Deep Fault System And Its Controlling On The Distribution Of Permian Volcanic Rocks In Southwestern Sichuan Basin

In recent years,with the breakthrough of natural gas exploration in Permian volcanic reservoirs in Sichuan Basin,more and more attention has been paid to volcanic reservoirs.Permian volcanic rocks are distributed in the west of Sichuan basin,and there are various types of volcanic rocks.So it becomes very important to conduct research on volcanic lithology,lithofacies and their distribution.In addition,deep faults in the western Sichuan Basin are usually used as volcanic channels.It is of great significance to discuss the control of faults on volcanic rocks.In this paper,the Permian volcanic rock section in the southwest of Sichuan Basin is taken as the research object,and the volcanic petrology and petrography are used as the theoretical basis.The data of core,rock slice,logging curve,seismic data,gravity magnetoelectricity and other data are also applied.The types of Permian volcanic rocks and lithofacies in Southwest Sichuan Basin are classified and their characteristics are summarized,and a three-dimensional distribution model of deep faults in southwestern Sichuan Basin is established.On this basis,the influence of deep faults on the distribution of Permian volcanic rocks is explored.On the basis of determining the lithology through the data of cores and thin slices,the logging curve characteristics of volcanic lithofacies in southwestern Sichuan Basin are summarized through the logging response characteristics of volcanic lithology.Fine interpretations on seismic profiles are made through well-seismic synthesis,and a volcanic seismic facies identification plate is summarized.It is confirmed that the explosive facies in the study area are mainly distributed near well Yongtan 1 in the northeast of the study area,Pujiang and Xinjin,and the diabase porphyrite is mainly distributed near well Yongtan 1.The effusive facies is widely distributed in the study area,but the transition between the effusive facies and the volcanic sedimentary facies can be seen in the East of the study area.11 deep faults have been identified in the study area.Based on the analysis of magnetic and electrical anomalies,volcanic lithofacies,volcanic thickness distribution,fault distribution and overburden of overlying strata,six relatively reliable volcanic edifices are found in the basin,which are distributed near faults F₂,F₅,F₆ and F₁₀.The area with thick volcanic rocks is usually in the hanging wall of the fault,the deep fault F₂ resurrects near Xinjin,and F₅,F₆,F₁₀0 resurrects near Longquan during the eruption of volcanic rocks to form a volcanic edifice.According to the seismic data,the identified volcanic edifice can be roughly divided into three types:the complete volcanic edifice of central eruption,the complete volcanic edifice of multi-point eruption and the complete volcanic edifice of fissure eruption.In the southwest of Sichuan basin,the explosive facies are mainly distributed near the faults.It reflects that magma takes faults as channels and erupts to the surface to form a volcanic channel.The location of deep faults controls the distribution of volcanic edifice.