Increasing the Penetration Depth of Microwave Radiation Using Acoustic Stress to Trigger Piezoelectricity

Electromagnetic waves as a mechanism of heat generation in the reservoir is a concept that has great potential to efficiently produce heavy oil and bitumen. However, as a result of large wave attenuation, the penetration depth of the wave is relatively small. This limits the economic viability of an otherwise technically proven technology. Taking advantage of the inherent piezoelectric phenomenon in quartz crystals enables the manipulation of the penetration depth of the wave. Acoustic waves were introduced simultaneously with a microwave to the core samples where the presence of the mechanical wave generated an infinitesimal stress. Mechanical stress achieved by the acoustic wave triggered piezoelectricity in two sandstone samples with a limestone sample serving as the control. All consolidated core samples were fully saturated with either oil or water to capture the effect of the pore space. The incremental stress manifests itself through change in the complex permittivity of the sample measured with a vector network analyzer. The penetration depth of the microwave was calculated as a function of the measured complex permittivity. Comparative analysis of the penetration depth of the varying imposed stress states illustrates the additive penetration achieved due to piezoelectricity. Piezoelectricity as the fundamental mechanism of penetration increase was further demonstrated by isolation of the quartz contribution through use of the limestone. Increase in penetration depth was realized for all oil-saturated sandstone cores. The presence of the acoustic wave introduced a stress component across the quartz crystals, generating a change in the electric potential. This created a dynamic polarization that corresponded to an absorption environment more conducive to microwave penetration.