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Published in the Indian Journal of Petroleum Geology, 17(2), 11-70, 2010 Polymerisation Theory – Formation of hydrocarbons in sedimentary strata (hydrates, clays, sandstones, carbonates, evaporites, volcanoclastics) from CH 4 and CO2: Part II: Formation and Interpretation of Stage 1 to Stage 5 Oils D.D.J. Antia, DCA Consultants Ltd., Haughend Farm, Bridge of Earn Rd., Dunning. Perthshire, PH2 9BX, UK.
[email protected] Abstract Experimental substoichiometric thermal degradation (50 – 80o C; 0.1 MPa) of angiosperm organic matter established the formation of four products, kerogen, gas, carbonyls, and microcrystalline paraffins (oil). Prolonged heating degrades the carbonyls to gas. The molar thermogenic oil distribution is positively skewed with an average melting point of >40o C. A new model for low temperature stoichiometric thermogenic degradation of organic matter is proposed. This model is a variant of the Diebold model. The principal products from the low temperature thermal degradation of organic matter are kerogen (30 wt %) + gas (CO2 + CO + CH4 + H2O + H2 + CH4 (>20 - >80 wt%)) + carbonyls + minor quantities of paraffinic oil. Oil extracts from Recent to Cretaceous sediments in DSDP Sites 467, 469, 571, 530A, 585, 586, 603B are used to develop a model for the formation of C2 – C8 hydrocarbons (aromatics, i-alkanes, alkylesters, and cycloalkanes) from CH4 and CO2. The impact of phillipsite and chabazite zeolites on oil formation in Cretaceous claystones and volcanoclastic sandstones is demonstrated. A methodology, which allows progressive deconstruction (or reverse engineering) of Stage 4/5 oil into its original Stage 2 or Stage 3 oil composition is defined. This deconstruction analysis has been used to derive the composition of the Stage 2 oil. It can therefore identify (i) the composition of the original Stage 1 oil involved in polyaddition (ii) the changes in an oil following formation of Stage 2 oil. Fluids and gases associated with oils and oil fluid inclusions in halite, anhydrite carbonate sequences in Tarim Basin and Sichuan (China) and halite and anhydrite (Zechstein, Permian, Poland) have been examined. The Stage 4/5 oils have been formed by extensive polymerisation by CO2/CH4 within the fluid inclusions. The associated pore fluid composition contains ions varying from Na-K-Mg-Cl-SO4 to Na-K-Mg-Ca-Cl. The reverse engineering methodology has been applied to the analysis of palaeo-oil fluid inclusions in quartz, and oil samples from the McKee oil/gas field (McKee Formation (Eocene) Taranaki Basin, New Zealand). This analysis has identified that 77% of the original gas (CH4) charge to the field has been converted within the sandstone reservoir to oil and that >97% of the oil in the field is derived from the in situ polymerisation of CH4. The typical oil/gas field in the Taranaki Basin is considered to have converted >35% of its gas charge to oil within the reservoir. The reverse engineering has been used to demonstrate that the distinctive C25 – C33 odd even ratios seen in many oils (e.g. Indian Ocean, Eastern Pacific Ocean, Blakes Ridge Hydrate Field (Western Atlantic Ocean)) are an artefact of polymerisation. The even numbered alkanes result from CH4 or CO2 polymerisation of Stage 2 oil and the odd-numbered alkanes result from polyaddition of Stage 1 oil with Stage 2 oil. This polyaddition is facilitated by CO2 or CH4. Keywords Polymerisation, oil, zeolite, phillipsite, chabazite, montmorillonite, smectite, chlorite, halite, anhydrite Oil, Hydrate, and Gas Fields Analysed Blakes Ridge (USA), Cascadia (USA), Cheal (New Zealand), Dukouhe (China), Fuchengzhai (China), Gaofengchang (China), Huanglongchuang (China), Jiannan (China), Kapuni (New Zealand), Kauri (New Zealand), Kupe (New Zealand), Luojianzhai (China), Longhuichang (China), Maari (New Zealand), Mangahewa (New Zealand), Maui (New Zealand), McKee (New Zealand), Ngatoro (New Zealand), North Qili (China), Pateke (New Zealand), Pohokura (New Zealand), Puguang (China), Radnor (New Zealand), Rimu (New Zealand), Surrey (New Zealand), Tahe (China), Taiki (New Zealand), Tieshanpo (China), Tieshan (China), Turangi (New Zealand), Waihapa (New Zealand), Windsor (New Zealand).
