Crosswell seismic tomography without ray tracing

Abstract

A tomographic inversion algorithm is applied to invert three crosswell seismic surveys acquired in the Glenn Pool field, Oklahoma. Instead of calculating the raypaths and traveltimes explicitly by standard ray tracing, this algorithm uses a finite-difference eikonal equation solver and minimises the traveltime differences between the observed and calculated P-wave traveltimes in a least square sense. The model is updated by an SIRT-like algorithm. A dynamic a-trimmed mean filter is applied to the cost-function gradient after each iteration. Three constructed velocity tomograms showed good correlation with each other as well as with the sonic logs. However, certain anisotropy artefacts due to the interpreted shale layers were also identified from the residual traveltime maps. This study demonstrated the great potential of crosswell seismic imaging in reservoir development.