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 Io Jansz gas field is situated in the Carnarvon Basin on the North West Shelf of Australia. It is Australia’s largest gas field, estimated to hold over 20 TCF of gas reserves and covering an area of over 2000 km2. Following a series of appraisal wells and a 3D seismic survey, this field is moving rapidly towards development. Image quality of the 3D provided significant uplift over existing 2D surveys in the area. Expectations for resolution and business targets have been met through careful planning and the provision of staged deliverables.Despite the exceptional data quality, a number of technical challenges were encountered that led to operational changes and adaptations by the project team. Source height statics and severe image distortion due to overburden are examples of some of the challenges addressed. Consideration of the exploration history of this field and its associated imaging gives insight into the improvements in image quality that can be realised by careful selection of acquisition and processing parameters, high levels of quality control (QC) and modern processing algorithms. The ultimate success of this project was achieved through close cooperation within interdisciplinary teams comprised of partner technical staff and the seismic acquisition and processing contractor.
The Jansz-Io gas field is located in production licenses WA-36-L, WA-39-L, and WA-40-L within the Carnarvon Basin, northwest shelf, Australia. It is 70 km (43 mi) northwest of the Gorgon gas field, 140 km (87 mi) northwest of Barrow Island, and 250 km (155 mi) from Dampier on the northwest coast of Western Australia. Water depths vary from 1200 to 1400 m (3937 to 4593 ft) across the field. The Jansz-Io gas field was discovered in 2000 by the Jansz-1 exploration well. A three-dimensional (3-D) seismic survey was acquired in 2004, and a further five wells were drilled between 2000 and 2009 to further delineate the field extent and size and characterize the resource to facilitate progress toward development. The Jansz-Io hydrocarbon trap extends over 2000 km2 (772 mi2) with both structural (faulted anticline) and stratigraphic (reservoir pinch-out) components. The stratigraphic component of the trap is defined by the reservoir extent, which is limited by depositional downlap to the northwest, and erosional truncation by Upper Jurassic and Lower Cretaceous unconformities to the southeast. The reservoir comprises muddy, bioturbated, predominantly very fine- to fine-grained sandstones deposited in a shallow-marine environment and is divided into two units. The upper wedge reservoir has 25 to 35% total porosity with 10 to 1000 md permeability, and the lower wedge reservoir has 15 to 25% porosity with 0.01 to 10 md permeability. Both reservoir units are expected to contribute gas during production. The original gas in place (OGIP) for the Jansz-Io Oxfordian reservoir has a probabilistic range from 320 to 946 Gm3 (11 to 33 tcf), with a P50 value of 632 Gm3 (22 tcf). The ultimate recovered gas for the field will depend on both the development plan and the reservoir performance over field life. For the current 15-well development plan, the resource estimates range from 201 to 442 Gm3 (7 to 16 tcf). The Jansz-Io gas field is a key part of the greater Gorgon liquified natural gas (LNG) project and will supply gas to the LNG plant that is being constructed on Barrow Island. The development concept includes subsea completions from three drill centers placed on the seafloor connected to a subsea production pipeline to carry gas to the LNG processing plant. For the first stage of field development, 10 development wells were successfully drilled and completed during 2012 and 2014. The second drilling campaign is planned to commence after field start-up with the timing dependant on field performance.
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