Technical Articles

The articles below have been written and contributed to by a number of sources including Task Geoscience team members and people throughout the geoscience industry. We would like to thank all the writers who contributed and all the companies and organisation that provided data.

Extended abstract: Prograding distributive fluvial systems—geomorphic models and ancient examples (Weissmann et al. 2013)

Recent work indicates that most modern continental sedimentary basins are filled primarily by distributive fluvial systems (DFS). In this article we use depositional environment interpretations observed on Landsat imagery of DFS to infer the vertical succession of channel and overbank facies, including paleosols, from a hypothetical prograding DFS. We also present rock record examples that display successions that are consistent with this progradational model. Distal DFS facies commonly consist of wetland and hydromorphic floodplain deposits that encase single channels. Medial deposits show larger channel belt size and relatively well-drained soils, indicating a deeper water table. Proximal deposits of DFS display larger channel belts that are amalgamated with limited or no soil development across the apex of the DFS. The resulting vertical sedimentary succession from progradation will display a general coarsening-upward succession of facies. Depending on climate in the sedimentary basin, wetland and seasonally wet distal deposits may be overlain by well-drained medial DFS deposits, which in turn are overlain by amalgamated channel belt deposits[...]

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Extended abstract: Soil development on modern distributive fluvial systems: preliminary observations with implications for interpretation of paleosols in the rock record (Hartley et al. 2013)

Understanding of controls on the distribution of soils in modern sedimentary basins facilitates interpretation of paleosols in the rock record. Here, we present information on soil distribution from a number of modern distributive fluvial systems (DFSs) in sedimentary basins developed in different climatic and tectonic settings. DFSs form an important part of modern alluvial sedimentary basins, and an understanding of the controls on soil development in these settings should facilitate interpretation of the alluvial rock record. The studied areas include: the Pilcomayo and Bermejo DFSs in the Andean foreland of Argentina, the Tista DFS of the Himalayan foreland basin in northern India, and the Okavango DFS developed in an intracontinental rift basin in Botswana. Soils in each of the examples are relatively immature and weakly developed. Where present, downdip changes (over distances .100 km) from relatively well-drained, relatively dry soils in sandy proximal areas to more poorly drained, relatively wet soils in more distal, clay-rich areas can be recognized. In the Andean example, this change is considered to be related to a downdip increase in precipitation and decreasing depth to water table. In the Himalayan system, this is considered to be due to a combination of decreasing depth to water table and increased surface flooding due to direct, monsoon-driven precipitation on the DFS surface. An increase in poorly drained soil development occurs near the toe of the DFS in Botswana, despite high transmission losses across the system[...]

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Abstract: Geomorphic elements on modern distributive fluvial systems (Davidson et al. 2013)

Analysis of over 400 fluvial megafans (>30 km in length) in aggradational continental sedimentary basins reveals that geomorphic channel and floodplain changes on these distributive fluvial systems (DFS) generally behave in predictable ways with increasing distance from the apex. These changes can include: a decrease in discharge, a decrease in bed material transport and calibre of sediment, a decrease in stream power, an overall decrease in channel width, an overall decrease in channel depth, an increase in avulsive behaviour, and sinuosity becomes more variable.

Three generic geomorphic element models are proposed – reflecting observed changes in channel behaviour – based on measurable changes in channel width and planform characteristics with increasing distance downstream. The three models are derived from (1) a single braided channel that bifurcates downstream into low sinuosity channels; (2) a dominant, sinuous, single-thread channel that anabranches and bifurcates with distance downstream, creating smaller channels with varying sinuosity; and (3) a dominant multi-thread channel that anabranches and bifurcates with distance downstream, creating smaller channels with varying sinuosity[...]

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Abstract: A quantitative approach to linking drainage area with distributive fluvial system area in dryland, endorheic basin settings (Davidson and Hartley)

Aggradational fluvial and alluvial systems that display distributive planforms under the most recent (Quaternary) climate regimes have been recognized as the dominant depositional form in modern continental sedimentary basins (Hartley et al., 2010; Weissmann et al., 2010; 2011; Davidson et al., 2013). These Distributive Fluvial Systems (DFS) (>30km in length) have been defined by Weissmann et al. (2010) as a radial network of channels and associated deposits dispersed below an apex where a river emerges from valley confinement and enters a sedimentary basin. DFS exist at a range of scales along a continuum and are commonly referred to as megafans, alluvial fans and fluvial fans in geomorphic and sedimentological literature. Previous work has derived empirical relationships between alluvial fan area (<30km in length) and contributing drainage basin area (Bull, 1962, 1964; Denny, 1965; Hooke, 1967; Harvey, 1997).

For the first time, this paper establishes regression relationships between DFS area and drainage basin area. The results suggest that DFS area is predictable as derived from the contributing drainage basin area; furthermore, the results indicate that DFS area can be used as a proxy to predict the quantity of fluvially-transported sediment deposited in a sedimentary basin. As with all work done of this kind, the aim is to provide a tool to better reconstruct and predict preserved sedimentary fluvial facies and basin-fill architecture in the rock record.

