Abstract：The whole-well length Q including a stable deep Q value and near-surface Q value is used for seismic inverse Q filtering.The stable deep Q value can be estimated by the improved spectral fitting method on zero-offset VSP data.However,zero-offset VSP shallow data affected by casing waves has poor quality.Its first arrivals are unclear,and cannot estimate near-surface Q.When the near-surface is thicker,multiple ghosts can be clearly seen on downward waves of walkaway VSP data.Therefore,a method for estimating near-surface Q is proposed based on walkaway VSP data.This Q value can be regarded as its thickness equivalent Q.When a shot point is located at the top of the high-velocity layer,statics of the shot point can be obtained on walkaway VSP.The statics are half of the time difference when the Q value is calculated by the spectral ratio method.Then a near-surface Q of a single shot is estimated with the spectral ratio method,and the whole near-surface Q values on walkaway data can be obtained in turn.So the whole-well length Q can be obtained on walkaway VSP and zero-offset VSP data.
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