Cretaceous petroleum origin in well PSBX1 in the southwestern Tarim Basin

Well PSBX1 is located in the high part of anticlinal structure no. 1 on the Markit slope in the Tarim Basin, and has oil and gas in the Cretaceous. However, the hydrocarbon origin still remains under discussion. Light hydrocarbons from well PSBX1 indicated that the oils were mainly derived from type I source rocks. Saturated hydrocarbon features indicated that argillaceous materials were the dominant contributors to hydrocarbon generation, which was different from the Ordovician crude oils in the Tahe and Yubei areas. Two-dimensional chromatographic analyses showed that the Cretaceous crude oils from well PSBX1, the Ordovician crude oils from Yubei and Tahe areas, and the Devonian crude oils from Bachu area were sourced from marine mudstones. Carbon isotope characteristics of crude oils from well PSBX1 suggested poorer source quality compared with the Ordovician crude oils from Yubei area and the Carboniferous crude oils from Bachu area. Crude oils from well PSBX1 had higher maturity than those from Ordovician in the Yubei area. Analysis of the Cretaceous crude oils from well PSBX1 and four typical source rocks from adjacent areas in the southwestern Tarim Basin indicated that:(1) the Cretaceous crude oils from well PSBX1 mainly originated from the Cretaceous marine facies source rocks in the southwestern Tarim Basin; and (2) natural gas from the well was mainly sourced from Jurassic humic organic matter, which was similar to that in the Kekeya gas field. The study of the origin of Cretaceous petroleum in well PSBX1 would help oil and gas exploration in the Mesozoic and Cenozoic clastic rocks in the southwestern Tarim Basin.