciences AND Langfang Branch of Research Institute of Petroleum Exploration and Development, Petro- China. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 258 A. Ma / Journal of Natural Gas Geoscience 1 (2016) 257e265

CD) to enrich diamondoids. This method has a high recovery of the diamondoids in the oils and can satisfy the compound- speciﬁc isotope analysis (CSIA).

3. Application of diamondoids in organic geochemistry

3.1. Maturity determination of high mature to overmature oils and source rocks

The stability of diamondoids relies on the methyl substitution position. For the reason that methyl substitution Fig. 1. Diamondoid structure (after Ref. [3]). attached to a bridgehead position, 1-methyl adamantane, and 4-methyl diamantane showed more stability than that of diamondoids with methyl substitution positioned at the qua- 2. Diamondoid detection method, internal standards, and ternary carbon. Based on the aforementioned mechanism, pretreatment Chen et al. [18e20] proposed two diamondoid maturity ratios: Wingert [7] used MIDeGCeMS to identify the diamondoids in petroleum. In mainland China, Zhao et al. [8] Methyl adamantane index I, MAI ¼ 1-MA/(1-MA þ 2- adapted MIDeGCeMS to detect diamondoids in marginal MA) mature source rock, in which it can reach the triamantane Methyl diamantane index II, MDI ¼ 4-MD/(1-MD þ 3- series. Both the GCeMS and GCeMSeMS methods were MD þ 4-MD) applied to detect the diamondoids in the Molecular Organic Geochemistry Laboratory at Standford University [9].Liang Both MAI and MDI, showing good correlation with vitri- et al. [10,11] proposed that the sensitivity of the nite reflectance (Table 1), were widely used as maturity in- GCeMSeMS is about 4e66 times higher than that of the dictors for high mature oils and condensate in China [20e29]. GCeMS, considering that the former has a better recovery. In addition, Fu et al. [30] made use of the preceding ratios to Through the development of technology, the comprehensive determine the maturity of gas from the southern Qiongdong two-dimensional gas chromatography coupled to time-of- Basin in China. The determined result is consistent to that of flight mass spectrometry, this was adapted to assess the dia- the maturity obtained by carbon isotope of methane from the mondoids in crude oil. Using GC/GC-TOFMS, over 100 gas. compounds of adamantane, diamantane, and triamantane can Some other diamondoids maturity ratios are as follows be identified [12,13]. [3135]: The Molecular Organic Geochemistry Laboratory super- vised by K. E. Moldowan at the Standford University has the DMDI-1(dimethyldiamantane index 1) ¼ 4,9-DMD/(4,9- most advanced technology of determining diamondoid con- DMD þ 3,4-DMD) centrations by using six internal standards including D4-ada- DMDI-2 (dimethyldiamantane index 2) ¼ 4,9-DMD/(4,9- mantane, D3-1-methyladamantane, D3-1-methyldiamantane, DMD þ 4,8-DMD) D4-diamantane, D4-ethyldiamantane, and D4-triamantane. EAI (ethyladamantane index) ¼ 1-EA/(1-EA þ 2-EA) Quantitation of alkyl-adamantanes, diamantanes, and tri- DMAI-1(dimethyladamantane index 1) ¼ 1,3-DMA/(1,3- amantanes were achieved by integrating peak heights with DMA þ 1,2-DMA) respect to corresponding standards: D3-1-methyladamantane, DMAI-2(dimethyladamantane index 2) ¼ 1,3-DMA/(1,3- D3-1-methyldiamantane, and D4-triamantane, respectively. DMA þ 1,4-DMA) D4-adamantane, D4-diamantane, and D4-triamantane were TMAI-1(trimethyladamantane index 1) ¼ 1,3,5-TMA/ used to quantify adamantane, diamantane, triamantane, and (1,3,5-TMA þ 1,2,4-TMA) tetramantane, respectively. Meanwhile, D5-1-ethyldiamantane TMAI-2(trimethyladamantane index 2) ¼ 1,3,5-TMA/ was used to quantify ethyl diamantanes. Their standard devi- (1,3,5-TMA þ 1,3,6-TMA) ation was less than 8% [9]. Inland, Ma et al. [14] used two internal standards (D16-adamantane and D3-1- methyldiamantane) to quantify the concentration of dia- Table 1 mondoids in oils. Azevode et al. [15], Spriner et al. [16], and Relationship between the diamondoids' parameters and vitrinite reflectance Liang et al. [10,11] adapted the diamondoid kits from the (after Ref. [18]).

