Petroleum evolution within the Tarim Basin, northwestern China: Insights from organic geochemistry, fluid inclusions, and rhenium-osmium geochronology of the Halahatang oil field

The newly discovered Halahatang oil field in the northern Tarim Basin has a potential resource of more than 70 billion bbl of oil. Oil organic geochemical data from the Halahatang oil field indicate that the oils are of moderate maturity, biodegraded, and represent one oil family, derived from the same Paleozoic marine source. Modeling of coeval aqueous and hydrocarbon-bearing inclusion data provide fluid trapping temperatures and pressures of 100 degrees C to 110 degrees C and approximately 39 to 59 MPa (similar to 5656-8557 psi), respectively. The fluid inclusion data coupled with the previous basin model studies suggest a single prolonged oil migration event during the Permian. The Re-Os isotope data of the oil yields an early Permian Re-Os age of 285 +/- 48 Ma. The age agrees with the timing of maturation of the Paleozoic source via burial history modeling but is slightly older (similar to 5-55 m.y.) than the oil migration and accumulation timing implied by the basin modeling coupled with fluid inclusion analysis and the published reservoir illite K-Ar dates. Thus, the oil Re-Os date suggests that oil generation in the Halahatang depression of the Tarim Basin occurred during the early Permian rather than the Silurian as previously proposed, with subsequent oil migration and accumulation occurring during the middle-late Permian as recorded by basin modeling, coupled with fluid inclusion analysis and illite K-Ar dating. In addition to promoting petroleum exploration in the Tarim Basin, this study, which combines crude oil Re-Os isotope dating and traditional analytical methods (organic geochemistry and fluid inclusion analysis) to constrain petroleum evolution, is applicable to hydrocarbon systems worldwide.