The effect of supercritical CO2 on failure mechanisms of hot dry rock

Li, Honglian; Jiang, Xiang; Xu, Zhi; Bowden, Stephen A.

doi:10.46690/ager.2022.04.07

Cited by 4 publications

(4 citation statements)

References 37 publications

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“…𝜎 = −3197.25𝜙 + 273.2, R 2 = 0.852 (7) where 𝐸 is the elastic modulus, GPa; 𝜎 is the compression strength, MPa.…”

Section: Correlation Analysis Between Porosity and Mechanical Paramet...mentioning

confidence: 99%

“…Except hydraulic fracturing, which is the main means of reservoir reconstruction in granite [4], the supercritical CO 2 fracturing technology is often applied, which can also store the CO 2 in the formation, decreasing the CO 2 emission in the atmosphere [5,6]. These strong stimulation methods, including hydraulic fracturing and supercritical CO 2 fracturing at high fluid injection pressure, increase the risk of induced micro-seismic events and even destructive earthquakes [7][8][9][10][11]. In EGS engineering, the poor hydraulic connection between production wells/injection wells is often encountered due to the improper fracture network in granite by the strong fracturing stimulation.…”

Section: Introductionmentioning

confidence: 99%

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Permeability and Mechanical Response of Granite after Thermal and CO2 Bearing Fluid Hydro-Chemical Stimulation

et al. 2022

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The large scale extraction of geothermal energy can reduce CO2 emissions. For hot dry rocks, the key to successful utilization depends on the efficiency of reservoir reconstruction. The chemical and thermal stimulation methods are always used in geothermal reservoir reconstruction except in hydraulic fracturing with high fluid injection pressure, which is believed to reduce the seismic hazard by applying before the high-pressure hydraulic fracturing stimulation. However, at the laboratory scale, there are still very limited experimental studies illustrating the combined effects of chemical and thermal stimulation on the permeability and mechanical properties of granite, which is regarded as the main type of hot dry rock. In this paper, comparative stimulation experiments were carried out, including thermal/cold stimulation, CO2 bearing solution hydro-chemical stimulation, combined thermal and CO2 bearing fluid stimulation. By means of nuclear magnetic resonance analysis, permeability test and triaxial compression test, the changes of the micro-structure, permeability and mechanical properties of granite under various stimulation conditions were analyzed. The experimental results show that, compared with the single thermal stimulation and CO2 bearing fluid hydro-chemical stimulation, the superposition effect of thermal and CO2 bearing fluid hydro-chemical stimulation can increase the number of micro-fractures in granite more effectively, thus increasing the permeability, while the elastic modulus and compressive strength decrease. Moreover, the cooling mode on the granite also has a certain influence on the stimulation effect. After water-cooling on the heated granite (300 °C), combined with the CO2 bearing fluid stimulation (240 °C, 20 MPa), the permeability of granite is the highest, increasing by 17 times that of the initial state, and the porosity also increases by 144.4%, while the elastic modulus and compressive strength decrease by 14.3% and 18.4%, respectively. This implies that the deterioration of mechanical properties due to the micro-fractures increased by the thermal and chemical stimulation can enhance the fluid conductivity and heat extraction of granite. The methods in this paper can provide a reference for the combined application of thermal and chemical stimulation technology in artificial reservoir reconstruction of hot dry rocks.

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“…𝜎 = −3197.25𝜙 + 273.2, R 2 = 0.852 (7) where 𝐸 is the elastic modulus, GPa; 𝜎 is the compression strength, MPa.…”

Section: Correlation Analysis Between Porosity and Mechanical Paramet...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Permeability and Mechanical Response of Granite after Thermal and CO2 Bearing Fluid Hydro-Chemical Stimulation

et al. 2022

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“…These formations have relatively recent diagenetic ages and certain special properties, such as weak cementation, easy weathering, and ease of becoming muddy and sandy when in contact with water. Consequently, mining operations in these formations face significant challenges (Liu et al, 2020;Liu et al, 2021;Liu et al, 2022;Asif et al, 2022;Liu et al, 2022;Li et al, 2022;Liu et al, 2023). This difficulty necessitates indepth research on utilizing the geological characteristics of western China to implement targeted measures for preserving the weakroof rock layer and regulating the working face weighting (Xu et al, 2018;Wang et al, 2023a;Wang et al, 2023b;Wang et al, 2023c).…”

Section: Introductionmentioning

confidence: 99%

Principle and practice of hydraulic softening top-cutting and pressure relief technology in weakly cemented strata

Wang,

Xu,

Liu

et al. 2024

Front. Earth Sci.

