Polymerisation Theory - Formation of Hydrocarbons in Sedimentary Strata (Hydrates,Clays,Sandstones,Carbonates,Evaporites,Volcanoclastics) from CH4 and CO2:Part II: Formation and Interpretation of Stage 1 to Stage 5 Oils

摘要

Experimental substoichiometric thermal degradation (50 - 80° 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 >40° 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 (<10 - >30 wt %) + gas (CO2 + CO + CH4 + H2O + H2 + GH4 (>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,alkyl-esters 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 C_(25) -C_(33) 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.