The Jansz gas field is located in permit WA-268-P, 70 km northwest of the Gorgon gas field in the Carnarvon Basin. The Jansz–1 discovery well was drilled in April 2000 and intersected 29 m of net gas pay in an Oxfordian age shallow marine sandstone reservoir. The well drilled a stratigraphic trap on the western limb of the Kangaroo Syncline.The Io–1 well was drilled in January 2001 in the adjacent permit WA-267-P (18 km from Jansz–1) and intersected the same Oxfordian sandstone reservoir penetrated by Jansz–1, with a total of 44 m of net gas pay. The Tithonian and the Upper Triassic Brigadier Sandstone gas reservoirs at Geryon–1 (1999) and Callirhoe–1 (2001) in WA-267-P are in pressure communication with the Oxfordian gas reservoir at Jansz–1 and Io–1. Consequently, the three different age reservoirs comprise a single gas pool, with a common gas/water contact.The Jansz gas field has been delineated by four wells and 2D seismic. The gas sandstones have a prominent amplitude versus offset response, which defines the field limits. The Jansz gas field is confirmed by drilling to be an areally extensive (2,000 km2) gas accumulation with a gross column height of 400 m and an estimated 20 TCF (566 G.m3) recoverable sales gas, which represents 40% of the discovered gas resources in the deepwater Carnarvon Basin. The size of the Jansz gas field and its remoteness from existing pipeline gas markets suggests that an export LNG project will be the basis for its development.
The Geryon, Orthrus, Maenad and Urania Gas Fields are located in permit WA-267-P in approximately 1,200 m of water, and between 35 km northwest and 70 km north of the Gorgon Gas Field in the offshore Carnarvon Basin of Western Australia. Five wells were drilled in these fields between August 1999 and February 2001 as part of a six-well, three-year obligatory drilling program. The primary objectives were late Triassic sandstones of the upper Mungaroo Formation. The Geryon and Urania Fields are three-way footwall structures, while the Orthrus and Maenad Fields comprise four-way horst structures where progressively older units subcrop against the Callovian Unconformity. All objective reservoirs were amplitude associated and had strong AVO signatures, which was instrumental in the high exploration success rate and excellent exploration prediction of OGIP from seismic data.This paper will briefly discuss the description of late Triassic and early Jurassic reservoirs and the transition of the AA sand of the Mungaroo Formation from fluvial to marginal marine facies in the Greater Gorgon Area, the recent drilling results of the Triassic Prospects in WA-267-P, and the geophysical attributes of the AA sand Mungaroo Formation reservoirs.The WA-267-P Triassic Gas Fields are estimated to contain approximately 210 billion m3 (7.4 TCF) recoverable sales gas. The close proximity of these Triassic gas fields to each other, the clean gas composition and size of resource base suggests these fields are excellent candidates for a future gas development in Western Australia.
The objective in building the Gorgon reservoir characterisation and simulation model was to create a 3D, object based model in a sequence stratigraphic framework integrating core, log, engineering, and seismic attribute data. The project team specified that software and work flow must incorporate marked point - boolean processes with or without seismic conditioning, recognise uncertainties in reservoir and model input parameters, generate multiple model realisations for a probabilistic range of gas in place, and output the model in reservoir simulation format. Reservoirs are in stacked sands of the Mungaroo Formation, with a total formation thickness of greater than 2000 m beneath the major Jurassic unconformity. The Mungaroo Formation was subdivided into 11 intervals on the basis of regional sequence boundaries and systems tracts. Relative lowstand intervals are sand prone, relative highstand intervals much less sand-prone. Facies present include fluvial channels (single channels and amalgamated stacked channels), crevasse splays, and "background" shale (coaly siltstone, coal, and minor carbonate). 3D seismic data were used both for structural modelling and a statistical correlation between seismic attributes and channel sand distribution. Wireline pressure data were used to refine our understanding of stratigraphic compartmentalisation and fluid distribution. The fluvial reservoir architecture model was built using marked point process and simulated annealing for each of the 11 stratigraphic intervals. A range of endpoint net/gross ratios was established based on well penetrations and seismic attributes. The model was scaled-up from a 715 layer geologic model to a 46 layer simulation model, with no areal scale-up. Whilst the scaled-up model honoured the 11 original intervals, the majority of the layers were located in regions identified as key flow units. The resulting simulation model was then used to generate production profiles for various development scenarios. P. 305
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