EVALUATION OF FORMATION PROPERTIES FROM PROCESSING AND INTERPRETATION OF THE EVA TOOL LOGS

Abstract

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 properties

The 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.