Micromechanics of hydraulic fracturing and damage in rock based on DEM modeling
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ORIGINAL PAPER
Micromechanics of hydraulic fracturing and damage in rock based on DEM modeling Ingrid Tomac1 · Marte Gutierrez2 Received: 4 November 2019 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract This paper presents a study of the micromechanics of the coupled hydro-mechanical (H-M) behavior of brittle rock during hydraulic fracturing. The study is conducted using the discrete element method (DEM), which spatially discretizes a rock mass into discrete disc particles, coupled with a solver for modeling fluid flow through a network of connected pores. In the coupled H-M DEM modeling, fluid flows through newly formed hydraulic fractures due to pore pressure increase from fluid injection in a wellbore and is coupled with rock mechanical response across a wide range of flow rates. The micromechanical insights from the DEM modeling provide better understanding of coupled H-M processes which precede rock breakdown during hydraulic fracturing, and the transition in deformation in brittle rock from a single hydraulic fracture to branched hydraulic fractures and a diffused damage zone. The effects of the properties of the fracturing fluid and the rock matrix as well as the effects of loading flow rate on the development of pressure-induced deformation and fracturing in crystalline brittle rocks fracturing are investigated. The DEM models used properties that were obtained by calibrating flow-rate-dependent stress–strain response against previously published experimental data on brittle rocks (granite in particular). DEM results are compared with experimental results from a true-triaxial scale model testing on hydraulic fracturing in an analogue rock. The presented results are expected to enable better understanding of conditions which lead to successful fracture propagation versus damage and fracture arrest in geo-reservoirs. Keywords Hydro-mechanical modeling · Geo-reservoirs · Discrete element method · Hydraulic fracturing · Rock mass · Rock permeability enhancement
1 Introduction This paper investigates the mechanisms which lead to fracture propagation and/or damage in brittle rock mass during hydraulic fracturing processes. Hydraulic fracturing is a technique for permeability enhancement of rock masses in deep geo-reservoirs, which is achieved by propagating new fractures via pressurized fluid from a wellbore previously * Ingrid Tomac [email protected] Marte Gutierrez [email protected] 1
Department of Structural Engineering, University of California San Diego, 9500 Gilman Drive #0412, La Jolla, CA 92093‑0412, USA
Department of Civil and Environmental Engineering, Colorado School of Mines, 1610 Illinois St., Golden, CO 80401, USA
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drilled into the reservoir [1, 2]. In enhanced geothermal systems (EGS), the reservoir rock is typically crystalline and has permeability lower than 1 0−3 μD [3], and hydraulic fracturing is often employed to create a permeable path to circulate fluid and heat from an injection point to a producing well. Most hydraulic fracturing models used in practice
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