Chrion AS Company of Norway as the calibration solution and Index I: MAI/% Index II:MDI/% Ro/% used the n-C12D26, n-C16D34 as the internal standards to 50e70 30e40 1.1e1.3 quantify the adamantanes and diamantanes, respectively. 70e80 40e50 1.3e1.6 In the pretreatment of compound-speciﬁc isotope analysis 80e90 40e60 1.6e1.9 > > > of diamondoids, Huang et al. [17] used the b-cyclodextin (b- 90 60 1.9 A. Ma / Journal of Natural Gas Geoscience 1 (2016) 257e265 259

The research sample covering more lithology and maturity caused the dispute of the range application of the MAI and MDI to be stimulated [31e34,36]. Some authors suggested that the application range of MAI and MDI used as maturity was narrow. For example, Schulz et al. [31] argued that MAI and MDI only worked for samples with maturity above 1.3%. The result of thermal simulation experiment by Wei et al. [32] supported the conclusion of Schulz. Li et al. [33,34] suggested that MDI can be used as a maturity indicator for carbonate rock in high mature stage (Ro ¼ 0.9%e2.0%), and MDI is not a valid maturity indicator when the carbonate rock is overmature (Ro > 2.0%). Based on the golden tube pyrolysis results of the oil from Tarim Basin, Fang et al. [35,37] proposed that the MAI and MDI were not suitable for the maturity index. Some diamondoids Fig. 2. Cracking and mixed oil characteristics utilizing the concentration of ratios, such as DMAI-1, TMAI-1, EAI, and DMDI-2 showed a stigmastane and methyldiamantes (after Ref. [39]). linear correlation with Easy Ro% within the range of 1.0%e 3.0%, 1.5%e3.5%, 1.0%e2.5%, and 2.5%e3.5%, respectively. Fang et al. [35] suggested that MAI, EAI, DMAI-1, DMAI-2, Using this method, Schoell et al. [2] suggested that the TMAI-1, and TMAI-2 are good maturity parameters being reserve of the oil in the Gulf of Mexico should be restricted in within the range of 2.0%e3.0%, 1.6%e2.7%, 2.0%e3.5%, the Jurassic strata which depths ranged from 5000 m to 2.3%e3.5%, and 2.3%e3.5% Easy Ro, respectively. However, 6000 m. Later on, this method was used to assess the extent of through the golden tube pyrolysis results of mudstones from the oil cracking in the Tarim Basin, China [40], as well as the coal measure, Fang et al. [38] argued that the MAI, EAI, and basins from Brazil [15]. Although Dahl et al. [39] proposed TMA-1 showed correlation with Easy Ro within the range of that this method overestimated the extent of oil cracking, it is 1.3%e2.5%, 1.0%e2.5%, 1.5%e2.5%, respectively. more accurate than that of the GOR, because GOR can be From the results above, an obvious difference exists in the inﬂuenced by other factors such as migration fractionation, gas suitable range for diamondoids maturity index from the diffusion processes, and biodegradation. Accurate prediction different types of organic matter. of the extent of oil cracking relies heavily on the determination of the diamondoid baseline due to the different basin and their 3.2. Cracking and mixing oil baseline. Moldowan et al. [41] proposed that the diamondoid baseline is within the range of 4e5 ppm and it is unusual to Based on the method of determining the extent of evapo- ﬁnd a diamondoid baseline greater than 8 ppm. He suggested ration of salt water by analyzing salinity, Dahl et al. [39] that the diamondoid baseline of an unknown source rock is proposed the method of determining the oil-cracking value less than 10 ppm and probably less than 8 ppm [41]. by using the “3-methyl-þ4-methyl-diamantane” and stigmas- Nevertheless, Fang et al. [37] found that in the oil pyrolysis tane concentration. The key to the method is that diamondoids results, the concentration of 3-þ4-methyldiamantane barely are neither destroyed nor created. The concentration increases varied in the range of 0.8%e2.0% Easy Ro. The yield grad- it's diamondoids as a result of the cracking of other liquid ually increased in the range of 2.0%e2.7% Easy Ro, and then hydrocarbons. Thus, diamondoids can be considered as an rapidly decreased to less than 2.7% Easy Ro. Fang et al. [37] “internal standard” by which the extent of cracking can be suggested that the method of determining the extent of oil determined [39]. The cracking oil usually has high contents of cracking using the concentration of diamondoid and sterane diamondoids and low content of C29 steranes. If both high proposed by Dahl et al. [39] may be not valid for the high contents of diamondoids and C29 steranes were observed in an mature oil and it's only useful for the oil with a maturity that is oil, the oil may be a mixed oil derived from both a low lower than 2.0% Easy Ro [37]. maturity, biomarker-rich source, and a high-maturity, highly cracked, and diamondoid-rich source (Fig. 2). 3.3. Organic facies The equation of calculating the extent of oil cracking using the methyldiamantanes in the oil is: Three ratios were proposed by Schulz et al. [31] to distinguish between Type II carbonate, Type II marine sili- CR ¼ (1Co/Cc)*100% clastic, and Type III organic facies. The ratios are as follows:

Where CR is the cracked ratio, Co is the concentration of Dimethyl diamantane index 1(DMDI-1) ¼ 3,4-DMD/(3,4- methyldiamantanes in the uncracked oil samples (termed as DMD þ 4,9-DMD) diamondoid baseline), and Cc is the methyldiamantanes con- Dimethyl diamantane index 2(DMDI-2) ¼ 4,8-DMD/(4,8- centration of any cracked oil sampled sourced from the same DMD þ 4,9-DMD) starting oil. Ethyl adamantane index (EAI) ¼ 2-EA/(2-EA þ 1-EA) 260 A. Ma / Journal of Natural Gas Geoscience 1 (2016) 257e265

The DMDI-1 values for the Type II marine source rocks and Type III coal samples were 65% and 85% (Fig. 3), respectively. The DMDI-I value of carbonate rocks slightly increases with the increasing maturity in the beginning of the oil windows. However, the DMDI-2 value showed to be very stable in the carbonate rocks. The DMDI-2 values for other facies types also showed relatively stable values with increasing maturity, and the difference between them was not significant to distinguish between the different facies. In the dimethyl diamantane composition, the relative distribution between 4,9-DMD, 4,8-DMD, and 3,4-DMD can distinguish the different organic facies [31]. EAI ratio can reflect the facies of the source rock, but the ratio is obviously affected by maturity. The EAI ratio of Type II source rocks is about 70%, whereas in the Type III coal extract the value is greater than 85%. The EAI ratio of Type II Fig. 4. Relationship between EAI and DMDI-1 of marine and lacustrine oils in source rocks increases with the increasing maturity, whereas the Tarim Basin, China. those with the maturity greater than 1.3% Ro, the ratio of Type III samples would decrease rapidly. Both EAI and DMDI-1 ratios showed dissimilarities for the marine oils and lacustrine oils in the Tarim Basin, China. EAI and DMDI-1 ratios are lower than 65% for the marine oils from the Tahe Oilfield, whereas the two ratios are greater than 65% for the lacustrine oils from the Yingmali Oilfield (Fig. 4), thus, this backs that the ratios can be used to classify the marine and lacustrine oil. Based on the distribution of diamondoids from 11 oil samples, Gordadze [42] pointed out that the relative content of adamantane with varying alkyl substituted homologues can be used to distinguish marine oils and terrestrial oils as well as the times of the oils. Marine oils usually have a low content of C13 adamantane, in which relative content is lower than 25%; whereas terrestrial oils have a low content of C11 ada- mantene, about 15%, and high content of C12 adamantane, about 47%e48%. Proterozoic oils contain a high amount of C29 sterane among all the sterane (85%), low amount of C13 adamantanes (23%), and high amount of C12 adamantane (58%) (Fig. 5). Fig. 5. Adamantanes and steranes in crude oils of various origin (a) and ages (b) (after Ref. [42]).

