Ultra-deep liquid hydrocarbon exploration potential in cratonic region of the Tarim Basin inferred from gas condensate genesis

• Oil and gas condensate are formed at wide maturity range and genetically related.
• Gas condensates can be classified into thermogenic, retrograde and mixed types.
• Thermal cracking and TSR alteration occur in deeper strata than current penetration.
• Reservoir temperature history and pressure depression support deeper oil prospects.

A suite of gas condensate and crude oil samples from cratonic region of the Tarim Basin has been analyzed by routine GC–MS technique to elucidate their molecular compositions and genetic origins. Maturity parameters derived from biomarkers, aromatic hydrocarbons and diamondoids suggest very different maturity ranges for both condensates and oils, implying different stages of hydrocarbon emplacement and entrapment. Similar maturity range in two sample types without depth control suggests that condensates and oils are genetically close but different in gas oil ratios. Using diamondoid concentrations as a measure of loss of oil due to cracking indicates that majority condensates are not formed by thermal cracking of oils. The key controls on hydrocarbon phases are multiple charges and subsequent dysmigration. Thermal cracking and thermochemical sulfate reduction occur mainly at the depth deeper than current penetration (around 7000 m). The window of liquid hydrocarbon preservation may be shifted towards greater depths and previously unrecognized deep-basin oil and condensate resources are expected.