Although a variety of precursors have been proposed for the formation of high molecular weight hydro-carbons (HMWHCs) in crude oil, their precise origin re-mains elusive. Quantitative studies of macrocrystalline wax a...Although a variety of precursors have been proposed for the formation of high molecular weight hydro-carbons (HMWHCs) in crude oil, their precise origin re-mains elusive. Quantitative studies of macrocrystalline wax and microcrystalline wax content of source rock extracts from the Damintun depression, Liaohe Basin, a typical high wax producing area, coupled with microscopical maceral composition studies and pyrolysis-GC analysis indicate that oil shale enriched in lacustrine biomass makes a primary contribution to wax in oil. The main precursors of high wax oil are lacustrine alginites and their amorphous matrix, which are highly aliphatic in nature and have high genera-tive potential for HMWHCs. Wax generation efficiency could be affected by organic material abundance and matur-ity. The high abundance and low maturity of organic mate-rial are favorite for the formation of high quantity of wax, which declines with decreasing organic abundance and in-creasing thermal maturity. This suggests that wax is derived from organic-rich lacustrine biomass at early stages of maturation (RO = 0.4%—0.7%). Although the contribution of high plant cuticular wax and sporopollen cannot be ruled out, lacustrine biomass is more important in the formation of high wax oil.展开更多
ABSTRACT： The Damintun （大民屯） depression, a small （about 800km^2 in area） subunit in the Bohai （渤海） Bay basin, hosts nearly 2×10^8 t of high-wax oils with wax contents up to 60%. The high-wax oils have...ABSTRACT： The Damintun （大民屯） depression, a small （about 800km^2 in area） subunit in the Bohai （渤海） Bay basin, hosts nearly 2×10^8 t of high-wax oils with wax contents up to 60%. The high-wax oils have high consolidation temperatures and viscosities. The high-wax oils were generated from the fourth member of the Shahejie Formation （Es4）, which is also important source rocks for oils in other subunits of the Bohai Bay basin. Yet high-wax oils have not been found in significant volumes elsewhere in the Bohai Bay basin. Geological conditions favourable for high-wax oil enrichment were studied. This study shows that the unusual concentrations of high-wax oils in the depression seem to result from at least three different factors： （1） the presence of organic-matter rich source rocks which were prone to generate wax-rich hydrocarbons; （2） the formation of early overpressures which increased the expul- sion efficiency of waxy hydrocarbons; and （3） reductions in subsidence rate and basal heat flows, which minimized the thermal cracking of high molecular-weight （waxy） hydrocarbons, and therefore prevented the high-wax oils from being transformed into less waxy equivalents.展开更多
文摘Although a variety of precursors have been proposed for the formation of high molecular weight hydro-carbons (HMWHCs) in crude oil, their precise origin re-mains elusive. Quantitative studies of macrocrystalline wax and microcrystalline wax content of source rock extracts from the Damintun depression, Liaohe Basin, a typical high wax producing area, coupled with microscopical maceral composition studies and pyrolysis-GC analysis indicate that oil shale enriched in lacustrine biomass makes a primary contribution to wax in oil. The main precursors of high wax oil are lacustrine alginites and their amorphous matrix, which are highly aliphatic in nature and have high genera-tive potential for HMWHCs. Wax generation efficiency could be affected by organic material abundance and matur-ity. The high abundance and low maturity of organic mate-rial are favorite for the formation of high quantity of wax, which declines with decreasing organic abundance and in-creasing thermal maturity. This suggests that wax is derived from organic-rich lacustrine biomass at early stages of maturation (RO = 0.4%—0.7%). Although the contribution of high plant cuticular wax and sporopollen cannot be ruled out, lacustrine biomass is more important in the formation of high wax oil.
基金supported by the National Natural Science Foundation of China (No. 40772089)
文摘ABSTRACT： The Damintun （大民屯） depression, a small （about 800km^2 in area） subunit in the Bohai （渤海） Bay basin, hosts nearly 2×10^8 t of high-wax oils with wax contents up to 60%. The high-wax oils have high consolidation temperatures and viscosities. The high-wax oils were generated from the fourth member of the Shahejie Formation （Es4）, which is also important source rocks for oils in other subunits of the Bohai Bay basin. Yet high-wax oils have not been found in significant volumes elsewhere in the Bohai Bay basin. Geological conditions favourable for high-wax oil enrichment were studied. This study shows that the unusual concentrations of high-wax oils in the depression seem to result from at least three different factors： （1） the presence of organic-matter rich source rocks which were prone to generate wax-rich hydrocarbons; （2） the formation of early overpressures which increased the expul- sion efficiency of waxy hydrocarbons; and （3） reductions in subsidence rate and basal heat flows, which minimized the thermal cracking of high molecular-weight （waxy） hydrocarbons, and therefore prevented the high-wax oils from being transformed into less waxy equivalents.