3.4. Biodegradation

Diamondoids have a strong resistance to biodegradation [43]. Williams et al. [44] found that the alkyl adamantane kept constant in biodegradation oils. Even in the oil whose biodegradation level has reached 7, an abundant unaltered C2- adamantanes were found. Since biodegradation prefers to consume n-alkane, the ratio of diamondoid/n-alkane can be used to assess biodegradation level. Wingert [7] suggested that adamantane/n-alkane is an indicator of biodegradation, but only limited to low biodegradation level. Grice et al. [45] proposed that with the increasing biodegradation, the ratio of MA/nC11 increased from 0.04 (biodegradation level is 0) to 4.9 (biodegradation level is 3e4), whereas the ratio of MA/A increased from 5.3 (non-biodegraded oil) to 15.1 (seriously Fig. 3. Triangular plot of the relative distribution of 4,9-DMD, 4,8-DMD, and biodegraded oils); MA/A has obvious changes only when the 3,4-DMD presenting the different organic facies (after Ref. [31]). oil were biodegraded heavily. In addition, the combined the A. Ma / Journal of Natural Gas Geoscience 1 (2016) 257e265 261 ratios of MA/A and MA/nC11 can describe the percentage of Baltimore Canyon Trough, US Atlantic. Due to the lower the biodegraded oil in the mixed oil. Although adamantane maturity of the known source rocks developed in the Atlantic, and diamantane were affected by biodegradation, the the concentration of diamondoids and the carbon isotope of mentioned ratios were not significantly affected by any dif- condensate, mismatching to that of the known source rock, are ferences in maturity. By way of increasing biodegradation, the similar to condensate generated by the Upper Jurassic ratio of alkyladamantane/adamantane increases, whereas the Smackover Formation of the US Gulf Coast, a laminated lime ratio of alkyldiamantane/diamantane stays constant [45]. mudstone with shale facies. Sassen et al. [56] suggested that Weietal.[46] found that the concentration of adamantane the oil originated from the Smackover laminated lime noticeably decreases whenever the biodegradation level has mudstone source rocks that were deposited during the Jurassic reached 3 e 4, whereas the concentration of diamantane and rifting of the Pangaean supercontinent. Using MDI, Duan et al. triadamantane only show a slight change when biodegradation [57] proposed that two oil charging direction exited in the has reached level 8. In oil samples, the diamondoids are Lower Ordovician oil from Tahe Oilfield. One is from the resistant to biodegrade like the C19eC24 tricyclic terpanes, south to north and the maturity is relatively lower, probably gammacerane, oleananes, diasterane, Ts, Tm C29 Ts, and 25- representing the earlier petroleum migration, and the other is norhopane. from the east to west with the maturity being relatively higher, Due to the strong resistance to biodegradation, the probably representing the latter petroleum migration from 9 impression of diamondoids can be to correlate the biodegra- blocks of east to 2 blocks of the west. Using a series param- dation oil and non-biodegradation oil, as well as the black oil eters calculated by the diamondoids eluting earlier versus to and condensates [31]. that of the eluting later in the chromatograph, the migration fractionation of the oil from the Dawaqi Oilfield. Tarim Basin, 3.5. TSR China, was analyzed by Ren et al. [58]. Generally speaking, the oils mainly show the vertical migration process, but in the Thermochemical sulfate reduction (TSR) is an organic- zones developing a deep large fault, the parameters showed a inorganic effect occurring in the deep hot carbonate reser- low-value zone. Adjacent, the migration direction of the oil in voir in which the organic matter from petroleum is oxidized by the Dawanqi Oilfield is from south to north [58]. sulfate (anhydrite) from the reservoir rocks which in turn are transformed to hydrogen sulfide, carbon dioxide, mercaptan, 3.7. Gas washing and phase fractionation elemental sulfur, and pyrobitumen [47e50]. Many reservoirs in the world have recorded their corresponding TSR. In a Great difference lies in the solubility of different compo- handful of deep hot natural reservoir, TSR can form significant nents in the natural gas when oil has suffered gas-washing. n- sour H2S gas, in which its content can reach as much as 10%e alkanes of light carbons are likely to solute in the dry gas and 80%. As a result, abundant concentration of diamondoids and escape from the original oil reservoir accompanying migration compounds containing sulfur, such as thiadiamondoids and with natural gas, this reduces the light component of the adamantanethiols can be detected in the oils and condensates original reservoir. In a natural gas pool-forming of Kela-2 altered by TSR [51e53]. In TSR altered oils, the concentration Gasfield, Tarim