Fluid inclusion evidence for petroleum accumulation in northern Qaidam Basin

Based on the results of fluid inclusion study (microscopic characteristics, homogenization temperatures and grains with oil inclusions), the pool-forming time of the Nanbaxian and Mabei 1 oilfields in northern Qaidam Basin was discussed in this paper. Fluid inclusions in northern Qaidam Basin are relatively abundant, including aqueous inclusions and hydrocarbon inclusions. These inclusions are small (5–10 μm), and mainly distributed in quartz fissures, overgrowths and cementations. The abundances of grains with oil inclusions (GOI) are commonly low. The GOI values of most samples are between 2.0%–10.5%, and those of about 40 percent of total samples exceed 5%. The homogenization temperatures of fluid inclusions in different samples are markedly dissimilar, indicating that these inclusions were formed in different periods. According to the measured homogenization temperatures of fluid inclusions and in combination with burial history and thermal evolution history, the Nanbaxian and Mabei 1 oilfields are deduced, which have experienced two hydrocarbon charging periods, with the former of N1-N2 1 and N2 2–N2 3, and the latter of N1 and N1 end −N2, respectively.