Acousticimpedance, the product of seismic velocity and density, is a basic physical property of rocks.Seismic traces are converted into pseudoreflection-coefficient time series by appropriate initial processing. then into acoustic impedance by the inversion of the time series. Such pseudologs are rough11 equivalent to logs recorded in wells drilled at every seismic trace location. They yield important information concerning the nature of the rock and variations in lithology To obtain the best quality pseudologs, careful initial processing is necessary: true-amplitude recovery. appropriate deconvolution. common-depth-point (CDP) stack. wave-shaping, wave-equation migration, and amplitude scaling. The low frequencies from moveout velocity information are inserted. Both the short-period information computed from reflection amplitudes and the long-period trend computed from reflection moveout are displayed on acoustic impedance logs. Possible causes of pseudolog distortions are inaccuracies of amplitude recovery and scaling, imperfection of deconvolution and migration. and difficulties of calibrating the pscudolog to an acoustic Iof derived from well logs. Such calibration increases the precision; facies variations observed in well logs cau bc extrapoled to large distances from the wells. leadin, (7 to a more accurate estimation of hydrocarbon resel.ves.

In well seismics, when operating with a three‐component tool, particle velocities are measured in the sonde coordinate system but are often needed in other systems (e.g., source‐bound or geographic). When the well is vertical, a change from the three orthogonal components of the sonde to another orthogonal coordinate system can be performed through one rotation around the vertical axis and, if necessary, another one around a horizontal axis (Hardage, 1983). If the well is deviated, the change of coordinate system remains easy in the case when the source is located at the vertical of the sonde, or in the case when the source stands in the vertical plane defined by the local well axis. In the general case (offset VSPs or walkaways) or when looking for unknown sources (such as microseismic emissions induced by hydraulic fracturing), coordinate rotation may still be performed, provided that we first get back to a situation in which one of the axes is vertical.

International audienceThe future development of safe CO2 storage on land needs a particular effort on monitoring methods. In the specific geological context of the sedimentary Paris Basin (France), the Geocarbone-Monitoring project carried out from 2006 to 2008 the evaluation and testing of different monitoring methods. The targeted reservoirs are either depleted reservoirs in the carbonate Dogger formation or saline aquifers in the silico-clastic formations of the Triassic. To map the migration of the CO2 plume, the project evaluated geophysical methods as active seismic, electrical resistivity and gravity. Results show that the geological context implies further research to be conducted to overcome problems related either to data acquisition in the case of gravity or to the geological context in the case of seismic and electrical resistivity. The InSAR remote sensing method was not able to detect ground deformation over seasonal gas storage, mainly because of the dense vegetation cover. Methods for soil gas measurement at the surface were successfully tested on natural analogs, revealing the complexity of mechanisms involved in the origin of the CO2 flux, its temporal and spatial variations, as well as the need for continuous surface measurements in order to control seasonal variation

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