Department of Petroleum Engineering Texas A&M University College Station, TX (USA) Antu Xie Modelling Concepts for Fracture Initiation and Propagation in Shales 2016 Student Paper Contest | 30 January 2016 Texas A&M University | College Station, TX 2016 Student Paper Contest | 30 January 2016 Texas A&M University | College Station, TX Modelling Concepts for Fracture Initiation and Propagation in Shales Antu Xie Slide — 1/12

● Estimating the production rate and EUR after fracturing is often quite difficult Shale: Certainly Uncertain Slide — 2/12 Production History – Vaca Muerta (STB/D)Normalized EUR Estimates (%) Example: EUR estimate from 100 days of production history of a horizontal multi-fractured well (Collins et al. 2015) Using assumptions of a SRV with a set of bi-wing fractures, there is a 64% spread in EUR estimates 2016 Student Paper Contest | 30 January 2016 Texas A&M University | College Station, TX Modelling Concepts for Fracture Initiation and Propagation in Shales Antu Xie

● At all size scales, shale structure is heterogeneous and random ● Goal: Use micro-scale data to reduce macro-scale uncertainty ● Method: A framework that uses micro-scale shale structures into an estimate of stimulated volume length and permeability, with shale composition and fracturing conditions and parameters A Reason for Uncertainty: Multi-scale Shale Heterogeneity Slide — 3/12 (SEM Image of Shale) (Fuentes-Cruz et al. 2014) 2016 Student Paper Contest | 30 January 2016 Texas A&M University | College Station, TX Modelling Concepts for Fracture Initiation and Propagation in Shales Antu Xie

Framework Overview Material Parameters (Moduli, Fracture Constant) Mechanical Deformation & Flow Simulation Localized Pressure-Stress Relationship & Deformation Micro-scale Simulation Generated Shale Structures, Stress Regimes Multiple Simulation Runs Estimate SRV as a function of fracturing pressure and time Experimental Framework 2016 Student Paper Contest | 30 January 2016 Texas A&M University | College Station, TX Modelling Concepts for Fracture Initiation and Propagation in Shales Antu Xie Slide — 4/12

● Assumption: Still in continuum mechanics (linear elastic) regime ● Energy of a pressurized crack: ● Treat fracture propagation as phase change problem ■ Computationally feasible to model ■ Fracture pathway not pre-arranged, determined by moduli and fracture energy Modeling – Deformation, Fracturing Two Propagating Pressurized Fractures (Heister et al. 2015) 2016 Student Paper Contest | 30 January 2016 Texas A&M University | College Station, TX Modelling Concepts for Fracture Initiation and Propagation in Shales Antu Xie Slide — 5/12

● Finite-Element Library of choice: ● For any time step, seek a displacement vector and phase value that minimizes deformation energy ● Can translate raw 3D scan data into meshes for deal.II Implementation – Mechanical Simulation ● Can then deform and fracture in deal.II 2016 Student Paper Contest | 30 January 2016 Texas A&M University | College Station, TX Modelling Concepts for Fracture Initiation and Propagation in Shales Antu Xie Slide — 6/12

Implementation – Video of deformation Red: Elastic Modulus = 1000 G c = 0.27 Blue: Elastic Modulus = 500 G c = Fracture initiates in weaker section 2016 Student Paper Contest | 30 January 2016 Texas A&M University | College Station, TX Modelling Concepts for Fracture Initiation and Propagation in Shales Antu Xie Slide — 7/12

● Assumption: Laminar flow in continuum regime (Re < 2300) ● Use Knudsen number (λ / L) to determine flow regime model ■ Continuum flow:Kn ≤ ■ Slip flow:0.001 < Kn < 0.1 ■ Transition flow:0.1 < Kn < 10 ● Intended solution for < Kn: Discrete Monte Carlo (DSMC) Modeling – Flow Knudsen diffusion dominates in very small capillaries (Javadpour 2009) DSMC flow streamlines, more accurate than continuum for ‘high’ Kn (Bobzin et al. 2014) 2016 Student Paper Contest | 30 January 2016 Texas A&M University | College Station, TX Modelling Concepts for Fracture Initiation and Propagation in Shales Antu Xie Slide — 8/12

● Fluid flow simulation library of choice: ■ Finite volume simulation ■ Open-source, reliable, modifiable ■ Pre-existing packages for continuum CFD and DSMC ■ Can be coupled with deal.II Implementation – Flow Extracted flow “channel” (phase threshold set high for illustration purposes) OpenFOAM-generated flow through 3D channel (Christou 2015) 2016 Student Paper Contest | 30 January 2016 Texas A&M University | College Station, TX Modelling Concepts for Fracture Initiation and Propagation in Shales Antu Xie Slide — 9/12

● Complete fluid simulation ● Complete 1-step coupling of mechanical deformation/fracturing with fluid flow simulation ● Begin studying fracturing under near-stress wall conditions Next Steps: Generated Shale Structures, Stress Regimes Multiple Simulation Runs Estimate SRV as a function of fracturing pressure and time Experimental Framework ● Simulated/Extract structure ● P = 3000 – 5000 psi ● Fractured volume ● effective permeability ● Estimate effective strength ● Reduce uncertainty 2016 Student Paper Contest | 30 January 2016 Texas A&M University | College Station, TX Modelling Concepts for Fracture Initiation and Propagation in Shales Antu Xie Slide — 10/12

● Goal: Create a framework to use shale microstructure data to model fracture performance and reduce reservoir uncertainty ● What's been developed so far? ■ Conversion utility of FIB/SEM shale structure into 3D mesh ■ A 3D phase-field fracture model ● What remains to be done? ■ Accurate flow modeling in OpenFOAM ■ Run simulation experiments Conclusion 2016 Student Paper Contest | 30 January 2016 Texas A&M University | College Station, TX Modelling Concepts for Fracture Initiation and Propagation in Shales Antu Xie Slide — 11/12 Normalized EUR Estimates (%)

2016 Student Paper Contest | 30 January 2015 Texas A&M University | College Station, TX Slide — 12/12 Department of Petroleum Engineering Texas A&M University College Station, TX (USA) Antu Xie Modelling Concepts for Fracture Initiation and Propagation in Shales 2016 Student Paper Contest | 30 January 2016 Texas A&M University | College Station, TX Modelling Concepts for Fracture Initiation and Propagation in Shales Antu Xie