Characteristics And Distribution Of Volcanic Facies In The Paleogene BZ 34-9 Oilfield,Huanghekou Sag,Bohai Bay Basin,China

The Bozhong34-9 oilfield is located on the southern slope of the Huanghekou Sag in the Bohai Bay Basin.The eight deep exploration wells in the oilfield encountered volcanic rocks in the Paleogene.The volcanic lithology is complex and formed by multi-phase volcanic eruption.The volcanic rocks,as non-reservoirs,destroys the integrity of the clastic reservoir.Due to the unclear spatial distribution of volcanic rocks,it affects drilling efficiency and increases the risk of well location deployment.In this study,the volcanic facies in Paleogene of the Bozhong34-9 Oilfield was taken as the research object.Based on the overall characteristics of the volcanic edifice,the lithology and facies of different volcanic rocks were studied.Identification of different volcanic facies were established through drilling and seismic data.Seismic facies are used to study the vertical configuration relationship between different volcanic facies.Using seismic attributes to describe the planar distribution characteristics of volcanic rocks in various periods of the Paleogene,and to clarify the evolution of volcanic facies.Finally,the volcanic eruption pattern was summarized by three-dimensional geological body probing.Studies have shown that volcanic rocks in the Bozhong34-9 Oilfield included basalt,andesite,tuff,volcanic clastic sedimentary rocks and diabase.The volcanic facies of the Bozhong34-9 oilfield are mainly volcanic channel facies,overflow facies,explosive facies,volcanic sedimentary facies and subvolcanic facies.The distribution of different volcanic facies between wells were predicted with logging and seismic identification marks.The volcanic edifices are staggered and stacked vertically.The contact relationship between volcanic facies can be divided into interactive stacking,single stacking,inset and isolated.The Paleogene has experienced weak-strong-weak evolution from the E₂s₂ to E₃d₁.The E₂s₂ and E₂s₁ are mainly subvolcanic facies.The sedimentary facies are widely distributed in the E₃d₃ and volcanic sedimentary facies are mainly distributed in the E₃d₂^L.E₃d₂^U and E₃d₁ are mostly overflow and explosive facies.The volcanoes in E₃d₂^U are all active,with 83 active volcanoes.The total area of volcanic facies accounts for 90.09%in E₃d₂^U.The area of volcanic channels are mainly less than 0.4 km²,and the area of volcanic channels generally increases from deep strata to shallow strata.There are three main volcanic eruption patterns in the Bozhong34-9oilfield:central composite layered volcanic eruption,central hydrothermal volcanic eruption and central-fractured composite layer volcanic eruption.The volcanic edifices has formed a"roof-support-floor"system in space,which is conducive to the formation of high-quality reservoirs.By finely characterizing the volcanic rocks in space,this study guided the design of well location schemes in the oilfield,reducing the risk of development,and it has extremely important reference significance for the characterization of special bodies in clastic basins.