Attenuation analysis of heavy oil sands based on laboratory measurements

Abstract

Analyzing elastic and attenuation characteristics of heavy oil sand is critical for understanding and interpreting sonic and seismic data for their use in exploration and reservoir monitoring. The attenuation characteristic of oil sands is inherently complicated because of its loose frame, large porosity, and highly temperature-dependent viscosity of heavy oil. During thermal production, the attenuation of heavy oil sands undergoes significant changes due to the effects of pressure, temperature, and gas. Therefore, we have performed laboratory measurements of heavy oil sands under different physical conditions. By applying spectral-ratio method on the recorded wave signals, we are able to investigate the attenuation of the oil sands under different pressure and temperature conditions. For the measured sample, the [Formula: see text] decreases from 0.083 to 0.043 for a differential pressure increasing from 1.38 to 9.65 MPa. A peak of [Formula: see text] occurs at the middle temperature (approximately 60°C) for the wet sample, whereas the weakest [Formula: see text] occurs at the low temperature. Comparisons between the as-is (partially saturated) and wet (fully saturated) samples suggest that attenuation ([Formula: see text]) of the oil sands can be significantly affected by the presence of gas at a high temperature (greater than 60°C). In the end, the Havriliak-Negami model is used to capture the temperature-dependent attenuation characteristics of fully saturated oil sands. Although the measurements are conducted at ultrasonic frequency, the presented results indicate some implications for field-reservoir monitoring and also offer insights into applying attenuation attribute to characterize heavy oil reservoir during thermal production.