Fluid inclusions in reservoirs of Weixinan Sag, Beibuwan Basin

To make sure the petroleum migrating direction and pool-forming model in the Weixinan sag, 4 wells were chosen to do research on fluid inclusions and petrography. The petroleum inclusions have three types: type I occurs in early cracks of quartz debris grains or the overgrowths inside, type II in the margins or overgrowths of quartz grains, and type III in late cracks of quartz debris grains. According to PVTsim, Ptr and Ttr are modeled and calculated. The results are: type I is 97.9 °C and 19.13 MPa; type II 112.6 °C and 35.05 MPa; type III 157.4 °C and 47.52 MPa. Based on burial history, three fluid-charging events occurred about 33Ma, 26.5Ma and 7Ma ago, respectively. Migration directions and pool forming models are: Fluid type II migrated towards westnorth and northeast respectively to form structural and lithologic reservoirs; Fluid type II migrated to areas surrounding the sag and formed block faulted and buried hill reservoirs; Fluid type III migrated to slopes to form anticlinal reservoirs.