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Proprietary Notice
Copyright © Schlumberger. All rights reserved.
No part of this document may be reproduced, stored in a retrieval system, or translated in any form or by any means, electronic or
mechanical, including photocopying and recording, without the prior written permission of Schlumberger.
Use of this product is governed by the License Agreement. Use of this product is governed by the License Agreement. Schlumberger.
Schlumberger makes no warranties, express, implied, or statutory, with respect to the product described herein and disclaims without
limitation any warranties of merchantability or fitness for a particular purpose.
Patent information
Schlumberger ECLIPSE reservoir simulation software is protected by US Patents 6,018,497, 6,078,869 and 6,106,561, and UK Patents
GB 2,326,747 B and GB 2,336,008 B. Patents pending. Schlumberger FrontSim reservoir simulation software is protected by US Patent
2004/0015295A1.
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Table of Contents3
Table of Contents
List of Figures ..... ...................................................................................................................................................................7
List of Tables ...... ...................................................................................................................................................................8
Chapter 1 - New developments........................................................................................................ 9Developments for 2007.1 .......................................................................................................................................................9
Developments for 2005A ......................................................................................................................................................10
Developments for 2004A ......................................................................................................................................................11
Chapter 2 - The Most Asked Questions About PVTi.................................................................... 15
Introduction......... .................................................................................................................................................................15
Chapter 3 - Introduction ................................................................................................................. 27
General information..............................................................................................................................................................27
Chapter 4 - Getting started............................................................................................................. 31
Starting PVTi ...... .................................................................................................................................................................31
Chapter 5 - Tutorials ....................................................................................................................... 32
Overview............. .................................................................................................................................................................32
Fluid Properties Estimation...................................................................................................................................................34
Creating a fluid system.........................................................................................................................................................37
Simulating experiments ........................................................................................................................................................43
Fitting an equation of state to experimental results ..............................................................................................................50
Exporting ECLIPSE Black Oil PVT tables.............................................................................................................................54
Converting a black oil run to compositional..........................................................................................................................58
Workflow Tutorial .................................................................................................................................................................61
Multiphase Flash .................................................................................................................................................................69
Exporting an ECLIPSE Thermal model ................................................................................................................................73
Data analysis and quality control..........................................................................................................................................77Removing contamination from samples................................................................................................................................84
Converting old projects to the current version ......................................................................................................................87
Chapter 6 - Reference section....................................................................................................... 89
General information..............................................................................................................................................................89
Main PVTi window ................................................................................................................................................................90
The PVTi main module .........................................................................................................................................................91
The fluid model ... .................................................................................................................................................................98
COMB - Compositional Material Balance ...........................................................................................................................112
Simulation using PVTi ........................................................................................................................................................117
Regression in PVTi.............................................................................................................................................................126
Exporting keywords ............................................................................................................................................................133
VFP module........ ...............................................................................................................................................................138Utilities ................ ...............................................................................................................................................................144
Batch system and keywords...............................................................................................................................................152
Error handling ..... ...............................................................................................................................................................165
Chapter 7 - Keywords ................................................................................................................... 167
PVTi keywords.... ...............................................................................................................................................................167
Keywords A-D..... ...............................................................................................................................................................168
ACF: Acentric factors......................................................................................................................................................... 169
ACHEUH: A-coefficient for Cheuh-Prausnitz BICs............................................................................................................ 170
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ALLDRY: Dry Gas Tables for Each Sample ...................................................................................................................... 171
BIC: Binary interaction coefficients .................................................................................................................................... 172
BLACKOIL: Start of the BLACKOIL section....................................................................................................................... 174
CALVAL: Specify calorific values....................................................................................................................................... 175
CHARACT: Components to be characterized.................................................................................................................... 176
CNAMES: Component names ........................................................................................................................................... 177
COATS: Blackoil tables...................................................................................................................................................... 178
COMB: Start of the COMB section .................................................................................................................................... 179COMBINE: Group existing components ............................................................................................................................ 180
CORRACF: Splitting correlation for ACFs ......................................................................................................................... 181
CORRCP: Splitting correlation for critical properties ......................................................................................................... 182
DRYGAS: Dry gas tables................................................................................................................................................... 183
DEADOIL: Dead oil tables ................................................................................................................................................. 184
DEBUE: Select output to debug file................................................................................................................................... 185
DEBUG: Select output to debug file................................................................................................................................... 186
DEFBIC: Default binary interaction coefficients ................................................................................................................. 187
DEGREES: Temperature convention ................................................................................................................................ 188
DIFFERENTIAL: Blackoil tables ........................................................................................................................................ 189
DREF: Reference densities ............................................................................................................................................... 190
Keywords E-K ..... ...............................................................................................................................................................191
ECHO: Insert PVI file into PVP file ...................................................................................................................................... 192
EOS: Defines the required Equation of State ..................................................................................................................... 193EOSOUT: EoS data for ECLIPSE 300................................................................................................................................. 194
EXP: Experiments .............................................................................................................................................................. 195
EXPIND: Set Status of Experiments .................................................................................................................................. 200
FIT: Perform fit by regression ........................................................................................................................................... 201
FRAC: Specify plus fraction data ........................................................................................................................................ 202
FRAGOR: Blackoil tables..................................................................................................................................................... 203
FVFREF: FVF reference conditions.................................................................................................................................... 204
GI: Define GI nodes for E200 tables ................................................................................................................................. 205
GROUP: Start of the GROUP section.................................................................................................................................. 206
GRBYALL: Start of the GROUP section.............................................................................................................................. 207
