Download - OLGA.ppt
The Transient Multiphase Flow Simulator
Contents • Introduction
• Physical models and numerical solutions
• Network topology
• How to make fluids flow
• Fluid properties
• Heat transfer
• Process equipment and modules
• File structure and execution
Fundamental features
• OLGA is– transient ( df/dt # 0 )– one-dimensional (along pipe axis)– “complete”– a modified “two-fluid” model– realised with a semi-implicit numerical solution
• staggered grid– made for (relatively) slow mass transients
The dynamic three phase flow simulator
OLGAOLGA
8 Conserv. Equations
mass (5)momentum (2)
energy (1)
Fluid Properties
Closure Laws
mass transfermomentum transfer
energy transfer
BoundaryConditions
Initial Conditions
The OLGA three phase flow model• Mass conservation
– Gas– Hydrocarbon bulk– Hydrocarbon droplets– Water bulk– Water droplets
• Momentum conservation– Gas + droplets– Liquid bulk
• Energy conservation– Mixture
• Constitutive equations
Variables
• Primary variables– 5 mass fractions (specific mass)– 2 velocities– 1 pressure– 1 temperature
• Secondary variables– Volume fractions– Velocities– Flow rates– Fluid properties
Conservation of mass
Conservation of energy
energy = mass (thermal energy + kinetic energy + potential energy)spec
energy flow + work = mass flow (enthalpy + kinetic energy + potential energy)
Force balance equation(Conservation of momentum)
j j+1
Pj Pj+1
dZj
liquid
gas
M - MomentumV - Velocitym - Mass M = m ·V
S = Shear = wall shear + interfacial shearG = Gravity = m · gravity accelerationF = Force = pressure · flow areaMT = Momentum Transfer =
mass transfer - entrainment + deposition
dM /dt = ((M·V )j - (M·V )j+1) /dzj - S j + G j + F j + F j+1+ MT
The OLGA volume equation
Qi
i i+1
Qi+1Pi
source / sink
i
for all sections the local fluid volume time variations
The OLGA volume equationCombine all mass conservation equations
T and RS constant 0= CdP/dt = Qin - Qout [m3/s]
+ volume change by mass transfer+ volume change by mass sources+ Volume Correction
C = “compressibility” i.e. dVfluid/dP [m3/Pa]
Net change of total fluid volume in a section = 0
0)t/T)(T/V( temperature change is assumed to be zero in this step :
Calculation sequence
for each time step:
b) solve momentum - and volume equation simultaneously U and P
d) solve mass equations
c) perform flash
first for gas
and then for water film and water droplets
then for oil film and oil droplets
a) solve model relations to give friction factors etc.
e) solve energy equation Tf) perform flash
Sources of numerical errors in general• Linearisation of strongly non-linear
models– Iteration is not performed
• Thermal expansion or contraction– Temperature decoupled from pressure may give volume errors
• Local changes of total composition neglected in standard OLGA – taken into account in CompTrack
Volume errorAt each time step when all equations have been solved the net fluid volume change in each section usually is 0and the volume error can be expressed as
VOLi = 1- Vi f / Vsectioni 0 f
Vi f = mif /i f
Vi f = fluid volume in section no imif = mass in pipe section no i
i f = density of fluid in section no i
(f indicates liquid , gas and droplets)
.
Volume error cont.
The main source of high volume error peaks is change of phase velocity direction from one time step to the next (i.e. from time step tn to tn+1).The volume flow at tn+1 is based on massflows from tn and thus the volume flow and velocities may have opposite directions.
The volume error is corrected by “adding or subtracting fluid volume” over several time steps (not by iteration).
This correction may also cause unphysical pressure and/or temperature peaks.
(VOL is an output variable which should be plotted together with phase velocities during fast transients)
Modeling the pipeline profile in OLGAThe assumption
OLGA topology
• GEOMETRY is a sequence of PIPES– a PIPE is defined by its
• LENGTH• INCLINATION• INNER DIAMETER• ROUGHNESS and• WALL
OLGA topology cont.
a BRANCH consists of one GEOMETRY and two NODES
a BRANCH has flow direction
NODE-1NODE-2
OLGA topology cont.
An OLGA network consists of a number of BRANCHES
a NODE is either TERMINAL or MERGE or SPLIT 1)
1) v 4.00
OLGA topology cont.
PIPE_1
1 2 3 4
PIPE SECTIONS
1 2 3 4 5
PIPE SECTION BOUNDARIES
1
2
3
OLGA topology cont.
OLGA calculates different types of output variables:
VOLUME VARIABLES e.g. pressure (PT), temperature (TM) and volume fractions (e.g. HOL) are calculated in the midpoints of the pipe sections.
BOUNDARY VARIABLES e.g. velocities, flowrates and flow patterns which are calculated on section boundaries.
e.g. a VALVE is always positioned on a section boundary.
OLGA topology cont.
BOUNDARY of type ”CLOSED” –i.e. no flow across boundary
BOUNDARY of type ”PRESSURE” –i.e. flow across boundary.
