Application of multiwave joint inversion to the prediction of relatively high-quality reservoirs——an example from the prediction of deep tight clastic sandstone reservoirs in the western Sichuan Basin

Clastic sandstones of delta facies were developed in the fourth member of the Tertiary Xujiahe formation(T3x4) in the western Sichuan Basin and they are tight with low porosity and low permeability.The sandbodies are large in thickness,but their gas-bearing reservoirs are thin.The wave impedance of these reservoirs is similar to the surrounding rocks—tight sandstone and mudstone.It is very difficult to accurately predict the distribution of these reservoirs using conventional seismic methods.Taking advantages of 3D3C exploration,we have carried out a joint inversion of P-wave and converted shear wave.Based on the analysis of petrophysical parameter sensitivity,we have proposed the idea of quality sandstone in sandstone.The multiwave attribute data volume such as Poisson's ratio and P-wave impedance are selected for multi-volumes crossplot interpretation to recognize mudstone and tight sandstone.In this way the relatively high-quality reservoirs within tight sandstones can be accurately identified.