GRBYMIX: Start of the GROUP section.............................................................................................................................. 208
GRBYSAM: Start of the GROUP section.............................................................................................................................. 209
GRPBYWGT: Grouping by molecular weight ........................................................................................................................ 210
HYDRO: Define component as hydrocarbon or non-hydrocarbon....................................................................................... 211KVTABLE: Request K-value table for ECLIPSE 300 output ............................................................................................... 212
Keywords L- O .... ...............................................................................................................................................................213
LBC: Lohrenz-Bray-Clark viscosities.................................................................................................................................. 214
LBCCOEF: Set non-default LBC coefficients ...................................................................................................................... 215
LIVEOIL: Live oil tables .................................................................................................................................................... 216
LNAMES: Specify library names.......................................................................................................................................... 217
MAXIT: Max. number of regression iterations.................................................................................................................... 218
MAXSTEP: Maximum step size allowed in regression ........................................................................................................ 219
MDP: Data for Whitson splitting .......................................................................................................................................... 220
MESSAGE: Echo message to file and screen...................................................................................................................... 221
MINDELP: Minimum pressure difference ........................................................................................................................... 222
MINSTEP: Minimum step limit allowed in regression ......................................................................................................... 223
MIX: Mix samples .............................................................................................................................................................. 224
MODSPEC : Denotes start of the run specification section .................................................................................................. 225MODSYS : Start of the MODSYS section ........................................................................................................................... 226
MOSES : Blackoil tables..................................................................................................................................................... 227
MW : Specify molecular weights......................................................................................................................................... 228
MWS : Define plus fraction mole weight for CMF splitting.................................................................................................. 229
NCOMPS : Specify number of components ..................................................................................................................... 230
NEWPVI : Request new output PVI file ............................................................................................................................ 231
NEWPVO : Request new output PVO file......................................................................................................................... 232
NOECHO : No insertion of PVI file into PVP file ................................................................................................................ 233
OBS : Specify observations.............................................................................................................................................. 234
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OBSIND : Specify observation weights ............................................................................................................................ 235
OMEGAA/B: Specify EoS omega values........................................................................................................................... 237
OPTIONS : Set various program options ......................................................................................................................... 238
OUTECL3 : Start of the OUTECL3 section ...................................................................................................................... 240
Keywords P- S.... ...............................................................................................................................................................241
PARACHOR : Define parachors........................................................................................................................................... 242
PCRIT : Critical pressures................................................................................................................................................ 243
PEARCE : Blackoil tables................................................................................................................................................. 244PEDERSEN : Specify Pedersen viscosities..................................................................................................................... 245
PRCORR : Peng-Robinson correction ............................................................................................................................. 246
PSEUCOMP : Start of the PSEUCOMP section.................................................................................................................. 247
RECOVERY : Liquid production for recovery estimates................................................................................................... 248
REGRESS: Start of the REGRESS section....................................................................................................................... 249
REGTARG : Regression target ........................................................................................................................................ 250
RTEMP : Reservoir temperature for ECLIPSE Compositional......................................................................................... 251
RUNSPEC : Denotes start of the run specification........................................................................................................... 252
SALINITY : Specify sample salinity ................................................................................................................................. 253
SAMPLE : Specify fluid sample........................................................................................................................................ 254
SAMPLES : Specify fluid samples.................................................................................................................................... 255
SAMPLES : Specify fluid samples.................................................................................................................................... 256
SAMTITLE : Specify titles of fluid samples....................................................................................................................... 257
SAVCOMP : Save compositions ...................................................................................................................................... 258SCT : Defines Semi-Continuous Thermodynamics split................................................................................................... 259
SG : Specify specific gravity............................................................................................................................................. 260
SIMULATE : Start of the SIMULATE section.................................................................................................................... 261
SPECHA-D: Specify specific heat capacity coefficients.................................................................................................... 262
SPLIT : Start of the SPLIT section................................................................................................................................... 263
SSHIFT : Dimensionless volume shifts for PR3 ................................................................................................................ 264
STCOND : Standard conditions......................................................................................................................................... 265
SYSTEM : Start of the SYSTEM section........................................................................................................................... 266
Keywords T - Z ... ...............................................................................................................................................................267
TBOIL : Specify boiling points.......................................................................................................................................... 268
TCRIT : Specify critical temperatures............................................................................................................................... 269
THERMX : Thermal expansion coefficient for volume shifts............................................................................................... 270
TITLE : Specify run title ................................................................................................................................................... 271
TLOW : Define lowest temperature for VFP tables ............................................................................................................ 272TREF : Specify reference temperatures............................................................................................................................ 273
UNITS : Specify unit conventions..................................................................................................................................... 274
VAR : Specify regression variables ................................................................................................................................... 275
VCRIT : Specify volumes.................................................................................................................................................. 278
VCRITVIS : Specify volumes for LBC viscosity calculations ........................................................................................... 279
VERSION : Version of PVTi .............................................................................................................................................. 280
VFP : Start of the VFP section.......................................................................................................................................... 281
WAT100 : Output water properties .................................................................................................................................... 282
WAT200 : Output water properties .................................................................................................................................... 283
WAT300 : Output water properties .................................................................................................................................... 284
WATVFP : Output water properties .................................................................................................................................... 285
WETGAS : Wet gas tables.................................................................................................................................................. 286
WHIT : Defines Whitson splitting....................................................................................................................................... 287
WHITSON : Blackoil tables ................................................................................................................................................ 288X/YMFVP: XMFVP and YMFVP ECLIPSE tables.............................................................................................................. 289
ZCRIT : Specify critical Z-factors...................................................................................................................................... 290
ZCRITVIS : Specify critical Z-factors for LBC calculations.............................................................................................. 291
ZI : Specify sample composition...................................................................................................................................... 292
ZMFVD : Composition versus depth table ......................................................................................................................... 293
Chapter 8 - Technical Description ............................................................................................... 294
Overview............. ...............................................................................................................................................................294
