Relationship of hydrocarbon and source-rock in Nos.3-5 tectonic belts of the Lenghu area,northern Qaidam Basin

Based on analyses of the components of crude oil hydrocarbons and carbon isotopes,the content of normal alkane decreased from 49.00% to 20.10% when moving from the No.3 to No.5 tectonic belt of the Lenghu area of the Qaidam Basin,while cycloalkanes increased from 30.00% to 52.20% and aromatic and branch chain alkanes increased gradually as well. The maturity of sterane in crude oil is higher than that of its source-rock,which shows that the hydrocarbons were generated from a deep source-rock of high maturity around the tectonic belts of the Lenghu area. The analysis of the characteristics of carbon isotopes also shows that these isotopes of hydrocarbon compounds in the No.4 and No.5 tectonic belt are apparently heavier than those in the No.3 belt. The results of our research show that the hydrocarbons in the No.3 tectonic belt are mainly from a relatively rich sapropelic substance,while the hydrocarbons in the No.4 and No.5 tectonic belt originated mainly from organic matter of a relatively rich humic type substance.

Modeling of the whole hydrocarbon-generating process of sapropelic source rock

Based on experimental data from hydrocarbon generation with a semi-open system, hydrocarbon generation kinetics modeling in gold tube of closed system, high temperature pyrolysis chromatography mass spectrometry experiment with open system and geological data, the characteristics of whole hydrocarbon-generating process, hydrocarbon expulsion efficiency and retained hydrocarbon quantity, origins of natural gas generated in high-over mature stage and cracking temperature of methane homologs were investigated in this study. The sapropelic source rock has a hydrocarbon expulsion efficiency of 30%-60% and 60%-80% in the major oil generation window(with Ro of 0.8%-1.3%) and high maturity stage(with Ro of 1.3%-2.0%) respectively; and the contribution ratio of kerogen degradation gas to oil cracking gas in total generated gas in high maturity stage is about 1:4. The degradation gas of kerogen accounts for 20%, the retained liquid hydrocarbon cracking gas accounts for 13.5%, and the amount of out-reservoir oil cracking gas(including aggregation type and dispersed oil cracking gas) accounts for 66.5%. The lower limit of gas cracking is determined preliminarily. Based on the new understandings, a model of the whole hydrocarbon-generating process of source rock is built.

A simple method to model the reduced environment of lake bottom sapropel formation

The Kambala and Barchin brackish lakes （Baraba steppe, southern West Siberia） contain an organic-rich sapropel layer that was formed in oxygen-depleted waters. We measured the bulk sediment elemental composition, the water chemistry and determined the mineralogical composition and predominant biota species （Diatoms and Cyanobacteria in phytoplankton community respectively） in the lakes. The result indicates that the first lake has a siliceous type of sapropel and the second a carbonaceous one. A computer thermodynamic model was developed for chemical interaction in water-bottom sediment systems of the Kambala and Barchin Lakes. The surface sodium bicarbonate waters are supersaturated with respect to calcite, magnesite （or low Mg-calcite）, quartz and chlorite with minor strontianite, apatite and goethite （pH 8.9-9.3, Eh 0.3 V）. Nevertheless, it is shown that during sapropel deposition, deep silt waters should be anoxic （Eh〈0 V）. The virtual component CH20 has been used to create an anoxic environment suitable for pyrite formation due to the biotic community impact and abiotic reduction. Thermodynamic calculation has shown that silt water is not necessarily euxinic （anoxic and sulfidic）. Depending on Eh, sulfate sulfur can dominate in solution, causing the formation of gypsum together with pyrite. An attempt was made to find a reason for solution supersaturation with respect to Ca and Mg ions due to their complexation with humic acids.

ON THE CHARACTERISTIC FEATURES OF THE BAOHETANG COAL FROM MIDDLE HUNAN

Ⅰ. INTRODUCTIONThe coal mine of Baohetang is located in Shaodong County, Hunan Province. The Longtan group, up to 220 m in thickness, contains 4 coal seams, and the lower 2 seams, generally speaking, are not suited for mining, whereas the upper 2 seams are recoverable, thicknesses of which are separately 0.60 m and 1.19 m on an average. The results of the