Evaluation of the regional top seal in the Gippsland Basin: implications for geological carbon storage and hydrocarbon prospectivity

Abstract

GeoScience Victoria and partners have undertaken the first detailed basin-wide study of the regional top seal in the Gippsland Basin. The Gippsland Basin is an attractive site for geological carbon storage (GCS) because of the close proximity to emission sources and the potential for large-scale storage projects. This top seal assessment involved the analysis of seal attributes (geometry, capacity and mineralogy) and empirical evidence for seal failure (soil gas geochemical anomalies, gas chimneys, hydrocarbon seepage and oil slicks). These datasets have been integrated to produce a qualitative evaluation of the containment potential for GCS, and also hydrocarbons, across the basin. Mineralogical analysis of the top seal has revealed that the Lakes Entrance Formation is principally a smectite-rich claystone. The geometry of the top seal is consistent with deposition in an early post-rift setting where marine sediments filled palaeo-topographic lows. The seal thickness and depth to seal base are greatest in the Central Deep and decrease toward the margins. There is a strong positive relationship between seal capacity column heights, seal thickness, depth to seal base and smectite content. At greater burial depths (below 700 m) and where smectite content is greater than 70%, seal capacity is increased (supportable column heights above 150 m). Natural hydrocarbon leakage and seepage onshore and offshore is correlated with fault distribution and areas of poor seal capacity. This study provides a framework for qualitatively evaluating seal potential at a basin scale. It has shown that the potential of the regional top seal over the Central Deep, Southern Terrace, central eastern Lake Wellington Depression and the southern to central near shore areas in the Seaspray Depression are most suitable for the containment of supercritical CO2. Further toward the margin of the regional seal in both onshore and offshore areas, containment of supercritical CO2 is less likely.

Lithospheric evolution, thermo-tectonic history and source-rock maturation in the Gippsland Basin, Victoria, southeastern Australia

“…Its offshore part can be subdivided into three main structural domains: the Northern and Southern platforms, and the Central Deep. The curved and complex east-west-striking Lake Wellington Fault System (LWFS) in the north and the deeper, more continuous west-northwest-east-southeasttrending Foster Fault System (FFS) in the south represent the two main boundary fault systems (Figure 1b) Goldie Divko et al, 2010;. They are associated with intra-basinal second-order fault systems: the LWFS is accompanied by the east-westdirected Rosedale Fault System (RFS), and the west-northwest-east-southeast-trending Darriman Fault System (DFS) trends parallel to the FFS.…”

“…The sedimentary sequence can be subdivided into three major units: the Upper Jurassic to Lower Cretaceous Strzelecki Group, the Upper Cretaceous to upper Eocene Latrobe Group and the Oligocene to Recent Seaspray Group (Bernecker & Partridge, 2001;Goldie Divko et al, 2010;Nøttvedt et al, 1995;Partridge et al, 2015).…”

“…The Gippsland Basin is located at the southeastern edge of the Australian margin between Victoria and Tasmania (Figure 1a) and can be subdivided into an offshore and an onshore part. The basin hosts giant oil and gas fields offshore and extensive lignite deposits onshore, although its deep-water region remains underexplored (Goldie Divko et al, 2010).…”

“…The applied workflow serves as a case study for thermal modelling studies of rift basins and supports the general geological understanding of the interplay of dynamic basin-forming processes. Divko et al, 2010), basement topography within the area of interest (AOI) (grey isolines after Power et al, 2001). The black lines indicate the orientation of 2D sections (Figures 4 and 14).…”

Seismic Reflection Methods in Offshore Groundwater Research

“…Data have been acquired through the years in successive campaigns focused on oil and gas The basin extends from onshore to offshore and hosts depositional sequences ranging in age from Early Cretaceous to Holocene. The main deep aquifer is hosted in the Latrobe Group sediments, of Cretaceous to Oligocene age, composed of siliciclastic sediments, ranging from alluvio-fluvial sediments at the base to marginal-marine, deltaic and increasingly marine sediments, sealed by the confining aquitard of the Lake Entrance formation (marine shales of late Oligocene age) and by the Strzelecky aquitard below (sandstones and shales of Albian age) (Figure 16) [151,152,154]. The The basin extends from onshore to offshore and hosts depositional sequences ranging in age from Early Cretaceous to Holocene.…”