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Theoretical background of PVT ..........................................................................................................................................295
Equation of state. ...............................................................................................................................................................316
Basic laboratory experiments..............................................................................................................................................338
Regression ......... ...............................................................................................................................................................347
Output for ECLIPSE simulators ..........................................................................................................................................353
Analysis techniques ............................................................................................................................................................371
Recommended PVT analysis for oil reservoirs...................................................................................................................372
Recommended PVT analysis for gas condensate reservoirs .............................................................................................377Consistency tests and correlations .....................................................................................................................................381
Fluid Properties Estimation.................................................................................................................................................384
Regression in PVT analysis................................................................................................................................................386
Wax and asphaltene precipitation in PVTi ..........................................................................................................................394
Cleaning samples contaminated with oil-based mud..........................................................................................................398
Mixing and recombination of samples.................................................................................................................................400
ECLIPSE Thermal Export Module ......................................................................................................................................401
Appendix A - Units........................................................................................................................ 409
Units.................... ...............................................................................................................................................................409
Appendix B - Symbols.................................................................................................................. 413
Symbols .............. ...............................................................................................................................................................413
Appendix C - Bibliography........................................................................................................... 415
Appendix D - Index ....................................................................................................................... 421
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List of Figures7
List of Figures
Figure 5.1 .......... Fingerprint Plot .......................................................................................................................................40
Figure 5.2 .......... Phase Plot ..............................................................................................................................................41
Figure 5.3 .......... The plotted simulation results .................................................................................................................46
Figure 5.4 .......... Plot of Oil FVF, Viscosity and Rs versus pressure for the output black oil property tables ....................56Figure 5.5 .......... Phase Diagram for Schrader Bluff Fluids ...............................................................................................70
Figure 5.6 .......... The phase envelope plot. .......................................................................................................................78
Figure 5.7 .......... The main display shows messages indicating the quality of the data.....................................................79
Figure 5.8 .......... The main plot window after zooming in ..................................................................................................80
Figure 5.9 .......... The plot of k values versus pressure. .....................................................................................................81
Figure 5.10 ........ The Hoffman-Crump plot ........................................................................................................................82
Figure 5.11 ........ Hoffman-Crump-Hocott plot. ...................................................................................................................83
Figure 5.12 ........ The original sample, the cleaned sample and the estimated contaminant.............................................85
Figure 6.1 .......... The main PVTi window ...........................................................................................................................91
Figure 6.2 .......... Fingerprint Plot .....................................................................................................................................109
Figure 6.3 .......... Phase plot.............................................................................................................................................110
Figure 6.4 .......... Ternary Plot .........................................................................................................................................111
Figure 6.5 .......... Main display after performing material balance ....................................................................................113
Figure 6.6 .......... COMB module - vapor versus pressure plot ........................................................................................114Figure 6.7 .......... The VFP module...................................................................................................................................138
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8 PVTi Reference ManualList of Tables
List of Tables
Table 5.1 The Fundamentals panel .........................................................................................................................35
Table 5.2 Component and fluid definitions...............................................................................................................37
Table 5.3 Program Options data..............................................................................................................................39
Table 5.4 Constant Composition Expansion experiment at 220o F (* indicates bubble point pressure)..................44Table 5.5 Differential Liberation Experiment at 220o F (* indicates bubble point pressure).....................................47
Table 6.1 List of library components ........................................................................................................................95
Table 6.2 Observation data....................................................................................................................................123
Table 6.3 Set PVTi Program Options panel...........................................................................................................145
Table 6.4 Keywords for introducing sections .........................................................................................................156
Table 6.5 RUNSPEC keywords .............................................................................................................................156
Table 6.6 SYSTEM keywords ................................................................................................................................157
Table 6.7 SPLIT keywords.....................................................................................................................................158
Table 6.8 GROUP keywords..................................................................................................................................159
Table 6.9 COMB keywords ....................................................................................................................................159
Table 6.10 SIMULATE keywords.............................................................................................................................160
Table 6.11 REGRESS keywords .............................................................................................................................160
Table 6.12 BLACKOIL keywords .............................................................................................................................161
Table 6.13 PSEUCOMP keywords ..........................................................................................................................162Table 6.14 OUTECL3 keywords ..............................................................................................................................162
Table 6.15 VFP keywords........................................................................................................................................163
Table 6.16 APITRACK keywords.............................................................................................................................163
Table 6.17 Error codes ............................................................................................................................................165
Table 7.1 Output indices ........................................................................................................................................185
Table 7.2 Output indices ........................................................................................................................................186
Table 7.3 Required data for experiments...............................................................................................................195
Table 7.4 Keyword arguments ...............................................................................................................................196
Table 7.5 Restrictions for EXP keyword arguments...............................................................................................198
Table 7.6 Component Types..................................................................................................................................211
Table 7.7 Equation of State omega values ............................................................................................................237
Table 7.8 Default limits for variables......................................................................................................................276
Table 8.1 Alkanes ..................................................................................................................................................297
Table 8.2 Napthenes..............................................................................................................................................298Table 8.3 Aromatics ...............................................................................................................................................298
Table 8.4 Physical properties.................................................................................................................................299
Table 8.5 Multi-component (ii) mixtures.................................................................................................................299
Table 8.6 CVD Report............................................................................................................................................308
Table 8.7 Equation of State coefficients ................................................................................................................318
Table 8.8 Equation of State constants ...................................................................................................................319
Table 8.9 Parameter estimation data. N is the number of experimental points .....................................................335
Table 8.10 Parameter Values for Pure Component Viscosity Correlation ...............................................................335
Table 8.11 Physical Properties of Methane and Decane.........................................................................................336
Table 8.12 PVTi defaults for Fluid Property Estimation ...........................................................................................385
Table A.1 Units.......................................................................................................................................................410
Table A.2 Constants...............................................................................................................................................411
Table A.3 Conversion factors .................................................................................................................................411
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PVTi Reference Manual New developments
Developments for 2007.19
Chapter 1
New developments
Developments for 2007.1
Maintenance of this application is continuing until further notice.
