Experimental study on the effects of chemical or microwave treatment on the tensile strength of hot dry rock

Abstract

The Brazilian disc (BD) specimens were heated to high temperatures up to 100–500 °C followed by immersion in chemical solutions or irradiation in a microwave oven. The Brazilian splitting tests were then performed at high temperatures, and acoustic emission (AE) events were recorded. Meanwhile, the longitudinal wave velocity and open porosity of the rocks were measured, and the scanning electron microscope (SEM) was applied to identify the influence of chemical or microwave treatment on the microstructure in specimens. The experimental results show that: (1) the chemical or microwave treatment exacerbates the damage to the heat-treated rocks and that either treatment has significant effect on heat-treated rocks with diverse lithologies. (2) The specimens with a high proportion of soluble minerals are chemically dissolved and the specimens with a high percentage of powerful microwave absorption minerals were irradiated by the microwaves, resulting in lower longitudinal wave velocity, lower tensile strength, higher open porosity, and more severe microstructural damages. (3) Rock tensile strength is closely related to the breakdown pressure of hydraulic fracturing, implying that chemical or microwave-assisted fracturing techniques have significant impact on various hot dry rocks, and these auxiliary fracturing techniques considering rock lithology are novel and important for EGS projects.