Jitendra S. Gulati

Analyzing three‐component 3D vertical seismic profiling data

A three‐component 3D vertical seismic profile (VSP) was acquired over the Blackfoot oil field in Alberta, Canada. The VSP survey was recorded simultaneously with a surface seismic program. The objectives of the VSP were to develop recording logistics, data handling, and processing procedures and to determine if the 3D VSP volumes could image the glauconitic sand reservoir of the Blackfoot field.Dynamite shots from the surface seismic survey, which fell within a 2200‐m offset from the recording well, were used in the VSP analysis. The shots were recorded by a string of three‐component borehole receivers that was moved seven times, resulting in a receiver depth range of 400 to 910 m. The borehole data were processed using basic VSP processing techniques that included hodogram analysis, wavefield separation using median filters, and VSP deconvolution. The final P‐P and P‐S image volumes were obtained by VSP common‐depth point and VSP common‐conversion point stacking the upgoing wavefields followed by f‐xy de...

Vertical hydrophone cable acquisition and imaging on land

We acquired seismic data using a vertical hydrophone cable in a shallow, fluid‐filled borehole over the Blackfoot oil field in Alberta, Canada. The hydrophone data were recorded simultaneously with a surface seismic survey using dynamite sources. In addition, buried three‐component (3‐C) geophone data were acquired near the vertical cable. We observe that events on the hydrophone records are in phase with corresponding geophone data. Tube waves, which can be a problem on hydrophone data, are suppressed using a predictive deconvolution operator. Imaging, using the hydrophone data, results in a section that correlates well with a surface seismic image from vertical‐component geophone data. An anomaly, interpreted to be associated with the sand reservoir in the area, is evident on the hydrophone image (as well as on the surface seismic sections). The vertical hydrophone cable promises excellent imaging potential for land applications.

Seismic exploration through high‐velocity layers

A seismic model based on log data from northeastern Ireland, which is covered by high-velocity basalts on the surface, is used to study seismic imaging problems over high impedance layers. Zoeppritz responses at the top and bottom of the high-velocity layer (HVL) of the model predict strong modal conversions for an incident P-wave. Raytracing leads to an intuitive reasoning for the strong P-to-S conversions, the wave tends more towards preserving its moveout than its mode at the HVL interface. Synthetic seismograms demonstrate that the presence of the various mode-converted (multimode) arrivals leads to complicated reflection events. Separation of various arrivals is important prior to interpretation. The P-S reflection equation is modified to a form which gives physical insight into the amplitude variation with offset of converted waves. Finally, this equation is shown to isolate the multimode arrivals and can be the basis of a modal filter.

Land vertical cable acquisition and analysis: Results from the Blackfoot high-resolution 3-C seismic survey

During November 1997, the CREWES Project at the University of Calgary acquired a high-resolution 3C-2D seismic survey at the Blackfoot field located east of Calgary. To test the feasibility of vertical cable acquisition in a land environment, a 48-channel hydrophone cable was deployed in a 100 m cased and water-filled hole located in the centre of the profile. The additional hydrophone channels were patched into the surface recording spread which allowed for the simultaneous recording of all 151 dynamite shots into the surface geophones and the vertical cable. Initial results of a VSPCDP stack of the entire hydrophone data revealed a continuity of reflectors across the section and good correlation with the surface seismic results. An average of the VSPCDP stacked traces near the hydrophone cable spliced between the surface seismic section demonstrated the ability to obtain reliable images from the hydrophone cable data.

Analysing 3C-3D VSP Data: The Blackfoot, Alberta Survey

Summary A simultaneous surface and borehole 3C-3D survey was acquired over the Blackfoot field in southern Alberta. Along with the land surface 3C-3D seismic program covering about 15 sq. km., 3-C VSP measurements were made over depths from 400 to 910m. In this paper, we outline the acquisition and processing considerations involved with the Blackfoot 3C-3D VSP experiment. Final P-wave and converted-wave images from the 3-D VSP tie reasonably well with those from the surface survey. A method was also developed for rapid VSPCDP mapping and results are shown for the VSP data.