Effects of Thermally-Induced Secondary Cracks on Hydraulic Fractures
Date
2013-06-17
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Abstract
The purpose of this research is to investigate the change in geometry of a hydraulic fracture aperture over time when cold frac fluid is injected into a hot reservoir. Secondary cracks may occur around the surface of a hydraulic fracture if there is large difference between frac fluid and the formation temperature. The study is organized as follows:
1. Literature review and development of fundamental equations (Chapter 1 & 2): Literature related to hydraulic fracture stimulation is reviewed, to support this study’s importance and explain how it will enrich the research in the field of hydraulic fracturing. Fundamental equations of flow and deformation, which form the basis of this this research, are developed.
2. Initiation and propagation of secondary cracks (Chapter 3): Using the finite element method, initiation and propagation of secondary cracks in porous media is calculated under varying combinations of pore pressure, temperature, Young’s modulus, initial effective stress, pressure and thermal diffusivity, leakoff conditions and crack spacing. The initiation time and growth of the length and width of the secondary cracks are computed.
3. Growth and decay of a hydraulic fracture (Chapter 4): Aperture formulae, based on the continuum thermo-poroelasticity for a KGD (Khristianovic-Geerstma-de Klerk) fracture model under 2D plane strain and plane stress conditions, are developed. These new, simple formulae consider the effects of poroelasticity and thermo-elasticity, as well as the distances the pressure and temperature propagate into the medium (penetration depth). The aperture formulae are validated by comparing their results with the results of the finite element method. The comparison shows that the simplified formulae provide excellent results with significant reduction in computation time.
4. Effects of secondary cracks on the aperture of hydraulic fracture (Chapter 5): This phenomenon is quite new in the hydraulic fracturing stimulation. Under given boundary conditions, secondary cracks will appear on the fracture surface and propagate into the formation. When the secondary cracks occur, fracture aperture magnitude and shape change. Therefore, the presence of secondary cracks will significantly influence the fracturing stimulation process.
Discussion and recommendations for further studies are provided at the end of the dissertation in Chapter 6. The results emphasize the important role that geomechanics plays in the simulation of hydraulic fracturing.
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Engineering--Civil, Engineering--Mechanical, Engineering--Petroleum
Citation
Tran, D. V. (2013). Effects of Thermally-Induced Secondary Cracks on Hydraulic Fractures (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/25834