Prediction Of High-quality Volcanic Reservoirs In The Permian Fengcheng Formation In Wuxia Area,Junggar Basin

In recent years,with the continuous improvement of oil and gas exploration technology,volcanic oil and gas reservoirs at home and abroad have been continuously discovered,a number of volcanic reservoirs have also been discovered in the Junggar Basin.Despite numerous previous studies,the volcanic strata of the Fengcheng Formation in the Wuxia area has not been systematically investigated because of the complicated lithology(e.g,deep burial depth of volcanic rock formation)and complex reservoir space.Hence,it has been very difficult for researchers to predict the volcanic reservoirs for many years,which can also be due to the low exploration level.In this study,we investigate the characteristics of volcanic reservoir via their physical properties,patrology,reservoir space by analyzing geological and seismic data.;we also focus on stuying the plane distribution characteristics of volcanic rocks with comprehensive assessment and prediction for volcanic reservoirs in Wuxia area by using geophysical technologies(e.g,geophysical frature analysis,seismic attribute analysis,seismic forward modeling,and seismic inversion).Based on the observations,we found that the main reservoirs of volcanic rocks are the volcaniclastic rocks that located at the bottom of the Fengcheng Formation in the Wuxia area are.Basically,the major type of reservoir space is primary pores with relatively low level of fracture development and semi-filled pores with extensive development.Surface water infiltration in faulted area is prone to produce calcium and silicon that leads to fill the gas pores of volcanic rocks,which is part of the low-to-medium porosity and low permeability reservoirs.Moreover,the breccua tuff with high porosity has the characteristics of well logging response of low-to-medium resistivity,high gamma,and medium-to-high acroustic wave time difference and low density.The experimental results based on forward modeling reveal the seismic reponse characteristics of volcanic rocks with different degree of pore filling.It also tells us that the level of pore-filling has good correlation with the layer velocity and amplitude value.For example,the lower the porosity and level of filling,the stronger the amplitude and the higher the energy,and vice versa.We implement the seismic inversion method and Bayesian-based seismic physical parameter method,combined with seismic attributes,to analyze the characteristics of reservoir plane distribution.Then we classifiy the types of reservoirs and seek for high-quality volcanic reservoirs with high porosity permeability.Finally,we predict that the lithologic trap in the west of Xia 72 well area is the most likely benifit objective.