Seismic reservoir prediction and exploration prospect analysis of shallow gas reservoirs in the Qujing Basin,Yunnan province

The gas reservoir of Ciying Formation in Qujing basin is a typical lithologic gas reservoir with super-shallow burial depth of 300-450 m.The major reservoir has high porosity and moderate permeability,and its lithology is medium-fine sandstone in point bar of delta plain facies and shows very rapid lateral change.As no specific seismic reservoir prediction technologies are available before,success rate of exploration and development was low.Based on analyses of reservoir physical properties and wave impedance characteristics,forward modeling and seismic response,we established a reservoir prediction model,i.e.,mound or lenticular low frequency strong wave trough impedance and low impedance.It was successfully used to predict the distribution of favorable sedimentary facies through analyses of seismic facies and seismic attribute.The interpretation traps of mudstone and coal seam were effectively eliminated.By AVO analyses and multi-wavelet decomposition,a gas reservoir identification model,i.e.,type-Ⅲ AVO,strong low frequency and weak high-frequency was built and applied to predict the distribution of gas reservoirs.The reservoir and gas potential prediction results are integrated to comprehensively evaluate lithologic traps.Several favorable lithologic traps are discovered and successfully verified by drilling,significantly improving exploration success rate.The Neogene basins are widely distributed in Yunnan Province and have great exploration potentials,but are still underexplored by now.The technique of seismic reservoir prediction can be applied for exploration and development of similar gas reservoirs.