Depositional Environment Maps Research Articles

Session 10. Oral Presentation for: Gross depositional environment mapping in the onshore South Australian Otway Basin: an example of data integration

Session 10. Oral Presentation for: Gross depositional environment mapping in the onshore South Australian Otway Basin: an example of data integration

Gross depositional environment mapping in the onshore South Australian Otway Basin: an example of data integration

As part of a greater petroleum systems modelling project, gross depositional environment maps were made for six key intervals in the onshore portion of the Jurassic to Late-Cretaceous Otway Basin in South Australia. This mapping interpreted varied depositional systems including anoxic, extensive ice-influenced lacustrine, lacustrine turbidite, extensive fluvial/lacustrine, fluvial/flood plain and growth fault-bound ribbon-like alluvial fan aprons.

Shipwreck and Sherbrook supersequence regional gross depositional environments, offshore Otway Basin

The Shipwreck and Sherbrook supersequences together constitute the upper Cretaceous succession in the Otway Basin that was deposited during an extensional basin phase. In the Shipwreck Trough, where the upper Cretaceous succession is well explored, gas fields are hosted by the Shipwreck Supersequence (SS). Elsewhere, the upper Cretaceous interval is lightly explored, and the deep-water area is considered an exploration frontier. We present regional gross depositional environment (RGDE) maps for the LC1.1 and LC1.2 sequences of the Shipwreck SS, and the LC2 Sherbrook SS. Fluvial Plain, Coastal-Delta Plain and Shelf RGDEs were interpreted from wireline logs, cores, and seismic facies. The Fluvial Plain and Coastal-Delta Plain RGDEs are mostly restricted to the inboard platform areas and the inner Morum Sub-basin. The mud-prone Shelf RGDE is widespread across the deep-water Morum and Nelson depocentres. The extent of the Fluvial and Coastal-Delta Plain belts progressively increases up-section, imparting a regressive aspect to the succession, and delineating a large fluvial-deltaic complex in the north-west of the basin. Thick seal development across the greater Shipwreck Trough, potentially mature source rocks in the deep-water basin, and thick reservoir development in the hanging wall of growth faults in the inner Morum Sub-basin are insights derived from this study, and will inform area selection for detailed gross depositional environment mapping, formulation of new hydrocarbon and carbon dioxide storage plays, and inputs for petroleum systems modelling.

New approaches to the architectural analysis of deltaic outcrops: Implications for subsurface reservoir characterization and paleoenvironmental reconstruction

This study defines a new workflow to investigate the internal facies architecture of a river-dominated delta deposit using outcrops of the Cretaceous Panther Tongue of the Star Point Sandstone in central Utah, U.S.A. Photorealistic virtual outcrop models (VOM) were created from ~13 linear-km of outcrop. The VOMs, alongside field observations, were used to identify and map facies and facies associations over the ~25 m-thick stratigraphic interval. In order to investigate this system as a potential subsurface reservoir analog, a database of measurements was constructed using 60 digital sections that were measured within the VOMs at 152 m (~500 ft) spacing. This database characterizes a total of 508 sandstone beds by their thickness, length, and dip, from which the average thickness (0.78 m), bed length (330 m), and bed dip (2˚ towards the south) were calculated. Thinning rates were also calculated in both depositional strike and depositional dip directions (1.37x10-2 and 1.01x10-2 respectively). These comparable values suggest that the sandstone beds thin equally laterally and longitudinally from the sediment source, a characteristic typical of modern-day river-dominated deltas. The dataset also includes siltstone unit thickness data, recording an average thickness of 0.81 m, and a trend of increasing siltstone abundance and thickness moving from proximal areas where siltstones comprise 3% of the succession, and 77% in the most distal areas. The impact of observational scale was also investigated by querying the database at multiple physical length scales to include more typical well spacings of 305 and 610 m (500 and 1000 ft). This additional analysis emphasizes the role of variability in lithologically heterogeneous systems and underscores the utility of outcrop analogs to better understand sources of uncertainty. From these data, a series of depositional environment maps was constructed, illustrating the evolution of eight delta lobes that encompass the preserved depositional history of the study area. These maps document the compensational stacking of individual lobes and the progressive southward directed trajectory of the Panther Tongue delta system. Results of this analysis provide insight into depositional processes and scales of heterogeneity of the Panther Tongue and, by extension, analogous river-dominated delta systems. The workflow established in this study is exportable to other sedimentary outcrops and environments, thus demonstrating that VOMs can be used as a basis for quantitative database development and reservoir modeling inputs.