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10 New developments PVTi Reference ManualDevelopments for 2005A
Developments for 2005A
Maintenance of this application is continuing until further notice.
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Developments for 2004A11
Developments for 2004A
ECLIPSE Thermal Export facility
For the 2003A version of PVTi a new ECLIPSE Thermal support module was available where
you were able to interactively develop a correlation which accurately predicted K-values for
each component in a given fluid. For the 2004A version this module has been extended to a full
export facility where you can write out files that are suitable for use as PVT input for ECLIPSE
Thermal. The motivation behind this is so that, just as you can export files to use as PVT input
for ECLIPSE BlackOil and ECLIPSE Compositional, they will now be able to do the same for
ECLIPSE Thermal.
PVTi will export a series of keywords when an export for ECLIPSE Thermal is performed. For
a workflow description and brief summary of these keywords see "Compositional Data for
ECLIPSE Thermal" on page 367. For a more technical outline of how the exported keywords
are used in ECLIPSE Thermal see "ECLIPSE Thermal Export Module" on page 401.
Export for API Tracking option in ECLIPSE
BlackOil
The API Tracking facility enables ECLIPSE BlackOil to model the mixing of different types of
oil, having different surface densities and PVT properties.
Without the API Tracking facility, the presence of different types of oil in the reservoir could be
handled with the aid of PVT region numbers. Oil in PVT region 1 would have its properties
determined from PVT table number 1, and so on. However, this method cannot model the
mixing of oil types. Oil flowing from region 1 into region 2 would appear to take on the
properties associated with region 2.
The API Tracking facility essentially replaces the concept of PVT regions for oil. The PVT
tables used for determining the oil properties are selected at each time step according to the
average API of the oil in each grid block (or to be more precise, its average surface density).
For a overview of the workflow involved to export PVT tables suitable for use in ECLIPSE
BlackOil with the API Tracking option turned on see "Export for API Tracking option in
ECLIPSE BlackOil" on page 134. For a more technical description of the API Tracking model
in ECLIPSE as well as an explanation of how PVTi calculates suitable PVT tables see "Model
for API Tracking option in ECLIPSE BlackOil" on page 364.
Batch Mode
For the 2004A version of PVTi the batch mode has undergone a significant revamp. Over the
last few years the user interface of PVTi has evolved rapidly and the existing batch mode facility
no longer adequately supports more recent functionality. There have been 3 significant
modifications to the PVTi batch mode:
1 The way a batch mode is executed has changed. The new way to launch a batch mode run
on a PC is to use the command $pvti -batch filename where filename is the
name of your PVTi project. See "General information" on page 152 for more details on
running batch mode with other platforms.
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2 HEATVAPS.
This keyword is used to store the Heat of Vaporization at the standard temperature for each
component.
Sections
There is a new section called APITRACK. This is used when preparing batch files if the APITracking export facility is to be made use of in batch mode. It is essentially the same as the
BLACKOIL section but has an extra keyword called SAMPLES, which records the samples for
which PVT tables will be exported.
Manual
1 The section "The Most Asked Questions About PVTi" on page 15 has been updated with
questions regarding the Batch Mode, ECLIPSE Thermal Export and API Tracking
functionality.
2 A number of the tutorials have been amended - in particular the tutorial entitled “Using the
ECLIPSE Thermal Support Module” has been replaced by a tutorial called "Exporting an
ECLIPSE Thermal model" on page 73.
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PVTi Reference Manual The Most Asked Questions About PVTi
Introduction15
Chapter 2
The Most Asked Questions
About PVTi
Introduction
This section has been designed as a reference section so that you can quickly access information
about common problems encountered with PVTi without having to spend time looking through
the manual for the relevant section. The questions in this section have been constructed using
the most common support issues and also the InTouch database. Cross-references are provided
where necessary so that readers can access the appropriate parts of the manual for more detailed
information on a particular topic if required.
The questions are:
• "What is PVTi used for? Why do we need it?" on page 16
• "Where do I start? How do I set up a project within PVTi?" on page 16
• "How do I create an experiment along with a series of observations?" on page 17
• "What are the data limitations in PVTi?" on page 18
• "What is the Fluid Properties Estimation facility in PVTi?" on page 19
• "How do I perform regression on multiple fluid samples?" on page 19
• "What regression parameters should I choose?" on page 21
• "What is the difference between normal regression, special regression and automatic (PVTi
selects) regression?" on page 20
• "How does PVTi support gas condensate simulation?" on page 22
• "Can Black Oil tables be extended above the liquid bubble point in PVTi?" on page 22
• "Can PVTi be used if you know the composition of a fluid but do not have any
observations? And vice-versa?" on page 22
• "What black oil correlations are available in PVTi?" on page 23
• "How do I generate the asphaltene phase envelope using PVTi?" on page 23
• "How does PVTi support ECLIPSE Thermal?" on page 24
• "How do I Use PVTi’s Batch Mode?" on page 25
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16 The Most Asked Questions About PVTi PVTi Reference ManualIntroduction
• "How Can I Export PVT Tables to use the API Tracking Functionality in ECLIPSE
BlackOil?" on page 25
What is PVTi used for? Why do we need it?
PVTi is a compositional PVT equation-of-state based program used for characterizing a set offluid samples for use in our ECLIPSE simulators.
We need PVTi because it is vital that we have a realistic physical model of our reservoir fluid
sample(s) before we try to use them in a reservoir simulation. PVTi can be used to simulate
experiments that have been performed in the lab on a set of fluid samples and then theoretical
predictions can be made of any observations that were performed during a lab experiment, in
order that we can test the accuracy of our fluid model.
Any differences between the measured and calculated data are minimized using a regression
facility which adjusts various Equation of State parameters. This ‘tuned’ model is then exported
in a form suitable for one of our ECLIPSE simulators.
