Abstract:  There are favorable lava reservoirs in the Mesozoic Yixian Formation in the Bohai Bay basin, but lava reservoirs vary greatly in different phase structures, and there is an urgent need to establish the relationship between lithofacies and reservoirs applicable for early exploration. This study takes the lava of the Cretaceous Yixian Formation in Jianshan, Xingcheng, western Liaoning as an example. Comprehensive research on lithology, lithofacies, reservoir types, and reservoir controlling factors has been conducted using geological surveys, rock and mineral identification, major element analysis, and image analysis. The research results indicate that, based on the geometric shapes and petrofabric characteristics of volcanic rocks, the subfacies of subaqueous lava dome within the extrusive facies and the subfacies of subaqueous lava flow within the effusive facies have been identified. In the aquatic lava dome subfacies of the intrusive facies, the reservoirs are dominated by fissures, with no vesicular development, and the reservoirs are of average quality, showing a distribution pattern of good in top layers and poor in lower layers, low reserve-to-strata ratio, few reservoir layers, and limited distribution range. In the aquatic lava flow subfacies of the extrusive facies, the reservoir space of the simple lava flow microfacies is dominated by vesicular amygdale, and the reservoir is of good quality, showing a distribution pattern of good in upper layers and poor in lower layers, high reserve-to-strata ratio, a large number of reservoir layers, and large distribution range. The lava domes in the caldera-near caldera facies belt and the simple lava flows in the near-source facies belt of the volcanic edifice in the study area have been modified by tectonics and weathering. The lava domes experience great changes in physical properties, while the simple lava flows do not change significantly. In conclusion, when encountering residual lava-like volcanic edifices in volcanic exploration, simple lava flows with good reservoir properties in the near-source facies belt should be the first target, and lava domes with average reservoir properties in the caldera-near-caldera facies belt should be the secondary target.

Key words: lava, volcanic rock reservoir model, volcanic edifices, Yixian Formation, Cretaceous, Bohai Bay basin, Liaoning