Experimental and numerical studies on hydraulic fracturing characteristics with different injection flow rates in granite geothermal reservoir

Abstract

Geothermal energy has been widely proposed as a potential renewable energy to replace traditional fossil fuel energy. Hot dry rock (HDR) reservoirs were the main geothermal energy resources and usually consist of low‐permeability hard granite without fluid. Developing HDR requires water cyclically flowing between injection and production wells to extract heat energy. Hydraulic fracturing, as a key reservoir stimulation technology, can create the path of fluid cyclically flowing. However, few studies have investigated hydraulic induced artificial fractures in HDR geothermal formations. This paper investigated HDR geothermal reservoir stimulation characteristics and fracture patterns under different injection flow rates. Numerical simulations were conducted to model the laboratory tests. Results showed they were in good agreement, and this indicated the possibility of numerical simulation to predict hydraulic fracturing behavior under different injection flow rates. With the increase of injection flow rate, the fracture initiation pressures and breakdown pressures increased, and the propagation times and postfracturing pressures decreased. The fracture geometries were observed and analyzed, mean injection power was proposed, and results showed that it could be used to roughly estimate the fracture total lengths. Moreover, the fracture permeabilities based on the pressure data were calculated. These results can provide some reasonable advice for implementing reservoir stimulations on application to field‐scale HDR operation.

Hydraulic Fracture Propagation in Layered Heterogeneous Rocks with Spatially Non-Gaussian Random Hydromechanical Features

“…In Sect. 3.1 of this paper, numerical results of the fluid pressure variation inside the HF are compared to the experimental data (Cheng et al 2021). Afterwards, in Sects.…”

“…The mean values are chosen the same as reported by Cheng et al (2021), while the standard deviations are assumed. The critical energy release rate ( G c ) is calculated from the tensile strength and the chosen length-scale parameter using the relationship G c = 256 2 t l 0 ∕ 27E � , as recommended by Miehe et al ( 2015).…”

Experimental Study to Quantify Fracture Propagation in Hydraulic Fracturing Treatment

“…There are many ways to describe the effects of hydraulic fracturing, such as artificial sample description, CT scanning, acoustic emission monitoring, and permeability testing. 7 − 11 The permeability test under true triaxial stress is a technique to quantitatively evaluate fracture propagation. Permeability often varies in different stress environments.…”

“…At present, physical experiments of fracture propagation are mainly carried out to simulate field hydraulic fracturing by cracking artificial rock samples or natural rock samples by pumping the fracturing fluid under different environmental conditions. There are many ways to describe the effects of hydraulic fracturing, such as artificial sample description, CT scanning, acoustic emission monitoring, and permeability testing. − The permeability test under true triaxial stress is a technique to quantitatively evaluate fracture propagation. Permeability often varies in different stress environments.…”

Response Characteristics of Coal Measure Strata Subjected to Hydraulic Fracturing: Insights from a Field Test

“…Worldwide, scholars have hitherto carried out numerous gas control and extraction experiments in collieries. Hydraulic fracturing (HF) has been proved to be an effective method to improve low-permeability coal seam methane drainage as well as coal and gas outburst control, which has provoked extensive research interests. , Cheng et al investigated hot dry rock geothermal reservoir stimulation characteristics and fracture patterns under different injection flow rates by numerical simulation and true triaxial HF apparatus. Zhou et al analyzed distribution patterns of hydraulic fractures under different bedding densities and mechanical properties through numerical simulation.…”