Basin, China, Zhang et al. [59] suggested of the adamantanethiols ranges from 1 to 100 ppm, whereas that gas washing reduces the n-alkane in the oil, this phe- the concentration of thiadiamondoids changes greatly, ranging nomenon greatly enriches the diamondoids and polycyclic from several ppm to several thousand ppm. Such compounds, aromatic hydrocarbons whose solubility are low in the natural especially 2-thiaadamantanes, can be used as molecular in- gas. The content of light aromatic hydrocarbons would also dicators for the occurrence of TSR, and to predict the sour gas increase resulting in an increase in aromaticity and a reduction content in the petroleum exploration and development [54]. in paraffinity. Gas-washing can change the relative mass percentage of the diamondoids [59].Wuetal.[60] proposed that 3.6. Migration the oils that suffered gas washing is characterized by 1- methyladamantane enrichment and depletion of 1,3- According to the pool-forming theory of reservoir dimethyladamantane, 1,4-dimethyladamantane (trans), 1,4- geochemistry, the petroleum migration/filling history has a dimethyladamantane (cis), 3-methyl-1-ethyladamantane, and relatively long geological process, in which the latter oils 1,2-dimethyladamantane. having higher maturity drive the former oils with lower maturity in the form of a wave front, thus, keeping migration/ 3.8. Source identification of the spilled oil of the marine filling forward until the filling process finished. Acertaining change in the maturity of oils in the reservoir internal and In the progressive development of the offshore petroleum heterogeneity in the chemical composition and physical exploration and transportation, oil spill often occurs and make property would be produced [55]. serious damages in the marine ecology. In the incident of spill Sassen et al. [56] detected the abundance of diamondoids accidents, spill identification in time is the important base for (4742 ppm) from condensate oils with heavy carbon isotope ascertaining the accident responsible party, settling suitable (23.7‰~24.5‰) from the Upper Jurassic and Lower arrangement, and evaluating the accident results [61,62]. Cretaceous reservoirs in the Hudson Canyon area of the Wang et al. [63] used concentration of diamondoids and 262 A. Ma / Journal of Natural Gas Geoscience 1 (2016) 257e265 diagnosing ratio to distinguish the spilled oil and refined oil synthesize higher diamondoids up to now; the only highest product. Zhang et al. [64] used semi-quantitation methods of diamondoids synthesized is the tetramantanes. Meanwhile, the diamondoids impressions to screen for large sets of samples fluid from deep oil reservoir contains tetramantanes, pentam- quickly and reduce the zone of the questionable source of the antanes, and hexamantanes [4,6]. Moreover, the oils from the spill. Based on the characteristic ratios of diamondoids in the carbonate strata have Lewis acids that are either absent or oil, Yang et al. [65] realized the rapid separation of the oils present minor, causing the origin of diamondoids to be with the evident dissimilarity using principle component complex. analysis method (PCA). 4.2. The process of generation, enrichment, and 4. The origin of diamondoids in oils destruction of diamondoids

4.1. Complex analyzation of diamondoids' oil origin Recent research found that during maturation evolution, diamondoids undergoes generation, enrichment, and destruc- Although it has been over eighty years since diamondoids tion. Through analyzing coals and rocks from natural evolution were discovered in oils, its origin is still unclear. It is generally with different maturity and different lithology, Wei et al. [74] accepted that diamondoid is the product of polycyclic hydro- suggested three main phases of diamondoid life: diamondoid carbon polymerization catalyzed by strong Lewis acid under generation (Ro < 1.1%), enrichment (1.1% < Ro < 4.0%), and high-temperature thermal condition [7]. Pyrolysis of high destruction (Ro > 4.0%) (Fig. 6). Pyrolysis experiment on the molecular mass paraffin and cycloparaffin fractions (bp above diamantane showed that diamantane stays stable up to 550 C. 350 C) catalyzed by Bronsted and Lewis acids at 190e286 C At 600 C, the pyrolysis of diamantane yield 15% aromatics temperature yield newly formed adamantane and diamantane and 83% gas and other products (e.g. pyrobitumen). However, [66e69]. The distribution of C10eC13 adamantanes in crude only a small amount of diamantanes remains. Based on the oils correlates well with that of the products of thermal carbon isotope analyses, Schoell et al. [39] proposed that some cracking of high molecular mass saturated fraction. Pyrolysis diamondoids are accountable for cracking at high- of non-hydrocarbon and asphaltenes fractions of oil generated temperatures. both the adamantane