Marine Acquisition

Fugro-LCT is recognized worldwide for providing the most advanced gravity and magnetics acquisition services in the industry. With the advent of the fully digital, real-time marine gravity meter and implementation of an intensive operator training program, supported by the comprehensive marine operators manual (MOM), our field operations have further advanced their tradition of quality and performance. Gravity and magnetic acquisition projects have been successfully completed under all conditions, and worldwide marine environments. Fugro-LCT has developed new technologies for acquiring marine gravity in conjunction with 3D seismic surveys as an aid in interpreting complex 3D data. Fugro-LCT has also developed a software product, LCTSEIS-3D, which provides a comprehensive toolkit for the application of high-resolution gravity and magnetic data to seismic velocity modeling.

For marine gravity acquisition Fugro-LCT provide a complete range of marine gravity meters. These include the LaCoste and Romberg Model S marine gravity meter (with Ultrasys, ZLS, SeaSys or SAGE digital control systems), the Bell BGM3 gravity system, widely accepted as the best in the business, and the BodenSeewerk meter. These systems are supplied complete with UNISON digital data acquisition logging system, and a complete spares inventory.

DGPS navigation data including position, speed and heading information is also recorded by Fugro-LCT at a nominal 1-second sample rate. Additionally, Fugro-LCT is usually supplied with final navigation data in P1/90 format in order to merge the geophysical data with shot point and bathymetry. The navigation data are used in gravity data processing to remove the effects of the survey vessel motion.

In order to tie a gravity survey to the international gravity standardization network it is necessary to calibrate the marine gravity meter to a known absolute gravity station at the dockside. Depending upon port of mobilization, there may be an existing station or else a new land tie will need to be established. During the survey planning stage Fugro-LCT can advise on the status of absolute stations and the methodology required to accurately tie the survey.

Tie-lines are required for data processing. This is no problem with a 2D grid but these are usually additional to a 3D seismic program.

Fugro-LCT has a number of types of magnetometers available for marine deployment, both proton precession and the more recent Overhauser effect SeaSpy™ system. The advantage of the Seaspy™ magnetometer is that the signal is digitized in the magnetometer fish which allows deployment in Fugro-LCT's unique GunMag™ mode to minimize interference with multi-streamer seismic operations.

For marine magnetic surveys, Fugro-LCT will advise on the availability of diurnal magnetic data from existing observatories or the need to established a dedicated diurnal magnetic monitor station.

All surveys are subject to the INTEGRAV™ project management system. This is designed to keep the client fully informed during all stages from survey planning through to delivery of final products. Especially important during the data acquisition phase is the provision of data snapshots showing examples of data quality.

On completion of data acquisition a comprehensive acquisition report is produced which documents the survey and includes appendices of detailed line logs, day logs and a production log.