InterPore2024

Investigation of the Effect of Thermal Stresses on Hydraulic Fracturing in Geothermal Reservoirs

16 May 2024, 11:50

15m

Oral Presentation (MS17) Complex fluid and Fluid-Solid-Thermal coupled process in porous media: Modeling and Experiment MS17

Speaker

Mozhdeh Sajjadi (Assistant Professor, Institute of Petroleum Engineering, School of Chemical Engineering, College of Engineering, University of Tehran)

Description

Geothermal energy has been widely proposed as a potential green energy resource to replace traditional fossil fuels. The most ubiquitous form of geothermal energy is found in hot dry rocks which are usually composed of granite (or other types of volcanic rocks) with very low permeability and are developed as enhanced geothermal systems (EGS). Hydraulic fracturing is a powerful technology to increase the permeability, enhance the water – rock contact and maximize the economic potential of EGS.
Due to the high cost associated with hydraulic fracturing operations, it is important to build reliable tools for predicting how the formation will respond to water injection. Numerical modeling of hydraulic fractures is an important method for studying fracture parameters such as length, width and fluid leak-off. In enhanced geothermal systems, the typical temperature difference between the reservoir and the injected fluid can range from 200◦C to 300◦C. As a result, the injected fluid rapidly cools down the near wellbore area and the resulting thermal contraction generates thermal tensile stress. This stress reduces fracture breakdown and extension pressure. Increase in injectivity near injection wells resulting from thermal contraction has been reported by researchers [1, 2] at the beginning of the injection process.
Hydraulic fracturing is widely used for improving permeability in hydrocarbon reservoirs [3], hazardous solid waste disposal [4, 5], for leaching processes and fault reactivation in mining [6], and soil and groundwater remediation [7] as well. The studies have shown that even for such non-geothermal applications, cryogenic effects help to reduce the water consumption, formation damage, and the environmental impact of water-based fracturing [8].
Modeling of thermal stresses in hydraulic fracturing requires coupling of hydro-thermal physics with fracture mechanics. In this study, a more accessible method than developing a complex finite element code for this purpose has been proposed. Hydraulic fracturing was modelled by creating a three-dimensional model using Abaqus software, and thermal effects were incorporated using heat-sink boundary conditions. The results were validated against analytical and experimental studies. Investigation of the influence of thermal properties of rock and the hydraulic fracturing design parameters, on fracture geometry and pressure showed that the temperature difference between rock and injected fluid, thermal expansion coefficient of rock, and thermal conductivity of rock are the most significant factors in defining hydraulic fractures’ geometry and fracking pressure in geothermal reservoirs. In general, hydraulic fractures exhibit greater opening and less extension under thermal stresses compared to non-thermal fracturing processes.