Volcanic Reservoir Characteristics Of The Huoshiling Formation In The Longfengshan Area Of The Changling Fault Depression And Its Relationship With Hydrocarbon Distribution

In recent years,an important breakthrough has been made in oil and gas exploration of volcanic rocks in the Lower Cretaceous Huoshiling formation in the Longfengshan area,Changling fault depression.However,the characteristics of the volcanic reservoir and its relationship with oil and gas distribution are still unclear,which restricts the effectiveness of oil and gas exploration.Through core observation,thin-section identification,scanning electronic microscopy,mercury injection,and CT scanning,combined with well-logging,seismic,oil testing,and production data,the characteristics and controlling factors of the volcanic reservoir in the Huoshiling formation are studied,the genetic model of the volcanic reservoir is established,and the relationship between the reservoir and hydrocarbon distribution is clarified.The results show that the volcanic rock types of the Huoshiling formation include volcanic lava,pyroclastic lava,pyroclastic rock,and sedimentary pyroclastic rock.The lithofacies types include explosive facies,effusive facies,and volcanic sedimentary facies.According to the geological and logging methods,volcanic rocks of the Huoshiling formation can be identified as two cycles and three periods.Based on the difference of seismic reflection characteristics and volcanic facies association,the volcanic institution can be divided into near-source,middlesource,and far-source facies belt.The volcanic reservoir space of the Huoshiling formation includes pore and fracture,mainly composed of intergranular solution pore,intragranular solution pore,matrix solution pore,and structural fracture.The reservoir mainly belongs to medium porosity and medium permeability reservoir,and the better physical properties are andesitic tuff,andesitic breccia of explosive facies,and some andesites of effusive facies.The pore structure of volcanic reservoir in the study area is poor,which is dominated by the fine state of II and the slight fine state of III,characterized by medium sorting,poor connectivity,high displacement pressure,and low maximum mercury saturation.The development of the volcanic reservoir in the study area is controlled by both internal and external factors,the internal factors are volcanic apparatus-cycle,lithology,and lithofacies,and the external factors are weathering and leaching,acid fluid dissolution,and tectonism.Three genetic models of the primary reservoir,weathering crust reservoir,and fault-corrosion reservoir are established.The primary reservoir is developed in the upper part of lava flow and the interface of the eruption cycle;The weathering crust reservoir is developed in the high part of the structure;The fault-corrosion type reservoir is developed at the interface of the eruption cycle near the faults and hydrocarbon-generating sags.The volcanic reservoir plays a significant role in controlling the distribution of oil and gas.The lithofacies control the degree of oil and gas,the thickness of favorable lithofacies is bigger,the thickness of the oil and gas layer is bigger;The genetic types of the reservoir control the differential enrichment of oil and gas,and the fault-corrosion type reservoir has the highest enrichment degree;The vertical distribution of oil and gas is controlled by the unconformity and periodic interface,and oil and gas are mainly distributed in the range of 100 m below the unconformity and near periodic interface;High-quality reservoir controls the location of oil and gas enrichment,and the location of high-quality reservoir development leads to high oil and gas production.