Underexplored but not forgotten: assessing the energy resources potential of the greater Pedirka Basin region through play-based mapping

The Pedirka, Simpson and western Eromanga basins in central Australia have had a chequered exploration history which has seen only 42 wells drilled across a study area of ~210 000 km2. Exploration initially focused on conventional hydrocarbons from the 1950s–1980s, before shifting towards coal seam gas (CSG) opportunities in the mid-2000s. Active petroleum systems have been proven in the region by a non-commercial oil discovery at Poolowanna 1 in 1977, and by several wells that showed evidence of residual oil columns. CSG exploration programs have confirmed the presence of thick, marginally mature coal intervals on the flanks of the basins, but are yet to evaluate the CSG potential of the deeper troughs. Geoscience Australia, the Northern Territory Geological Survey and the South Australian Department for Energy and Mining have been collaborating on the Australia’s Future Energy Resources project to undertake an assessment of the resource potential for conventional and unconventional hydrocarbons, and the geological storage of CO2 (GSC) potential of the greater Pedirka region. The project has applied a play-based exploration approach to qualitatively assess the resource potential of the region. The Carboniferous to Cretaceous stratigraphic interval was divided into 14 plays which were evaluated for the presence of sediment-hosted energy resources through post-drill analysis, gross depositional environment mapping and common risk segment mapping. The analysis identified energy resources and GSC potential across multiple plays and locations within the study area. These results demonstrate, that while the region is underexplored, it should not be overlooked by future exploration activities.

Cretaceous depositional environment interpretation of offshore Otway Basin cores and wireline logs; application to the generation of basin-scale gross depositional environment maps

Gas production from the Inner Otway Basin commenced in the early 2000s but the deep-water part of this basin remains an exploration frontier. Historically, the understanding of plays in this region were largely model driven and therefore the ground-truthing of depositional environments (DE) and gross depositional environments (GDE) are critical. This aspect has been investigated for the Sherbrook Supersequence (SS) by the integration of legacy wireline and core data, with regional 2D seismic facies mapping of new and reprocessed data from Geoscience Australia’s 2020 Otway Basin seismic program. Core observations were matched to wireline logs and seismic facies with resulting well-based DE interpretations calibrated to seismic resolution Regional GDE intervals. Integration of well and seismic observations led to the compilation of a basin-wide Regional GDE map for the Sherbrook SS. This GDE map indicates the distribution of Sherbrook SS play elements such as source rock, seal and reservoir, especially across the Deep-water Otway Basin where well data is sparse.

Making the most out of historical cores for geothermal exploration

Abstract During the current trend of the energy transition, many stratigraphic intervals that previously were thought as uneconomical from an oil and gas business perspective are being re-evaluated for low-carbon energy resource potential such as geothermal. This study presents a case study from the Vienna Basin, Austria, where the Early Badenian Rothneusiedl Formation has been targeted for a re-evaluation, utilizing existing sparse subsurface datasets of vintage quality. The historical cores were subjected to diverse analytical techniques covering sedimentological, petrophysical and thermophysical aspects. These analysis techniques provided the fundamental lithological characteristics and led to the creation of a synthetic conceptual sedimentological log, resultant selection of samples for further analyses, as well as the creation of gross depositional environment maps. The reservoir and thermal properties guided by the core-based lithofacies were required for evaluating the feasibility of the target strata. Overall, the limited and historical cores provided significant and robust data that proved crucial for assessing uncertainties and identifying sub-areas of the Vienna Basin for harnessing geothermal energy. This study demonstrates an important case example of the utilization of historical cores to their maximum potential and reiterates the value of core-derived data amongst digital technologies of the twenty-first century.

