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A detailed correlation of Hetianhe condensates versus typical source rocks from the Tarim Basin was established. Moreover, the genetic relationship between the condensates and their associated gases was also studied based on their geochemical compositions and fluid inclusion data. Hetianhe condensates are characterized by high pristine/phytane (Pr/Ph) ratios, high relative abundances of C regular steranes, C-C triaromatic steroids, and triaromatic dinosteranes, and relatively heavy stable carbon isotopic compositions. They geochemically correlate well with the Cambrian source rocks, indicating that these condensates are derived from the Cambrian rocks. Based on several molecular maturity parameters, the condensates are recognized as being moderately to highly mature, which are too low in maturity to extensively crack into gases. The gases and condensates of the Hetianhe Field are derived from the same source rocks and the gases are from oil-cracking; however, clear evidence indicates that the gases were not cracked from their associated condensates and that the gas generation from oil-cracking did not occur in the present reservoirs. The liquid condensates produced from wellheads were likely dissolved in their associated gases underground and carried into the reservoirs by the gases. [ABSTRACT FROM AUTHOR]

The geochemistry, origin and charge history of oils from the Yuqi area of Tarim Basin have been investigated, through GC, GC-MS and fluid inclusion microthermometry analysis. The Yuqi oils accumulated mainly in three intervals: (1) in the Lower-Middle Ordovician Yingshan Formation (O 1-2 y ) carbonate reservoirs; (2) in the overlying Upper Triassic Halahatang Formation (T 3 h ); and (3) in the Lower Cretaceous Yageliemu Formation (K 1 y ) sandstones. Oils from different reservoirs have distinct physical properties, varying from extra-heavy (O 1-2 y), heavy (T 3 h ), to light oils (T 3 h and K 1 y ). However, their geochemical compositions show a high degree of similarity, which indicates that they derive from the same source rock. Abundant tricyclic terpanes, gammacerane, dibenzothiophene and C 21 C 22 steranes, together with a low level of diasteranes, indicate an anoxic marine source rock for oils in the Yuqi area. Oil-oil correlation shows that Yuqi oils derive from the same source bed as Tahe oils. The co-occurrence of intact n -alkanes and 25-norhopanes in all the samples supports the proposition that there is a mixture of an early filled severely biodegraded oil and a late filled fresh oil. In this study, charge history is examined on the basis of integration of fluid inclusion homogenization temperature data with 1D burial-thermal history models. Two episodes of oil charging are identified in the O 1-2 y reservoir (well YQX1-1) at around 436-420 Ma (Middle-Late Silurian) and 10-3 Ma (Miocene to Pliocene), respectively. For the samples from the T 3 h and K 1 y intervals, only one episode of oil charge is indicated by the homogenization temperatures of coexisting aqueous inclusions with an inferred timing around 10-3 Ma. The T 3 h heavy oil reservoir is assumed to be a secondary hydrocarbon pool, which accumulated by re-migration and re-distribution of hydrocarbons from O 1-2 y hydrocarbon pools. The few early biodegraded oils in the K 1 y light oils were probably picked up along the migration pathway during the late fresh oil charging. [ABSTRACT FROM AUTHOR]

The Ordovician reservoir in the Halahatang Depression is one of the most commercially prolific oil reservoirs in the Tabei Uplift of the Tarim Basin, NW China. For this study, a total of 94 oil samples were collected from 88 exploration/production wells in this oilfield. All of the oils possess similar organic molecular compositions and belong to the same oil population. Oil-to-source correlation results indicate that oil accumulations discovered in Halahatang Oilfield were derived from the Upper Ordovician source rocks. The homogenization temperatures of fluid inclusion in the Ordovician reservoir in the Halahatang Oilfield range from 90 °C to 100 °C and from 140 °C to 160 °C. The bimodal distribution pattern shown in a histogram of the homogenization temperatures indicates that the Ordovician oil reservoir in the Halahatang Oilfield has been charged twice. Coupling this information with the reconstructed burial and geothermal histories by 1-D basin modeling, the homogenization temperatures can be related to the relative geological ages of 419 Ma to 410 Ma and 16 Ma to 8 Ma, namely, the Middle to Late Silurian and the Middle Miocene respectively, representing the two phases of oil charging and entrapment. The oil migration orientation and charging pathways can be traced using molecular indicators, such as Ts/(Ts + Tm) and TMNr parameters. The overall oil migration orientation in the oilfield is generally from south to north. Therefore, the source kitchen for the Halahatang Oilfield is predicted to be to the south side of the depression. The southern part of the Halahatang Depression, along the oil charging pathways, is identified as the most promising region for oil exploration. [ABSTRACT FROM AUTHOR]