Oil chemometrics and geochemical correlation in the Weixinan Sag, Beibuwan Basin, South China Sea

Abstract

The oil–oil and oil–source rock correlations, also termed as geochemical correlations, play an essential role in the construction of petroleum systems, guidance of petroleum exploration, and definition of reservoir compartments. In this study, the problems arising from oil–oil and oil–source rock correlations were investigated using chemometric methods on oil and source rock samples from the WZ12 oil field in the Weixinan sag in the Beibuwan Basin. Crude oil from the WZ12 oil field can be classified into two genetic families: group A and B, using multidimensional scaling and principal component analysis. Similarly, source rocks of the Liushagang Formation, including its first, second, and third members, can be classified into group I and II, corresponding to group B and A crude oils, respectively. The principle geochemical parameters in the geochemical correlation for the characterisation and classification of crude oils and source rocks were 4MSI, C27Dia/C27S, and C24 Tet/C26 TT. This study provides insights into the selection of appropriate geochemical parameters for oil–oil and oil–source rock correlations, which can also be applied to other sedimentary basins.

The Geochemical Study of Oil-Oil and Oil-Source Rock Correlations in the Wushi Sag of the Beibu Gulf Basin, South China Sea

“…Hierarchical cluster analysis (HCA) and principal component analysis (PCA) are valuable tools to identify genetic relationships among crude oils and source rocks based on age-and sourcerelated biomarker ratios (Peters et al, 2007;Peters et al, 2013;Wang et al, 2018b). Similarly, multidimensional scaling (MDS) is also a reliable method for a detailed oil-oil and oil-source rock correlation (Wang et al, 2016;Wang et al, 2018a;Wang et al, 2020a). The Wushi oil samples were divided into two groups, as shown in Figure 6.…”

“…The method is use of multivariate statistics to identify and remove noise from the data, and show affinities among samples or variables (Peters et al, 2005). Chemometric methods have been used to evaluate data in many disciplines (Dong et al, 2021;Oliveira et al, 2021;Panseriya et al, 2021), including multivariate geochemical data (Zhan et al, 2019;Wang et al, 2020a). The application of chemometric method in geochemical correlation has been paid more and more attention due to the complexity of petroleum exploration and geological background.…”

“…Among them, hierarchical clustering analysis (HCA) and principal component analysis (PCA) are the two commonly used methods (Peters et al, 2005;Asemani and Rabbani, 2021). Additionally, the method for oil-oil and oil-source rock correlations also includes factor analysis (Zumberge, 1987;Chakhmakhchev et al, 1996), star diagram (Justwan et al, 2006;Mashhadi and Rabbani, 2015), K-nearest neighbor (Peters et al, 2007;Peters et al, 2008), multidimensional scaling (Wang et al, 2016;Wang et al, 2020a), discriminant analysis (Zhang et al, 2019;Shi et al, 2020), t-distributed stochastic neighbor embedding (Tao et al, 2020). Meanwhile, geochemists try to introduce new methods (Asemani and Rabbani, 2021), indicating that chemometrics has great potential in coping with the problem of geochemical correlation.…”

Geochemical Characteristics of Three Oil Families and Their Possible Source Rocks in the Sub-Sag A of Weixinan Depression, Beibuwan Basin, Offshore South China Sea

“…As outlined above, these previous organic geochemical studies on the crude oils from the Weixinan Depression were conducted on the samples mostly from sub-sag B, such as the WZ12 oil field. 6 Nevertheless, the geochemical characteristics and possible source rocks of crude oils from the sub-sag A have not yet been studied in detail. Compared to the sub-sag B, the petroleum system of sub-sag A remains unclear.…”

“…In comparison, Fan et al believed that the first type of oils was derived from the bottom of the first member of the Liushagang Formation (E l 1 ) and the top of the second member of the Liushagang Formation (E l 2 ), the last two types of oils were generated from the bottom of the E l 2 formation and the top of the third member of the Liushagang Formation (E l 3 ) in the Weixinan Depression. The studies on the WZ12 oil field by Jin and Wang et al revealed that these oils were from the E l 2 and E l 3 source rocks. As outlined above, these previous organic geochemical studies on the crude oils from the Weixinan Depression were conducted on the samples mostly from sub-sag B, such as the WZ12 oil field .…”