Autonomous Vehicles Benefit From 3-D Seismic Arrays
The use of autonomous marine vehicles (AMVs) for offshore oil and gas activity continues the trend of exploiting robotics technology to support safety, lower costs, and improved data acquisition and quality. In particular, AMVs combined with a 3-D sensor array (3DSA) have proven effective for seismic acquisition in many environments and operating conditions to complement the proven towed streamer technology. These applications include shallow water, infill around obstructions as close as 100 m (330 ft), environmentally sensitive areas such as coral reefs, acquisition of long-offsets as long as 30 km (18.6 miles), rough terrain, deep water—to avoid using an ROV—and acquisition of full-azimuth data for velocity model-building.
Recent field tests conducted offshore Abu Dhabi and in the Green Canyon area of the Gulf of Mexico show comparable data quality between data acquired with the 3DSA platform and data acquired by other methods like towed streamer, ocean-bottom nodes (OBN) or ocean-bottom cables (OBC).
The AMV used in seismic application comprises a surface float and a subsurface glider connected by an umbilical. The propulsion system works on a combination of wave and mechanical energy and thus requires no onboard fuel. As the surface float rises on the crest of a wave, the vertical wave motion is transferred via the umbilical to the glider section. This causes the glider’s wings to move up and down, which provides constant forward motion. The surface float includes solar panels and a battery, GPS and a communication link, a vertical management computer, and a mini-acquisition system for acquiring and storing high-density seismic data.
AMVs can be programmed to receive commands via satellite from a pilot in an onshore operations center. Typically, they can hold station simulating a “floating node,” and once acquisition is complete, the entire fleet can be ordered to move to the next position through a series of waypoints. Based on survey type, AMVs can either be held in a grid formation or a receiver line every few hundred feet apart. While the AMV used in this survey was wave-powered, other AMVs are coming on the scene that use other forms of energy such as wind, solar and battery power.