A lateral photovoltaic detection for the anisotropic response of invisible-bedding tight shale
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A lateral photovoltaic detection for the anisotropic response of invisible‑bedding tight shale Xinyang Miao1,2 · Xue Peng1 · Wanting Lu1 · Xuecong Liu1 · Shanzhe Zhang1 · Honglei Zhan2 · Kun Zhao1,2 Received: 3 July 2020 / Accepted: 7 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
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.
1 Introduction Anisotropy is widely existed in the strata, which has become an important issue in geophysical exploration [1]. Shales have been found in a series of global sedimentary basins, being estimated to form about 75% of sedimentary rocks all around the world [2]. They are finely grained rocks mainly composed of clay, quartz, feldspar, pyrite, and organic matters. Most recently, requirements for clean fuels have promoted the exploration of organic shales as significant unconventional natural gas resources [3]. Due to the laminated structure, shales are distinguished from other mudstones; meanwhile, as the outcomes of aligned clay particles, layers, cracks, and pores, they often exhibit anisotropic properties [4, 5]. Such anisotropy of shales plays an important role in * Xinyang Miao [email protected] * Kun Zhao [email protected] 1
Key Laboratory of Oil and Gas Terahertz Spectroscopy and Photoelectric Detection, Petroleum and Chemical Industry Federation, China University of Petroleum, Beijing 102249, China
College of New Energy and Materials, China University of Petroleum, Beijing 102249, China
2
engineering activities, e.g. oil-well drilling, wellbore stability, wellbore perforation and so on [6, 7]. It also affects the formation and extension of gaps and fractures, controlling the flow and seepage of the fracturing water [8]. Therefore, the anisotropic properties of shales must be taken into account during the exploration of petroleum resources. In terms of natural geological resources, tight shales with low porosity, low permeability, s
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