and diamantane. The distribution of adamantanes in oils is the same as that of the high molecular 4.3. Possible origin of diamondoids in oils mass saturated fraction (>350 C), nonhydrocarbon, and asphaltenes, suggesting that low-molecular-mass petroleum Based on the results of the closed system of golden tube adamantanes, high-molecular-mass saturated fraction, and pyrolysis experiments of oils, Fang et al. [37] suggested that non-hydrocarbon, asphaltenes contain the adamantane moiety the diamondoids in the oil have three different origins: (1) Free in their structure. In addition, the distribution of diamantanes diamondoids that probably formed during the generation of the of the pyrolysis of non-hydrocarbon and asphaltenes fraction oils, this component is in the Tarim oil, which can be deter- is the same as that of the pyrolysis of high molecular mass mined in the original oil, comprises 359 mg/g of adamantanes saturated fraction differing to that of the oil. and 79.8 mg/g of diamantanes. (2) Diamondoids preserved in The result of pyrolysis experiment showed that lower dia- oil and in other forms. Details on the structures of this mondoids can be formed by immature sediments, peat, component are not clear, however, they are released or trans- kerogen, oil, and other components including saturated frac- formed at relatively low level of maturity. (3) Diamondoids tion, polar fraction, and n-alkane compounds, such as C16,C19, formed during oil cracking, a certain proportion of diamond- C22,C34,C36, and b-ionone. b-ionone can form diamondoids oids are present in the oils, the formation of abundant through acted with activated carbon. b-ionone with the alkane cyclohexane hydrocarbon skeleton, occurring in the sediments, can form tricyclic adamantane structure through 1,3- dehydrocyclisation reaction. In addition, the model compound of adamantane heated with the activated carbon in a closed system, hydrogen exchange, demethylation, methyl transfer, and isomerization reactions were observed [70]. Dehydrogenation, cyclization, and aromatization reaction of n- alkane on the surface of activated carbon through hydrogen exchange were well documented in the study [71,72]. It is relatively easy to synthesize adamantanes from other hydrocarbons in the laboratory. Burn et al. [73] made a higher member of diamondoid family by adding two new rings with four carbon atoms (single homologation) or a second higher member by adding four new rings utilizing eight carbon atoms (double homologation). Using this method, Burn et al. [73] Fig. 6. Relationship between the concentration of 3-þ4-methyl diamantanes synthesized anti-tetramantane successfully. It is difficult to and the Ro from coals and source rock extracts (after Ref. [74]). A. Ma / Journal of Natural Gas Geoscience 1 (2016) 257e265 263 diamondoids occurs at relatively high levels of maturity. [4] R. Lin, Z.A. Wilk, Natural occurrence of tetramantane(C22H28), pen- Earlier formed free adamantanes and diamantanes account for tamantane(C26H32) and hexamantane(C30H36) in a deep petroleum e 29.5% and 36.2% of the maximum yields of adamantanes and reservoir, Fuel 74 (10) (1995) 1512 1521. [5] J.E.P. Dahl, J.M. Moldowan, T.M. Peakman, J.C. Clardy, E. Lobkovsky, diamantanes, respectively. Late-formed adamantanes and M.M. Olmstead, P.W. May, T.J. Davis, J.W. Steeds, K.E. Peters, diamantanes are predominantly generated within the maturity A. Pepper, A. Ekuan, R.M.K. Carlson, Isolation and structural proof of range 1.0%e2.3% and 1.6%e2.5%, respectively, and they are the large diamond molecule, cyclohexamantane (C26H30), Angew. Chem. dominantly derived from the saturated fraction, which ac- Int. Ed. 42 (18) (2003) 2040e2044. counts for 58%e72% of total adamantanes and 25%e62% of [6] J.E.P. Dahl, S.G. Liu, R.M.K. Carlson, Isolation and structure of higher diamondoids, nanometer-sized diamond molecules, Science 299 (11) total diamantanes generated in this stage. The next most (2003) 96e99. abundant sources of late-formed adamantanes and dia- [7] W.S. Wingert, GC-MS analysis of diamondoid hydrocarbons in smack- mantanes are the resin and aromatic fractions, whereas con- over petroleum, Fuel 71 (1) (1992) 37e43. tributions from the asphaltene fraction are negligible. [8] Hong Zhao, Zhansheng Wang, Junzhang Zhu, Qi Chen, Peirong Wang, MID/GC/MS analysis and geological significance of diamondoid hydrocarbons in oils and extract of source rock, J. Chin. Mass Spectrom. 5. Conclusions Soc. 15 (4) (1994) 43e48. [9] Z. Wei, J.M. Moldowan, A. Paytan, Diamondoids and molecular bio- (1) The evolution of diamondoids from different types of markers generated from modern sediments in the absence and presence organic matters should be carried out. The evolution of of minerals during hydrous pyrolysis, Org. Geochem. 