The gravitational attraction between the sun, moon, and the earth gives birth to oceanic tides which are visible and sometimes large, and to earth tides whose amplitudes are small due to the low compressibility of the earth compared to that of water. Tidal effects are observed quite often in open pits, and also in closed well reservoir systems. The purpose of this study was: (1) to develop a theory which describes the pressure variations in closed well-reservoir systems caused by the earth tides, (2) to study the important parameters which determine the amplitude of the response, and (3) to inspect different sets of field data for gas and oil reservoir systems for which accurate pressure information is available.A new expression for the pressure induced at the borehole by a periodic tidal stress was derived. The important parameters for the amplitude response of a cloced well-reservoir system are the permeability, the porosity, and the rock and fluid compressibilities.

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values and a wide range of real materials. Because of the form of its frequency-dependence and the relatively low center source frequency used in well logging surveys, the viscous coupling coefficient can be approximated by the value in the cylindrical duct geometry. ReferencesBerryman, J. G., 1980, Confirmation of Biot' s theory: Appl. Phys. Lett., 37, 382-385. Biot, M. A., 1956, Theory of propagation of elastic waves in a fluid saturated porous solid: J. Acoust. Sot. Am., 28, 168-191. Schmitt, D. P., Bouchon, M., and Bonnet, G., 1985, Full wave synthetic acoustic logs in saturated porous media, Part 1, Theory and simple configuration: Presented at the 54th Annual SEG Meeting, Atlanta. FrameToday more than ever, a lot is expected from full waveform acoustic logging to enhance the knowledge of underground fluid reservoirs. This study is meant to apply new interpretation schemes to data from fractured crystalline formations. Qualitative analysis of acoustic amplitude, traveltime, and discontinuity-generated (DG) waves is made with reference to conventional logs. It shows that amplitudes of compressional, shear, and Stoneley waves discriminate zones containing fluid, whereas traveltime of compressional and shear waves, and DG waves, are better fit for precise lithologic identification of clean rock and fractured zones. A newly developed theory based on an energy transfer mechanism between borehole fluid and formation fluid relates the amplitude of Stoneley waves to fracture permeability. This theory is applied in a quantitative analysis of the data, to give estimates of fracture permeabilities. Introduction and tool description

With the development of full waveform acoustic tools, geophysicists have tried to extract more and more information from acoustic parameters and to relate to the data to formation propertiesThe new tool, EVA (Evaluation of Velocity and Attenuation), is a 4-transmitter/12-receiver long spacing tool permitting recording of the complete waveform and processing of all information contained in the acoustic signal.The key point for optimum results is a robust and automatic processing which allows quantitative estimation of different parameters such as velocity, amplitude, and period of all the three main types of waves, i.e. compressional (P), shear (S), and Stoneley (ST) waves.In parallel with the processing phase, the analysis of the raw data leads to a qualitative and very rapid interpretation of the recordings.Once the processing is completed and all parameters obtained, these may be applied to a quantitative interpretation of the EVA data. Such interpretation can then be utilised for automatic lithology estimation, estimation of porosity and shale content, and to the detection of fractures and eventually the estimation of permeability.Further applications such as the detection of invaded zones, estimation behind casing, estimation of elastic moduli, and the reconstitution of a density log can provide significant data for exploration and production engineers.