Current Situation and Application in Coal- Generated Hydrocarbons

The characteristics and research methods of terrigenous organic hydrocarbon - generated source rock in coal measures are studied in this thesis. After abundance of organic matters, pyrolysis parameter of rocks and hydrocarbon generated capacity of macerals are basically discussed in coal measures of the Cretaceous Muleng- Chengzihe formation in Suibin depression in Sanjang basin, the hydrocarbon generated grade in coal- generated source rock is ascertained in this depression. At last, we think that it is a main attack prospect in coal - generated hydrocarbons study in the future to research the macerals of coal measures organic source rock and to build a criterion to classify the coal- generated hydrocarbons in Northeast region.     

Bitumen biomarkers in the Mid-Proterozoic Ilímaussaq intrusion, Southwest Greenland - A challenge to the mantle gas theory

GC and GC/MS/MS analysis on rock extracts has shown that the bitumen in the peralkaline Ilímaussaq intrusion, previously assumed to be abiogenic, is biotic in origin. A biotic origin is in accordance with previously published stable carbon isotopic data on bituminous matter in the rocks. The biomarker distribution in the bitumen, including the less common bicadinanes, resembles that of oil seeps on the central West Greenland coast 2200 km farther north, whose source rocks and migration history are relatively well established. We use a recent re-construction of the subsidence and later exhumation of the West Greenland coastal region during the Mesozoic-Cenozoic (Japsen et al., 2006a, b) to anticipate that hydrocarbons migrated from deeper parts of the basin offshore west of Greenland. The rocks of Ilímaussaq were probably more deeply invaded than the surrounding granites due to their higher proportion of corroded minerals, which may explain why bitumen has not been observed elsewhere in the area.Hydrocarbon gases (C1-C5) present in fluid inclusions were also analysed, after having been released by treatment with hydrochloric acid that resulted in an almost complete disintegration of the Ilímaussaq intrusion rocks. The acid extraction method proved generally more efficient than the crushing procedure applied by others, but gave similar results for the chemical composition of the gas (CH₄: 88-97%) and isotopic ratios (δ¹³C₄CH: −1.6 to −5.0‰; δ¹³CC₂H₆: −9.2 to −12.5‰), with the exception of hydrocarbons hosted in quartz, which showed significantly lower isotopic values for methane (Graser et al., 2008). Previous researchers have suggested an abiotic origin for these hydrocarbon gases, but we suggest a biotic origin for the majority of them, not just those in quartz, assuming that the isotopic ratio of the constituents have changed due to loss of gas by diffusion. The assumption of gas loss via diffusion is supported by published studies on micro-fissures in minerals typical of the Ilímaussaq and field investigations showing diffusive loss of gas from the peralkaline Khibina and Lovozero massifs on the Kola Peninsula, Russia, which are, in many respects of mineralogy and hydrocarbon content, similar to the Ilímaussaq intrusion.Both the hydrocarbon gases and bitumen in the Khibina and Lovozero massifs have been cited as prime examples of a deep mantle source, although the carbon isotopic ratio of the bitumen clearly pointed to an organic origin. The trends in carbon isotopic ratio of methane released with time from freshly exposed rocks also supports our hypothesis of ¹³C enrichment of the methane remaining within the rock. Thus, there is good evidence that the hydrocarbons in the Kola alkaline massifs are mostly biotic in origin, in which case the probability of finding economic hydrocarbon accumulations from a deep mantle source seems exceedingly small.     

Magnetite compositions and oxygen fugacities of the Khibina magmatic system

Most titanomagnetite in the Khibina alkaline igneous complex, sampled through 500 m of a vertical cross-section, is represented by Ti-rich varieties. The ulvöspinel component is most commonly around 55 mol%, rarely reaching up to 80 mol%.

We calculated an f_O2–T diagram for magnetite + ilmenite + titanite + clinopyroxene + nepheline + alkali feldspar and magnetite + titanite+ clinopyroxene + nepheline + alkali feldspar phase assemblages at a hedenbergite activity of 0.2. The diagram shows that magnetites with 55 mol% of ulvöspinel crystallized at oxygen fugacities just slightly below the quartz–fayalite–magnetite buffer. More Ti-rich varieties crystallized at higher temperatures and slightly lower ΔQMF values, whereas more Ti-poor magnetites crystallized at or below about 650 °C.

Under the redox conditions estimated for the apatite-bearing intrusion of the Khibina complex (close to the QFM buffer), substantial quantities of methane may only form during cooling below 400 °C in equilibrium with magma. However, even at higher orthomagmatic temperatures and redox conditions corresponding to ΔQMF = 0, the hydrogen content in the early magmatic stage is not negligible. This hydrogen present in the gas phase at magmatic temperatures may migrate to colder parts of a solidifying magma chamber and trigger Fischer-Tropsch-type reactions there. We propose therefore, that methane in peralkaline systems may form in three distinct stages: orthomagmatic and late-magmatic in equilibrium with a melt and — due to Fischer-Tropsch-type reactions — post-magmatic in equilibrium with a local mineral assemblage.     

On saturation of magnesian cordierite with alkanes at high temperatures and pressures

 Incorporation of hydrocarbons (CH₄, C₂H₆, C₃H₈, C₄H₁₀) in cordierite channels was experimentally studied at 700 °C and at pressures from 200 to 1000 MPa, (avoiding recrystallization). The maximum concentrations of hydrocarbons determined by gas chromatographic analysis are CH₄=78.3, C₂H₆=134, C₂H₄ + C₂H₆=26, C₃H₈=28, C₄H₁₀=32, C₅H₁₂=23, and C₆H₁₄=7 × 10⁻³ wt%). According to IR spectroscopy data, the channel forms of hydrocarbons differ from the forms on the surface. As a result of interactions with the framework oxygen, normal hydrocarbons are converted to saturated oligomers and their fragments. Small amounts of water molecules of the first and second types (up to 0.3 wt%) are formed in the same way. As pressure grows from 200 to 1000 MPa, the total content of structural hydrocarbons is nearly doubled. Special runs on cordierite saturation in mixtures of hydrocarbons with water showed that low contents of hydrocarbons in natural cordierites correspond to their large concentrations in fluid. Received: 7 May 2001 / Accepted: 17 July 2001