Conoco Inc.

William S Harlan

Shein S Wang

Douglas W Hanson

A method for rapidly and efficiently generating traveltime tables for application in depth migration initially includes receiving a velocity model which may include a plurality of velocities in multiple layers between various subsurface reflectors. The model is plotted on a two dimensional grid with the subsurface reflectors identified. A traveltime to the first reflector is determined. Traveltimes from the sources on each layer boundary to all grid points above the next reflector are determined. For the initial iteration, the layer boundary is the surface and the source is the actual source used in shooting the line. For layers below the surface there will be more than one source or secondary source. The actual determination of traveltimes for these lower layers may be done by comparing the traveltimes to all points on the first reflector. The minimum traveltime is selected as the true traveltime to the first reflector. Next, all points where the reflector intersects the grid are found. Using these intersection points, the traveltimes to the second reflector may be generated in a similar manner, determining traveltimes from a predetermined point on the reflector to the second reflector.

Efficient generation of traveltime tables for two dimensional and three

A method for calculation of raypaths and wavepaths from traveltime tables for the tomographic estimation of transmission velocities includes picking the earliest traveltime of waves transmitted between different source and receivers locations. A velocity model that describes transmission velocities in a region of interest is obtained. Traveltime from each source position to each point in the region of interest and traveltimes from each receiver loaction to each point in the region of interest are extrapolated. The extrapolated traveltimes from the source and receiver to each point in the region of interest are added together to quantify the path of a wave between one source and one receiver. All points in the region of interest whose total traveltimes are less than half a wavelength greater than the minimum traveltime are found. A representative raypath that passes through the center of the estimated wavepath region for each source and receiver location are saved. The previous model of velocities are improved by tomographic means to increase the match between the recorded and modeled traveltimes along the representative raypaths.

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Ponca City, OK, United States of America

William S Harlan