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Abstract: Large-diameter burrows from Mid-Triassic core and FMI image interpretation, East Irish Sea Basin, UK (Davidson and Buck)

Over recent years burrow casts with diameters >10cm have been identified on the modern-day continents of South America (Colombi et al. 2012), North America and Antarctica (Hasiotis et al. 2004) and South Africa (Bordy et al. 2010; Groenewald et al. 2001) and Europe (Talanda et al. 2011). The structures indicate a relatively common vertebrate behaviour during the Permo-Triassic period. The burrows are interpreted as behavioural adaptation by terrestrial vertebrates as protection against the extreme climatic conditions of low- to mid-latitude Pangea. The burrows are commonly interpreted to have been formed by Mesozioc tetrapods.

Previously published data are based on studies of outcropping sedimentary strata allowing extensive interpretation of laterally-equivalent sedimentary facies and facies associations. The consensus from these studies suggests that the burrows were formed in fluvial overbank and floodplain deposits, frequently displaying evidence of episodic sub-aerial exposure and pedogenesis in a dryland setting. In addition, these large burrows form a network of multiple branches with numerous chambers, shafts and tunnels.

This paper presents the findings of core and high quality FMI image interpretation from the mid- to late-Triassic sediments of the East Irish Sea Basin (EISB). For the first time large diameter burrows have been indentified from 4 inch core in sabkha and marginal playa facies associations.

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Paper: The Kujung Formation in Kurnia-1: a viable fractured reservoir play in the South Madura Block (Magee, Buchan and Prosser)

Task Geoscience staff co-authored this paper with Trevor Magee of Cooper Energy for presentation at the Indonesian Petroleum Association Thirty-Fourth Annual Convention & Exhibition, May 2010.

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Abstract: Sedimentology, Structure and Reservoir Model - West Dikirnis Field, Nile Delta

Abstract from a presentation by Nicloa Capuzzo at the AAPG 2009 meeting in Denver, entitled Sedimentology, Structure and Reservoir Model of Late Miocene Fan Delta Successions from the West Dikirnis Field, Nile Delta (Egypt) and produced in conjunction with Melrose Resources Plc.

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Abstract: Structural Analysis of Highly Fractured Basement, Yemen

Extended abstract from a poster presented by Ann Murray at the AAPG 2008 meeting in Cape Town, entitled Structural Analysis of Highly Fractured, Heterogeneous Basement, Say’un-Masila Basin, Yemen and produced in conjunction with Dove Energy.

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Abstract: Outcrop Characterisation of Turbidite Reservoir Analogues deformed by Fluidisation

Abstract from a presentation by Olivier Stanzione at the AAPG 2009 meeting in Denver, entitled Outcrop Characterization of Turbidite Reservoir Analogues Deformed by Fluidization - Implications for Reservoir Models (Panoche-Tumey Hills, California , USA) and produced in conjunction with the Injected Sands Group, Dept. of Geology and Petroleum Geology, University of Aberdeen.

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360° core imaging - measuring the detail

This short poster demonstrates the uses of digitally acquired 360° core images to augment and calibrate borehole image data.

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Go With The Flow (Part 1)

Palaeotransport analysis is a valuable sedimentological tool in reservoir and basin characterisation. Such interpretations can be derived using borehole images. This document provides an introduction to palaeotransport analysis from borehole images and dipmeter data. It details the applications, methodology and pitfalls associated with such an analysis. This will enable the reader to help plan image tool campaigns, comprehend technical approaches and enable them to get the most from an interpretation report.

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Finding Yourself in Deep Water (Part 2)

Part I of this article reviewed the types of borehole image tools and the styles of geological features which can be resolved in deepwater sediments. The general approach to interpretation was outlined and considered in the context of the major depositional environments which can be found in a deep marine setting.

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Finding Yourself in Deep Water (Part 1)

Spectacular successes in deep water drilling have led to a new era in exploration within turbiditic systems around continental margins.

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Get to know your faults

In the last decade, 3-D seismic techniques have completely revolutionised the structural and stratigraphic modelling of reservoirs and have led to a remarkable resurgence, world-wide, in the discovery of new fields. Some fields previously interpreted as lacking any significant structural control have for the first time been shown by 3-D surveys to contain important fault and fracture trends, such as the super-giant Ghawar Field of Saudi Arabia. However, most faulting within reservoirs occurs at a sub-seismic scale and the complexities of fault zones are often not considered. The details of these faults and fractures are best revealed by a combination of borehole images and cores.

This article discusses the occurrence of fault damage zones in which cataclastic fracturing has a profound influence upon reservoir properties. Examples are given of modern techniques of borehole imaging and core analysis to characterise the importance of such fracture systems.

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SPWLA 2007 LWD azimuthal density logging

A logging while drilling (LWD) Azimuthal LithoDensity (ALD) imaging tool was run in horizontal dual lateral wells 110/15-L13 and 110/15-L13z with the aim of identifying fault and fracture intersections. The wells are located in the BHPBilliton operated Lennox Field, in the Liverpool Bay area of the East Irish Sea Basin, United Kingdom Continental Shelf (UKCS).

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