37 (8) (2006) e coal diamondoids and mudstone diamondoids were 891 911. [10] Qianyong Liang, Yongqiang Xiong, Chenchen Fang, Yun Li, Comparison researched in the reference despite lacking the evolution of two methods for determination of diamondoids in crude oils, Geo- comparison among different sediment environments and chimica 41 (5) (2012) 433e441. different types of organic matters. Researching on the [11] Q.Y. Liang, Y.Q. Xiong, C.C. Fang, Y. Li, Quantitative analysis of dia- generation, enrichment and destruction of diamondoid mondoids in crude oils using gas chromatography-triple quadrupole mass e from different organic matters would be meaningful in spectrometry, Org. Geochem. 43 (1) (2012) 83 91. [12] R. Silva, R.S.F. Silva, E.V.R. Castro, K.E. Peters, D.A. Azevedo, understanding the generation mechanism. Extended diamondoid assessment in crude oil using comprehensive two- (2) The evolution of diamondoids from different oil types dimensional gas chromatography coupled to time-of-flight mass spec- should be carried out. The generation and concentrations trometry, Fuel 112 (5) (2013) 125e133. of diamondoids from a single oil type and four compo- [13] G. Wang, S. Shi, P. Wang, T.G. Wang, Analysis of diamondoids in crude nents of oil (i.e, saturated, aromatic, non-hydrocarbon, and oils using comprehensive two-dimensional gas chromatography/time-off- flight mass spectrometry, Fuel 107 (5) (2013) 706e714. asphaltene fractions) were studied in the reference, lacking [14] Anlai Ma, Zhijun Jin, Cuishan Zhu, Shoutao Peng, Weibiao Zhang, evolution comparison between the terrestrial oils (such as Quantitative analysis on absolute concertration of diamondoids in oils hypersaline, brackish, and freshwater environment) and from Tahe Oilfield, Acta Pet. Sin. 30 (2) (2009) 214e218. marine oils. Researching on the evolution and baseline of [15] D.A. Azevedo, J.B. Tamanqueira, J.C.M. Dias, A.P.B. Carmoa, ç diamondoids of different types of oils would be beneficial L. Landaub, F.T.T. Gon alves, Multivariate statistical analysis of diamondoid and biomarker data from Brazilian basin oil samples, Fuel 87 to understanding the depth limits of the deep oil reservoir. (10e11) (2008) 2122e2130. [16] M.V. Springer, D.F. Garcia, F.T.T. Goncalves, L. Landau, D.A. Azevedo, Diamondoid and biomarker characterization of oils from Foundation item Llanos Orientales Basin, Colombia, Org. Geochem. 41 (9) (2010) 1013e1018. [17] L. Huang, S.C. Zhang, H.T. Wang, X.F. Fu, W.L. Zhang, Y.R. Xu, Supported by China State Fundamental Research Program C.Y. Wei, A novel method for isolation of diamondoids from crude oils (2012CB214800, 2005CB422108); Scientific and Technical for compound-specific isotope analysis, Org. Geochem. 42 (5) (2011) Research Project of SINOPEC (P07021); China National 566e571. Scientific & Technical Major Project (2011ZX05005, [18] J. Chen, J. Fu, G. Sheng, D. Liu, J. Zhang, Diamondoid hydrocarbon 2008ZX05005). ratios: novel maturity indices for highly mature crude oil, Org. Geochem. 25 (3e4) (1996) 179e190. [19] Junjong Chen, Jiamo Fu, Guoying Shen, The structure characterization Conflict of interest and geochemical signification of diamondoid hydrocarbons, Chin. Sci. Bull. 41 (6) (1996) 524e527. The author declares no conflict of interest. [20] Junhong Chen, Jiamo Fu, Guoying Shen, The research in the distribution characteristic of diamondoid hydrocarbons in crude oils, Adv. Nat. Sci. 7 (3) (1997) 363e367. References [21] Luofu Liu, Chunjiang Wang, Jianfa Chen, The distribution and significance of diamondoid in Ordovician oil from Dagang Oilfield, Adv. Earth [1] S. Landa, V. Machacek, Adamantane, a new hydrocarbon extracted from Sci. 12 (6) (1997) 584e586. petroleum, Collect. Czech. Chem. Commun. 5 (1) (1933) 1e5. [22] Sumei Li, Xiongqi Pang, Haijun Yang, Qiaoyuan Gu, Yujiang Li, [2] G. Ali Mansoori, P.L.B. de Araujo, E.S. de Araujo, Diamondoid Mole- Geochemical characteristics and implication of high thermal maturity cules with Applications in Biomedicine, Materials Science, Nanotech- oils in Tazhong-I faulted slope break zone, Oil Gas Geol. 29 (2) (2008) nology & Petroleum Science, World Scientific Publishing Co Pte. Ltd., 210e216. Singapore, 2012, pp. pp.1e424. [23] S. Zhang, H. Huang, Z. Xiao, D. Liang, Geochemistry of Paleozoic [3] M. Schoell, R.M.K. Carlson, Diamondoids and oil are not forever, Nature marine petroleum from the Tarim Basin, NW China: Part 2. Maturity 399 (5) (1999) 15e16. assessment, Org. Geochem. 36 (8) (2005) 1215e1225. 264 A. Ma / Journal of Natural Gas Geoscience 1 (2016) 257e265

