Land Acquisition Systems: From Centralized Architecture to Autonomous Sources & Receivers
Mougenot, Denis *1
(1) Sercel, Carquefou, France.
Application of new technologies to Land acquisition systems has opened the way to various survey architectures. On both the source and the receiver sides, we have the option to keep field equipment centralized (e.g. cable systems) or to have it autonomous thanks to GPS synchronization (e.g. cableless systems). Such flexibility has increased crew productivity to such level that high-density 3D surveys can now be performed in more difficult areas.
With centralized architectures, receivers are connected via cables to the Central Unit and the sources are triggered by radio from the recorder. Synchronization as well as real time quality control and data recovery are made easy. However, as the spread size increases and the areas to be surveyed get more obstructed, this type of architecture presents some constraints.
The recently availability (2005) of high sensitivity and low power GPS chips has been the enabling technology to move beyond this centralized architecture while preserving accurate synchronization (30 ns). On the receiver side, it is possible to lay-out autonomous field units equipped with GPS, memory and battery. Such cableless spreads provide the easiest access to difficult terrain, reduced environmental footprint and more flexibility on spread geometry. The key feature for the latest generation of cableless systems is the harvesting of data in the field using WiFi, rather than waiting until units are returned to the base-camp.
On the source side, vibrators equipped with GPS for both positioning and timing may also be disconnected from the recorder. The Central Unit or the autonomous units record a continuous stream of GPS time stamped seismic samples. As the vibrators record the start time of each sweep, a simple correlation by the pilot is able to extract the corresponding Vibrating Point (VP) from this continuous record. Thus, without waiting for any command, vibrators can sweep as soon as they are ready (ISS from BP) or in accordance with a predefined GPS time table (V1 from CGGV). Both methodologies enable more than 10 vibrator fleets to operate at the same time. They have increased significantly VibroSeis productivity in open terrain (more than 1000 VP’s per hour).
By combining autonomous sources and receivers, a completely different way of performing Land acquisition has been achieved.
AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain