Genetic features of gas-condensate reservoirs in the Kekeya Field,southwest depression in the Tarim Basin,China

Oils,condensates and natural gases in the Kekeya Field,southeast depression of the Tarim Basin were studied for their geochemical characteristics. According to the distribution analysis of the C2/C3 values with C1/C2 values,C2/C3 values with C1/C3 values,as well as C2/C3 values with dryness index,there are two different types of natural gases in the studied field,which are spatially regularly distributed. One is the oil cracking gas,located on shallow reservoirs over X52 reservoir,namely Upper oil legs;the other is kerogen cracking gas,located on X72 reservoirs,X8 reservoirs and E2k reservoirs,namely Lower oil legs. In addition,the distribution patterns of molar concentration of oils and condensates with different carbon numbers of the n-alkanes in the Kekeya Field indicate that the crude oils have experienced several kinds of secondary alterations,which were closely related to the charging of gaseous hydrocarbons after petroleum accumulation. These results indicate that,based on the research of δ13C values of individual hydrocarbons,heptane values and isoheptane values of light hydrocarbons and aromatic maturity parameters for oils,condensates and natural gases,oils and gases were charged at different geological time in the Kekeya Field.