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Porosity and saturation are two important petrophysical properties among many others that play a crucial role in the study of reservoir characterization, flow modeling, simulation etc. Well logging techniques supplemented with geostatistical methods could provide a very high resolution estimate of those properties; but it becomes severely constrained due to availability of limited number of wells only at sparse locations. An overall estimate of porosity and saturation over a wide spatial extent (both vertically and laterally) is nonetheless necessary for a detailed study of a reservoir. We demonstrate that full waveform inversion of prestack seismic data can be a useful tool in estimating porosity and saturation of a reservoir. We conduct sensitivity analysis of porosity and saturation on seismic velocities. We use modified Biot-Gasmann equations for sensitivity analysis and forward modeling computation. A gradient-based technique aided with adaptive regularization is used for inverse modeling of full-waveform prestack seismic data. We present the results of numerical experiment on both synthetic and field seismic data.

Conventional deep reflection profiles usually image upper to middle crustal levels quite well. The ability of this methodology to image the lower crust and transition to the mantle is often limited. We have made a step forward in developing a methodology for processing, interpreting and presenting near-vertical reflection, wide-angle reflection and refraction seismic data and velocity information derived from the three data sets within a unified approach. The key elements of this approach are: pre-stack depth migration of wide-angle reflection and refraction data; wave field analysis of the refraction and wide-angle reflection data prior to and after depth migration; unified analysis of seismic velocity information. For the finite-difference continuation of the wave field we use a special oblique time-spatial grid. The time field calculation is based upon a finite-difference approximation of the eikonal equation and the grid used in this task is curvilinear. The coordinate lines are based on ray paths and wave fronts in the medium. Such a grid is particularly effective at large offsets. The overall configuration of the oblique grid used for the downward continuation of the time field is determined for the domain where the solution of the eikonal equation exists. The initial conditions are defined by the recorded travel times. We demonstrate how this approach works on an example from the Petrel sub-basin, Australian North West Shelf, where conventional CDP (near-vertical reflection) data were supplemented by the wide-angle reflection and refraction data recorded by ocean-bottom seismographs. Depth migration of refraction/wide-angle seismic data presents them in the same style as the conventional reflection data thus radically enhancing the seismic image of the lower crust where the CDP data lacks detail.

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In mid-1991, the Bureau of Mineral Resources (BMR; now the Australian Geological Survey Organisation, AGSO) commenced a program of deep-seismic acquisition on the southern North West Shelf with the intention of providing a regional framework data set for explorersin this highly prospective segment of Australia's continental margin. This program is part of a wider program that is acquiring a regional grid of deep-seismic data along the length of the North West Shelf. In particular, the program aims to: *Determine the broad regional structural framework of the southern North West Shelf byexamining the boundaries between the major structural elements; *Determine the deep crustal structure of the region; *Assess the control of deep structure on the development of the major hydrocarbon fieldsand plays, and in particular the structural and depositional effects resulting from reactivation of these structures; and *Acquire a set of high-quality seismic tie lines linking the deeper exploration wells throughout the region, to allow regional seismic correlations. To address these aims, a multi-cruise program was devised during which deep-seismic data are being recorded. The first survey, SNOWS-1 (for Southern h_Torth Eest Shelf; AGSO Survey 101) was concentrated in the Barrow and Dampier Sub-basins and inner Exmouth Plateau. 1654 km of good-quality seismic data tied to 20 exploration wells were recordedand processed; these data frequently show basin structure down to a depth of at least 10 s two-way time (TWT). The second survey, SNOWS-2 (AGSO Survey 110), acquired morethan 2800 km of high-quality deep seismic data along 13 lines in the Beagle, Dampier, and Barrow Sub-basins, and over the full width of the Exmouth Plateau in mid-1992. These lineswere tied to 21 exploration wells, of which 3 were also tied during SNOWS-I, and again show reflections down to 12 s TWT. The third survey in the program, SNOWS-3 (AGSO Survey 120), took place in July-August 1993, and acquired a total of 4052.5 km of high-quality deep-seismic data along 14 lines, tiedto 6 exploration wells (of which 2 were also tied on SNOWS-2) and Ocean Drilling Program Site 765 in the offshore Canning Basin, northeast extremity of the Carnarvon Basin, andO^Argo Abyssal Plain. SNOWS-3 ties in with the SNOWS-2 survey to the southwest and withthe Browse Basin deep-seismic survey (AGSO Survey 119, acquired in June, 1993) to the northeast. The seismic data were recorded from a 4800 m streamer, configured with 192 x 25 m active groups. The record length was 16 seconds and the sample interval 2 msec. The seismicsource consisted of tuned airgun arrays with a total volume of 49 litres (3000 cu in). Shots were fired every 50 m at an average ship speed of 5 knots, providing 48-fold coverage.Streamer noise levels were low, with the average noise levels on acceptable channels generally being less than 1.5 rnicrobars. Navigation for the survey was provided by two differential Global Positioning Systems (DGPS), using shore reference stations in Dampier and Broome, adjacent to the survey area.Full differential coverage was achieved for all but a few minutes of the survey. Positionalaccuracy is estimated to be probably better than +I- 10 metres. The offshore Canning Basin is a complex amalgam of a WNW-ESE trending EarlyPalaeozoic intra-cratonic basin overlain by a NE-SW trending Late Palaeozoic to Mesozoicpassive margin basin (the Westralian Super-basin)

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Seismic acquisition for the joint BMR-Woodside Petroleum program in the Dampier Sub-basin started at 0800 am on October 24, 1990 and was completed at 1150 am on Sunday October 28, 1990. A total of 352 km of high resolution seismic data was collected along the 17 agreed survey lines, of which 336 km were full stack data with a total 390 magnetic tapes being used. Data quality appears to be good. In addition to the seismic, a total of 530.6 km of water column geochemical data were also collected.

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