[24] Xuejun Zhang, Xingyou Xu, Pingan Peng, Maturity assessment of light [45] K. Grice, R. Alexander, R.I. Kagi, Diamondoid hydrocarbon ratios as oils in Chepaizi Uplift and re-understanding of its source rock, Geo- indicators of biodegradation in Australian crude oils, Org. Geochem. 31 chimica 42 (2) (2013) 180e187. (1) (2000) 67e73. [25] Zhilin Chen, Xuan Liu, Honhrui Jin, Zhong Wang, Linye Zhang, Study [46] Z. Wei, J.M. Moldowan, K.E. Peter, Y. Wang, W. Xiang, The abundance on condensate maturity and type using methyl diamantine parameter, and distribution of diamondoids in biodegraded oils from the San Joaquin Acta Sedimentol. Sin. 26 (4) (2008) 705e708. Valley: implications for biodegradation of diamondoids in petroleum [26] Xianzheng Zhao, Fengming Jin, Jingkui Mi, Zhouqi Cui, Jimao Wang, reservoirs, Org. Geochem. 38 (11) (2007) 1910e1926. Hui Li, Kun He, Han Ding, Charasteristics of diamondoids and light [47] R.H. Worden, P.C. Smalley, N.H. Oxtoby, Gas souring by thermochem- hydrocarbons from Niudong Field and implication for oil/gas origin, Nat. ical sulfate reduction at 140C, AAPG Bull. 79 (5) (1995) 854e863. Gas. Geosci. 25 (9) (2014) 1395e1402. [48] H.G. Machel, H.R. Krouse, R. Sassen, Products and distinguishing [27] Jian Wang, Quan Wang, Yulei Shi, Xuefeng Ma, Xuemei Zhong, criteria of bacteria and thermochemical sulfate reduction, Appl. Geo- Xiangyang Li, Feiyu Wang, The cause of ultra-seated oil and gas of chem. 10 (4) (1995) 373e389. Paleogene in Baxian Sag, Nat. Gas. Geosci. 26 (1) (2015) 21e27. [49] Guangyou Zhu, Shuichang Zhang, Yingbo Liang, Jinxing Dai, Jian Li, [28] Jianping Bao, Xingyu Liang, Cuishan Zhu, Xingchao Jiang, Diamondoid Isotopic evidence of TSR origin for natural gas bearing high H2S con- hydrocarbons and their geochemical significances in condensate from the tents within the Feixianguan formation of the northeastern Sichuan Zhujiadun gas reservoir in the Yancheng Sag, Nat. Gas. Geosci. 26 (3) Basin, Southwestern China, Sci. China Earth Sci. 48 (11) (2005) (2015) 505e512. 1960e1971. [29] Wenxiang He, Peirong Wang, Xianzhuang Pan, Yijiang Tang, The study [50] Z. Wei, P. Mankiewicz, C. Walters, K. Qian, N.T. Phan, M.E. Madincea, of maturity of crude oil in Yingqiong Basin, Nat. Gas. Geosci. 15 (4) P.T.H. Nguyen, Natural occurrence of higher thiadiamondoids and dia- (2004) 387e390. mondoidthiols in a deep petroleum reservoir in the Mobile Bay gas fields, [30] Ning Fu, Youchuan Li, Diamondoid hydrocarbon ratios as indicators of Org. Geochem. 42 (2) (2011) 121e133. maturity in natural gas, Acta Sedimentol. Sin. 19 (1) (2001) 145e149. [51] Z. Wei, C.C. Walters, J.M. Moldowan, P.J. Mankiewicz, R.J. Pottorf, [31] Xiaowen Guo, Sheng He, Honghan Chen, Discussion and application of Y. Xiao, W. Maze, P.T.H. Nguyen, M.E. Madincea, N.T. Phan, the maturity indicators of methyl double diamantane hydrocarbons, Geol. K.E. Peters, Thiadiamondoids as proxies for the extent of thermochem- Sci. Technol. Inf. 26 (1) (2006) 71e76. ical sulfate reduction, Org. Geochem. 44 (1) (2012) 53e70. [32] L.K. Schulz, A. Wilhelms, E. Rein, A.S. Steen, Application of dia- [52] Naihuang Jiang, Guangyou Zhu, Shuizhang Zhang, Zhengjun Wang, mondoids to distinguish source facies, Org. Geochem. 32 (3) (2001) Detection of 2-thiaadamantanes in the oil from well TZ-83 in Tarim 365e375. Basin and its geological implication, Chin. Sci. Bull. 53 (3) (2008) [33] Z. Wei, J.M. Moldowan, S. Zhang, R. Hill, D.M. Jarvie, H. Wang, 396e401. F. Song, F. Fago, Diamondoid hydrocarbons as a molecular proxy for [53] Guangli Wang, Ningxi Li, Bo Gao, Xianqing Li, Baosheng Shi, thermal maturity and oil cracking: geochemical models from hydrous Tieguan Wang, Thermochemical sulfate reduction in fossil Ordovician pyrolysis, Org. Geochem. 38 (3) (2007) 227e249. deposits of the Majiang area:Evidence from a molecular-marker inves- [34] J. Li, P. Philp, M. Cui, Methyl diamantane index(MDI) as a maturity tigation, Chin. Sci. Bull. 58 (33) (2013) 3450e3457. parameter for Lower Palaeozoic carbonate rocks at high maturety and [54] S. Hanin, P. Adam, I. Kowalewski, A. Huc, B. Carpentier, P. Albrecht, overmaturity, Org. Geochem. 31 (4) (2000) 267e272. Bridgehead alkylated 2-thiaadamantanes: novel markers for sulfurisation [35] Jinggui Li, Mingzhong Cui, Qian Zhang, A discussion about diamantes processes occurring under high thermal stress in deep petroleum reser- ratios as maturity indicators of Lower Paleozoic carbonate source voirs, Chem. Commun. 16 (7) (2002) 1750e1751. rocks at high and over mature stage, Pet. Explor. Dev. 25 (2) (1998) [55] W.A. England, The organic geochemistry of petroleum reservoir, Org. 83e85. Geochem. 16 (1e3) (1990) 419e425. [36] C.C. Fang, Y.Q. Xiong, Q.Y. Liang, Y. Li, Variation in abundance and [56] R. Sassen, P. Post, Enrichment of diamondoids and 13C in condensate distribution of diamondoids during oil cracking, Org. Geochem. 47 (1) from Hudson Canyon, US Atlantic, Org. Geochem. 39 (7) (2008) (2012) 1e8. 147e151. [37] C.C. Fang, Y.Q. Xiong, Y. Li, Y. Chen, J.Z. Liu, H.Z. Zhang, [57] Yi Duan, Chuanyuan Wang, Zhaoyang Zheng, Baoxiang Wu, Distribu- T.A. Adeosu, P.A. Peng, The origin and evolution of adamatanes and tion of double diamantine hydrocarbons in crude oils from Tahe Oilfield diamanteanes in petroleum, Geochim. Cosmochim. Acta 120 (11) (2013) and its implication for oil and gas migration, Nat. Gas. Geosci. 