Prospectivity of the Triassic successions of the North West Shelf of Australia: New insights from a regional integrated geoscience study

The North West Shelf (NWS) of Australia is a prolific hydrocarbon province hosting significant volumes of hydrocarbons, primarily derived from Jurassic and Cretaceous targets. A new regional, integrated geoscience study has been undertaken to develop insights into the paleogeography and petroleum systems of Late Permian to Triassic successions, which have been underexplored historically in favor of Jurassic to Cretaceous targets. Within the NWS study area, graben and half-graben depocenters developed in response to intracratonic rifting that preceded later fragmentation and northward rifting of small continental blocks. This, coupled with contemporaneous cycles of rising sea levels, brought about the development of large embayments and shallow, epeiric seas between the Australian continental landmass and outlying continental fragments in the early stages of divergence. Key elements of the study results discussed herein include the study methodology, the paleogeographic and gross depositional environment mapping, and the reservoir and source kitchen modeling. The study results highlight the presence of depocenters that developed within oblique rift zones due to regional Permo-Triassic strike-slip tectonics that bear compelling similarities to modern-day analogues. These intracratonic rift zones are well-known and prominent tectonic features resulting from mantle upwelling and weakening of overlying lithospheric crust, initiating the development of divergent intraplate depocenters. The comprehensive analysis of these depocenters from a paleogeographic and petroleum system perspective provides a basin evaluation tool for Triassic prospectivity.

Geologically-Realistic Facies Distribution in Static Reservoir Models for CO2 Sequestration: From Core to Wireline Logs to Grid Cells

The Precipice Sandstone and Evergreen Formation are an important target for potential carbon sequestration in the Surat Basin, Australia. However, the geological data necessary to characterize flow units and build reliable static reservoir models is mostly absent from the basin centre where prospective storage is the highest. To deal with this limitation, detailed facies analysis was undertaken on the relatively limited core dataset, comprising 8 wells and over 2000 m of cumulative section. From this, neural networks were trained to recognize facies using wireline logs as a means to predict the distribution of geological units across the basin. Facies from 186 wells were used to produce basin wide gross depositional environment maps and the maps allowed type locations to be identified to showcase the range of possible scenarios at the basin centre where injection potential is the highest. Facies predictions were upscaled to grid cells and these then helped guide object modelling of geobodies. The result was geologically-realistic facies distributions that controlled parameterization of three alternative static models. This work is an important contribution to the world of reservoir modelling, as it shows an important method that can be used to predict a range of possible geobody distributions and corresponding flow units in areas where data is limited.

Regional paleodepositional environment of the Cretaceous in the Great Australian Bight – a support for frontier exploration

To reveal the development of the depositional environment in the Great Australian Bight, regional and high-resolution 3D-seismic interpretation and palynological evidence from well data was integrated with tectonic plate- and paleo topographical-reconstructions. Results from that work explain the drainage patterns and changes in the sedimentary evolution. A maximum transgression at the Cenomanian–Turonian boundary causes the deposition of the expected main source rock interval at the base of the Tiger mega-sequence. This is supported by Integrated Ocean Drilling Program wells (2017), asphalite strandings and dredge samples from the basin. A relative sea-level drop in the mid-Turonian initiates a forced regression and sand deposition in more distal parts of the basin. As a third mega-sequence the Hammerhead Formation progrades into the basin, depositing several thousand metres of deltaic sandstones and lagoonal shales. Our source to sink model based on our gross depositional environment maps could explain the presence of source rocks and reservoir intervals within this frontier exploration basin.

