simulation of hydraulic stimulation of rock as key for economical gas production … ·...

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Simulation of Hydraulic Stimulation of Rock as Key for Economical Gas Production Petro thermal Power Plant Design

ANSYS Conference & 31. CADFEM Users‘Meeting 2013Mannheim, 19. Juni 2013

© Dynardo GmbH 2013

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To mine gas or geothermal energy stimulation of the reservoir rock becomes necessary for a profitable gas or energy production out of EGS (Enhanced Geothermal Systems).

Hydraulic stimulation is used to create a network of fractures which connects the production wells with the greatest possible volume of reservoir rocks- Vertical or Horizontal wells are drilled in the reservoir layer. - Water pressure is opening natural fractures and planes of weakness and create new fractures- Proppant is added to keep fractures open after fluids have been removed and pressure has been subsided.

Hydraulic Stimulation

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Since 2008 Dynardo supports US companies to understand and optimize shale gas production.

Unconventional gas production

- more than 60.000 wells drilled in USA for unconventional gas production- Since 2009 USA is the biggest gas producer worldwide- also unconventional Oil production has started to be significant

- Successful applications at different US gas fields

- Successful calibration of reservoir models

- Successful optimization of stimulation design

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Challenge of modeling hydraulic stimulation• Rock is initially jointed as well as new joints are created • anisotropic deformation, strength and conductivity behavior dominate

fracture growth• Therefore 3D geometric model including deformation, strength and

conductivity anisotropies mandatory

• Rock mechanical challenge or the question: “Discrete or homogenized modeling of joints”• Discrete joint modeling of stimulated volume in

3D result in computational and parameter overkill

• Therefore we used homogenized continuum approach which was established for 3D FEM simulation in jointed rock for dam applications in 1980’/90’s• allows numerical efficiency for simulation as

well calibration

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homogenized continuum approach mechanics

Major fault

Sets of joints: K1, K2, Sch

But major faults will be modelled “discrete” with a layer of volume elements, having plane of weakness and “matrix” material.

(picture from Wittke, W.: Rock Mechanics, Theory and Application with Case Histories, ISBN/EAN: 3540527192

Homogenized continuum approach does not model joints discrete. Jointed rock will be modelled as volume having “intact rock” and sets of strength anisotropies (joints). Matrix and joints will be evaluated at every discretization point!

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THM=Thermo-mechanical-hydraulic analysis- First order physical phenomena needs to be identified- For calibrating of the reservoir models it is recommended to reduce coupling and calibration to first order phenomena


Stimulation of gas and EGS reservoirs:Hydro-mechanical coupling most important:- Update of damage (fracture) induced and stress related jointed rock mass

conductivity- Fracture grow based on flow forces update out of pore pressure gradients

Stimulated rock volume

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Constitutive equations of jointed rock

Anisotropic Mohr-Coulomb model

Yield surface of intact rock Yield surface of joint sets

- Initial joints and planes of weakness are oriented with dip magnitude and dip direction

- New fracture have fixed orientation regarding stress state and fracture mode

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Figure : filter velocity in case of one set of joints (picture from Wittke)

• Fluid flow will occur mainly in the joint system. The homogenized permeability kTF is defined with an anisotropic permeability tensor. Using Darcy’s laminar flow approach in a homogenized continuum having a joint system the flow velocity in the direction of a joint set result to

• vFT flow velocity• 2ai joint thickness• A cross section• d joint frequency

v qA

= k 2ad

IFT TFi

homogenized continuum approach hydraulics

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• After every fluid time increments the incremental change in mechanical forces from pore pressure chance will be introduced in the mechanical analysis.

• FStr force vector• I gradients of pore pressure• w water density and VG related volume

Fluid flow analysis and coupling

F V IStrW G

Kini

Kmax

K

• After every mechanical step the anisotropic permeability's needs to be updated.

Conductivity update

Flow force update

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3D-hydraulic stimulation simulator

Input parameters

FE-model

Initial pore pressure

Initial effective stresses Mechanical

analysis

Transient hydraulic analysis

Schematics of 3D coupled hydraulic-mechanical simulation

Outputs/results

Main loop

Flow force update

Conductivity update


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Hydraulic stimulation needs Calibration

Sensitivity, Calibration & Optimization

3D-hydraulic stimulation simulator

FEA SolverCalibrator Optimizer

Because of the large amount of uncertain jointed rock and reservoir parameter the reservoir model needs advanced calibration procedure.


- including new hydraulic elements

- provide material models for jointed rock

- calibration with large number of uncertain parameter as well as optimization

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Calibration is the keyMS1) Setting up a three dimensional model which can represent

reservoir conditions including in situ joint systems - coupled fluid flow mechanical analysis, including propagation of fractures

MS2) Calibration of important model parameters with measurements (fracture initiation/stop pressure, bottom hole pressure and slurry rate signals and seismic fracture measurements)

MS3) Using the calibrated model for sensitivity analysis of operational conditions to understand the mechanism and to optimize the stimulation setup

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Because of the numerous uncertainties in reservoir conditions calibration of the simulator is mandatory and important.

After calibration the reservoir model should have sufficient forecast quality to be used for optimization of hydraulic fracturing design.

Dynardo‘s calibration process checks plausibility and balance of all inputs (single values and windows of uncertainties) including

- ensure that in situ strength and stress/pore pressure values does not result in plastic deformation

- ensure that the model starts and stops fracturing at fracture initialization/stop pressure

- ensure that the model represents fracture growth in time and space by match the pressure and the pumping rate histories

- Ensure that the model represents the fracture direction, extension, density as well as fracture barriers by matching micro seismic density functions

Calibration is the key

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Calibration of reservoir modelSensitivity evaluation of 200 rock parameter and the hydraulic fracture design Parameter due to seismic hydraulic fracture measurements

Blue:Stimulated rock volumeRed: seismic frac measurement

With the knowledge about the most important parameter the update was significantly improved.