What is especially important to note when using the ECLIPSE Compositional simulator is that
PVTi and ECLIPSE Compositional use the same flash algorithm. This is vital as the flash has been used to simulate the experiments and predict values for experimental observations and is
therefore inherent within the fluid model itself which has been exported by PVTi. If ECLIPSE
Compositional used a different flash then the fluid model exported by PVTi would no longer be
valid.
Where do I start? How do I set up a project within
PVTi?
Defining a Fluid Sample
If you want to open a new project then start PVTi as instructed in "Getting started" on page 31
for your machine-type and choose a filename. PVTi starts; recognizes that it has a new project
and immediately opens the Fundamentals panel. This panel has been specifically designed to
make setting up a new project as easy as possible. Simply fill in the Components and ZI
columns with the component names and mole fractions respectively, which is the minimum
required to have a project within PVTi.
To fill in the component names simply type the standard shorthand names for the components
in your fluid, for example, C1, N2, CO2, H2S, IC5, etc. For more information on shorthand
names and component types see "Component types" on page 102. The mole fractions can be
entered as fractions or percentages by selecting the appropriate option on the panel. Also,
weight fractions/percentages can be entered for the components instead of mole fractions/
percentages.
Your Mole/Weight data must add up to 1 if entering as fractions and up to 100 if entering as
percentages. If they do not then PVTi asks you if you want it to renormalize your data when you
close the Fundamentals panel. If you want to add some components then select No,- otherwise
select Yes.
Warning If you try to perform operations on a fluid with incorrectly normalized mole/
weight fractions then the operation may fail.
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PVTi Reference Manual The Most Asked Questions About PVTi
Introduction17
Once the Fundamentals panel has been completed you will see have a sample called ZI on the
tree view on the left-hand side of the main window.This is the fundamental sample for the
project and the name ZI cannot be changed.
Creating Other Fluid Samples
Other fluid samples can be created in a project by selecting Edit | Samples | Name... . Simplytype in the name of the new fluid sample you want to create. The composition information can
then be entered for this fluid by selecting the Edit | Samples | Compositions... option.
Additional fluid samples to the project must always be subsets of the ZI sample in terms of the
component names, for example you cannot have a C8 component in an additional fluid sample
called OIL if C8 was not defined in the ZI sample. If you open the Edit | Samples |
Compositions... panel you can see why this has to be the case in PVTi.
Note Just because a component is defined in the ZI sample it does not mean there has to be
any of it there. It only has to be defined in the ZI sample to be used in other fluid
samples. If the mole fraction of a C8 component in the ZI sample is set to be 0.0 then
the C8 component can then be use in the OIL sample and the mole fractions set as
required.
Once at least one fluid sample (the ZI sample) has been defined then any experiment supported
within PVTi can be simulated as well as operations such as phase plots, fingerprint plots and
splitting.
For more information on creating fluid samples see "Defining Samples" on page 107.
How do I create an experiment along with a series
of observations?
Creating Experiments
To create an experiment select the Edit | Experiments... option and the experiment Entry panel
opens. The existing experiments are listed and you can edit them by selecting one of them and
clicking the next button. To create a new experiment click add in the top left of the panel and
select the experiment you wish to create. Choose the fluid sample you want to perform the
experiment on and then navigate through the panels by filling in the required information and
then clicking next, which takes you to the next panel. The information generally consists of
temperature and/or pressure information but not always, it depends on the experiment.
Once an experiment has been created an experiment button, along with an experiment name,
appears below the fluid sample which the experiment was performed on.
Creating Observations
If there are no observations at all for a particular experiment then to create one you need to select
the Edit | Observations... option and the Observations panel appears.
On the Experiments column on the left-hand side there is a list of all the experiments that are
available within PVTi and * symbols are next to the ones that you currently have defined within
your project.
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If one of these experiments is selected then in the Experiment List column a list of all the names
of the experiments of that type in your project appears for example, BUBBLE5, DEW3, DL1.
If one of these is selected then all the possible observations available within PVTi for that type
of experiment are displayed in the Observation Type column. Again observation types with a
* next to them means that there are values already defined for this particular experiment in your
project. Simply click on one to see and edit the values. To create a new observation select the
one you want and then click on the + button on the top left of the panel. Values and weights canthen be entered for the observation.
Note Currently defined observations for an experiment can be edited in the Observations
folder on the experiment Entry panel.
For more information on creating and editing experiments/observations see "Simulation using
PVTi" on page 117 and/or the tutorial "Simulating experiments" on page 43.
What are the data limitations in PVTi?
Pre-2003A
Up to and including the 2002A_1 release (pre-2003A) the following data constraints were
present in PVTi:
• 50 fluid samples
• 50 components per fluid sample* (see below)
• 50 experiments per fluid sample
• 300 observations per experiment
Note *When a splitting operation was performed it was possible to have more than 50
components (up to 100 in fact) but the components had to be grouped back so that therewere less than 50 before any experiment simulation could take place.
2003A
These pre-2003A data constraints have been present in PVTi for 4 to 5 years and, in-line with
the huge increase in computing power in the last few years, we have decided to enhance the data
constraint capability of PVTi so that the following is now available:
• 100 fluid samples
• 100 components per fluid sample* (see below)
• 100 experiments per fluid sample
• 300 observations per experiment
Note It is now possible to read in, save, split and group with fluids containing up to 100
components. However, the limit is still 50 components for any functionality involving
the EoS flash.
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What is the Fluid Properties Estimation facility in
PVTi?
The Fluid Properties Estimation (FPE) facility in PVTi is designed so that it can be used when
you have minimal data at your disposal, at the well-site for example. In this scenario, a full lab
analysis of multiple fluid samples from the reservoir has not yet been performed. Typically, just
a single sample would be available and minimal fluid behavior known for example, saturation
pressure at a particular temperature.
