The Maichen Sag in the Beibuwan Basin has different types of source rocks, sedimentary systems, and reservoir-cap combinations. There are lacustraline facies and coal-bearing source rocks, large rivers-delta and underwater fans sedimentary systems, and Liushagang Fm and Weizhou Fm reservoir-cap combinations. This diversity results in different reservoir types, such as faulted nose-fault block reservoirs in the north slope zone and subtle reservoirs controlled by fans in the southern fault zone.