|Publisher||Society of Exploration Geophysicists||Language||English|
|Content Type||Conference Paper|
|Title||Frequency Dependent Elastic Properties And Attenuation In Heavy-oil Sands: Comparison Between Measured And Modeled Data|
|Authors||Agnibha Das, Michael Batzle, Colorado School of Mines|
|Source||2010 SEG Annual Meeting, October 17 - 22, 2010 , Denver, Colorado|
|Copyright||2010. Society of Exploration Geophysicists|
We have measured elastic (bulk and shear modulus) and acoustic (compressional and shear wave velocities) properties of heavy-oil sands over a range of frequencies (2 − 2000Hz) covering the seismic bandwidth and at ultrasonic frequencies (0.8MHz). The measurements were carried on heavy-oil sand sample from Asphalt Ridge, Utah at a constant temperature ( 20oC) and different confining pressures using the low frequency experimental setup at Colorado School of Mines. Four different modes of intrinsic attenuation, extensional (QE−1), shear-wave (QS−1), compressional-wave (QP−1) and bulk compressibility (QK−1) were estimated. Both compressional and shear wave velocities show significant dispersion probably due to both the the inherent viscoelastic property of heavy oil and viscoelasticity arising due to oil and sand interactions. The measured attenuation (Q−1) values are significantly high indicating significant loss of energy during wave propagation. We made an attempt to model the measured acoustic properties using effective medium theories. The results show reasonably good agreement between the measured data and modeled response especially at non-zero confining pressures. The measured attenuations were modeled using the Cole-Cole model.
Heavy-oil sands are an important unconventional energy resource. The total inplace volume of heavy-oil is much larger than that of conventional light oil. Current methods of production from heavy-oil reservoirs are dominated by thermal techniques such as in-situ combustion, THAI (Toe to Heel Air Injection) and SAGD (Steam Assisted Gravity Drainage). Acoustic Impedance (AI) difference maps are extensively used for quantitative seismic monitoring of heavy-oil reservoirs undergoing production. Correct understanding of the rock physics of heavy-oil and heavy-oil sands is important for interpreting the AI difference maps in terms of temperature, fluid property and fluid saturation changes. Heavy-oil can exist in three different phases: solid, liquid and quasi-solid (Han et al., 2009). In the quasi-solid state heavy oils have a non-negligible shear modulus that is highly temperature and frequency dependent. Laboratory measured data over a range of frequencies are important for developing our understanding of the frequency depdendent behavior of heavy-oil and heavy-oil sands. Over the last few years laboratory measured elastic properties of heavyoil and heavy-oil sands have been published by a number of researchers (Han et al., 2009, 2008, 2007; Behura et al., 2007). However, most of the published data has been measured either at ultrasonic frequencies or over a limited range of frequencies only. We have measured bulk modulus (K), shear modulus (μ), pwave velocities and s-wave velocities for a heavy oil sand sample sample from Asphalt Ridge, Utah over a wide frequency band that covers the seismic bandwidth and ultrasonics. The measurements were done both as a function of frequency and confining pressure. The studied sample comprises of unconsolidated quartz grains held together only by viscous heavy-oil. The porosity of the sands are approximately 36% and the permeability is also very high. Oil saturation in the sands lie between 85−90%. The remaining 10−15% of the porosity is filled water, but, since the sample comes from an outcrop most of that is expected to have dried out.
|File Size||450 KB||5|