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Petroleum Geoscience

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ISSN (Print) 1354-0793 - ISSN (Online) 2041-496X
Published by Geological Society of London

[9 journals]

Geologically-based permeability anisotropy estimates for tidally-influenced reservoirs using quantitative shale data
- Authors: Burton, D; Wood, L. J.
  Pages: 3 - 20
  Abstract: The effect of the vertical to horizontal permeability ratio (kv /kh ) on many displacement properties is significant, making it an important parameter to estimate for reservoir models. Simple ‘streamline’ models have been developed which relate kv /kh at the reservoir scale to shale geometry, fraction and vertical frequency. A limitation of these models, especially for tidally-influenced reservoirs, is the lack of quantitisative geological inputs. To address this lack of data, detailed shale characteristics were measured, using Lidar point clouds, from four different tidally-influenced reservoir analogues: estuarine point bar (McMurray Formation, Alberta, Canada), tidal sand ridge (Tocito Sandstone, New Mexico), as well as both unconfined and confined tidal bars (Sego Sandstone, Utah). Estuarine point bars have long (x = 67.8 m) shales that are thick and frequent relative to the other units. Tidal sand ridges have short shales (x = 8.6 m dip orientation) that are thin and frequent. Confined tidal bars contain shales that are thin, infrequent and anisotropic (x– = 16.3 m dip orientation). Unconfined tidal bars contain nearly equidimensional shales of intermediate length (x = 18.6 m dip orientation) with moderate thicknesses and vertical frequency. The unique shale character of each unit results in a different distribution of estimated kv /kh values. Estuarine point bars have lower average kv /kh values (x = 8.2 x10–4) than any other setting because of the long shales they contain. Tidal sand ridges have short, but frequent shales, which results in moderate kv /kh estimates (x = .011). Estimates of kv /kh are typically highest in confined tidal bars (x = .038), which contain anisotropic and infrequent shales. Unconfined tidal bars have moderate lengths and frequency resulting in kv /kh estimates averaging 0.004. The results of this study highlight the link between heterogeneity, reservoir architecture and flow parameters.
  PubDate: 2013-02-01T02:02:50-08:00
  DOI: 10.1144/petgeo2011-004|hwp:resource-id:petgeo;19/1/3
  Issue No: Vol. 19, No. 1 (2013)
Sedimentology and stratigraphy of an intra-cratonic basin coal seam gas play: Walloon Subgroup of the Surat Basin, eastern Australia
- Authors: Martin, M. A; Wakefield, M, MacPhail, M. K, Pearce, T, Edwards, H. E.
  Pages: 21 - 38
  Abstract: Large gas reserves are trapped in the coals of the Middle Jurassic (Callovian) Walloon Subgroup (lower part of the Injure Creek Group) in the Surat Basin, eastern Australia. The series is divided into the Juandah Coal Measures (upper), Tangalooma Sandstone and Taroom Coal Measures (lower). The upper and lower units are locally further subdivided. These economically important coals were deposited in an alluvial plain setting within an interior basin, which has no recorded contemporaneous marine influence. The coals are typically bituminous, perhydrous and low rank with a high volatile content. Despite individual ply (bench) thicknesses typically less than a metre, series of plies or seams of coals up to 10 m thick have historically been tentatively correlated across the entire play area (over 150 km).
  PubDate: 2013-02-01T02:02:50-08:00
  DOI: 10.1144/petgeo2011-043|hwp:resource-id:petgeo;19/1/21
  Issue No: Vol. 19, No. 1 (2013)
Characterization of dense zones within the Danian chalks of the Ekofisk Field, Norwegian North Sea
- Authors: Gennaro, M; Wonham, J. P, Saelen, G, Walgenwitz, F, Caline, B, Fay-Gomord, O.
  Pages: 39 - 64
  Abstract: The Ekofisk Field is a giant field which has been producing at a high level for more than forty years and, since 1987, this production has taken place with the support of sea-water injection. The Danian-aged chalk deposits of the Ekofisk Formation and the Maastrichtian Tor Formation form the main reservoir units in the Ekofisk Field. The Ekofisk Formation principally consists of porous resedimented chalks intercalated with relatively thin and lower porosity beds, called dense zones. A multi-scale study of dense zones, from scanning electron microscopy to wells and seismic impedance data, has allowed the characterization and mapping of these deposits. Five main dense zone lithotypes have been identified: (1) argillaceous chalk; (2) chalk with abundant flint nodules; (3) chalk beds cemented with silica/nano-quartz; (4) calcite-cemented chalk; and (5) stylolitized chalk. The different types of dense zones tend to cluster in certain stratigraphic intervals, such as the EE and EM reservoir units at the base and in the middle part of the Ekofisk Formation. Dense zones have different mechanical properties compared to porous chalks and, depending on the connectivity of their fracture networks, they can act as preferential conduits or baffles for the reservoir fluids. An increased understanding of the distribution, characteristics and geological factors at the origin of the dense zones is fundamental to better define the reservoir architecture and ultimately identify unswept zones for future infill drilling targets. Supplementary material Descriptions of analytical procedures, composition, poro-perm and well log values of dense zone samples is available at: www.geolsoc.org.uk/SUP18573.
  PubDate: 2013-02-01T02:02:50-08:00
  DOI: 10.1144/petgeo2012-013|hwp:resource-id:petgeo;19/1/39
  Issue No: Vol. 19, No. 1 (2013)
Integrated tectonic basin modelling as an aid to understanding deep-water rifted continental margin structure and location
- Authors: Roberts, A. M; Kusznir, N. J, Corfield, R. I, Thompson, M, Woodfine, R.
  Pages: 65 - 88
  Abstract: An integrated workflow has been devised for the investigation of deep-water rifted continental margins. At a margin this allows us to predict the crustal structure, the distribution of continental-lithosphere thinning and the location of the ocean–continent transition with a new degree of confidence. The workflow combines the analytical techniques of 2D or 3D gravity inversion, 2D or 3D flexural backstripping with reverse thermal subsidence modelling, upper-crustal fault analysis and rifted margin forward modelling. No one technique on its own can provide all of the required answers, nor can it provide answers without some degree of uncertainty. The use of a combination of techniques, however, provides answers to several different problems and, crucially, more confidence in these answers. The workflow provides direct information on the present-day geometry of rifted margins and leads towards a better understanding of the geodynamic evolution of these margins. It also provides information which can inform the exploration process by making predictions about crustal structure at the ocean–continent transition, the location of the continent–ocean boundary, stretching-factor, heat-flow magnitude and history, palaeobathymetric history and subsurface palaeostructure. Application of the workflow is illustrated here with reference to the continental margins of West India, Brazil, West Australia, Norway and Newfoundland–Iberia.
  PubDate: 2013-02-01T02:02:50-08:00
  DOI: 10.1144/petgeo2011-046|hwp:resource-id:petgeo;19/1/65
  Issue No: Vol. 19, No. 1 (2013)