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Extremely thick and hard roofs are difficult to break in the mining of a working face, and the large area of the suspended roof easily induces a strong ground pressure or dynamic impact disasters. The roof control of a coal mining face in a mine in western China was taken as a case study. The mineral composition, microstructure, and hydrophysical properties of the hard roof overlying the coal seam were analyzed. The characteristics of the weak-cementation strata that are prone to mud and collapse when encountering water were targeted to investigate the hydraulic softening roof-cutting and pressure relief technology. It was found that the clay mineral composition in the roof plate accounts for 60.6%. After 24 h of natural immersion, the rock strength decreased by approximately 10.3%–49%, and further immersion caused disintegration. By arranging high and low double-row water injection softening drilling holes in the cutting hole and roadway of the working face, the strength of roof rock strata in the target area was reduced, and the initial weighting step distance and weighting strength of the working face were reduced. The hydraulic softening roof-cutting pressure relief technology effectively regulated the weighting step distance of the hard roof and the peak weighting of the working face.

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“…Given HDR's extremely low porosity and permeability, large-scale hydro-fracturing is usually required before geothermal exploitations to provide channels for flow and heat exchange (None 2009;Wang et al 2012aWang et al , 2012bLi et al 2022). However, the fractures created by hydro-fracturing can be blocked under geo-stress and water-rock interactions, rendering geothermal resources unexploitable (Xu and Pruess 2004;Pruess 2006).…”

Section: Introductionmentioning

confidence: 99%

Optimized geothermal energy extraction from hot dry rocks using a horizontal well with different exploitation schemes

Huang

et al. 2023

Geotherm Energy

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In the foreseeable future, the geothermal exploitation from hot dry rocks (HDR) using a horizontal well will bear potential. Thus, in-depth studies should be conducted on the selection of injection-production scheme (IPS) and working fluid, design of reinjection parameters, optimization of wellbore structure and materials, and analysis of geological settings. This paper proposed a fully coupled model to study the above scientific questions. For Model A, the working fluid was injected into the annulus and then flowed out of the thermal insulation pipe (TIP). Its temperature passes through two stages of temperature rise and two stages of temperature decline. But for model B, the working fluid was injected into the TIP and then flowed out of the annulus. Its temperature undergoes five stages, four stages of temperature rise and one stage of temperature decline. The results show that the Model A is the best IPS owing to its high outlet temperature, stable thermal recovery, and low fluid injection volume. In Model A, when the working fluid was supercritical carbon dioxide and the liquid injection volume was 135.73 m3/d, the heat recovery ratio (HRR) was as high as 85.40%, which was 17.85% higher than that of the Model B whose working medium was water, and its liquid injection volume was only 25% of that. Meanwhile, over ten years of continuous production, the outlet temperature decreased by 7.5 °C and 18.38 °C in the latter. The optimal working fluid has a low volume heat capacity and thermal conductivity for any IPS. Sensitivity studies showed that for the area that met the HDR standard, the effect of reinjection temperature on the outlet temperature can be ignored. As for Model A, HRR drops sharply by 6.74–9.32% when TIP goes from completely adiabatic to nonzero thermal conductivity. Meanwhile, the horizontal segment length of the TIP is shorter when Model A obtains the optimal outlet temperature compared with Model B. In addition, the correlation between the outlet temperature and different formations of thermophysical properties was seriously affected by the IPS and exploitation period, which was summarized in detail.

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The effect of supercritical CO2 on failure mechanisms of hot dry rock

Cited by 4 publications

References 37 publications

Permeability and Mechanical Response of Granite after Thermal and CO2 Bearing Fluid Hydro-Chemical Stimulation

Permeability and Mechanical Response of Granite after Thermal and CO2 Bearing Fluid Hydro-Chemical Stimulation

Principle and practice of hydraulic softening top-cutting and pressure relief technology in weakly cemented strata

Optimized geothermal energy extraction from hot dry rocks using a horizontal well with different exploitation schemes

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