Hydraulic-mechanical coupling

Solver: ANSYS/multiPlas

Design evaluations: 160

Will J.: Optimizing of hydraulic fracturing procedure using numerical simulation; Proceedings Weimarer Optimierung- und Stochastiktage 7.0, 2010, Weimar, Germany, www.dynardo.de


http://www.dynardo.de

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Pressured volume at 193 min (end of pressuring)

initial design stage1Barnett Volume=24.2 e6

Improved frac designBarnett Volume=30.2 e6

By improving just one fracture design parameter, the stimulated volume could improve by 25%.

Optimization of Gas Production


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Application of Hydraulic Fracturing Analysis

other Reservoirs, US2010/2011

calculate and calibrate joint network creation including stage and well interaction

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Simulator improvements since 2010

following improvements are implemented:- Parametric models of multiple stages- Improvement of hydro mechanical coupling, calculation of joint set

openings and related anisotropic conductivity updates - Introduction of influence of Joint Roughness Coefficient (JRC) and

ratio of geometric and effective hydraulic opening to fluid flow in fractures

- Introduction of perforation efficiency- Investigation of “stress shadowing” between stages and wells

calculate and calibrate jointed set opening, investigate stage interaction and sensitivities of reservoir and hydraulic fracturing design parameter

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Ongoing simulator improvementsIndustrial projects - Improvement of parametric to model and calculate multiple stages

at multiple well to investigate well interaction and re-stimulation

- Speed up simulation process and minimize memory requirements by implementing user defined elements for flow analysis

- Implementation of stress dependent conductivity decline to run flow back and production

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Acceptance of business

Marketing at Houston International Airport

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Acceptance of business- Simulation is necessary to improve and ensure economical gas

production as well as to investigate potentials of reservoirs- Simulation is necessary to improve public acceptance- Simulation is necessary to improve “green” shale gas development

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EGS has large Potential for energy production, but so fare only pilot power plants realized. Germany aims at developing EGS towards an energy form capable of covering the basic load.Dynardo enhanced the simulator for EGS application supported by funding from state of Thuringia. Joint project between Saxonia and Thuringia supports realization of industrial EGS projects in Germany.

Enhanced Geothermal Systems (EGS)

Tiefengeothermie in Thüringen Partner:JENA GEOS Ingenieurbüro GmbHFriedrich Schiller Universität JenaDYNARDO GmbHDBI Gas- und Umwelttechnik GmbHTU Bergakademie Freiberg

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Using multiple fracture zones between inflow and outflow well the project goal is to create meta models for well design optimization and project risk estimation using parametric CAE models (DYNARDO Simulator, MFRAC & UDEC/3DEC) and optiSLang.

Enhanced Geothermal Systems (EGS)

1000m Granit layer5000 deep>150°C hot

Resulting stimulated rock volume using on perforation

JUNGGEOTHERM

Illustrating the multi fracture approach

study having 1000 m Granit layer

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Because of the very low permeability's nuclear waste disposals are placed in shale layers.

The integrity of the containment, preserving the very low permeability's has to be shown for very long times.

Main loading of nuclear waste due to thermal heat.

Drilling and completion induced increase of permeability's (damage excavation zone) needs to be minimized.

Same technology needed to proof nuclear waste disposals

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THM=Thermo-mechanical-hydraulic analysis- First order physical phenomena needs to be identified- It is recommended to reduce coupling and calibration to first order phenomena


Stimulation of integrity of underground laboratories:Thermo-Hydro-mechanical coupling necessary - Drilling induces damage excavation zone show high conductivities- Heating may produce thermoplastic effects which further increase conductivities- Prove of heat and pressure regime for very long time

Source: www.grs.de

http://www.grs.de

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Sector for the Calculation

Details of the Mesh


Calibration of Heating Tests for Underground Laboratories

Schlegel R; at all.: Parameter Identification of Claystone in Underground Laboratories; Proceedings WOST 9.0, 2012, Weimar, Germany, www.dynardo.de

http://www.dynardo.de

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Claystone (Callovo-Oxfordian)

- friction anglec - cohesionft - tensile strength

Isotrope matrix

bedding plane

Matrix +bedding plane

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Parameteridentifikation – best designResult after 600 days of heating and pressuring regime

Temperature Pore pressure Damage

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Keys for the succesful Calibration and ResultsKeys for the successful parameter identification:• Thermal-Hydraulic-Mechanical Coupling completely in ANSYS • Description of anisotropic material model with multiPlas• Speed up of Calculations – Possibility for Sensitivity Analysis / Optimization• optiSLang functionalities for large number of parameters (LHS, CoP/MOP)

High CoP‘s indicate that the important parameters are selected

With the identified parameters the measurement results (time=600 days) can be calibrated in very good agreement


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SummaryHydraulic stimulation is a key technology for energy production (Gas and oil)

Enhanced Geothermal power plants needs hydraulic stimulation to generate heat exchanger

- We need a better understand of the physics of fracture grow and conductivity decline

- to introduce risk management - to establish “green” hydraulic stimulation by

removing/replacing chemicals- to ensure economical production

ANSYS+multiPlas+optiSLang is ready to address the task.

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Thank you for your attention!


simulation of hydraulic stimulation of rock as key for economical gas production … ·...

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