Specifically, the FPE facility assumes that a single fluid sample with compositional information
is available which includes a single plus fraction (for example C7+) component of which the
weight fraction is known. Typically, this weight fraction data is fairly accurate but the mole
weight, which is used to characterize the critical properties of the plus fraction, is not. The FPE
functionality allows you to perform a quick look simulation that regresses on the mole weight
of the plus fraction, and keep the weight fraction constant, in order to fit to a saturation pressure
observation at a particular temperature.
The FPE facility is available in the top right-hand corner of the fundamentals panel whenever a
new project is created. Alternatively it can be accessed using the Edit | Properties Estimation
(FPE)... option. For more information on this facility see "Fluid Properties Estimation" on
page 384. For an example of how it works see the tutorial "Fluid Properties Estimation" on
page 34.
How do I perform regression on multiple fluid
samples?
General
The fluid samples that PVTi performs regression on is determined by the structure of the tree
view on the left-hand side. By default, PVTi performs a regression on every experiment which
has observations defined, even if there are multiple fluid samples, each with their own
experiments. The reason for this is that, within a project, all fluid samples are considered to be
relevant to each other and so the same fluid model should be applied to all samples, even if the
compositional make-up of each sample is different
Note If two of your fluid samples are not relevant to each other for example they come from
different wells/reservoirs then a separate project should be created for each one.
Disabling Experiments/Observations
You can prevent PVTi from including an experiment in the regression by right-clicking on theexperiment and selecting Don’t use in Regression. A cross appears on the experiment
indicating it is not currently available within the regression facility.
You can disable an observation so that it is not used within the regression by again right-clicking
and selecting Don’t use in Regression. Alternatively, by right-clicking and selecting Set
Weight and then entering zero the observation is also not included in the regression.
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Note If an experiment is disabled then, as you would expect, all the observations are
automatically disabled.
Regression Weights
In general there will be a set of values in an observation. For example, if we have a differentialliberation (DL) experiment defined then a viscosity observation would have a value for each
pressure. We have two types of weight: there are single weights for each value of an observation
and global weights that apply to every value in an observation.
By right clicking on an experiment observation the global weight can be set. As mentioned
above, by setting this to zero none of the values in the observation would be used. Alternatively,
you may want to set a global weight for an experimental observation particularly high, for
example, matching the bubble point of a fluid is normally very important if one wants to ensure
that it is a single-phase liquid at the temperature and pressure of the reservoir.
Or maybe you do not trust the accuracy of a particular observation value, for example an oil
formation volume factor (FVF) value in a DL experiment.You may then not want to use a global
weight as all the other observation values look ok. In this case setting a single-value weight to
a very low value helps you match all the other values in the observation during regression as therogue, inaccurate value no longer inhibits convergence.
Both the single-value and global weights for an experimental observation can be set in the
Observations panel by selecting the Edit | Observations... option, highlighting the
appropriate observation and then simply typing in your chosen weights.
For a good example of how to use the regression facility, see the tutorial "Fitting an equation of
state to experimental results" on page 50.
What is the difference between normal regression,
special regression and automatic (PVTi selects)
regression?
There are 3 types of regression: normal, special and automatic. The difference between them
depends entirely on what kind of variables are being regressed on.
Normal regression parameters are equation of state variables relating to a particular component,
for example, critical pressure, , critical temperature, , acentric factor, . and the binary
coefficients. The full set of normal regression variables can be viewed using the regression
panel using the Run | Regression... panel. Select normal as the regression type and then click
variables - the upper table shows the single-valued normal regression parameters for each
component and the lower panel shows the binary coefficients table. For more information on
setting normal regression see "Setting normal variables" on page 127.
Special regression parameters are global Equation of State variables, for example, the thermal
expansion coefficient or the Cheuh-Prausnitz A factor for binary coefficients. There may also
be some splitting parameters available as special regression variables depending on whether a
multi-feed split has been performed on the plus fraction. See "Multi-feed Split (also called semi-
continuous thermodynamic (SCT) split)" on page 106 for more details on this facility. For more
information on setting special regression variables see "Setting special variables" on page 129.
P c T c ω
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Introduction21
The automatic regression facility or PVTi Selects as it is called on the Regression panel
attempts to choose the best normal variables to regress on for you before actually doing the
regression and reporting the answer. It should be noted that there is no substitute for a good
engineer in the sense that one should not just use this automatic facility all the time in the belief
that PVTi will do all the work. For example, the automatic facility will not use special variables
to regress on and so it is up to you to decide whether this would be necessary or not.
However the automatic facility can still be a useful tool in obtaining a good match to PVT data.The way the algorithm chooses the regression parameters is essentially based on 2 criterion. No
parameters are allowed to have more than a 90% correlation on any other parameter. Secondly,
no parameter is allowed to have less than 1% of the sensitivity of the most sensitive parameter
For a detailed discussion of the automatic regression algorithm see "A consistent methodology
that can be applied automatically" on page 389.
For more general information on the regression facility see "Regression in PVTi" on page 126.
What regression parameters should I choose?
It should be noted that there are no concrete rules for getting a good match to observations
relating to multiple fluid samples, but there are some general guidelines of what is often a goodidea, and what you should definitely not do.
Library components tend to have properties that are very well known and any of these will not
normally be good choices of regression variables. Properties of non-library components and
characterized components are much less well known and these are often good choices. In
general, the following set of variables are normally good things to initially regress on:
• and of any non-library component.
• and of any component with mole weight of C7 or heavier (as these are effectively
mixtures of different molecule types and so may differ from library values).
• and of any component with mole weight C7 or heavier. Again because these are
mixtures.
• No binary inter-active coefficients because of the risk of over-fitting.
• No viscosity-specific parameters, again because of the risk of over-fitting.
