- •Basics of Reservoir Simulation
- •with the
- •Eclipse Reservoir Simulator
- •Lecture Notes
- •Øystein Pettersen
- •Introduction
- •Prerequisites
- •1. Overview – minimum required data input
- •1.1 The grid
- •1.2 Petrophysics
- •1.3 Fluid properties
- •1.4 Soil properties
- •1.5 Equilibration
- •1.6 Well specification
- •1.7 Dynamics
- •1.8 Output
- •1.9 Simple Eclipse data file contents
- •A. Syntax
- •B. Data file (“BASIC data input example”)
- •A note on units
- •2. The RUNSPEC section
- •Grid dimension – keyword DIMENS
- •Phases
- •Unit system
- •Start date
- •Unified / Non-unified files (chapter 11)
- •Data checking only
- •Table dimensions
- •EQLDIMS
- •NSTACK (chapters 17-18)
- •Aquifer specifications – AQUDIMS (chapter 14)
- •Grid options (chapter 13)
- •Rock compressibility options (chapter 6)
- •Local Grid Refinement (chapter 15)
- •3. Structured grids (Corner point grids) (GRID section)
- •The Corner Point Grid
- •Defining a corner point grid in Eclipse
- •Moderately complex grids – FILL
- •4. Petrophysics (GRID section)
- •Average permeability
- •Transmissibility
- •Inactive cells
- •5. Fluid properties (PROPS section)
- •Tables in Eclipse
- •Relative permeability and Capillary Pressure
- •Two-phase curves (water – oil)
- •Three-phase relative permeabilities
- •PVT data
- •Water
- •Dead Oil
- •Live Oil
- •6. Soil compressibility (PROPS section)
- •7. Initialisation (SOLUTION section)
- •Datum depth
- •Contacts
- •Equilibrium – discussion – advanced issues
- •8. Time dependent input data (SCHEDULE section)
- •8.1 Well definitions and control
- •Well Specification (WELSPECS keyword)
- •Well Completions (COMPDAT keyword)
- •Production / Injection data (Keywords WCONPROD / WCONINJE)
- •Economic well constraints (keywords WECON, WECONINJ)
- •Other often used Well control keywords
- •8.2 Time stepping
- •Order of actions
- •8.3 Convergence Control I (keyword TUNING)
- •9. Regions
- •10. Simplified input and modification of Eclipse arrays
- •EQUALS
- •ADD, MULTIPLY
- •COPY
- •COPYBOX
- •11. Eclipse output, formats and files
- •File names
- •Textual output
- •The RPTXXX keywords
- •Time dependent vectors – SUMMARY data
- •Restart data and restart files
- •12. Restarting a simulation
- •The SKIPREST keyword
- •13. Fault modelling – Non-neighbour connections
- •The 7-point stencil
- •The fault layout – non-neighbour connections
- •Fault transmissibility multipliers
- •Defining a fault manually – the ADDZCORN keyword
- •14. Aquifer Modelling (GRID section)
- •Aquifer definition
- •Aquifer connection to reservoir
- •15. Local Grid Refinement
- •15.2 LGR on an irregular volume – Amalgamation
- •15.3 Wells on local grids – Horizontal wells
- •15.4 Horizontal wells and friction
- •16. Numerical Solution of the Flow Equations
- •The IMPES method
- •Solution of Non-linear Equations – the Newton-Raphson method
- •17. Iteration methods for linear systems
- •Direct, simple approach
- •The Gauss-Seidel method
- •Accelerators – the point SOR method
- •Conjugate Gradients – ORTHOMIN
- •Preconditioning
- •Preconditioning and Orthomin
- •Determining a preconditioner – Nested Factorisation
- •18. Convergence Control II – TUNING parameters
- •TUNING keyword summarized
- •19. Non-neighbour Connections and System Structure
- •A. GRF files in GRAF
- •A simple straightforward GRF file
- •Advanced GRF file
- •B. Some Considerations Regarding Grid Consistency
- •Grids planned for use in rock mechanics simulations
- •Embedding
- •Non-vertical coordinate lines
- •Honouring material properties of non-reservoir rock.
For such cases we have available the keyword GECON – group economic control. The keyword is similar to WECON, with the slight variation we need:
GECON
Gname* MinORAT MinGRAT MaxWCUT MaxGOR MaxWGR Workover EndRunFlag
Gname*
Group name wildcard. For our purpose this will always be FIELD, in which case the constraints apply to the field as whole.
MinORAT MinGRAT MaxWCUT MaxGOR MaxWGR
These are exactly as in WECON, except they are now understood as group (field) quantities, not single well. (default as WECON)
Workover
NONE
CON
CON+
WELL (PLUG
EndRunFlag
YES
NO
Often both WECON and GECON will be used, they are not mutually exclusive.
Other often used Well control keywords
WELTARG
When well control data has been defined by WCONPROD or WCONINJE, typically only target rates are changed later. In stead of repeating all the data every time a small change is made to already defined constraints, the keyword WELTARG can be used. It is suited for situations where only one parameter for a previously defined well shall be changed. The syntax is,
WELTARG
Wnm* ControlToChange NewValue
Example
All constraints have been defined for well OP1, but at a certain time we wish to change the target oil rate from its previous value to 3000 Sm3/day.
This can be done by,
WELTARG
OP1 ORAT 3000 /
/
The advantage goes beyond a shorter syntax, as it is clear to the reader that only the one constraint was changed.
WCONHIST / WCONINJH
These keywords are very similar to WCONPROD / WCONINJE, but are used to define actual historical rates and pressures. The advantage is primarily in the post-processing phase, when target data can be compared to simulated results.
WEFAC
Wells are never on production 24 hours a day, 7 days a week. Some down-time is unavoidable. If a well is operative 80% of the time with a producing rate Q, simulation production rate could of course be defined as 0.8Q, ensuring correct grand total. This would however not be entirely correct, as the bottomhole pressure calculations would be based on an erroneous rate. A correct solution can be obtained by use of the WEFAC keyword (well efficiency factor), which is used to specify the factor of producing time to total time.
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