The textbook asks a few questions that aren’t directly answered in material, so this section is complete. I’ll get to work on filling in the blanks but for the time being here it is.
*Identify what questions the simulation is expected to address
*Identify what data is required as input to perform the desired calculations
Most data files will be separated into the following areas:
- Model dimensions
- Grid and rock properties
- Fluid properties
- Initial conditions
- Output requirements
- Production schedule
Individual parts of the input data can also be setup by programs and this falls under pre-processing.
Pre-processing may be used to:
- Define grid and rock properties
- Define fluid properties
- Convert the results of special core analysis data to a form that can be used in the simulation
- Upscale rock data so that it is appropriate for the size of grid cells being used
- Define vertical flow performance tables setup the production schedule
Also need to input initial conditions. This is usually done after defining the rock and fluid properties, we must then enter initial pressure and saturation conditions to satisfy initial conditions requirements. We can do this in three ways:
This method sets pressure, oil and water saturations in the same method as permeability and porosity are set at time = 0. This method is the least commonly used because it is the most complicated.
A pressure at a reference depth is defined in the input data, the model then extrapolates pressure information from this point using previously entered density information and accounting for the hydrostatic head. This method is the simplest and most commonly used.
- Restart from a previous run
This method is used where a model has been history matched to the current point in time. We can use one of the output files from the previous run to define the new starting conditions at t = 0.
*Format data correctly, taking account of keyword syntax and required units
Eclipse uses free format, which means as little or as many spaces, tabs and new lines may be used as desired. However, there is merit in setting up your file with columns aligned to improve readability, thus reducing typographical errors and saving time in the long run.
The following are a list of rules to follow when creating a file in Eclipse:
- Each section starts with a keyword
- All information associated with a key word must appear on the subsequent lines
- There must be no other characters (or spaces) on the same line as a keyword (i.e. each keyword must start in column 1, and be immediately followed by a new line keystroke)
- Data entry is terminated by a forward slash (/)
- Lines beginning with two dashes (–) are ignored and treated as comment lines
- Blank lines are ignored
*Select required output of calculations
Parameters that should be output are highlighted in the summary section of a simulation. Most of the output keywords consist of four letters that follow a basic convention as follows.
F – field
R – region
W – well
C – connection
B – block
O – oil (STB in field units)
W – water (STB in field units)
G – gas (MSCF in field units)
L – liquid (oil + water) (STB in field units)
V – reservoir volume flows (RB in field units)
T – tracer concentration
S – salt concentration
C – polymer concentration
N – solvent concentration
P – production
I – injection
R – rate
T – total
So say we use the keyword – FGPT, this requests that the Field Gas Production Total be output. Keywords with the letter F at the beginning require no additional information as this refers to the field as a hole. When using a different first letter which defines a specific location of the field, there must be accompanying information terminated with /a.
*Quality check output data to check for errors in input
*Identify purpose of each output file and use post-processors to analyse data
*Identify impact of reservoir engineering principles in calculation performed
*Identify numerical effects and impact of grid block size and orientation on results
Grid block size has a direct effect on the accuracy of results. As grid block size is reduced and thus grid block density increases, the simulation model can more accurately reflect the changing nature of reservoir properties over the entire area of the field. As grid block size decreases to zero, accuracy approaches 100%.
*Perform simple upscaling calculation to address numerical diffusion