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Recently Ouenes etused extensively simulated annealing to generate permeability and porosity fields. In this paper, the Simulated Annealing Method (SAM) is applied to a gas storage reservoir. The permeability field predicted in four geological layers preserves the spatial distribution and honors the actual measured data from the field. These known data at the wells lead to isotropic and anisotropic variograms which were matched by SAM. In this approach, contrasting the usual conditional simulation, no interpolation technique is used to smooth data at unknown locations. The generated field is compared to a kriged field by using a 3D advanced gas reservoir simulator. When using permeability fields generated by SAM, gas and water pressure data obtained through simulation become very close to observed field pressure data. On the other hand, the pressure obtained with the kriged field clearly shows that the smooth representation introduced by the kriging is not realistic, and the heterogeneities which affect considerably the flow behavior are not well described.

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The spatial distribution of many of the physical parameters connected with a gas reservoir is of primary interest to both engineers and geologists throughout the study, development, and operation of a field. It is therefore desirable for the distribution to be capable of statistical interpretation, to have a simple graphical representation, and to allow data to be entered from either two-or threedimensional grids. To satisfy these needs while dealing with the geographical variables, new methods have been developed under the name "geostatistics." This paper describes briefly the theory of geostatistics and its most recent improvements for the specific problem of subsurface description. The external-drift technique has been emphasized in particular, and in addition, four case studies related to gas reservoirs are presented to show the wide range of geostatistics application.

The operation of an aquifer gas storage can be distinguished from the production of a classical gas field by two fondamental points:–the flow rates in an aquifer storage are much more important, with gas/water displacement sometimes becoming instable–the alternating movement of fluids brings about variations in petrophysical properties despite apparently identical conditions These two principal problems need to be carefully treated to correctly forecast and strictly monitor the development and operation of an aquifer storage. This paper presents the results of a study which was conducted on a small scale model of metric size, allowing the visualization and quantification of the different phenomena observed. The effect of different parameters (inclination angle, gas flow-rate, number of cycles, etc.) on stability, geometric characteristics of the gas bubble, the allowable quantity of gas injected, and the Trapped Gas Ratio were investigated. Results were enhanced by the use of video-taping as interpreted by image processing.