Progress of Basin Volcanic Facies:New Results of Intermediate-Mafic Volcanic Lava and Volcanic Facies of Subaqueous Eruption
Volcanic facies is the sum of volcanic material eruption type,transport mode,emplacement environment and state.The classification of volcanic facies is the basis for characterizing the distribution of volcanic rocks in a basin and searching for favorable volcanic reservoirs,which plays an important role in the exploration of volcanic oil and gas in a basin.Based on the"lithology,petrofabric and petrogenesis"of volcanic rocks,a classification scheme of"5 facies and 15 subfacies"of volcanic rocks in the basin was established,which greatly promoted the exploration process of deep volcanic rocks in China basins.At present,the large-scale volcanic oil and gas exploration in basins in China has gone through a course of more than 20 years,and with the in-depth exploration,the lithofacies classification scheme has been improved and enriched:For the intermediate-mafic volcanic lava,the intermediate-mafic effusive lava flow facies has been established,and three sub-facies have been divided into braided lava flow unit,tabular lava flow unit and the lava dome.Aiming at subaqueous volcanic eruption in lacustrine basin,three subfacies and facies models of subaqueous volcanic eruption phase,gas-supported hot pyroclastic flow subfacies,water-laid density current subfacies and subaqueous fallout subfacies are established.A new classification scheme of"7 facies and 21 subfacies"was formed.In the intermediate-mafic volcanic lava facies,the braided lava flow subfacies has the best development conditions,followed by the hyaloclastic rock subfacies and the tabular lava flow subfacies.Gas-supported hot pyroclastic flow subfacies control the spatial distribution of effective reservoirs in the subaqueous volcanic eruption facies.The establishment of the intermediate-mafic effusive lava flow facies overcomes the difficulty in characterizing the subfacies of the basic lava due to the thin monolayer thickness and the difficulty in drilling and seismic characterization.The establishment of subaqueous volcanic explosive facies has realized the accurate characterization of volcanic facies in different eruptive environments of sedimentary basins from land to subaqua.The establishment of the two lithofacies provides a basis for further exploration of the reservoir development law in the intermediate-mafic effusive development area and the subaqueous volcanic eruption pyroclastic rock development area and searching for favorable reservoirs.
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