TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe Alwyn North complex is located in Block 3

Block 22, located offshore in the North Coast Marine Area (NCMA) of Trinidad and Tobago, contains the Cassra gas accumulation discovered by the Cassra-1 and Cassra-2 wells. Both wells encountered dry, biogenic gas in early Pliocene, shoreface–shelfal sandstone reservoirs. A best-practice modelling methodology is documented to capture a range of subsurface uncertainties for use in reservoir simulation to generate production profiles in support of pre-development project planning. Calibration of a sequence stratigraphic interpretation from seismic with core data was instrumental in generating a depositional model, within which sedimentary facies could be stochastically distributed and used to constrain the population of petrophysical properties. Static geological uncertainties were modelled using an uncertainty workflow methodology in commercial three-dimensional (3D) geomodelling software, resulting in multiple, static model realizations and probabilistic GIIP (Gas Initially In Place) distributions for Cassra and some nearby prospects. The multi-regional model required careful selection of realizations for reservoir simulation, based on a ranking scheme that combined GIIP, GRV (gross rock volume) and net:gross (net to gross ratio), and not simply P90–P50–P10 percentiles from the global distribution. The reservoir simulation phase included a dynamic uncertainty workflow using commercial experimental design modelling software. By including dynamic uncertainties such as horizontal/vertical permeability and well productivity in the workflow, a more objectively defined suite of production profile predictions was achieved.

In 1971, the Bluewater III semi-submersible rig drilled the first wildcat well, KK6-1, some 40km north west of Tobago's Buccoo Reef, in the Paria Sub-Basin of the North Coast Marine Area, resulting in the Orchid discovery. The subsequent appraisal well, KK6-2 discovered gas in a series of stacked Late Miocene (NC30) – Pliocene (NC80) sandstones. The lowermost and thickest of these gas charged sandstones was found unconformably overlying Cretaceous metamorphic basement, and has since been termed the Basal Sand. In 2011 a 4370sqkm 3D seismic survey was jointly acquired over NCMA and Block-22 by Niko Resources and Centrica Energy, allowing for extensive regional mapping and the potential to resolve the Orchid Basal Sand gas discovery. Detailed mapping on basement revealed extensive areas with pronounced dendritic drainage, potential islands and shelfal platforms. Seismic amplitude extractions at this interval point to a number of low impedance anomalies, one of which ties very well to the KK6-2 gas discovery. In the absence of Basal Sand core at Orchid, present day analogues were selected for reservoir sampling and analysis. Integration of regional well data, sea bed samples, ocean current data, seismic impedance volumes, thin sections from side wall cores and cuttings as well as palinspastic restorations resulted in the generation of a regional NC30 Basal Sand gross depositional map, depicting the drowned mountain ridge of ‘Isla de la Asumpción', carbonate mounds and potential Orchid Basal Sand look-alike plays within the Paria Sub-Basin.

SummaryThis core view presentation focuses on the sedimentological analysis of shallow marine reservoirs from the Upper Cretaceous Lower Grudja reservoirs from the Sasol-operated, Pande and Temane fields of the Southern Mozambique basin. Conventional cores were acquired as part of the various exploration and appraisal drilling campaigns and although of highly variable quality, they can be used for sedimentological analysis and calibration of petrophysical and reservoir properties for the main reservoir sands, informally named in sequential order from the G6 to G12. This core viewing opportunity focuses on both legacy and recent conventional whole core acquisition from the G6 reservoir in Pande and G8 reservoirs in Temane Fields. The key sedimentological features and trends will be demonstrated along with how the core data is used for calibration of petrophysical properties and the basis for reservoir characterisation studies. In addition, the process of preserving this invaluable data source for the benefit of future use will be highlighted.

Mark Shephard's 'The Simpson Desert' is a very well-produced book. It is excellent in design and overall presentation. The print is a good readable size and the photographs, both those of historical nature and the recent coloured ones, are very well chosen. The South Australian Branch of the Royal Geographical Society of Australasia is to be commended, along with the author, for the fine quality of the publication.