摘要
Based on the analyses of C5-C7 light hydrocarbons,geochemical studies including oil maturity,source rocks organic-matter types and hydrocarbon-generating temperature are carried out.The heptane and isoheptane values can be used to distinguish oils and source rock organic-matter types.These two values of the Ordovician crude oils from the Halahatang depression range from 31.0 to 38.3 and 1.0 to 2.5,with the average of 36.0 and 2.2,respectively.And according to both parameters,the samples are highly mature and the source rocks organic-matter type is type Ⅰ-Ⅱ.The composition characteristics of C5-C7 light hydrocarbons are usually used to determine the source rock organic-matter types.In oil samples,the C5-C7 light hydrocarbon fraction is dominated by normal alkanes,while the C7 light hydrocarbons is dominated by isoalkanes.It is estimated that the source rock is dominated by sapropelic organic-matter.The Mango light hydrocarbon parameters including the K1,K2 values and RP are widely used to estimate the source rock organic-matter types and calculate the hydrocarbon-generating temperature.The K1 values for the oil samples range from 0.97 to 1.07 with an average of 1.03 and the K2 values range from 0.18 to 0.22 with an average of 0.20.The oil samples possess 3RP and 6RP,hence,it is concluded that the source rock is dominated by sapropelic organic-matter,which is the same to the result conducted from the C5-C7 and C7 light hydrocarbons composition characteristics.Besides,the hydrocarbon-generating temperature ranges from 119.0℃ to 125.9℃.