Resin composition: An indicator of oil maturity as revealed by fourier transform ion cyclotron resonance mass spectrometry

A pyrolysis experiment was carried out on a Dongying Depression kerogen sample to separate the resin from the oil. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with a positive-ion detector was used to detect the relative proportional changes in the compounds of the resin. During the whole pyrolysis experiment, the relative ratio of resin exceed 10% of the soluble component at each temperature point. Five compounds were detected from the resin: N1, N1O1, N1O_(2), O1, and O_(2). To research the changes in the proportions of the compounds during pyrolysis clearly, these five compounds were divided into three classes: N1, N1Ox, and Ox. The N1 class has the largest proportion in resin at the beginning of the pyrolysis, while Ox class has the least proportion. And the relationship between the number and the molecular mass of three classes compound was researched. With increasing maturity, the proportion of N1 and the N1Ox class decreased rapidly, while the Ox class increased slowly. Through researching these resin compounds, it was found that an inversion in the proportions of above three compounds appeared at the end of the oil window. At the same time, we found that the DBE and carbon number of resin compounds have changed obviously during the pyrolysis: the DBE increased, while the carbon number decreased significantly. And the details of the change of each compound have been researched. This research extends our knowledge of judging the maturity of crude oil during the pyrolysis through the characteristics of compounds in resin and provides the new index based on resin for the evaluation of thermal evolution stage and hydrocarbon generation capacity of source rocks.

Origin and genetic family of Huhehu oil in the Hailar Basin, northeast China

The Huhehu Sag is one of the most important oil and gas depressions in the Hailar Basin. However, the origin of Huhehu oil is still controversial. Previous studies on source rocks have mainly focused on the Nantun Formation(K1 n); a few studies have investigated the Damoguaihe Formation(K1 d). Based on the Rock–Eval pyrolysis parameters, 172 drill cutting samples from the Huhehu Sag were analyzed to evaluate their geochemical characteristics. Based on the Rock–Eval data, the mudstones from the first member of the Damoguaihe Formation(K1 d1) and the second member of the Nantun Formation(K1 n2) have moderate to high hydrocarbon generation potential, while mudstones from the first member of the Nantun Formation(K1 n1) have poor to good hydrocarbon generation potential.Additionally, both the K1 n1 and K1 n2 coal members have poor to fair hydrocarbon generation potential, but the K1 n2 coal member has a better generative potential. Fifteen Huhehu oils were collected for molecular geochemical analyses to classify the oils into genetic families and to identify the source rock for each oil using chemometric methods. The Huhehu oils were classified into three groups with different maturity levels using hierarchical cluster analysis and principal component analysis. Group A oils(high maturity) are characterized by relatively moderate ratios of Pr/Ph, Pr/n-C17, and Ph/n-C18, as well as an abundance of C29 steranes, mainly derived from the K1 n2 and K1 n1 mudstone members. In comparison, group B oils(moderate maturity) have relatively low Pr/Ph ratios,moderate Pr/n-C17 and Ph/n-C18 ratios, and low concentrations of C29 steranes. Group C oils(low maturity) show relatively high ratios of Pr/Ph, Pr/n-C17, and Ph/n-C18, as well as high concentrations of C29 steranes. Furthermore,group B oils derived from the K1 d1 mudstone member and group C oils derived from the K1 n2 coal member were also identified by principal component analysis score plots.Correlation studies suggest a major contribution from the K1 n mudstone Formation and the K1 d1 mudstone member to the oils of the Huhehu Sag. So, the Nantun Formation and relatively shallow strata of the Damoguaihe Formation(e.g., the K1 d1 member) represent important targets for future oil-reservoir exploration in the Huhehu Sag.