Mature, source rocks

Geochemists and the oil industry routinely screen rock samples for bio-markers that indicate the age and source of hydrocarbon constituents. The conventional extraction takes 48 hours and requires extract clean-up by thin-layer chromatography to separate the alkanes from aromatic hydrocarbons and heteroatom containing species (16). Here the selectivity of SFE in extracting only the alkanes from a mature source rock... 

The hydrocarbons expelled from the mature source rocks in separate phase, may initially occur in a very finely dispersed state. At depths corresponding to the peak phase of hydrocarbon expulsion in actively filling and subsiding basins, the hydrodynamic condition is characterized by the intermediate or the deep subsystem of burial-induced groundwater flow. Initially, the very finely dispersed hydrocarbons will move along with the burial-induced groundwater... 

When the distribution of mature source rocks is known, the first step of the above-described method can be carried out in a comparable way. The pattern of lateral hydrocarbon migration is derived from the basin geometry at the level of the source rock. 

Furthermore, the existence of carbonates of different origins may complicate the data. Soils derived from matured source rocks, particularly carbonates, always contain very high concentrations of hydrocarbons with compositions of matured oily sources. If the parent rock of the soil was transported by a surface agency such as water, wind or ice, gas anomalies reflect the source area of the sediments rather than the oil or gas potential of the underlying strata. The western part of the Bayinhaote Basin of west China is characterised by Archaean metamorphic rocks covered by thousands of metres of Cenozoic red clastic sediments with no oil or gas potential. Acid treatment of soils revealed very high C1-C5 concentrations (up to 600 pl/kg of C and 70 pl/kg C2). However, it was found that the anomalous soils were derived from carbonate fragments... 

The Lixian Depression, some 500 km south of Xi an, is filled by about 10,000 m of Palaeozoic and Mesozoic sediments. Mature source rocks occur throughout the stratigraphic sequence, but the complicated geological structure has impeded exploration and there are as yet no commercial discoveries of oil or gas. Located in southern China, the region has a very wet climate and is largely covered by rice fields, so that soils in the region are invariably moist. 

The configuration of the Western Canada Sedimentary Basin, with highly mature source rocks in a folded foredeep, facilitating migration onto a wide foreland homocline (Michael Bachu 2001), suggests that a large sample of oils... 

This pattern of repeated filling events from a progressively maturing source rock basin, structural trap tilting, and migration up the fault zone, coupled with phase fractionation and separation of petroleum into oil and gas phases in the reservoir intervals (Fig. 32), which were subsequently progressively sealed off due to increased quartz cementation in response to increased burial, may explain the complex patterns of variable GOR, API and carbon isotope values observed in Smorbukk (cf. Fig. 14). 

We selected six oil samples (Fig. 1, Table 1) where structural relationships and proximity to mature source rock(s) suggested an origin as follows ... 

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