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    Modeling the interaction between hydraulic and natural fractures using three dimensional finite element analysis

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    Author
    Nikam, Aditya Balasaheb
    Chair
    Awoleke, Obadare
    Ahmadi, Mohabbat
    Committee
    Dandekar, Abhijit
    Chen, Gang
    Ahn, Il Sang
    Metadata
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    URI
    http://hdl.handle.net/11122/6866
    Abstract
    Natural fractures are present in almost every formation and their size and density definitely affect the hydraulic fracturing job. Some of the analysis done in the past shed light on hydraulic fracture (HF) and natural fracture (NF) geometries. The interaction of the HF with existing NF in a formation results in a denser fracture network. The volume of rock covering this fracture network is called the stimulated reservoir volume (SRV). This SRV governs the hydrocarbon production and the ultimate revenue generation. Moreover, past studies show that a microseismic interpreted SRV can be different than the actual SRV. Additionally, there is always limited subsurface access, which makes it imperative to understand the HF – NF interaction to plan and execute a successful hydraulic fracturing job. A three layered, three dimensional complex geomechanical model is built using commercially available finite element analysis (FEA) software. A propagating HF approaching mainly orthogonal NF is studied and analyzed. Cohesive pore pressure elements in FEA software capable of modeling fluid continuity at HF – NF intersection are used to model the HF – NF interaction. Furthermore, a detailed sensitivity analysis considering the effect of stress contrast, job design parameters, NF properties, and properties of the formation is conducted. The sensitivity analysis of properties such as principal horizontal stress contrast, job design parameters, NF properties and properties of target formation reveals a broad variation in the impact of the sensitivity parameters on the HF, NF, and HF-NF geometry and interaction. The observations and the corresponding conclusions were based on broadly classified sensitivity parameters. The most important parameters solely for HF resultant geometry are observed to be a high stress contrast with stress reversal, highest injection rate, and farther NF distance from the injection point. The least important parameter is observed to be the scenario with almost equal horizontal stresses. However, the most important parameter solely for resulting NF geometry is only the high stress contrast with stress reversal. Conversely, for the considered sensitivity cases, the least important parameters are the injection rate, lower injection viscosity (10 cP), higher NF leak-off coefficient, target formation thickness, Young’s modulus, and lowest value of target formation Poisson’s ratio. Collective conclusions for considering HF-NF are also obtained.
    Description
    Thesis (M.S.) University of Alaska Fairbanks, 2016
    Table of Contents
    Chapter 1. Introduction -- 1.1. Alaska’s Unconventional Oil and Gas Potential -- 1.2. Need for HF – NF Interaction Research -- 1.3. Outline of Present Research -- 1.4. Summary of Subsequent Chapters -- Chapter 2. Literature review -- 2.1. Hydraulic Fracture Modeling -- 2.1.1. 2D Models -- 2.1.2. 3D Models -- 2.2. Modeling Hydraulic Fractures in the Presence of Natural Fractures -- 2.3. General HF-NF Modeling Approaches -- 2.4. Commercial Software Based HF-NF Modeling Approaches -- 2.4.1. Abaqus -- 2.4.2. Unconventional Fracture Modeling (UFM) -- 2.4.3. COMSOL -- 2.4.4. FLAC 3D -- 2.4.5. Combinational Approaches -- Chapter 3. Modeling the interaction between hydraulic and natural fractures using three dimensional finite element analysis -- 3.1. Model Construction -- 3.2. Theory -- 3.2.1. Modeling the Rock Matrix -- 3.2.2. Modeling Fluid Flow -- 3.2.3. Modeling Deformation and Damage -- 3.3. Model Validation -- 3.4. Base Case -- 3.5. Sensitivity Analysis -- 3.5.1. Effect of In-Plane Stress Contrast -- 3.5.2 Effect of Job Design Parameters -- 3.5.2.1. Effect of Injection Rate -- 3.5.2.2. Effect of Injection Fluid Viscosity -- 3.5.3. Effect of NF Properties -- 3.5.3.1. Effect of NF Strength -- 3.5.3.2. Effect of NF Positioning -- 3.5.3.3. Effect of NF Orientation -- 3.5.3.4. Effect of NF Leak-off Coefficient -- 3.5.4. Effect of Formation Properties -- 3.5.4.1. Effect of HF Leak-off Coefficient -- 3.5.4.2. Effect of Target Formation Thickness -- 3.5.4.3 Effect of Target Formation Young’s Modulus -- 3.5.4.4 Effect of Target Formation Poisson’s Ratio -- 3.6 Summarized Observations -- Chapter 4. Conclusions and recommendations -- 4.1 Conclusions -- 4.2 Recommendations -- References.
    Date
    2016-08
    Type
    Thesis
    Collections
    Engineering

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