Brian H. Hoffe

Analyzing the effectiveness of receiver arrays for multicomponent seismic exploration

This paper uses an experimental seismic line recorded with three‐component (3C) receivers to develop a case history demonstrating very little benefit from receiver arrays as compared to point receivers. Two common array designs are tested; they are detrimental to the P‐S wavefield and provide little additional benefit for P‐P data. The seismic data are a 3C 2‐D line recorded at closely spaced (2 m) point receivers over the Blackfoot oil field, Alberta. The 3C receiver arrays are constructed by summing five (one group interval) and ten (two group intervals) point receivers. The shorter array emphasizes signal preservation while the longer array places priority on noise rejection. The effectiveness of the arrays versus the single geophones is compared in both the t−x and f−k domains of common source gathers. The quality of poststack data is also compared by analyzing the f−x spectra for signal bandwidth on both the vertical receiver component (P‐P) and radial receiver component (P‐S) structure stacks produc...

Applications of OBC recording

In recent years, there has been much interest in seismic imaging within the marine environment via four-component (4-C) ocean-bottom-cable (OBC) recording. The 4-C OBC sensor is equipped with a single hydrophone (pressure detector) plus a three-component (3-C) geophone (particle velocity detector). The 3-C geophone records the full three-dimensional ground motion via one vertical component and two orthogonal horizontal components. 4-C OBC recording has several advantages over conventional towed-streamer technology.

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.

Some binning issues for 4C-3D OBC survey design

Summary In this paper, we demonstrate that depth-specific conversion point (DSCP) binning is superior to asymptotic conversion point (ACP) binning for 4C-3D seismic survey design. P-S fold patterns at target levels depend on Vp/Vs, and in the case of ocean-bottom cable (OBC) data, also on water depth. These issues are illustrated in a simple design example.

Analysis of the Effectiveness of 3-C Receiver Arrays For Converted Wave Imaging

During November 1997 the CREWES Project at the University of Calgary recorded a 3C-2D seismic survey at the Blackfoot field east of Calgary. This survey consisted of recording dynamite shots into a combination of conventional 20 m and high-resolution 2 m receiver intervals. We used this high-resolution data to examine two alternative approaches to array design by simulating 3-C receiver arrays via convolution in the t-x domain. The effectiveness of each approach was then evaluated by analyzing the response in both the t-x and f-k domains. The post-stack effect was also compared by analyzing the f-x response of both the final P-P and P-S structure stacks produced using these two array design philosophies.

Depth imaging by elastic wavefields—where P meets S

In November 1997 the CREWES Project at the University of Calgary, with assistance from Boyd Petro‐Search Consultants and PanCanadian Petroleum, recorded a unique, high‐resolution 3-C, 2-D seismic survey at the PanCanadian‐owned Blackfoot Field some 50–55 km east of Calgary, Alberta, Canada. The producing formation is a Lower Cretaceous, cemented, glauconitic sand deposited as incised channel‐fill sediment above the Mississippian carbonates. The sandstone is about 1500 m below surface. Its thickness ranges up to 45 m. Average porosity is near 18%. Cumulative production throughout southern Alberta exceeds 200 million bls oil and 400 billion ft3 gas.

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.