The variables mentioned above are all normal regression variables. The following set of special
regression variables can also often prove useful to get a match between samples:
• Do a multi-feed split to split the plus fraction into 2 or 3 pseudo-components. The ,
SCTMW and K w parameters, which control the splitting are then very good choices.
• The Cheuh-Prausnitz A binary parameter if using Cheuch-Prausnitz binaries.
• The mole weight of a plus fraction (if no split on the plus fraction has been performed).
For a detailed explanation of why some of the above are good and bad choices for regression parameters, see "Regression in PVT analysis" on page 386. There are also more specific
guidelines for choosing regression parameters depending on whether one is dealing with an oil
reservoir, see "Recommended PVT analysis for oil reservoirs" on page 372 - or a gas-
condensate reservoir, see "Recommended PVT analysis for gas condensate reservoirs" on
page 377.
Finally, for a tutorial illustrating the use of the normal and special regression facilities in a
typical workflow see the new "Workflow Tutorial" on page 61.
P c T c, ω
P c T c, ω
Ω A Ω B
α
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How does PVTi support gas condensate
simulation?
Gas condensate simulation is modeled in PVTi using the Constant Volume Depletion (CVD)
experiment. In most gas condensate reservoirs liquid does reach a high enough saturation to
become mobile as the pressure drops. Thus, gas and oil, to a good approximation, do not move
with respect to each other and so the CVD experiment models this behavior very well. Other
experiments that tend to be used for gas condensates are the dew point and constant composition
expansion experiments. For more information see "Gas condensate systems" on page 340.
A common failing when analyzing gas condensate reservoirs is to attempt to establish an
equation of state representation without a through examination of the data on which it is to
based. Things to check in the data are the characteristics of the heavy components (use a
fingerprint plot), material balance information and other information such as K-values and Z-
factors. Once you are happy with the data that you will try to match there is a recommended
procedure, in terms of regression, which will work for most gas condensates. For a detailed
description on how to model gas condensates see the section entitled "Recommended PVT
analysis for gas condensate reservoirs" on page 377.
Can Black Oil tables be extended above the liquid
bubble point in PVTi?
Yes. You should make sure that the DL/CVD experiment you simulate in PVTi covers the full
range of pressure values you are likely to encounter within your reservoir. If ECLIPSE BlackOil
encounters a pressure outside the range in the black oil table you exported from PVTi then it
will have no choice but to try to extrapolate to estimate properties such as gas-oil ratio (GOR)
and formation volume factor (FVF). The extrapolation used is linear and uses the appropriate
quantities at the two highest pressures in the exported black oil table.
However, this extrapolation can sometimes run into difficulties as is common in any problemwhen you are trying to gain information about unexplored parameter space. The normal error is
that ECLIPSE throws up negative compressibilities for your fluid. If this happens then be sure
to check your black oil tables covered the appropriate range of pressures.
For a thorough description of the black oil model used by PVTi and how the tables are extended
above the bubble point see "Blackoil model" on page 353.
Can PVTi be used if you know the composition of
a fluid but do not have any observations? And
vice-versa?
You know the fluid composition
If you have compositional information about the fluid, but no observations, then you can do
anything you want within PVTi except use the Regression facility. This is because the
Regression facility tries to minimize the differences between lab observations and PVTi’s
theoretical predictions and this is not a sensible operation if no observations are defined.
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In fact, in PVT laboratories engineers tend to use the default fluid model (one that has not been
regressed on) for a given equation of state in PVTi to give them a ‘ball-park’ answer for their
particular experimental observation. This can give them some idea as to how to set their
experiment up as they now have information on the kind of answers they might expect to
measure.
You have observationsIf you have observations but no compositional information at all then PVTi does have the
facility to convert black oil tables into a fully compositional model. To do this you must have
black oil tables that were exported by PVTi using the 2002A release or later. The tutorial entitled
"Converting a black oil run to compositional" on page 58 will explain this workflow in more
detail.
Note If you have black oil tables exported from before and including 2001A_2 PVTi, or you
have no black oil tables at all then, unfortunately, PVTi will not be able to construct the
compositional model for you. !
What black oil correlations are available in PVTi?
PVTi is a compositional PVT program and at the moment does not support black oil correlations
within its functionality.
It can however export a black oil model, using the compositional model tuned by the user within
PVTi to a DL or CVD experiment, for the ECLIPSE BlackOil simulator by generating tables of
Rs, FVF, etc. as a function of pressure for a given reservoir temperature. To export a black-oil
model select File | Export Keywords... . If you want to export a black oil table from a DL
experiment then you generally use the Oil Reservoir... menu option and if you have a CVD
experiment then the Gas Reservoir...option is appropriate. For more information on exporting
keywords see the section entitled "Exporting keywords" on page 133.
How do I generate the asphaltene phase envelope
using PVTi?
Just like a phase curve has single phase regions for the vapor and liquid and a 2-phase region an
asphaltene phase envelope may exist for your fluid. The asphaltene phase envelope partitions
off a region in pressure-temperature space where an asphaltene phase exists, analogous to the
two-phase region in a standard phase curve.
The upper line partitioning a region in pressure-temperature space where an asphaltene phase
does and does not exist is called the Asphaltene Disappearance Pressure (WDP) line. The lower
line is called the Asphaltene Appearance Pressure (WAP) line. In PVTi 2003A both curves aresupported, whereas in PVTi 2002A/2002A_1 just the functionality for the appearance line is
available.
Unlike a standard phase curve though where, as long as you do not have a fluid consisting of a
single pure component, there will always be a two-phase region, this is not the case in terms of
an asphaltene phase envelope. Asphaltene may never be present no matter what temperature and
pressure your fluid is at.
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Introduction25
For more detailed information on the new thermal module see "ECLIPSE Thermal Export
Module" on page 401. For workflow information and a summary of the exported keywords see
"Compositional Data for ECLIPSE Thermal" on page 367.