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Published in the Indian Journal of Petroleum Geology, 17(2), 11-70, 2010 1.0 Introduction The theory of catalytic methane and carbon dioxide polymerisation to produce hydrocarbons has been documented by Antia (2008; 2009) and in Part I of this study. These studies have established a five stage sequence for oil formation by polymerisation from methane and carbon dioxide (Part I, Fig. 1). The initial product is Stage 1 oil (C2 – C8). Stage 1 oil forms as a continuous homologous series of nalkanes in the range C2 to C8, and may contain one or more polyaddition peaks in the range C 4 to C8. Subsequent polyaddition of these C2 to C8 peaks produces a discontinuous homologous series (Stage 2 oil (C10 – C21)). Subsequent polyaddition is focussed in the (C22 – C40) region to produce a discontinuous series of alkanes (Stage 3 oil). Polymerisation by CH4 and CO2 of the discontinuous polyaddition products results in the formation of a continuous series of n-alkanes. The initial polymerisation by CH4 and CO2 produces a continuous series of n-alkanes, which are multimodal with infill particularly between C 10 – C40 to form Stage 4 oil. Subsequent polymerisation in the C8 to C40 range results in the formation of a unimodal oil distribution (Stage 5 oil). The study is organised into eight sections:1. 2. 3. 4. 5. 6. 7.
8.
Identification of thermogenic oil, Relationship between “in situ” and migrated (reservoired oils) oils Formation of Stage 1 oil, particularly i-alkanes, aromatics and cycloalkanes. The formation of n-alkanes and alkenes was addressed in Part I. Formation of Stage 2 oil from Stage 1 oil. This analysis focuses on the formation of n-alkanes and alkyl-esters Formation and interpretation of Stage 3 oil from Stage 1 oil and/or Stage 2 Oil Formation of Stage 4/5 oil from Stage 2/3 oil and the reverse engineering of Stage 4/5 oil to determine the composition of its original Stage 2/3 oil. Case Study (McKee Field) to illustrate how polymerisation theory can be used to identify the charging history of a field. The study uses reverse engineering of Stage 5 oil from fluid inclusions and the oil field in order to elucidate the volumetric charging history of the field. Formation of Stage 3 oil n-alkane molar abundance peaks with particular emphasis on understanding how odd:even ratios form in C23 to C40 n-alkanes.
Appendix A contains information relating to molecule size. All the oils examined in this study have previously been interpreted as being of thermogenic origin. This study provides an alternative interpretation based on polymerisation theory. 2.0 Thermogenic Oils The traditional formational explanation for oil is that it is a thermal degradation product from the low temperature (0 – 150o C) heating of kerogen (e.g. Waples, 1984; Sahoo and Gogoi, 2007). While there is no doubt that the heating of organic matter yields oil, it also produces a variety of carbonyls (acids, aldehydes, ring structures, alcohols, etc.) and gas. The majority of the product is gas and non-oil organic chemicals. Oil (alkanes, aromatics and cycloalkanes) typically forms less than 5% of the total product. 2.1 Artificial Production of Low Temperature Thermogenic Oil A series of experiments were undertaken “in house” using a vertical internally heated reactor where a mixture of organic matter (lignin, cellulose, hemi-cellulose derived from angiosperms) was heated in a substoichiometric reducing environment (at 80o C and 0.1 MPa) containing CO2, CO, H2, CH4 and CxHxOy. The experimental results indicated:i) Oil (see Part I for composition) forms only a small part of the overall product (Figure 1a). The majority of the organic matter is converted to gas (Figure 1b) or organic liquids (Figure 2a) and a residual kerogen or char (heating time = 4 – 12 hrs). Additional gas, volatiles and oil can be released from the kerogen, or char, by heating the kerogen, or char, at elevated temperatures.
