Quantitatively unmixing method for complex mixed oil based on its fractions carbon isotopes: A case from the Tarim Basin, NW China

Deep mixed oils with secondary alterations have been widely discovered in the Tarim Basin, but current methods based on biomarkers and isotopes to de-convolute mixed oil cannot calculate the exact mixing proportion of different end-member oils, which has seriously hindered further exploration of deep hy-drocarbons in the study area. To solve this problem, we constructed a novel method based on the carbon isotope (813C) of the group components to de-convolute mixed liquid hydrocarbons under the material balance principle. The results showed that the mixed oil in the Tazhong Uplift was dominantly contributed at an average proportion of 68% by an oil end-member with heavier 813C that was believed to be generated from the Cambrian-Lower Ordovician source rocks, whereas the mixed oil in the Tabei Uplift was predominantly contributed at an average proportion of 61% by an oil end-member with lighter 813C that was believed to be generated from the Middle-Upper Ordovician source rocks. This indicates that, on the basis of the detailed description of the distribution of effective source rocks, the proposed method will be helpful in realizing differential exploration and further improving the efficiency of deep liquid hydrocarbon exploration in the Tarim Basin. In addition, compared to traditional 813C methods for whole oil and individual n-alkanes in de-convoluted mixed oil, the proposed method has a wider range of applications, including for mixed oils with variations in color and density, indicating potential for promoting the exploration of deep complex mixed oils in the Tarim Basin and even around the world. (c) 2022 The Authors. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).