The near-surface geological risk prediction technology for shale gas using electromagnetic methods under complex geological conditions has reached an internationally leading level.

On May 6, a third-party professional evaluation and appraisal meeting for the scientific and technological achievement "Key Technologies and Applications of Electromagnetic Exploration for Shale Gas in Complex Geological Conditions," led by the Geophysical Exploration Institute of Sichuan Natural Resources Investment Group and jointly completed with Chengdu University of Technology and Sichuan Changning Natural Gas Development Co., Ltd., was held at the Sichuan Provincial Archives of Scientific and Technological Research Achievements.

The expert panel for the achievement evaluation and appraisal meeting is headed by Academician Luo Pingya from the Chinese Academy of Engineering, with Liao Shimeng from the Natural Gas Professional Committee of the China Petroleum Society serving as the deputy head. The review experts are renowned specialists from institutions including the Southwest Geophysical Research Institute of Eastern Geophysical Corporation under CNPC, the Southwest Oil & Gas Branch of Sinopec, the Exploration Branch of Sinopec, the Southwest Oil & Gas Field Branch of PetroChina, and the Chengdu Geological Survey Center of the China Geological Survey.

At the appraisal meeting, Professor Cao Hui delivered a detailed report on the research background, research methods and approaches, research findings, key technologies and innovative aspects, as well as the application and promotion status of the study. This applied research primarily involves comprehensive analysis and investigation from several perspectives, including the geological characteristics of the southern Sichuan region, the integrated effectiveness of various geophysical methods, the macro- and micro-scale coupled electrical mechanisms in shale, and the geological origins and controlling factors of low-resistivity shales. Over nearly four years of experimentation and application, this research has yielded abundant intellectual property achievements and has already mentored 32 master’s and doctoral students.

The attending experts listened to the project team’s report, reviewed the relevant materials, and after questioning and discussion, reached a conclusion.

First, the technical documentation provided is complete and meets the requirements for evaluating scientific and technological achievements.

Second, in response to the practical challenges posed by the region’s rugged topography and complex geological structures in southern Sichuan—where seismic acquisition and imaging are particularly difficult—we have adopted surface electromagnetic methods and borehole-to-surface electromagnetic methods to predict drilling-related geological risks. By conducting a comprehensive evaluation from both geological and engineering perspectives, we have identified favorable areas for shale gas development and developed key technologies for electromagnetic exploration of shale gas under complex geological conditions, achieving three innovative results.

The first achievement is the development of an integrated inversion method that combines ground-based and borehole electromagnetic data processing and inversion, enabling accurate detection and identification of subsurface geological anomalies. By introducing the principal-axis anisotropy assumption into the borehole-ground electromagnetic governing equations and employing the finite-difference method to compute the anisotropic electromagnetic anomaly fields in borehole-ground systems, we use the LBFGS algorithm to perform three-dimensional anisotropic inversion on the ground-based electromagnetic data collected. This approach significantly enhances the accuracy of predicting subsurface geological anomalies.

The second achievement is the development of an integrated technology for predicting geological risks in shale gas drilling. This technology has established a systematic approach for accurately detecting and identifying underground geological anomalies at multiple scales and involving multiple parameters. It provides detailed interpretations and comprehensive predictions of geological anomalies such as lithology of subsurface strata, geological structures, mined-out areas in coal mines, and karst formations, thereby offering crucial geological support for the careful selection of shale gas well locations.

The third achievement is the development of a high-quality shale reservoir prediction technology based on electromagnetic methods. We have clarified the mechanism of coupled conductivity in rock pores and interfaces, explored the primary controlling factors behind low resistivity and their geological implications, established a macro-micro integrated control mechanism, developed an interpretative model for petrophysical electrical properties, delineated geoelectrically favorable intervals within the reservoir, and effectively guided shale gas exploration and development.

Third, the project has been granted 6 Chinese invention patents and 13 utility model patents (including 1 German utility model patent), registered 6 software copyrights, and published 25 papers.

Fourth, the research findings have been successfully applied to the efficient exploration and development of shale gas in the complex geological conditions of the Sichuan Basin, yielding significant socio-economic benefits.

In summary, the expert panel unanimously concluded that this research achievement as a whole has reached an internationally advanced level, with its electromagnetic method for near-surface geological risk prediction of shale gas attaining an internationally leading position.

Executive Producer | Zhang Guangda
Reviewed by | Zhou Huiying
Text | Yang Yuning
Figure | Wang Yuchen
Editor | Wen Han