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Published in the Indian Journal of Petroleum Geology, 17(2), 11-70, 2010 ii) The oil is characterised by a leptokurtosic, positively skewed distribution of n-alkanes where the largest carbon number, n, (or n-1) is the most abundant species (e.g. Figure 2b, 3a, 3b). The oil has a high melting point (Figure 3a) and boiling point (Figure 3b). The molar abundances indicate that the modal n-alkane is n-C27H58. Under most low temperature reservoir conditions containing polymerised oil (i.e. 0.5 and 1C2H4 :1 C3H6 (Figure 8b) Cyclic hydrocarbons can be formed in Mg-smectite and Fe-smectite (Figure 7, 8)
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Published in the Indian Journal of Petroleum Geology, 17(2), 11-70, 2010 (iii)
Ethene is preferentially used in the formation of cyclic hydrocarbons (Figure 8b) when zeolites are present. The lower ethene:propene ratio in zeolitic sediments is interpreted as indicating that zeolites catalyse the formation of the cyclic hydrocarbon from ethene (Figure 8b).
The principal cyclic hydrocarbons are interpreted as forming from alkenes and alkynes as:(a) Benzene 3Me-(CH)2 +3H+ = 3Me-H+ + C6H6 3Me-(CH2)2 = 3Me-H+ + C6H6 +3H+
ΔHo = ΔHo =
-635.0 -107.6
(4.1) (4.2)
(b) Cyclobutane (furan) 2Me-(CH2)2 +2H+= 2Me-H+ + C4H8
ΔHo =
-100.7
(4.3)
(c) Cyclopentane 5Me-(CH2)2 + 5H+= 5Me-H+ + 2C5H10
ΔHo =
-237.6
(4.4)
(d) Cyclohexane 6Me-(CH2)2 + 6H+= 6Me-H+ + 2C6H12
ΔHo =
-312.9
(4.5)
(e) Cycloheptane 7Me-(CH2)2 + 7H+= 7Me-H+ + 2C7H14
ΔHo =
-339.4
(4.6)
(f) Cyclo-octane 8Me-(CH2)2 + 8H+= 8Me-H+ + 2C8H16
ΔHo =
-376.5
(4.7)
ΔHo = enthalpy of formation (as kJ mol-1) at 298K and 0.1 MPa (expressed per mole cyclic hydrocarbon produced). There are a number of other routes, which may result in the formation of cyclic hydrocarbons. 4.1.1 Cycloalkanes vs. Aromatics Analysis of Stage 1 oil from a variety of DSDP sites indicates that aromatics are normally more abundant than cycloalkanes (Figure 9a) and that cyclic hydrocarbons are normally less abundant than n-alkanes (Figure 9a). There is a weak statistical tendency for cycloalkanes to become more abundant than aromatics as the pentane concentration in the Stage 1 oil increases (Figure 9b). There is a slightly stronger regression relationship between the molar concentration of aromatics and pentane (Figure 10a) and a still stronger regression relationship between the molar concentration of pentane and cycloalkanes (Figure 10b). A plot of moles aromatics vs. moles cycloalkanes indicates a regression relationship where aromatics are generally more abundant than cycloalkanes (Figure 11a). One possible interpretation of these observations are that pentane is dehydrated to form a cyclic hydrocarbon (e.g. cyclopentane) and this cyclic hydrocarbon is subsequently dehydrated to form benzene (i.e. cyclic alkanes are an intermediary). This implies a base catalytic molecule of the form Me-(CH2)5 or Me-(CH2)5CH3 where the reaction termination routes are:Me-(CH2)5 + 2H+ = Me-H+ + C5H10 Me-(CH2)5 + CH4 = Me-CH3 + C5H10+ H+ Me-(CH2)5 + 4H+ = Me-H+ + C5H12 Me-(CH2)5 + CH4 + H+ = Me-CH3 + C5H12 Me-CH3 + C5H12 = Me-C6H11 + 4H+ Me-H+ + C5H12 = Me-C5H9 + 4H+ Me-C6H11 + 2H+ = Me-CH3 + C5H10 Me-(CH2)3CH3 + CO2 + 6H+ = Me-H+ + C5H10 + 2H2O Me-(CH2)4CH3 + CO2 + 8H+ = Me-H+ + CH4 + C5H10 + 2H2O
ΔHo = ΔHo = ΔHo = ΔHo = ΔHo = ΔHo = ΔHo = ΔHo = ΔHo =
60.2 280.5 -66.1 8.5 -128.5 97.1 225.7 -107.2 -155.5
(4.8) (4.9) (4.10) (4.11) (4.12) (4.13) (4.14) (4.15) (4.16)
ΔHo =
57.1
(4.17)
Chlorides may be involved in the chain growth process. For example Me-C6H13Cl = Me-CH3Cl + C5H10
