Abstract: The A Oilfield is a large-scale oilfield in Huanghekou Sag, Bohai Sea, and covered by igneous rocks. It presents the characteristics of strong volcanic activity, complex geological structure, and various types of volcanic rocks. To clarify the characteristics and formation of igneous rocks in the study area, the types, development mode, distribution of igneous rocks, and the influence of igneous rocks on reservoir physical properties were studied by means of core analysis, thin section observation, and seismic facies analysis. Results show that: ① five volcanic lithofacies were distinguished in the study area, including explosive facies, volcanic channel facies, overflow facies, subvolcanic facies, and volcanic sedimentary facies. Two eruption modes i.e., central and fissure eruptions, were established; ② affected by the overflow facies in the low-lying area at the root of fault and the intrusive facies around the volcanic channel, the reservoir physical properties became worse in the areas due to strong fault activity and well-developed volcanic channels. Based on the above understanding, the volcanic rock mass was nested into the geological model by using the fine identification and tracking results of volcanic rock mass, and the shape modeling of igneous rock was realized. This study facilitated the implementation of development wells and provided guidance for the comprehensive adjustment and efficient development of the oilfield.