Effect of Cyclic Thermal Shock on Granite Pore Permeability

Qiang Sun,Cunbao Li,Jianjun Hu,Heping Xie,Dawei Hu

doi:10.2113/2021/4296301

Qiang Sun, Cunbao Li + Show 3 more

Open Access

https://doi.org/10.2113/2021/4296301

Copy DOI

Abstract

Abstract Geothermal development requires an understanding of changes in pore permeability caused by repeated thermal shock fatigue damage in hot dry rock. Research on the subject can aid the evaluation of the longevity and mining value of enhanced geothermal systems (EGS). However, few relevant studies are currently available. In this study, the change characteristics of pore permeability in granite following different heating–cooling cycle temperatures (250°C, 350°C, 450°C, 550°C, and 650°C) and numbers of cycles (1, 5, 10, 15, and 20 cycles) were analyzed. Results show that with increasing temperature, the uneven thermal expansion and thermal shock effect of minerals promote crack development, leading to increases in the porosity and permeability of granite, particularly at temperatures above 450°C. When the heat treatment temperature was below 450°C, the number of cycles only slightly affected the porosity and permeability; meanwhile, when the temperature exceeded 450°C, the porosity and permeability increased significantly with an increase in the number of cycles. Moreover, three-dimensional nonlinear fitted relationships among porosity (or permeability), cycle temperature, and number of cycles have been established for the first time with correlation coefficients (R2) above 0.9, which reveals the change rules of pore permeability after quenching in hot dry rock. The results can be used to evaluate the efficiency of geothermal reservoir energy extraction and aid in geothermal reservoir design.

Highlights

The depletion of traditional fossil fuels and the deterioration of the environment due to the combustion of fossil fuels render necessary the search for new alternative green and sustainable energy sources [1]
Hot dry rock (HDR) is a high-temperature rock mass that is generally buried 3–10 km below the ground surface in the absence of water or steam at temperatures typically ranging from 150°C to 650°C [12]
To explore the effect of changes in the cyclical temperature on the permeability of granite, its porosity after heat treatment was measured, and the results were used to evaluate the changes in permeability

Summary

Introduction

The depletion of traditional fossil fuels and the deterioration of the environment due to the combustion of fossil fuels render necessary the search for new alternative green and sustainable energy sources [1] One such renewable energy source, geothermal energy, is favored by many countries because of its wide distribution, rich reserves [2, 3], strong stability [4], low environmental impact [5], low greenhouse gas emissions [6], low unit cost, and the relatively easy and quick construction of geothermal plants. The United States has established Frontier Observatory for Research in Geothermal Energy (FORGE) for the promotion of EGS technology [16], which is mainly used to inject cold water into injection wells [17].

Results

Discussion

Conclusion