Chemical stimulation on the hydraulic properties of artificially fractured granite for enhanced geothermal system. (1st January 2018)

• Record Type: Journal Article
• Authors: Luo, Jin; Zhu, Yongqiang; Guo, Qinghai; Tan, Long; Zhuang, Yaqin; Liu, Mingliang; Zhang, Canhai; Zhu, Mingcheng; Xiang, Wei
• Is Part Of: Energy. Volume 142(2018)
• Page Start: 754
• Page End: 764
• Publication Date: 2018-01-01
• Subjects: Hot dry rock (HDR) -- Enhanced geothermal systems (EGS) -- Chemical stimulation -- Hydraulic properties -- Artificial fractures; Power resources -- Periodicals; Power (Mechanics) -- Periodicals; Energy consumption -- Periodicals; 333.7905
• DOI: 10.1016/j.energy.2017.10.086
• Languages: English
• ISSNs: 0360-5442

Abstract

Abstract: Hydraulic fracturing is often conducted to create artificial fractures as flow paths in Hot Dry Rock (HDR) geothermal reservoirs. However, the fractures could be closed due to the high geo-stress conditions, resulting in low efficiency of geothermal productivity. Hence, maintaining a high hydraulic permeability of the created fractures is a key point for the success of Enhanced Geothermal Systems (EGS). In this study, chemical stimulation was carried out to improve the hydraulic properties of fractured granite. The effects on the hydraulic properties of two sets of samples were examined by laboratory flowing tests. Results show that chemical stimulation solution with mixture of 12%HCl+5%HF improved efficiently permeability. The permeability was increased by four orders of magnitudes with an optimized reaction time. The mud acid was found to react fast with minerals such as feldspars and biotite, but rather inactive with quartz as revealed by the microscopic structure and ionic detection of the fluid and rocks. Thereby, the quartz particles can be used as fracturing proppant to support opening of aperture. The findings obtained from this study indicated that a hydraulic fractured granite based HDR geothermal reservoir can be effectively improved by chemical stimulation. Highlights: Chemical stimulation on artificially fractured granite is conducted. Mud acid with a HF concentration of 5% stimulated with highest efficiency. 480 h is estimated to be an optimal time for the chemical stimulation. 6.24–6.25 ml/cm 2 of chemical agent is optimized for the stimulation. Feldspar and biobite are more sensitively reacted with mud acid than quartz.