18 (5) 109e120. (2007) 693e696. [38] Chenchen Fang, Wei Wu, Dan Liu, Jinzhong Liu, Evolution character- [58] Xukang Ren, Guanghui Huang, Zhongyao Xiao, Min Zhao, istics and application of diamondoids in coal measures, Nat. Gas. Geosci. Baoshou Zhang, Hongxing Wei, Zhiyuan Ma, Application of diamond- 26 (1) (2015) 110e117. oids to hydrocarbon migration of Dawanqi oilfield, Tarim Basin, China [39] J.E. Dahl, J.M. Moldowan, K.E. Peter, G.E. Claypool, M.A. Rooney, Pet. Explor. 17 (2) (2012) 27e31. G.E. Michael, M.R. Mello, M.L. Kohnen, Diamondoid hydrocarbons as [59] Bin Zhang, Ling Huang, Ying Wu, Hui Wang, Jie Cui, Quantitative indicators of natural oil cracking, Nature 399 (5) (1999) 54e56. evaluation of crude oil composition changes by strong gas washing: a [40] S. Zhang, J. Su, X. Wang, G. Zhu, H. Yang, K. Liu, Z. Li, Geochemistry case study of natural gas pool in Kuqa Depression, Earth Sci. Front. 17 of Paleozoic marine petroleum from the Tarim Basin, NW Chian: Part 3. (4) (2010) 270e279. Thermal cracking of liquid hydrocarbons and gas washing as the major [60] Nan Wu, Zhongxian Cai, Response of phase fractionation of diamantine mechanisms for deep gas condensate accumulations, Org. Geochem. 42 compounds in crude oil in Lunnan uplift, Fault-Block Oil Gas Field 19 (11) (2011) 1394e1410. (4) (2012) 458e461. [41] J.M. Moldowan, J.E. Dahl, D. Zinniker, S.M. Barbanti, Underutilized [61] S.A. Stout, G.S. Douglas, Diamondoid hydrocarbons-Application in the advanced geochemical technologies for oil and gas exploration and chemical fingerprinting of natural gas condensate and gasoline, Environ. production-1. The diamondoids, J. Pet. Sci. Eng. 126 (1) (2015) 87e96. Forensics 5 (4) (2004) 225e235. [42] G.N. Gordadze, Geochemistry of cage hydrocarbon, Pet. Chem. 48 (4) [62] C. Yang, Z.D. Wang, B.P. Hollebone, X. Peng, M. Fingas, M. Landriault, (2008) 241e253. GC/MS quantitation of diamondoid compounds in crude oils and pe- [43] K.E. Peter, C.C. Walters, J.M. Moldowan, The Biomarkers Guide Vol- troleum, Environ. Forensics 7 (4) (2006) 377e390. ume 2: Biomarkers and Isotopes in Petroleum Exploration and Earth [63] Z. Wang, C. Yang, B. Hollebone, M. Fingas, Forensic fingerprinting of History, Cambrideg University Press, Cambrideg, 2005. diamondoids for correlation and differentiation of spilled oil and petro- [44] J.A. Williams, M. Bjoroy, D.L. Dolcater, J.C. Winters, Biodegradation in leum products, Environ. Sci. Technol. 40 (18) (2006) 5636e5646. South Texas Eocene oilsefeets on aromatics and biomarkers, Org. Geo- [64] Kuiying Zhang, Baijun Yang, Li Zhang, Jiaye Zang, Tianrong Zhan, chem. 10 (3e4) (1986) 451e461. Xiaoru Wang, F.S.C. Lee, Crude oil identification based on diamondoid A. Ma / Journal of Natural Gas Geoscience 1 (2016) 257e265 265

ﬁngerprinting concentrations by semiquantitative method, Chin. J. Anal. [70] L. Berwick, R. Alexander, K. Pierce, Formation and reactions of alkyl Chem. 39 (4) (2011) 496e500. adamantanes in sediments: carbon surface reactions, Org. Geochem. 42 [65] Baijuan Yang, Wei Hou, Xiaoru Wang, Crude oil identiﬁcation using (7) (2011) 752e761. principle component analysis based on characteristic ratios of dia- [71] R. Alexander, D. Dawson, K. Pierce, A. Murray, Carbon catalysed mondoid compounds, Mar. Sci. 37 (2) (2013) 84e88. hydrogen exchange in petroleum source rocks, Org. Geochem. 40 (9) [66] G.N. Gordadze, M.V. Giruts, Synthesis of adamantine and diamantine (2009) 951e959. hydrocarbons by high-temperature cracking of high n-alkanes, Pet. [72] R. Alexander, L. Berwick, K. Pierce, Single carbon surface reaction of 1- Chem. 48 (6) (2008) 414e419. octadecene and 2,3,6-trimethylphenol on activated carbon: implications [67] G.B. Gordadze, M.V. Ciruts, Synthesis of adamantine and diamantine for methane formation in sediments, Org. Geochem. 42 (5) (2011) hydrocarbons by high temperature cracking of high n-alkanes, Pet. 540e547. Geochem. 48 (5) (2008) 241e253. [73] W. Burns, M.A. McKervery, R.B. Thomas, J.J. Rooney, A new approach [68] M.V. Giruts, G.V. Rusinova, G.N. Gordadze, Generation of adamantanes to construction of diamondoid hydrocarbons, synthesis of anti-tetra- and diamantanes by thermal cracking of high-molecular-mass saturated mantane, J. Am. Chem. Assoc. 100 (3) (1978) 906e911. fractions of crude oils of different genotypes, Pet. Chem. 46 (4) (2006) [74] Z. Wei, J.M. Moldowan, D.M. Jarvie, R. Hill, The fate of diamondoids in 225e236. coals and sedimentary rocks, Geology 34 (12) (2006) 1013e1016. [69] M.V. Giruts, G.N. Gordadze, Generation of adamantanes and diamantanes by thermal cracking of polar components of crudes oils of different genotypes, Pet. Chem. 47 (1) (2007) 12e22.