Numerical modelling of coupled TH processes to facilitate analysis of geothermal reservoirs - Groß Schönebeck as an example- N Watanabe 1, G Blöcher 2, M Cacace 2, H Shao 1, O Kolditz 1 1 Helmholtz Centre for Environmental Research UFZ, Germany 2 Helmholtz Centre Potsdam GFZ, Germany 25.11.2016, EERA Conference in Birmingham, UK SEITE 1
Contents 1. Introduction 2. Techniques a) Pre-processing with MeshIT a) Numerical simulation with OpenGeoSys 3. Application to Groß Schönebeck (Germany) Page 2
Groß Schönebeck site Demonstration and investigation of geothermal power generation in the North German Basin Sandstone layer k = 10-15 -10-16 m 2 φ = 3-15 % Doublet system was finished in January 2007 Target horizon 3800-4300 m Temperature 145 C Hydraulic fractures for productivity enhancement Page 3
Challenges in Reservoir Simulation Page 4
Mixed-dimensional Element Approach Geological Units Fractures Injection & Production Well
Mixed-dimensional Physics Geological Units Fractures Injection & Production Well Permeability k = b2 12 (b: fracture aperture) k = r 2 8 (r: pipe radius) Page 6
Contents 1. Introduction 2. Techniques a) Pre-processing with MeshIT Blöcher G, Cacace M, Lewerenz B, Zimmermann G (2010) Three dimensional modelling a) Numerical of fractured simulation and faulted reservoirs: with OpenGeoSys framework and implementation. Chemie der Erde Geochem 70(3):145 153 1. Application to Groß Schönebeck (Germany) Cacace M, Blöcher G. (2015): MeshIt - a software for three dimensional volumetric meshing of complex faulted reservoirs. - Environmental Earth Sciences, accepted. Page 7
Software MeshIT Concept
Software MeshIT Concept Fully automized from input data to numerical simulation Easy mesh updating Broad software interface capabilities Existing: GoCad, EarthVision, ParaView, OGS, own format Planned: Feflow, Comsol, Petrel
Contents 1. Introduction 2. Techniques a) Pre-processing with MeshIT b) Numerical simulation with OpenGeoSys 3. Application to Groß Schönebeck (Germany) Page 10
OpenGeoSys (www.opengeosys.org) FEM based simulator for modeling THMC in porous and fractured media Source code on GitHub (https://github.com/ufz/ogs5) Page 11
EoS of saline water T Density Viscosity 70 C 1260 kg/m3 4.12e-4 Pa s 150 C 1203 kg/m3 1.92e-4 Pa s Diff 4.5% 53% *IAPWS-IF97 and HP Petroleum fluids (p=40mpa, C=265g/l) Page 12
Monolithic Solution Solving TH together in Newton-Raphson formulation Partitioned approach r p p r T p r p T r T T p T = - r p r T No Flow Heat transport Converge? Yes Jacobian matrix Page 13
Solver Nr. Iterations (1 st time step) Computing time (1 st time step) Adaptive dt Partitioned 3 87 s avg 11 d, max 86 d Newton (Exact J) 3 45 s max 0.9 d Newton + Modified J Newton + Modified J + Line search 3 42.3 s max 5.9 d 7 125 s > 3 years Newton with the exact Jacobian can be worse than Picard Modified Jacobian with line search was the most robust (dt>3years) Page 14
MPI parallelization using PETSc library Distribution of memory over computing machines Use of PETSc linear solver Matrix-vector decomposition by rows Total 100GB 5 GB 4 GB 6 GB Domain decomposition Matrix-vector decomposition by rows Page 15
OGS-PETSc parallelization using MPI Speedup up of a TH simulation (1 time step, 10 6 nodes) Page 16
Contents 1. Introduction 2. Techniques a) Pre-processing with MeshIT a) Numerical simulation with OpenGeoSys 3. Application to Groß Schönebeck (Germany) Page 17
Model Setup Consider only flow and heat transport (TH) Parameters Matrix: k = 10-15 ~10-16 m 2 ; porosity = 3-15 % Induced fractures: k = 10-10 m 2 Minor fault zones: k = 10-13 m 2 Operation scenario Injection: 30 m 3 /h, 70 C Production: 30 m 3 /h Page 18
Calibration (1) Cumulative inflow to the well CTL 2007 Page 19
Impacts of a permeable fault zone F21n Page 20
Comparison of exploitation strategies (Blöcher et al. 2015) Current: Matrix-dominated flow Field measurement PI = 6 m 3 /h/mpa Desired for economic use 60-120 m 3 /h/mpa (Hoffmann et al., 2014) Productivity Index PI = Q p Length:320m Height:185m Page 21
Fracture-flow dominated system No use of Gt Grsk4 New production well New hydraulic fracture Direct connection of injection and production via fractures Page 22
Hybrid of matrix- and fracture-dominated flow system Similar to case 2 Use Gt GrSk4 for injection (2 injection wells) New gel/proppant frac Page 23
Page 24 Matrix dominated
Matrix dominated Fracture dominated Page 25
Matrix dominated Fracture dominated Hybrid Page 26
Productivity Index and Thermal Breakthrough PI of current setup (Matrix-dominated) is not suitable for economic use Fracture-flow dominated can improve PI but results in earlier temperature drawdown Hybrid of matrix- and fracture-flow is the best # PI Breakthrough time (T=127 C) Matrix flow dominated 3.65 m 3 /h/mpa > 100 years Fracture flow dominated 8.11 m 3 /h/mpa 3.73 years Hybrid 11.19 m 3 /h/mpa 12.55 years Page 27
Summary Mixed-dimensional element approach developed for Groß Schöenebeck Good when homogenization is difficult Workflow based on open-source software Useful tool for thinking new reservoir designs Ongoing Supporting discontinuous solution across fractures (e.g. impermeable faults) Rock mechanics (THM) Page 28
References Blöcher G, Cacace M, Lewerenz B, Zimmermann G (2010) Three dimensional modelling of fractured and faulted reservoirs: framework and implementation. Chemie der Erde Geochem 70(3):145 153. Blöcher, G., Cacace, M., Reinsch, T., Watanabe, N. (2015) Evaluation of three exploitation concepts for a deep geothermal system in the North German Basin. Computers and Geosciences, 82, p. 120-129. Cacace M, Blöcher G. (2015): MeshIt - a software for three dimensional volumetric meshing of complex faulted reservoirs. Environmental Earth Sciences, accepted. Kolditz, O., et. al (2012) OpenGeoSys: an open-source initiative for numerical simulation of thermo-hydro-mechanical/chemical (THM/C) processes in porous media. Environmental Earth Sciences, 67 (2), 589 599. Watanabe, N., Wang, W., Taron, J., Görke, U.J., Kolditz, O. (2012) Lowerdimensional interface elements with local enrichment: Application to coupled hydromechanical problems in discretely fractured porous media. International Journal for Numerical Methods in Engineering, 90(8), 1010-1034. Page 29