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Published in the Indian Journal of Petroleum Geology, 17(2), 11-70, 2010 Me-C5H11Cl + CO2 +H+ = Me-CH3Cl + C5H10 + 2H2O
ΔHo =
-153.9
(4.18)
These processes create the observed correlation between pentane concentration and cycloalkane concentration (Figure 10b). The cycloalkane or Me-(CxHy) product is then degraded to form benzene:Me-CH3 + C5H12 = Me-H+ + C6H6 + 9H+ Me-CH3 + C5H10 = Me-H+ + C6H6 + 7H+ Me-CH3 + C5H12 + CO2 = Me-CH3 + C6H6 + 2H++ 2H2O Me-CH3 + C5H10 + CO2 = Me-CH3 + C6H6 + 2H2O Me-(CH2)6 = Me-H+ + C6H6+ 5H+ Me-(CH2)6 + CH4 = Me-CH3 + C6H6 + 7H+ Me-(CH2)5 + CO2 + H+ = Me-H+ + C6H6 + 2H2O Me-(CH2)5 + CH4 + CO2 = Me-CH3 + C6H6 + 2H2O + H+ Me-C6H13Cl + CH4 = Me-CH3Cl + C6H6 + 8H+ Me-C6H13Cl + CO2 = Me-CH3Cl + C6H6 + 2H2O
ΔHo = ΔHo = ΔHo = ΔHo = ΔHo = ΔHo = ΔHo = ΔHo = ΔHo = ΔHo =
76.5 10.4 44.1 -22.0 121.4 341.7 -82.2 138.1 287.8 -39.1
(4.19) (4.20) (4.21) (4.22) (4.23) (4.24) (4.25) (4.26) (4.27) (4.28)
This degradation of the cycloalkanes would be expected to produce a slightly weaker correlation between pentane and aromatics as cyclic alkanes produced from hexane may be involved in the process. The data set shows a slightly weaker correlation between pentane concentration and aromatic concentration (Figure 10a). This model of aromatic formation predicts that:i) cycloalkanes will be less abundant than aromatics. This is the observed position (Figure 11a) ii) cycloalkanes will be most commonly present in sediments with a high n-alkane polymerisation ratio (PR), as a high PR is required to produce pentane. This is the observed position (Figure 11b). The PR is calculated using the method described in Part I. iii) aromatic concentrations will increase as the n-alkane polymerisation ratio increases. This is the observed position (Figure 12a). However high concentrations of aromatics are present at low PR (Figure 12a) indicating that more than one formation route can produce the aromatics and that benzene can be produced from the direct dehydration of Me-((CH2)2)3 or Me-((CH2)3)2 or 3Me(CH2)2 or 2Me-(CH2)3. -----------------------Figures 6 to 12 to be placed around here ---------------------------------------4.2 Isomers Isomers are n-alkanes or cyclic hydrocarbons (e.g. cyclopentane, benzene) containing one or more attached methyl or ethyl groups. i-alkenes increase in abundance as the ethene:propene ratio increases (Figure 12b) and the proportion of alkenes increases (Figure 6b). An increase in i-alkane abundance may be associated with a decrease in the abundance of cyclic hydrocarbons (Figure 6a). Isomers are considered to form by either capture of an alkane, or alkene, or cyclic hydrocarbon by a Me-CH3, or Me-CH2 or Me-(CH2)2 or Me-CH2Cl or capture of a CH3Cl (or similar chlorinated alkyl). The relationship (Figure 12b) demonstrates that when zeolites are present, i-alkanes are associated with a ethene:propene ratio of 20. In the more flexible frameworks, the pore opening diameters vary with hydration. The channel (pore opening) dimensions vary with crystal face, composition and degree of hydration. The number of oxygen ions required to define the pore openings and the pore opening dimensions include (Ribeiro, 1984, p.586, 587; Xu et al., 2007, Table 2.6) 8 Ring Structures Analcime/Analcite (ANA) Irregular distorted 8 rings, typically 0.29 nm (0.658 nm hydrated) Chabazite (CHA) [001] 0.38 x 0.38 nm (0.658 nm hydrated) Phillipsite (PHI) [100] 0.38 x 0.38 nm, [010] 0.3 x 0.43 nm, [001] 0.32 x 0.33 nm Hydrated Phillipsite 0.42 x 0.44 nm, 0.28 x 0.48 nm, 0.33 x 0.33 nm 9 Ring structures Natrolite (NAT) (8) [100] 0.26 x 0.39 nm, [001] (9) 0.25 x 0.41 nm Each nano-crystal forms secondary building units (SBU’s). Large crystals, pseudomorphed clays, pore linings and pseudomorphed crystals are formed by joining SBU’s to form a large framework structure (i.e. observed zeolite). Each pore has finite dimension (length, width, height and pore aperture opening size. Only reactants (Appendix A) which can pass through the pore aperture can enter into the interior of the zeolite. 