A Cold War technology invented to stealthily guide the United States Navy’s nuclear submarine fleet is now serving a much more peaceful purpose: aiding in the search for oil and gas deposits. Far removed from the ocean depths, gravity gradiometry has evolved to become an increasingly sophisticated aerial technology that has been used to rapidly analyze the subsurface of every continent in the world. Since its introduction to the oil and gas industry in the 1990s, airborne gravity gradiometer (AGG) technology has become an increasingly popular greenfield exploration tool because of its ability to analyze wide areas onboard airplanes for a fraction of the cost of 3D and 3D seismic surveys. The Falcon system, from geoscience firm CGG, has been improved so it can be used with helicopters, which provide higher-resolution data by bringing the unit closer to the ground.
Late last year, CGG wrapped up a 28,000 km2 (10,810 sq mile) survey in an unexplored region of Papua New Guinea using its latest gravity gradiometer technology, Falcon AGG. The company, which acquired the technology from Fugro in 2012, said that the Falcon AGG delivers the highest resolution and lowest noise-to-data ratio of any such system in use today. AGG works by measuring the differences in the gravitational pull of nearby geological formations. Denser rocks will have a higher pull than those that are less dense, and aerial surveys give explorers the ability to interpret the density variations as they relate to hydrocarbons. “With that, it will help you understand the rock types, structures, and any other anomalous material, be it a sinkhole or oil,” said Chris van Galder, an AGG adviser at CGG.
The geologic structural information collected by AGG aids operators in the interpretation of the 2D target area and fills in other gaps. It can also be used to locate optimal shot points and receiver points for a 3D seismic survey.
Compared with 2D or 3D seismic surveys, van Galder said AGG surveys are a faster and cheaper by an order of magnitude and can optimize 2D or 3D survey operations by giving exploration companies a better idea of where to look for oil and gas. “If we can help them carve out areas where there is no need to (acquire) seismic data, not only have they gotten a better picture of the overall area, they have saved significant costs in their exploration budget,” he said. Exploration companies deploy this technology to remote places such as Papua New Guinea, where the terrain is rough and covered by dense vegetation, because it would be “next to impossible to actually acquire any data,” with ground-based surveying technology, said van Galder.