Eismic Prediction Of Permian Volcanic Reservoirs In Jianyang Area,Southwest Sichuan

At the end of 2018,Yongtan well 1,a risk well deployed by Petro China Southwest Oilfield Company,Petro China for Permian volcanic rocks in Southwest Sichuan Basin,encountered volcanic reservoirs in Permian,and high-yield gas flow was obtained in trial production,reaching 22.5%×10~4m~3/D,the effusive pyroclastic gas reservoir was found in this area for the first time,indicating that a major breakthrough has been made in the exploration of volcanic gas reservoir;This field is expected to become an important exploration replacement field in Sichuan Basin.This paper comprehensively uses geological,logging and seismic data,establishes volcanic eruption mode and seismic response identification mode,carries out fine comparison of volcanic rock top and bottom interface,and implements the distribution range of volcanic rocks in Jianyang area.Combined with the seismic response characteristics of volcanic rocks and model forward modeling,the seismic facies models of volcanic rocks in different facies zones are established to systematically describe the distribution of favorable volcanic facies;Through the quantitative study of volcanic reservoir facies control in Yongtan 1well area,the distribution of volcanic explosive reservoir is predicted,and the next favorable volcanic exploration area in Jianyang area is defined.The study shows that the Permian volcanic rocks in Southwest Sichuan mainly develop effusion facies,overflow facies and sedimentary volcanic facies,and the lithology includes tuff,basalt and pyroclastic lava.The volcanic rocks in the study area have special response characteristics in seismic reflection:the top is continuous strong wave crest reflection or intermittent medium strong wave crest reflection,the bottom is weak reflection,and the interior is chaotic,mound like,parallel or sub parallel reflection.According to the seismic reflection characteristics,five volcanic seismic facies are identified in the study area,namely class I explosive facies,class II explosive facies,overflow facies,volcanic sedimentary facies and normal sedimentary facies without volcanic rocks.Class I explosive facies are widely distributed in Chengdu Santai area.A total of 20 abnormal bodies of class I explosive facies are found,which are distributed in nearly east-west direction.They are densely distributed in Chengdu Zhongjiang area,with an area ranging from 6.2 km~2to 209.4 km~2.Yongtan 1 well area is the largest,with an area of 209.4 km~2.Class II explosive facies are widely distributed in Chengdu Jianyang Santai area;Overflow seismic facies is developed in Dashen 001 well area;Volcanic sedimentary facies are developed in Nanchong 2 well area,without volcanic rocks,and normal sedimentary facies are widely distributed.Volcanic reservoirs are controlled by many factors,including lithofacies and fluid transformation.Among them,lithofacies is the main factor affecting the distribution of Permian volcanic reservoirs.Based on a variety of data,it is considered that the high-quality volcanic reservoir is mainly developed in Chengdu Jianyang Santai area.The lithology is pyroclastic lava.It is a porous reservoir with porosity ranging from 9%to 13%and more than 11%in the core.It is continuously distributed on the plane and generally more than 120m thick.It is the most favorable zone for volcanic oil and gas exploration at present.