OLGA topology cont.
- Pressure, - Temperature, - Gas Mass Fraction - Water Mass Fraction
Pressure boundary
Gas fraction = 1
Gas fraction = 0
Pressure boundary; gas mass fractionAnalogy
Gas fraction = 0.5P,TP,T
P,T
How to make fluids flow
• a mass SOURCE• pressure boundaries• the standard WELL
a mass SOURCE
BOUNDARY TYPE = CLOSED
a mass source into the pipe
BOUNDARY TYPE = PRESSURE
Total mass rateTGas mass fractionWater fraction
SOURCE-1
OLGA calc. this P and T
mass SOURCE cont.
• a SOURCE feeds its mass regardless of the pressure in the pipe
• a SOURCE can be positioned anywhere• one pipe section can have several SOURCES• a SOURCE can be negative
a negative SOURCE
BOUNDARY TYPE = PRESSURE
a mass source out of the pipe
BOUNDARY TYPE = CLOSED
SOURCE-out
OLGA calc. this P
two PRESSURE BOUNDARIES
BOUNDARY TYPE = PRESSURE
BOUNDARY TYPE = PRESSURE
Pin Pout
Pin > Pout
Pin Pout
Pin < Pout
a WELL
BOUNDARY
TYPE = CLOSED
WELL-1
BOUNDARY
TYPE = PRESSURE
Reservoir P & T PI (productivity index) Injection indexGas mass fractionWater fraction
Pres
a WELL cont.
• a WELL is essentially a pressure boundary
• fluid flows into the well when the bottom hole pressure is less than the reservoir pressure
• a WELL can be positioned anywhere along a pipe • a pipe can have several WELLs
• the Advanced Well Module provides numerous additional options.
Starting the dynamic calculation sequence
calculated by the steady state pre-processor
calculated from user given Initial Conditions: i.e. profiles of T, P, mass flow, gas volume fraction, water cut
or be
conditions at t = 0 can either be
Steady state pre-processor
• Activated when setting STEADYSTATE = ON in mainkey OPTIONS
• Gives a full steady state solution at time 0 (when STARTTIME = ENDTIME = 0 in INTEGRATION)
• The subsequent dynamic simulation will tell you if the system is stable or not
time0
Wall heat transfer
• Standard heat transfer correlations• Averaged fluid properties• Radial heat conduction in pipe walls
Pipe wall discretisation How OLGA represents walls
liquid
gas
Need to input:
Conductivity
Heat capacity
Density
Calculated by OLGA: Heat transfer coefficient
Need to input: Heat transfer coefficient
Fluid propertiesGeneral
• The fluid properties are pre-calculated tables as a function of P and T and for one fluid composition– It follows that the total composition is constant
throughout a fluid table1)
• The exact value of a property for a given P and T is found by interpolating in the relevant property table
1) Compositional tracking available with OLGA 2000 v3.00
Properties in the fluid tables
More on Rs: the gas mass fraction
• the mass transfer between gas and liquid as a function of variations in P and T is determined by a rate of mass transfer (it takes time)
• the change of Rs w.r. to P and T determines this rate
• thus: Rs (P,T) = constant gives no mass transfer
mass of gas at P and T
mass of gas + HC-liquid at P and T Rs =
Restrictions - limitations• Table based fluid properties
– Total composition is constant for one fluid table.
• the solution is thus approximate due to slip, phase separation, network systems and varying sources of different compositions
Well B has
Fluid Table 2
Well A has
Fluid Table 1
Flowline has
fluid properties ?
Process equipment with OLGA 2000 basic
• Separators• Compressors • Heat exchangers• Chokes and Valves (CV)
- critical, sub-critical• Check valves• Controllers
PID,PSV,ESD etc.• Controlled sources and leaks• Pig/plug• Heated walls
OLGA 2000 Modules
• Slugtracking – with pigging
• Water
– three-phase flow• FEM -Therm
– conductive 2-D (“radial”) heat transfer– finite elements– integrated with OLGA bundle– grid generator
OLGA 2000 Modules • Comptrack
– compositional tracking• MEG-track• UBitTS
– Under Balanced interactive transient Training Simulator
• Advanced Well• Multiphase Pumps
– positive displacement– rotodynamic
• Corrosion• Wax
OLGA 2000 file structure
OLGA 2000
reflex of the Input File +results from OUTPUT
Trend Plot Fileresults from TREND
Profile Plot Fileresults from PROFILE
Restart File(binary)
Input File .inp
Fluid Properties File .tab
.out
.tpl.ppl
.rsw
ASCII file
Principles of OLGA 2000 execution
OLGA 2000 GUI
Input File .inp
OLGA 2000
PVTsim
Fluid Properties File .tab
.tpl
.ppl
.out .rsw
OLGA 2000 Support
• [email protected]– OLGA 2000 Helpdesk mail address
• http://www.olga2000.com– The OLGA 2000 web site
• [email protected]– OLGA 2000 News Network (ONN): Mailbox at
Scandpower for sending news and important messages to the OLGA users that have signed on.