4.5.2 Chabazite Catalysts Chabazite ((Ca,Na2)OAl2O34SiO26H2O) zeolites (including Na-chabazite, analcite, natrolite) contain an internal pore structure consisting of a three dimensional network of sorption cavities. Each cavity (or cage within an SBU) has a length of about 1.1 nm and a diameter of 0.65 nm (Eberley, 1976, p. 402). Entrance to the zeolite pore cavity is accessed through six elliptical pore openings with major and minor diameters (determined crystallographically) as 0.41 and 0.31 nm, respectively (Eberley, 1976, p. 402). The effective sorption size of these openings has been determined as 0.589 and 0.489 nm respectively (Eberley, 1976, p. 402). The effective sorption size defines the maximum dimensions of a molecule entering the cavity. This size allows small molecules (H2, CH4, and CO2) to be rapidly occluded, larger molecules (e.g. n-alkanes, n-alkenes) are occluded at moderate rates, but very large or deformed molecules (e.g. iso-alkanes, cyclo-alkanes, and aromatics) are excluded from these cavities. Linear C1 to C8 alkanes, alkenes and alcohols are absorbed into the chabazite zeolite. Larger molecules are excluded (Daems et al., 2007). The rate of n-alkane sorption into the cavities increases with pressure, temperature and the degree of cavity subdivision. The Henry absorption constant (KH) increases exponentially from CH4 to C6H14, reaches a minimum at C8H18 and then increases to C14H30 (Denayer et al., 2008). C7 – C10 alkanes adopt a coiled configuration within the cage (Denayer et al., 2008). From C11H24 onwards the alkanes are unable to fully fit within the cage and protrude through its opening (Denayer et al., 2008). The presence of cations on Nachabazite results in stronger energetic reactions which shifts the window protrusion to lower chain lengths (Denayer et al., 2008). 4.5.2.1 Chabazite Cage Capacity The maximum saturation capacity of each chabazite cage (nano-pore) (Figure 16a) is 6 molecules CH4, 5 molecules C2H6, 4 molecules C3H8, 2 molecules C4H10, C5H12, and 1 molecule C6H14 or C7H16 or C8H18 (Krishna and van Baten, 2008, Fig. 2). The bulk fluid phase fugacities (f/Pa) associated with filling the cage space with a specific molecule are (Figure 16a) (i) 1 molecule C6H14 or C7H16 or C8H18 = >10Pa (ii) 1 molecule C5H12= >10 Pa; (iii) 2 molecules C4H10 and C3H8 molecule = >1000 Pa; (iv) 1 molecule C3H8 = 5000 Pa, (v) C4H10 molecule = 1000 Pa; (vi) 3 molecules C3H8 = 1015 Pa; (vii) 2
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Published in the Indian Journal of Petroleum Geology, 17(2), 11-70, 2010 molecules C2H6 = 0.1 MPa, (viii) 4 molecules = 1000 MPa, (ix) 5 molecules 1015 Pa; (x) 6 molecules CH4 = 1010 Pa (Krishna and van Baten, 2008, Fig. 1). The fluid phase partial fugacities controls the product composition produced by the zeolite. At low fugacities C5) contains (by weight) 67% octane, 27% (toluene + benzene) and 6% n-alkanes/i-alkanes with a carbon number of C6 to C8. The comparatively small opening to the chabazite zeolite cage renders access to the interior of the cage impossible for aromatics and iso-alkanes, iso-alkenes and iso-carbonyls. However, isomerisation of