Use of comprehensive two-dimensional gas chromatography for the characterization of ultra-deep condensate from the Bohai Bay Basin, China

A gas condensate from well ND1 in the Jizhong Depression of the Bohai Bay Basin, China is characterized by two-dimensional gas chromatography with flame ionization detector (GC × GC–FID) and time-of-flight mass spectrometry (GC × GC–TOFMS). This condensate is sourced from the fourth member of the Shahejie Formation (Es4) but reservoired in the Mesoproterozoic Wumishan Formation carbonate at a depth of 5641–6027 m and the reservoir temperature is 190–201 °C. It is the deepest and the highest temperature discovery in the basin to date. The API gravity of the condensate is 51° and the sulfur content is < 0.04%. A total of 4955 compounds were detected and quantified. Saturated hydrocarbons, aromatic hydrocarbons and non-hydrocarbon account for 94.8%, 5.1% and 0.02% of the condensate mass, respectively. Some long chain alkylated cyclic alkanes, decahydronaphthalenes and diamondoids are tentatively identified in this condensate. The C6–C9 light hydrocarbon parameters show that the gas condensate was generated at relatively high maturity but its generation temperature derived from the dimethylpentane isomer ratio seems far lower than the current reservoir temperature. Some light hydrocarbon parameters indicate evaporative fractionation may also be involved due to multiple-charging and mixing. The diamondoid concentrations and gas oil ratio (GOR) suggest that the ND1 condensate results from 53.3–55% cracking. Since significant liquids remain, the exploration potential of ultra-deep buried hill fields in the Bohai Bay Basin remains high.