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Fitzsimmons K.E.,Max Planck Institute for Evolutionary Anthropology | Cohen T.J.,University of Wollongong | Hesse P.P.,Macquarie University | Jansen J.,University of Stockholm | And 10 more authors.
Quaternary Science Reviews | Year: 2013

In this paper we synthesise existing palaeoenvironmental data from the arid and semi-arid interior of the Australian continent for the period 40-0ka. Moisture is the predominant variable controlling environmental change in the arid zone. Landscapes in this region respond more noticeably to changes in precipitation than to temperature. Depending on their location, arid zone records broadly respond to tropical monsoon-influenced climate regimes, the temperate latitude westerly systems, or a combination of both.The timing and extent of relatively arid and humid phases vary across the continent, in particular between the westerly wind-controlled temperate latitudes, and the interior and north which are influenced by tropically sourced precipitation. Relatively humid phases in the Murray-Darling Basin on the semi-arid margins, which were characterised by large rivers most likely fed by snow melt, prevailed from 40ka to the Last Glacial Maximum (LGM), and from the deglacial to the mid Holocene. By contrast, the Lake Eyre basin in central Australia remained relatively dry throughout the last 40ka, with lake high stands at Lake Frome around 35-30ka, and parts of the deglacial period and the mid-Holocene. The LGM was characterised by widespread relative aridity and colder conditions, as evidenced by extensive desert dune activity and dust transport, lake level fall, and reduced but episodic fluvial activity. The climate of the deglacial period was spatially divergent. The southern part of the continent experienced a brief humid phase around ~17-15ka, followed by increased dune activity around ~14-10ka. This contrasts with the post-LGM persistence of arid conditions in the north, associated with a lapsed monsoon and reflected in lake level lows and reduced fluvial activity, followed by intensification of the monsoon and increasingly effective precipitation from ~14ka. Palaeoenvironmental change during the Holocene was also spatially variable. The early to mid-Holocene was, however, generally characterised by moderately humid conditions, demonstrated by lake level rise, source-bordering dune activity, and speleothem growth, persisting at different times across the continent. Increasingly arid conditions developed into the late Holocene, particularly in the central arid zone. © 2012 Elsevier Ltd.

Golab A.N.,Australian National University | Knackstedt M.A.,Australian National University | Averdunk H.,Australian National University | Senden T.,Australian National University | And 2 more authors.
Leading Edge (Tulsa, OK) | Year: 2010

Tight gas reservoirs exhibit storage and flow characteristics that are intimately tied to depositional and diagenetic processes. As a result, exploitation of these resources requires a comprehensive reservoir description and characterization program to identify properties which control production. In particular, tight gas reservoirs have significant primary and secondary porosity and pore connectivity dominated by clays and slot-like pores. This makes them particularly susceptible to the effects of overburden stress and variable water saturation. This paper describes an integrated approach to describe a tight gas sandstone at the pore scale in 3D. In particular, the primary and secondary porosity of a tight gas sandstone are identified and quantified in three dimensions using 3D X-ray micro-CT imaging and visualization of core material at the pore scale. 3D images allow one to map in detail the pore and grain structure and interconnectivity of primary and secondary porosity. Once the tomographic images are combined with SEM images from a single plane within the cubic data set, the nature of the secondary porosity can be determined and quantified. In-situ mineral maps measured on the same polished plane are used to identify different microporous phases contributing to the secondary porosity. Once these data sets are combined, the contribution of individual clay minerals to the microporosity, pore connectivity, and petrophysical response can be determined. Insight into the producibility may also be gained. This illustrates the role 3D imaging technology can play in a comprehensive reservoir characterization program for tight gas. © 2010 Society of Exploration Geophysicists.

Armitage P.J.,University of Liverpool | Faulkner D.R.,University of Liverpool | Worden R.H.,University of Liverpool | Aplin A.C.,Northumbria University | And 2 more authors.
Journal of Geophysical Research: Solid Earth | Year: 2011

The long-term success of the geological storage of CO2 is dependent on the integrity of the sealing horizons, yet there is a paucity of data on permeability, permeability anisotropy, and factors that affect them. Using samples from an ongoing field trial for CO2 sequestration, this paper presents measured vertical (kv) and horizontal (kh) permeabilities across a range of effective pressures. Petrological and petrophysical analyses highlight what are the dominant controls on permeability. The Krechba field in Algeria is one of the largest CO2 storage projects currently running with over 3M tonnes of CO2 injected since 2004. Experimental samples of the caprock and underlying storage domain were recovered from the base of the succession. Caprock permeability ranges from 10-23 to 10-19 m2. Permeability decreases with decreasing porosity and pore throat radius and increasing clay mineral content. Primary depositional heterogeneous distribution of clay minerals produced contrasting layers of relatively low and high permeability resulting in extreme kh/kv ratios of up to 50,000. Samples with the same porosity, mean pore throat size and clay mineral content can have k h/kv differing by >4 orders of magnitude. The data was used to model permeability using the Yang-Aplin model. Accuracy of the predicted permeabilites was found to reflect the measured permeability anisotropy. The results highlight that lateral migration of CO2 will be significant and that the caprock succession at Krechba should provide a good seal, even with decreasing effective pressure during injection, in the absence of significant modification by deformation and/or reaction with the CO2-rich fluids. Copyright 2011 by the American Geophysical Union.

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