Probing the Anisotropy of Shale by the Voltaic Response of Laser-Induced Plasma

Due to the complexity of geological structures, it is difficult to fully characterize unconventional oil and gas reservoirs in the existing geological exploitation theories and techniques. This article introduced a laser induced plasma transmission voltage (LIPTV) method for characterizing the isotropy of sandstone and anisotropy of shale. When the rocks receive a nanosecond pulsed laser, plasma is generated on the sample surface. Under the condition of applied electric field, the maximum voltage of 0.024 V can be obtained. Plasma transport was related to surface morphology and structure. The mechanism of plasma transport on the surface can be analyzed by simulating the voltage attenuation process with time. Rotation angle-dependent voltage peaks of shale presented a symmetry at the location of 180 degrees and was an oval in polar graph, where the long shaft and the short shaft were parallel and perpendicular to bedding direction, respectively (relative range = 150%). According to the relation between the double-exponential fitting tendency and the attenuation waveform, electric field controls the transport of the carrier in the horizontal and vertical directions in shale. For sandstone, a circle was obtained in polar graph because of the isotropy (relative range = 28%). Therefore, the direction characterization supported by LIPTV method is helpful for enhancing oil recovery in petroleum industry.

Automated summary

The article introduces a LIPTV method for characterizing the anisotropy of rocks, focusing on sandstone and shale. It analyzes the plasma transport voltage characteristics of rocks through the voltage attenuation process and the symmetry features presented by rotation angle-dependent voltage peaks. This method provides direction characterization that is helpful for enhancing oil recovery in the petroleum industry.