APPLICATION OF THE KAISER EFFECT IN IN-SITU STRESS MEASUREMENT IN ROCKS - AN OVERVIEW

Abstract

Knowledge of in-situ rock stress is one of the significant issues in many engineering problems. There are various methods for determining in-situ stress. Most of the common methods used for the determination of in-situ stress are time and cost consuming, and in many cases need specific accessibility. Therefore, attention to core-based methods is increasing. One of these methods is the acoustic emission technique based on the Kaiser effect. This method is among the stress stressing-destressing methods and is based on observing rock behaviour without having any important impact on it. Knowledge of the acoustic emission principles and acoustic signal parameters is the first step to use the Kaiser effect method for in-situ stress determination. Also, using the Kaiser effect method requires knowledge on the mechanism and theory associated with the Kaiser effect. In this research, different methods for determining the Kaiser effect in parametric (tangent method and maximum slope, etc.) and signal processing (Fourier transform, wavelet transform, etc.) terms were reviewed. The results obtained from the Kaiser effect method were compared to other common methods used for in-situ stress measurement, like over-coring and hydraulic fracturing methods, and based on the results, there was a good agreement between them. Also, the effective parameters on determining the Kaiser effect stress point were investigated. The important parameters were the testing procedure, confining pressure, physical properties of rock, delay time and retention time, direction and amount of loading, anisotropy angle and loading rate.

Keywords

• in-situ stress
• acoustic emission
• Kaiser effect
• signal processing
• wavelet transform