ABSTRACT

In the past, many dry boreholes have been drilled on the basis of false hydrocarbon indicators. In some cases, these have been thought to be related to ‘fizz water’ effects. Unfortunately, the identification of these effects is difficult, mostly due to the lack of reliable seismic methodologies for gas quantification and the subsequent misinterpretation of seismic data.

Understanding the acoustic response of partially gas saturated rock under different pressure and temperature conditions may help to develop better seismic methodologies and help in quantitative hydrocarbon detection and characterization, hence avoiding drilling costly dry wells.

New ultrasonic measurements on a partially gas saturated sandstone show that dissolved gas significantly affects the compressional wave velocity and attenuation of rocks only at low pore fluid pressures. At high pore pressure (above the bubble point) gas bubbles are dissolved in the water and the mixture behaves like a liquid with lower density.

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