Exploring for unconventional hydrocarbon plays in the Glyde Basin, Northern Territory, using FALCON® airborne gravity gradiometry (AGG) data

Abstract

A FALCON® AGG and magnetic survey in the Glyde Sub-basin aims to define the structural pattern to identify unconventional hydrocarbon plays. The survey area consists of variable thick fluvial and lacustrine to shallow marginal marine carbonate-siliciclastic sequences and lesser volcanic rocks. The dominant tectonic feature identified on the AGG data is the Emu Fault Zone: a major structure of the central-southern part of the McArthur Basin. Seismic and surface geology suggest its overall sub-vertical strike-slip nature with positive flower structure geometry. In the north, a regional size pop-up structure, reverse, transpressional and strike-slip faults, and abundant synclines and anticlines identified in the AGG data indicate sinistral transpression. In the south, a transtensional segment of the Emu Fault Zone formed several regularly oriented, fault controlled depocentres. A geological cross-section across the Glyde Sub-basin supported by gravity modelling indicates a system of inverted transtensional faults. Offsets and bifurcations are common, forming local-scale transtensional or transpressional areas. The relationship between dolomitic carbonaceous siltstone, fault-related hydrothermal dolomite (HTD), and the tectonic pattern strongly suggests that the Emu Fault Zone controlled fluid migration and fault-related HTD deposition. Brecciated HTD reservoirs are best developed where a combination of strike-slip movement and extension allowed dolomitising and porosity-generating fluids to migrate along fracture networks, especially in transtensional pull-apart structures, and along the principal faults bounding elevated parts of the basement. This is consistent with the results of the Glyde–1 ST1 exploration well, which drilled 122 m of gas charged dolomitic breccia.