Accumulation periods of Ordovician reservoirs in Tahe Oil Field

How many stages of accumulation have the Ordovician reservoirs experienced in the Tahe Oil Field, 2, 3 or even more? The debate causes different understandings of source rock location, hence leads to uncertainty in oil and gas exploration. After years of multidisciplinary joint research, using the most advanced technique of monomer inclusion component analysis, the geochemical features of single oil inclusion during different stages have been identified. The geochemical components of crude oils charged during 2 stages in the southeast of the Tahe Oil Field have been made clear. It has been concluded that the Ordovician reservoirs in the southeast of the Tahe Oil Field have experienced 2 stages of accumulation. The oil inclusions of the 1st stage are featured by yellow-brown fluorescence, higher aromatic component content than saturated hydrocarbon content, complete distribution of n-alkanes (nC₁₁-nC₃₀), and light hydrocarbon missing. They have lower maturity and mainly generate from early migration. The oil inclusions of the 2nd stage are featured by blue-light blue fluorescence, higher saturated hydrocarbon content than aromatic component content, narrow distribution of n-alkanes (nC₈-nC₂₈), and complete light hydrocarbon. They have higher maturity, indicating for late-stage light oil charging. Combined with the simulations of paleopressure and paleotemperature as well as the studies of mixed oil proportion, the charging time and contribution of crude oils of different stages have been discussed, which may guide source rock studies in the Tahe Oil Field.