Bimodal hydrocarbon generation and immature oil do not exist in the North Jiangsu Basin

A contradiction in the "immature oil in North Jiangsu Basin" theory prevails and the results of geological exploration is not consistent with it. After making a thorough analysis of previous work and validating the data, the following problems were noticed:misusing of raw data, taking outliers as evidence; multi-parameter consideration is lacking in the hydrocarbon generation model, which makes the inference invalid; the consistency of reservoir and hydrocarbon maturity was not verified after the oil-source correlation; hypotheses do not stand the test of source rock gas logging data and other prospecting results. These indicate that the "non-kerogen source rock early maturation & bimodal hydrocarbon generation model" could be incorrect, and the "immature oil" may not exist. After using big an extensive data set to analyze errors and exclude outliers, the sterane C₂₉S/(S+R) and C₂₉ββ/(αα+ββ), the terpane C₃₁S/(S+R) and C₃₂S/(S+R), as well as CPI and OEP maturity sensitive parameters of hydrocarbon and rocks were optimized. Crude oil from the thermal degradation of late kerogen can be divided into 3 types:low maturity oil, medium maturity oil and mature oil. It is pointed that the maturity parameters of a large quantity of medium maturity source rocks (R_o>0.70%) could match well with those of medium maturity oil; the maturity parameters of low maturity source rocks (0.60% ≤ R_o ≤ 0.70%) have only some matching relationships with a small number of low maturity oil maturity parameters; no crude oil matched the immature source rocks (R_o<0.60%). The results indicate that the non-kerogen immature oil does not exist. Prominent anomalous data can be detected in the medium maturity and mature source rock gas logging. Hydrocarbon traps with these source rocks usually have good exploration results, and 99.83% of the discovered oil reserves belong to this type. There is little or no anomalous data in the low maturity source rock gas logging. This source rock is unable to form a commercial scale reservoir, and only some shows of hydrocarbon may exist. No anomalous data can be found in immature source rock gas logging. If there is no mature oil supply from other places, reservoirs will not be formed.