VARIATION OF ELASTIC WAVE VELOCITY WITH SATURATION IN SANDSTONE

Abstract

The velocity of dilatational waves in four sandstones has been measured as a function of pressure in the range 50 to 1000 bars at room temperature and at 100°C. At least two cores from each sample were run, one dry and one saturated with water. In addition two cores from one sample were run at several partial saturations. The porosities of the samples varied from about 8 to 20 percent. The effect of water content is dependent on pressure. At low pressures (50 bars) the velocity rises sharply at small saturations (0–10 percent), remains constant with saturation 10 to 90 percent and then decreases as the saturation approaches 100 percent. At 50 bars the velocity at 100 percent saturation is generally higher than that at 00 percent saturation. Even for the one exception an extrapolation would indicate this to be true at atmospheric pressure. As the pressure is increased the rise at low saturations decreases; at 500 bars it disappears. The velocity is almost constant with saturation until about 90 percent saturation is reached. It then decreases rapidly as 100 percent saturation is approached. A qualitative explanation of these results is given.