Play-based exploration in the southern Cooper Basin: a systematic approach to exploration in a mature basin

Exploration within a mature basin poses many challenges, not least how to best utilise resources and time to maximise success and reduce cost. Play-based exploration (PBE) provides a team-based approach to combine key aspects of the petroleum system into an integrated and wholistic view of basin prospectivity. While the PBE methodology is well established, it is not often applied to its full extent on a basin scale. After a period of declining exploration success in parts of the South Australia Cooper-Eromanga Basin, this study was undertaken by a dedicated regional geoscience team with the aim of rebuilding an understanding of the basin, based on first principles and stripping away exploration paradigms. The study area comprises an acreage position in the South Australian and Queensland Cooper-Eromanga Basins covering 70 000 km2 in which Senex Energy has 14 oil fields, has drilled more than 80 exploration wells and has acquired 2D and 3D seismic material. A plethora of proven and emerging plays exist within the acreage ranging from high productivity light sweet oil (Birkhead and Namur Reservoirs) to tight oil (Murta Formation), conventional gas (Toolachee/Epsilon and Patchawarra Formation), tight gas (Patchawarra Formation) and the emerging deep coal play (Toolachee and Patchawarra Coals). Play-based exploration methodologies incorporating the integration of seismic data, log and palynological data, structural analysis, geochemistry, 3D basin modelling, consistent well failure analysis and gross depositional environment maps have allowed the systematic creation of common risk segment maps at all play levels. This information is now actively utilised for permit management, business development, work program creation and portfolio management. This paper will present an example of the work focussing on the southern section of the South Australian Cooper-Eromanga Basin.

Regional controls on Lower Tertiary sandstone distribution in the North Sea and NE Atlantic margin basins

Abstract Widely distributed deep-water fan sandstones of early Tertiary age form the reservoir for one of the most successful and prolific plays in the North Sea and NE Atlantic margin. Stratigraphic interpretation of a large well database provides the basis for mapping sand distribution and depositional environments in these two hydrocarbon provinces. Sand thickness maps for five Paleocene–Lower Eocene plays illustrate the intimate relationship between pre-existing structural features and sand distribution and facies in the North Sea. Large-scale depositional environment mapping gives an insight into the similarities and differences between basin evolution and sand distribution in North Sea and NE Atlantic margin basins. Both provinces were affected by the same succession of pre-break-up and syn-break-up tectonic and magmatic events that led to early Eocene continental separation and the formation of the NE Atlantic. The impact of these events was muted within the North Sea, which was protected from Paleocene rifting on the NE Atlantic margin by the Scotland–Shetland hinterland and from Paleocene–early Eocene volcanism by its more distant location. However, it was the combination of tectonic and thermal uplift of this clastic source area that contributed the large volumes of sand that accumulated in both these provinces.

Electromagnetic conductivity mapping for site prediction in meandering river floodplains

AbstractSpatial mapping using electromagnetic (EM) conductivity can quickly define past sedimentary environments within meandering river floodplain settings and, most important, those most likely to include archaeological materials. Natural levee and uplifted fluvial terrace environments would have been the most likely areas for people to place permanent settlements, as these topographically high areas would have remained dry during most annual floods. The spatial patterning of high and low electrical conductivity regions, when combined with geological core and auger information, can define a number of depositional environments in floodplains including channels, point bars, natural levees and oxbow lakes. Conductivity maps can then be used to predict the locations of prehistoric floodplain environments, and therefore the most likely locations for archaeological remains. Suitable areas can then be further tested for archaeological features using detailed geophysical surveys and other archaeological survey methods. Case studies are presented from California, Texas and Mississippi that integrate these methods for depositional environment mapping as a way of accessing the archaeological potential in meandering river floodplains. Copyright © 2008 John Wiley & Sons, Ltd.