3-D and 3-C seismic data analysis at Cold Lake, Alberta
J. Helen Isaac, Donald C. Lawton
3-D and 3-C seismic data have been acquired at Cold Lake, Alberta, where Imperial Oil Resources Ltd. is producing bitumen from the Clearwater Formation by means of cyclical steam stimulation of the reservoir. The data are intended for use in monitoring those changes in reservoir characteristics that can be detected seismically. The two time-lapse 3-D surveys were reprocessed in 1993 to minimize the differences between them above the reservoir. Analysis of these differences show that they are very small so that differences now observed within the reservoir section on the two surveys may be attributed to changes in reservoir conditions at the times of acquisition. 3-D inversion of the data using an extracted wavelet shows zones of low velocity at about the level of the perforations in the 1992 data, which were acquired during the steam cycle. The 1990 data, acquired during the production cycle, have low velocity zones, interpreted to be gas saturated zones.
A multicomponent survey acquired in 1993 with a P-wave source is being processed. The vertical channel data have been processed as regular P-P data through a processing stream that includes post-stack deconvolution and post-stack time migration. Shot gathers of the radial channel data show a great deal of incoherent noise but receiver gathers reveal coherent energy trains, including some P-wave energy. Preliminary processing indicates that there are very large receiver statics to be applied to the radial channel and that P-SV stacking velocities are low. Velocity data obtained from a well dipole survey indicate a Vp/Vs ratio of 2.4 above the reservoir and about 2.04 within the reservoir. It is anticipated that the introduction of steam into the reservoir will affect the Vp/Vs ratio. If the converted wave energy on the radial channel can be identified and processed to stack, this stacked section and the vertical channel stacked section may be used to determine changes in Vp/Vs along the line.