Effect of loading rates on accurate in-situ stress determination in different lithologies via Kaiser effect

• Published in: Arabian journal of geosciences 2021-07, Vol.14 (14), Article 1304
• Main Authors: Zhang, Yan, Okere, Chinedu J., Su, Guandong
• Format: Article
• Language: English
• Subjects: Acoustic emission; Acoustic emission testing; Acoustics; Comparative analysis; Cores; Development projects; Earth and Environmental Science; Earth science; Earth Sciences; Emission analysis; Evaluation; Experiments; Hydraulic fracturing; Kaiser effect; Limestone; Lithology; Load distribution; Loading rate; Measurement methods; Mudstone; Oil and gas fields; Oil field equipment; Oil fields; Original Paper; Rocks; Sandstone; Sediment samples; Sedimentary rocks; Stone; Stress
• ISSN: 1866-7511; 1866-7538
• DOI: 10.1007/s12517-021-07674-3

Acoustic emission and hydraulic fracturing are the direct methods for measuring the in situ stress of rock samples in the laboratory. The acoustic emission experiment (Kaiser effect experiment) is the most widely adopted technique which utilizes the Kaiser effect of rocks, in evaluating the in situ stress of core samples. However, during the Kaiser effect experiment, different loading rates exhibit a certain influence on core samples with varying lithology, and to the best of our knowledge, no scholar had critically addressed this issue. In this study, we performed Kaiser effect experiments on rock samples of different lithologies taken from six case study wells in Jidong Nanpu Oilfield, China. Then, we obtained curves showing the relationship between the stress corresponding to the Kaiser effect of limestone, sandstone, gritstone, and mudstone at different confining pressures. Based on the curves, the true values of the in situ stress were determined. The accuracy of the estimated stress from the acoustic emission experiment was validated via a comparative analysis of the in situ stress from the hydraulic fracturing method. The findings revealed that, for sandstone, gritstone, and mudstone, the stress corresponding to the Kaiser effect spots significantly increased with the loading rate, while for brittle rocks such as limestone, the loading rates had a minimal impact on the Kaiser effect. It is recommended to use an optimal loading rate for a better result during a Kaiser effect experiment. This study provides a reliable basis for the experimental evaluation of in situ stress that is relevant Oilfields and mining development projects.