FALCON? Airborne Gravity Gradiometry Provides a Smarter Exploration Tool for Unconventional and Conventional Hydrocarbons: Case Study from the Fitzroy Trough, Onshore Canning Basin

摘要

A FALCON~? airborne gravity gradiometer (AGG) survey was flown over the Yakka Munga area of the Fitzroy Trough, onshore Canning Basin in December 2011. The 3336.8 line km survey centred on the Ungani oil field over a survey area of approximately 1400 sq. km. Regional gravity and 2D seismic data, along with the Ungani-1 and 2 wells in the area and wells Yulleroo-2 and Frome Rocks-1 in the vicinity were utilised in an integrated interpretation of the AGG data. Integrated geological and geophysical interpretation, including depth to basement, 2D modelling and 3D inversion, revealed the particular usefulness of AGG data for mapping intra-sedimentary and basement faults, basement highs, sedimentary depocentres,salt diapirs and volcanic intrusions. Additionally, prospective structural and stratigraphic plays in the area are highlighted. Conventional vertical gravity (gD) from the AGG survey better defined the longer wavelength features, typically the major tectonic elements such as basin bounding faults, and relative sediment thickness. Comparisons with the regional gravity data showed that the gD reproduced all the information available in regional gravity. At shorter wavelengths, the vertical gravity gradient (GDD) of the AGG data has much higher sensitivity than the regional gravity dataset. The GDD is more sensitive to subtle density contrasts and has greater spatial resolution than gD, therefore, it provides more detail than gD by imaging smaller and shallower sources. The increase in resolution allows for contacts to be mapped more accurately, and significantly increases the confidence of the 2D seismic interpretation. Enormous potential exists for conventional and unconventional oil and gas in the Fitzroy Trough, a proven petroleum province. The AGG survey flown includes the simultaneous acquisition of high resolution gravity gradiometer, magnetic and DTM data from one airborne platform. The data acquired is used to generate a high resolution geological model over the study area which is then used as input in the 3D inversion. Following the calibration of the structural information present in the geologic model, the output density model and basement surface can be used to optimize exploration programs and plan future seismic acquisition through improved knowledge of the subsurface structural, density and depth distribution. A number of plays identified by the associated structural and stratigraphic interpretation may provide leads for shale gas, tight gas and conventional oil & gas exploration.