Nicolae Moldoveanu

Digiseis-enhanced streamer surveys (DESS) in obstructed area: A case study of the Gulf of Mexico

Following the successful 1992 field experiment which suggested that the Over/Under vertical hydrophone array technique is a viable way of undershooting obstructed areas, a full scale 3D Digiseis Enhanced Streamer Survey (DESS) was conducted in the Gulf of Mexico during the summer of 1993. Aside form gaining added operational experience from this survey, they were able to confirm the following previously observed advantages associated with the Over/Under technique: good signal to noise ratio, ease of merging with streamer data, robustness of deghosting process accurate placement of receivers, and flexibility in layout.

Survey evaluation and design (SED): A case study in Garden Banks, Gulf of Mexico

Hydrocarbon exploration in the Gulf of Mexico has reached its mature stages. Exploration objectives such as deep stratigraphic and pre-salt traps are becoming more dominant. As the exploration targets change, earlier 3D seismic surveys, designed for different objectives, become less able to meet the demands of the present day explorationist. Some areas of the Gulf of Mexico will require reacquisition of new 3D seismic data, redesigned to meet new objectives. Garden Banks is one such area. A major advantage of performing a survey evaluation and &sign (SED) in a mature area is the amount and diversity of available data. Geological profiles, reservoir characterizations, borehole wireline and surface seismic data, all serve to aid in the survey design. Given the exploration history and geological objectives, the geophysical analyses of resolution, signal loss, noise, fold, acquisition geometry, migration aperture, velocity anisotropy and others, may now be carried out in a much more specific manner. A thorough SED ensures that overall survey objectives will be met and reduces the possibility of over design on critical parameters. This generates the highest quality seismic survey for the most reasonable cost.

On the response of hydrophones and geophones in a transition zone environment

Acquiring seismic data in transition zone areas is typically done using multi-element geophone arrays (marsh phones). Recognizing the high level of noise usually associated with the rough shallow water environment and the delicate coupling problem of marsh phones, we started three years ago to use single hydrophones buried below the water bottom and into the wet mud as the detectors. In the ensuing years, the buried hydrophone techniques have consistently produced superior data quality in one survey after another. During a recent 3-D survey in southern Louisiana, a field experiment was conducted to first, establish a formal comparison between the field response of hydrophones and geophones, and second, examine the data quality as a function of the depth of burial of the detectors. This paper will describe the experiment and present the results.