Velocity measurement of North Sea heavy oil sands under changing pressure and temperature

Abstract The factors of rock components and reservoir conditions have significant influences on the elastic properties of heavy oil sands. We investigate the effects of these factors on the velocities of heavy oil sands from North Sea through measuring the velocities under changing pressure and temperature conditions. To inspect the influences of heavy oil and gas in pore space, we clean the samples (remove oil) and measure the corresponding velocities under dry and water-saturated conditions, and perform the measurements under as-is and fully saturated conditions. Besides, we also compare the measurements under changing confining and pore pressures, revealing that the increase of water bulk modulus is nonnegligible when pore pressure is large. Our results show that the velocities of oil sands increase with pressure and decrease with temperature while the Vp/Vs ratios show the opposite trends. The comparison of dry and water-saturated measurements suggests that rock frame is weak and oil sands properties are mainly affected by heavy oil. The as-is and fully saturated measurements comparison reveals the strong gas effect on P-wave velocity. Overall, our results highlight the effects of pressure, temperature, frame, gas, and oil on the elastic properties of heavy oil sands. The findings of this study can help for better understanding of the elastic properties of North Sea heavy oil sands under various conditions, which can facilitate the future rock physics modeling and provide important information for seismic characterization of North Sea heavy oil reservoir.