Multicomponent seismic technology for imaging deep gas prospects

Abstract

Across the Gulf of Mexico, operators are targeting deeper and deeper drilling objectives. For deep targets to be evaluated, seismic data require relatively long source-receiver offsets. Most shallow-water operators in the gulf consider 30 000 ft (9 km) to be the deepest target depth that will be drilled for the next several years. For geology at depths of 9 km to be imaged, seismic reflection data must be acquired with offsets of at least 9 km. We suggest in this paper that modern 4-C OBC data can provide good quality P-SV data to such depths and should be integrated into prospect evaluations. Long-offset surveys are difficult to achieve using towed-cable seismic technology in areas congested with production facilities, typical for many shallow-water blocks across the northern Gulf of Mexico shelf. Ocean-bottom-cable (OBC) and ocean-bottom-sensor (OBS) technologies are logical options for long-offset data acquisition in congested production ar-eas because ocean-floor sensors are immobile once deployed and can be positioned quite close to platforms, well heads, or other obstructions that interfere with towed-cable operations. An example illustrating the deployment of ocean-floor sensors through a congested platform complex in part of the area of study is illustrated in Figure 1. A 10-km diameter circle is positioned atop this map of production facilities to illustrate the difficulty of towing a 10-km cable across the area in any azimuth direction. In contrast, OBC lines AA, BB, and CC (actual profiles used in this study) pass within a few meters of several production platforms. Figure 1. 4-C OBC data acquisition across congested areas. An additional appeal of OBC seismic technology is that 4-C data can be acquired, allowing targeted reservoir intervals to be imaged with P-SV wavefields, as well as P-P wavefields. Once 4-C seafloor receivers are deployed, source boats can maneuver along a receiver line to …