The seafloor nodes used in production are the latest generation of vertical EM receivers developed by Allton. A decade of operational experience and data analysis has provided valuable input for the latest design which improves data quality and ensures efficient and safe operations. The nodes are shaped as 4m high tripods to provide the required vertical sensing dipole length and equipped with state-of-the-art electric field sensors for both vertical and horizontal fields. All while the nodes are kept light weighted for easy handling. The verticality is secured by active control and verified by acoustic communication to the vessel. The same acoustic unit is also used for positioning the nodes.
The design is robust and flexible allowing the receiver to be dropped from sea surface sinking freely to the seafloor or lowered to the seafloor by crane if required for reposition of historical locations or close to infrastructure.
Negative buoyancy is achieved by using sand chambers on the 3 legs. The receiver floats back to the surface when the sand is released from all 3 chambers by an acoustic trigger signal.
SOURCE & HANDLING SYSTEM
The source system developed by Allton is based on the use of a vertical dipoles sending bipolar pulses in a pre-planned pattern based on survey design work. Two pulse electrodes, separated vertically by a distance almost equal to the water depth, are fed by the out-put current of a pulse generator. The pulse generators are containerized and configured in pairs with an current output of 3,000A each. Each electrode, 2 pairs of 2 are connected to the generators via an umbilical.
Handling of the electrodes is efficiently done by the use two A-frames designed and built for the purpose.
For further questions related to the equipment please contact Allton´s Operations Director Joar Larsen.