alkanes, cycloalkanes and aromatics can occur at the pore openings. The sandstone and conglomerate samples (852 m and 868 m; DSDP Site 585 (Part I, Fig. 22a)) demonstrate (see Part I, Fig. 22a; 24b) that polymerisation can occur in chabazite enriched sandstones. Consequently, sediments, which do not contain high organic carbon content shales, but do contain zeolitic sandstones and siltstones, and migrating or reservoired CH 4 or CO2, can be predicted to generate Stage 1 oil (e.g. light condensate). ------------------------- Figures 16 placed around here -----------------------------------4.5.3 Phillipsite Catalysts Zeolite-smectite claystones at 418.51 to 499.11 mbsb, DSDP Site 585 contain phillipsite (Floyd and Rowbotham, 1986). This diagenetic zeolite is formed at a temperature, which is well below 60 o C (Shipboard Scientific Party, 1986, p.50). The associated clay is Fe-beidellite/montmorillonite (Chamley et al., 1986). The zeolites replace smectite and celadonite (Floyd and Rowbotham, 1986). The smectites occur as both laminated small non-polygonal sheets about 2000 nm in diameter (Chamley et al., 1986, Plate 1, 2) and a chaotic structure where plates 2000 nm long, and 15 nm thick are separated by inter-clod porosity (Chamley et al., 1986, Plate 1, 2). Phillipsite Structure: The zeolite, phillipsite (Cax, Nay,Kz)mAlnSipOq rH2O), topology comprises an orthorhombic, centro-symmetric cage capped by double 8- rings and three pore openings. The pore sizes can be changed by changing the K:Na ratio and by changing the SiO2:Al2O3 ratio. The average CaO/(CaO + Na2O + K2O) ratio varies in Site 585 from 0.416 for phillipsite, to 0.005 for analcite, to 0.457 for Na-chabazite, to 0.10 for natrolite (Viereck et al., 1986; Floyd and Rowbotham, 1986). The SiO2:Al2O3 ratio decreases as the Na2O/(Na2O + K2O) ratio increases (Kuhl, 1969; Viereck et al., 1986; Floyd and Rowbotham, 1986). Phillipsite Pore Sizes: Hydrated phillipsite has small pore opening diameters [100] 0.42 x 0.44 nm, [010] 0.28 x 0.48 nm, [001] 0.33 x 0.33 nm (Ribeiro, 1984, p.586). These dimensions are sufficient to allow access of H2 (0.289 nm) and H2O (0.28 nm) CO2 (0.33 nm) and CH4 (0.38 nm) through all the pore openings, but will only allow n-CxHyOH and n-CxHy (0.43 nm) to enter and leave through the [100] opening. Only part of an i-alkane (0.5 - >0.56 nm) molecule is able to enter the [100] opening. The cycloalkanes (>0.6nm) and aromatics (>0.6 nm) would not be able to enter the zeolite (e.g. Le Febre, 1989, Fig. 10). The zeolite cations in the pore mouth will be able to catalyse isomerisation of a blocked species or cleavage of a blocked species (e.g. Venuto, 1971, p. 275-6). n-alkanes (C2 –C8) can be formed inside the zeolite. The narrow pore aperture of phillipsite precludes the formation of i-
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Published in the Indian Journal of Petroleum Geology, 17(2), 11-70, 2010 alkanes, cycloalkanes or aromatics within the structure. Construction of these chemicals occurs outside the zeolite pore structure. Phillipsite Stage 1 Oil Formation: Stage 1 oils formed in sediments containing phillipsite contain about 30% i-alkanes + alkenes, 15 – 35% aromatics and 40% - 60% n-alkanes (Figure 6a, 7, 8a). They have ethene/propene ratios of 0.5 - 1.0 (Figure 8b, 12b, 15a), and ethane/propane ratios of 0.3 – 0.8 (15a). They have a much narrower product range and a narrower variability within their product range than the Stage 1 oils associated with chabazite zeolite. This narrower range and reduced product variability reflects the smaller pore sizes associated with the phillipsite zeolite. The chabazite zeolite focuses n-alkane formation towards hexane or octane (Part I, Fig. 22a). The phillipsite zeolite focuses n-alkane formation towards propane and hexane (Part I, Fig. 21a). Phillipsite Formation: Phillipsite (CAS Number 76774-74-8, zeolite ZK-19) can be formed from a mixture of an aluminium silicate (e.g. a smectite), sodium metasilicate (a water-soluble compound) and presidium (or tri-potassium) phosphate (Kuhl, 1969). Sodium metasilicate is formed as:Na2CO3 + SiO2 = Na2SiO3 + CO2
(4.53)
It is found in hydrated forms (water glass) containing between 5 and 9 H 2O (e.g. sodium silicate pentahydrate (Na2SiO3 5H2O), nonahydrate (Na2SiO3 9H2O)). The resultant zeolite crystals have a SiO2:Al2O3 ratio, which is controlled by the hydration of the metasilicate. Increasing the silicate hydration increases the SiO2:Al2O3 ratio. The Na2O/(Na2O + K2O) ratio can be altered by substituting one or more of (Na, K, Ca) in the zeolite lattice with a different cation. Ion-exchange occurs (to 70 >90% completion) in solutions of NaCl, KCl and CaCl2. Diagenetic zeolites crystallise in an alkaline environment (pH typically 12 – 14 and more specifically 13.3 – 13.7 for phillipsite, (Lechert, 2001)). 5.0 Formation of Stage 2 Oil Stage 2 oil is defined (Antia, 2008) as a discontinuous series of n-alkanes, which are produced by the polyaddition of Stage 1 oil. These primary polyaddition peaks are in the range C10 – C21 (Antia, 2008). An example series of polyaddition peaks is provided as:9Me-C6H13 + 6H+ = C12H26 + C18H38 + C24H50 + 9Me-H+ 14Me-C6H13 + 8H+ = C12H26 + C18H38 + C24H50 + C30H62 + 14Me-H+ 9Me-(CH2)6 + 15H+ = C12H26 + C18H38 + C24H50 + 9Me-H+ 14Me-(CH2)6 + 22H+ = C12H26 + C18H38 + C24H50 + C30H62 + 14Me-H+
(5.1) (5.2) (5.3) (5.4)
The process can be facilitated by the presence of CH4 or CO2. Equations 5.1 and 5.2 demonstrate that increasing chain length requires an increase in available hydrogen, and an increase in the number of participating catalytic sites. In this study, three Stage 2 oils are analysed. The first (Barkley Canyon Oil) is extracted from vent hydrates associated with the Cascadia Hydrate Field. The second oil is from a fluid inclusion in a PreCambrian Proterozoic dolerite from Northern Australia. A third oil from a Pre-Cambrian Proterozoic Bessie Creek Sandstone fluid inclusion, where the Stage 2 oil is subsequently polymerised by CH4 or CO2. 5.1 Barkley Canyon Oil Hydrate samples recorded from Barkley Canyon, North Cascadia Hydrate Field, East Pacific Margin, USA/Canada (Hyndman et al., 2008, Fig. 1) contain between 68.1 and 85.1% methane (Pohlman, 2006, Table 2), a Stage 1 oil (Figure 17a,b) and a Stage 2 oil. Stage 1 Oil n-alkanes: The Stage 1 oil has a high proportion of i-alkanes in its C4 and C5 fractions, specifically methyl-propane (i-C4), methyl-butane (i-C5) and dimethylbutane. These form between 30% and 65% of the C4 to C5 fraction (Pohlman, 2006, Table 2, p.38). Calculation of the polymerisation ratio of the Stage 1 oil from the n-alkanes indicates a value of 0.5 – 0.6 (Figure 17a); following consideration of i-alkanes the PR increases to 0.6 – 0.8 (Figure 17b). Stage 2/3 Oil Triglycerides: The Stage 2/3 oil is also associated with triglycerides (Figure 18a, b). Triglycerides (R) are commercially manufactured (as biodiesel) by hydrolysing fat or oil, e.g. Knothe
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Published in the Indian Journal of Petroleum Geology, 17(2), 11-70, 2010 and Dunn (2001). A triglycerol (e.g. vegetable oil) is mixed with an excess of alcohol (e.g. methanol) and a hydroxide (e.g. NaOH, KOH) at a temperature of