How do I Use PVTi’s Batch Mode?
The batch mode facility is accessed from the command line (if using a PC) using the command
‘$pvti -batch filename.pvi’ where filename is the rootname of your project. If using
a UNIX machine then use the command ‘@pvti -batch filename.pvi’. The
recommended way to prepare a file for use in the batch mode is as follows:
1 Open the project file in interactive mode which you wish to use.
2 Save the file using the File | Save (concise)... menu option.
3 Load this new ‘concise’ file back into PVTi and open the Set PVTi Program Options
panel by doing Utilities | Program | Options.... Set the last option Write Keywords for
Batch Mode to Yes.
4 Now perform the required workflow in interactive mode that you wish the batch mode to
reproduce e.g. simulation of experiment, splitting, grouping, export, etc.
5 When you have performed the workflow save the file using File | Save...
6 The saved file is now suitable for running in batch mode.
For a comprehensive review of the new batch mode functionality see "Batch system and
keywords" on page 152.
How Can I Export PVT Tables to use the API
Tracking Functionality in ECLIPSE BlackOil?
PVTi now has the capability to export multiple PVT Tables for use in ECLIPSE BlackOil’s APITracking. Without the API Tracking facility, the presence of different types of oil in the
reservoir could be handled with the aid of PVT region numbers. Oil in PVT region 1 would have
its properties determined from PVT table number 1, and so on. However, this method cannot
model the mixing of oil types. Oil flowing from region 1 into region 2 would appear to take on
the properties associated with region 2
Just like exporting a standard black oil table a depletion experiment must be defined in order to
do API Tracking export. The workflow is as follows:
1 Use the File | Export Keywords | API Tracking option in ECLIPSE BlackOil... menu
option to open the Export Panel for API Tracking.
2 Select the samples you wish to use in the export and move them to the Use box.
3 Choose the keywords you wish to export. Normally the Live Oil (PVTO) and Dead Gas(PVDG) keywords are used with the API Tracking option.
4 Select whether you wish to export a gas table for each sample or just a single gas table.
5 Select whether you wish to plot the tables in PVTi.
6 Select whether you wish to write to tables using full double precision numbers.
7 Select the separator you wish to use for the export.
8 Select the units you wish to export the table in.
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PVTi should then write the tables to a file and show them in the output display. This file is then
suitable to use as the PVT input for an API Tracking run in ECLIPSE BlackOil. For a similar
description of the API Tracking workflow see "Export for API Tracking option in ECLIPSE
BlackOil" on page 134. For a technical description of the API Tracking model in ECLIPSE as
well as an explanation of how PVTi calculates suitable PVT tables see "Model for API Tracking
option in ECLIPSE BlackOil" on page 364.
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General information27
Chapter 3
Introduction
General information
The PVTi program is an Equation of State based package for generating PVT data from the
laboratory analysis of oil and gas samples. The program may be used through an interactive
menu system or run in a batch mode. An interactive session can be saved as a batch input file,
which contains commands to reproduce the interactive operations. Alternatively, a batch input
file can be run from an interactive session.
Equations of state and viscosity correlation
Four equations of state are available, implemented through Martin’s generalized equation. This
enables the Redlich-Kwong, Soave-Redlich-Kwong, Peng-Robinson and Zudkevitch-Joffe
equations to be used. Two 3-parameter extensions of the Peng-Robinson Equation of State are
also available, one based on a Peneloux et al. volume shift, the other being an implementation
of the Schmidt-Wenzel Equation of State 2-parameter Peng-Robinson. The Soave-Redlich-
Kwong Equation of State similarly has a three-parameter extension.
Viscosities may be calculated using a method by Pedersen et al. based upon a corresponding
states comparison with methane, or by the Lohrenz-Bray-Clark method.
Fluid definition
Multiple fluid samples can be defined by specifying components as one of three types. Library
components require only that the appropriate component mnemonic be entered. Characterized
components define properties of plus fractions from a limited set of information. Finally all the
properties of a component can be defined, a facility which can be used selectively to edit the
properties of existing components.
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It is possible to group the components to reduce or pseudoise the fluid system (make a fluid
definition of the system using pseudo components), or to split the plus fraction into more
components, preserving molecular weight and mole fraction. Multiple samples having different
plus fraction properties, say mole weight and specific gravity, can be characterized by splitting
the plus fraction into two or more pseudo-components of fixed properties but variable
composition.
Fingerprint plots of mole fraction against molecular weight, or phase diagrams, are available.
Material balance checks
A compositional material balance can be performed on any gas condensate or volatile oil for
which a laboratory constant volume depletion or differential liberation experiment has been
performed. This can be used to estimate liquid compositions and hence K -values. The calculated
quantities can then be used to estimate the quality and consistency of the laboratory data.
Additionally, tests on recombination of separator data can be performed and estimates of
reservoir recovery can be made.
Simulation of experiments
Experiments may be performed on the fluid systems defined using the equation of state model.
Possibilities are:
• saturation pressures
• flash calculations
• constant composition expansions
• constant volume depletions
• differential liberations
• swelling tests
• multi-stage separator simulations.
Other experiments available are:
• composition versus depth
• vaporization test
• multiphase flash
• critical point
• saturation temperature
• first contact miscibility
• multiple contact miscibility (condensing and vaporizing).
• wax appearance temperature
• asphaltene appearance pressure
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Starting PVTi 31
Chapter 4
Getting started
Starting PVTi
Windows platforms
ECLIPSE Program Launcher
1 Start the ECLIPSE Program Launcher.
2 Click on the PVTi button.
3 Select the version and working directories as required.
Command line
1 Type the command $PVTI in a command prompt window.
UNIX platforms
1 Type the command @pvti at the command prompt.
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Overview 32
Chapter 5
Tutorials
Overview