Experimental Analysis on P-wave Attenuation in Tight Oil Rocks

Abstract

Summary Ultrasonic laboratory experiments are performed on the 12 rock samples which are collected from tight oil reservoirs in the Qingshankou Formation of Daqing oilfield in northeast China. The waveform data of tight oil rocks under different conditions with varying pore-fluid types and partial saturations are obtained by ultrasonic measurements. We calculate P-wave velocities by using of the first arrivals. The attenuation of P-waves (inverse quality factor, Q-1) is estimated by using the spectral ratio method. The results show that P-wave velocity decreases with the increase of gas saturation and oil saturation respectively. P-wave attenuation Q-1 is the most significant at full-gas saturation state, and it first decreases with an increasing gas saturation (till gas saturation of 15%) and then increases in the gas/water partially-saturated samples. The empirical relationships between P-wave attenuation and porosity/permeability are given by analyzing Q-1 at the full-gas saturation states. The physical mechanisms of viscous fluid flow and relevant relaxation which cause the attenuation variations are discussed.