Key Takeaways & Executive Findings
- •• A novel LIER model integrates laser-thermal effects, residual polarization fields, and thermionic emission to characterize shale anisotropy. • For out-of-plane anisotropy, the product of LIER parameters follows cubic/impulse functions under continuous laser and exponential under pulsed laser, with a threshold angle. • Tangential LIER measurements on cylindrical cores effectively separate bias voltage and laser power effects, enhancing model applicability. • LIER demonstrates potential as a real-time monitoring tool for shale anisotropy during laser drilling operations.
Abstract
Laser-induced electro-response (LIER), as a new method that complements conventional rock physics testing techniques, is expected to address issues such as of unclear mechanisms, model deficiency, inconsistent evaluation parameters, and difficulty in separating multiple coupling factors in shale anisotropy evaluation, and establish a more complete and reliable shale physical property evaluation system. A testing strategy for out of plane anisotropy (OPA) was proposed for characterising anisotropy by LIER, where the near infrared (NIR) continuous laser (CL) and nanosecond pulsed laser (PL) were used to irradiate the surface of oblique cut shale, and the transverse LIER of the surface was measured. A LIER detection model is constructed from the laser-thermal effect, residual transverse polarization electric field and thermionic emission transport mechanism, which is strongly relying on laser power, bias voltage, and inclination angle of the measurement direction relative to the bedding plane of shale. For OPA test on the slice of oblique cut shale under CL irradiation, the relationship between the product of LIER simulation parameters and the tilting angle can be described by a cubic function and an impulse function with a maximum value at the threshold angle. In addition, the thermal accumulation and transient thermal effects are induced in the shale under a high-energy short laser pulse irradiation, and the simulation results indicate that there is an exponential relationship between the product of parameters in the LIER model and the tilt angle. Thus, for OPA test under CL and PL irradiations, it is recommended to use the product of parameters as an evaluation index for shale anisotropy. Furthermore, to solve the problem of multiple influencing factors entangled in the exponential term of the LIER model, the tangential LIER measurement was performed on the side of cylindrical shale core, where the provided LIER model effectively presented the anisotropy of tight shale plug, especially the effects of bias voltage and laser power on LIER were relatively separated as independent variables. Finally, the LIER at the end of laser drilling is presented well using the optimized model under a focused ns NIR PL irradiation, indicating that LIER is expected to be a real-time means for characterizing shale anisotropy during laser drilling processes. These results show that the present work is fundamental for the precise evaluation and effective development of anisotropic shale reservoirs, and will drive the advances of LIER in the exploration for shale oil and gas.
1. Introduction
Shale oil and gas is a resource-rich clean energy and mainly located in sedimentary and metamorphic rock formations. Shales are not only a reservoir rocks with the ability to seal carbon dioxide, methane, etc., but also a source rocks [1]. Unlike conventional sandstone reservoirs, shales exhibit distinct bedding planes which are caused by preferentially orientated of clay minerals and organic matter [2]. Lamination is the most frequently cited influencing factor for shale anisotropy, which leads to different electrical, mechanical, thermal, seismic, and magnetic properties at directions parallel and perpendicular to their bedding planes, and has significant impact on energy industry and the research of geophysical properties in the Earth.
Traditional techniques such as magnetic susceptibility, seismic, mechanical, and geo-electrical response detections can reveal post-depositional anisotropic characteristics of shales with invisible details. However, these methods often suffer from limitations in resolution, cost, or the ability to decouple multiple influencing factors. Laser-induced electro-response (LIER) emerges as a complementary approach, offering potential for real-time, non-destructive evaluation of shale anisotropy. This study proposes a comprehensive LIER model and validates it experimentally, aiming to establish a more reliable evaluation system for anisotropic shale reservoirs.
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Xuecong Liu, Zhengchun Hong, Yuqi Jiao, Kun Zhao, Xinyang Miao (2025). Anisotropy of laser-induced electro-response in shale: Modelling and experimental validation. SinoTechIntel Verified Research. https://doi.org/10.1016/j.ijmst.2025.08.015
Research & Educational Purpose Only:The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntel are intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
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Frequently Asked Questions
What is laser-induced electro-response (LIER) and how does it relate to shale anisotropy?
LIER is a novel method that measures electrical responses generated when a laser irradiates shale. It complements traditional rock physics testing by providing a way to characterize shale anisotropy, which arises from bedding planes and affects properties like electrical conductivity. The method uses continuous or pulsed lasers to induce thermal and plasma effects, generating measurable electrical signals that correlate with the shale's anisotropic structure.
How does the LIER model account for different laser types and measurement configurations?
The LIER model incorporates laser-thermal effects, residual transverse polarization electric fields, and thermionic emission transport. For out-of-plane anisotropy tests, continuous laser (CL) irradiation yields a cubic or impulse function relationship between the product of model parameters and tilt angle, while pulsed laser (PL) irradiation results in an exponential relationship. Tangential measurements on cylindrical cores allow separation of bias voltage and laser power effects, improving model accuracy.
What are the key findings regarding the evaluation index for shale anisotropy using LIER?
The study recommends using the product of parameters in the LIER model as an evaluation index for shale anisotropy. This product shows distinct functional dependencies on tilt angle depending on laser type (cubic/impulse for CL, exponential for PL), providing a quantitative measure that can be used to assess anisotropy in shale samples.
Can LIER be applied in real-time during laser drilling?
Yes, the study demonstrates that LIER can be used to characterize shale anisotropy at the end of laser drilling. By optimizing the model under focused nanosecond NIR pulsed laser irradiation, the LIER response accurately reflects the anisotropy of the shale, indicating its potential as a real-time monitoring tool during drilling operations.
What are the advantages of LIER over traditional anisotropy measurement techniques?
LIER offers several advantages: it is non-destructive, can provide real-time data, and can separate multiple influencing factors such as bias voltage and laser power. It also addresses limitations of traditional methods like magnetic susceptibility or seismic techniques, which may have lower resolution or difficulty in isolating specific anisotropic contributions.
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