A lateral photovoltaic detection for the anisotropic response of invisible-bedding tight shale

Abstract

As the cap rock for oil and natural gas traps, tight shale with small interstitial spaces and invisible beddings were found to have large reserves and rich mining value. Precise identification of feature anisotropy in tight shale is of significance in the development of petroleum reservoirs. Here in this work, we demonstrate an application of a 532-nm laser to measure the lateral photovoltaic (LPV) response of a tight shale with the beddings invisible at different directions inside the upper surface. Although the layer orientations were not obviously for the tight shale, anisotropic response of LPV signals was observed with different peak amplitudes (Vp) as well as lateral and surface distributions. The bedding direction revealed by SEM was consistent with the LPV test results; meanwhile, a trigonometric angular-dependent Vp was observed, proving that the LPV measurements were able to predict the configuration orientation of tight shale with invisible beddings. Our results proved that the lateral photovoltaic response is sensitive to the structure of materials and thus has a great potential in the characterization of shale reservoirs.