Airborne Gravity Gradiometry for Rapid Mapping of Hydrocarbon Exploration Plays

Abstract

Introduction Over the past decade the Airborne Gravity Gradiometer (AGG) has been applied to a range of hydrocarbon exploration plays in settings from Australia to the Americas. Case study examples will illustrate that fixed-wing and helicopter borne AGG, when combined with high-resolution magnetics and available 2D seismic profiles, provide the means to rapidly, efficiently and safely explore for a variety of hydrocarbon exploration plays, including basement structural traps, salt structures and carbonate reefs. The AGG technology The Airborne Gravity Gradiometer (AGG) was designed and built explicitly for airborne use by the FALCON project (van Leeuwen, 2000) and called the FALCON AGG. Since 2005, this technology has used fully digital electronics. The digital AGG is smaller and lighter than other gravity gradiometers, permitting its installation in smaller aircraft, particularly helicopters. Improved airborne gravity data quality AGG provides twenty times better spatial resolution [150m versus 3,000m], and five times less noise [0.15 mGal versus 1.0 mGal] than conventional Airborne Gravity (Dransfield and Christensen, 2013). With the advent of a helicopter borne system AGG surveys can now be conducted as draped surveys in rugged terrain and at lower flight speed than by fixed wing aircraft, translating into additional improvement in the lateral resolution of the AGG data [45m]. Rapid AGG data acquisition The AGG system has been designed specifically for use in light aircraft and demonstrates minimum sensitivity to air turbulence. The system can operate in turbulent conditions and routinely acquires in excess of 4,000 line-km per week. This translates into very rapid data acquisition, when contrasted to ground-based gravity acquisition. Fernandez et al. (2010) published an AGG case study from Argentina, Figure 1. A ground gravity survey of similar resolution (300m by 150m gravity station spacing) would require ~70,000 ground gravity station, or nearly two years of ground crew field work. In contrast the AGG survey was completed in two months with no safety incidents.