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TitleOLGA Exercises
TagsGases Flow Measurement Fluid Dynamics Pipeline Transport Leak
File Size2.1 MB
Total Pages34
Document Text Contents
Page 1

FLOW ASSURANCE
WITH OLGA


EXERCISES

Page 2

FLOW ASSURANCE WITH OLGA - EXERCISES




TABLE OF CONTENTS

1. SLUGGING......................................................................................... 3
1.1 Preliminary Pipeline Sizing ........................................................ 3
1.2 Terrain Slugging – Normal Operation........................................ 7
1.3 Terrain Slugging – Mitigation Alternatives ................................. 9
1.4 Production Ramp-up................................................................ 10
1.5 Decretisation Sensitivity (Optional).......................................... 10
1.6 Slugtracking Module ................................................................ 11

2. PVTSIM – FLUID PROPERTIES...................................................... 13
2.1 Gas Condensate Fluid Property File ....................................... 13
2.2 Harthun Fluid Property File...................................................... 16
2.3 Mixing condensate and water.................................................. 17

3. PIPELINE SHUT-IN AND START-UP.............................................. 18
3.1 Shutdown Simulations ............................................................. 20
3.2 Start-up Simulations ................................................................ 21
3.3 Depressuring Simulations........................................................ 22
3.4 Depressuring Simulations – Comp. Tracking (Optional) ......... 23

4. GAS CONDENSATE PIPELINE....................................................... 24
4.1 Geometry Modification............................................................. 24
4.2 Steady State Simulations ........................................................ 27
4.3 Pigging Simulations ................................................................. 28
4.4 Turndown Ramp-up................................................................. 29

5. THREE PHASE FLOW – WATER MODULE ................................... 30

6. YOU GET A FAX – RESULTS WITHIN TWO HOURS?.................. 31

7. (OPTIONAL) SEPARATORS AND CONTROLLERS...................... 34

Page 17

FLOW ASSURANCE WITH OLGA – PVTSIM EXERCISE




Complete the following activities as for the gas condensate fluid above:-
• Input the Harthun composition as a new fluid.
• Make a phase envelope using Phase Envelope option.
• Make a PT flash at 15°C and 1 bara using the PT flash option.
• Generate an OLGA fluid property file termed {Harthun.tab}. Use ‘Harthun’

for the fluid label.

The OLGA table range should be:

• Pressure range = 1 to 200 bara
• Temperature range = -10 to 100°C
• Number of pressure points = 50
• Number of temperature points = 50


The OLGA fluid property file should contain data for two phases only. Everything
else is as per the default settings in PVTsim.


2.3 Mixing condensate and water

Select <Fluid> <Database> from the PVTsim main menu. Duplicate the composition
Condensate. The duplicated composition appears as the last composition and is
identical to the original, see below.




Select the duplicated composition, change the name to “Three phase” and add 0.05
mole % of water to the total composition and press Normalize.

Generate an OLGA fluid property file “threephase.tab” with the following
specifications:


• Pressure range = 1 to 120 bara
• Temperature range = -20 to 100°C
• Number of Pressure points = 50
• Number of Temperature points = 50
• Check three phase.


Use “GasCondWet” for the fluid label, the defaults for everything else and generate
the new fluid property file.

Page 18

FLOW ASSURANCE WITH OLGA – TRANSIENT EXERCISE




3. PIPELINE SHUT-IN AND START-UP

The main goal in this exercise is to conduct well shut-in and start-up simulations in
order to determine the thickness of the insulation layer needed to keep the fluid
temperature a minimum of 5°C above the hydrate formation temperature after a 8
hour shutdown period, (i.e. a ‘no-touch’ time of 8 hours during which time the
operators do not need to do anything to the pipeline). The hydrate formation curve
has been prepared based on the composition in the PVTsim exercise and is as
follows;-


Temperature
[°C]

Hydrate
Pressure

[bara]

-20 2.1

-15 2.7

-10 3.4

-5 4.2

0 5.3

5 11.4

10 23.3

15 48.6

18 78.2

20 138.9

21.1 200.0

At the end of the shutdown, the operator will then have two options, namely to
restart production or to depressure the pipeline to ensure that the pipeline contents
remain outside hydrate formation conditions in the event that production cannot be
restarted. The liquid surge volume out of the pipeline for both the start-up and
depressurisation options will be determined along with the gas rate to flare.

The Production Engineers have also provided the proposed well profile and the
expected reservoir conditions. You have been requested to include the wellbore in
the simulation model to allow the interactions between the well and the flowline to
be assessed.

The wellbore is a 1,000 m long deviated pipe with an inclination of 45° followed by
an 800 m long vertical pipe to the wellhead. The tubing has an inner diameter of
0.101 m and the thickness of the tubing wall is 6.88 mm. The inner roughness of
the tubing is assumed to be 0.025 mm.

The formation outside the tubing can be approximated by a 0.6 m thick concentric
formation layer. The formation layer should be modelled as a number of layers.
The physical properties of the formation rock are given below


Material Density
[kg/m³]

Specific Heat
[J/kg/K]

Thermal
Conductivity

[W/m/K]
Formation 2,243 1,256 1.59


Assume a linear geothermal temperature gradient between the perforations and the
seabed (70°C to 6°C).

Page 33

FLOW ASSURANCE WITH OLGA – TEST EXERCISE






Fluid analysis


Component Mol %
N2 0.69

CO2 0.54
C1 54.85
C2 4.85
C3 2.23
IC4 2.15
NC4 2.44
IC5 2.56
NC5 5.31
C6 5.57

C7+ 18.81

C7+ properties:
Molecular weight = 350 kg/kmol, Density = 870 kg/m3












131 ft (40 m)

5.6 miles (9 km)

295 ft (90 m) 265 ft (81 m)

80 ft (24 m)

Page 34

FLOW ASSURANCE WITH OLGA – SEPARATOR EXERCISE




7. (OPTIONAL) SEPARATORS AND CONTROLLERS

Case Description

In this exercise we will include a separator with controllers to demonstrate how to
combine a pipeline with receiving facilities. We will start from the input file made in
the Gas Condensate exercise with a flowrate of 20 kg/s and make the following
changes:


• Adjust the elevation of the last pipe in the flowline so that it is horizontal.
• Add an additional pipeline section at the end of the pipeline for the separator.

(Hint: This section can have the same diameter as the rest of the pipeline,
but the volume should be equal to the separator volume.) The separator is 8
feet in diameter and 20 ft long.

• Add two 150 m long sections after the section with the separator. These
sections will model the separator gas outlet.

• Add a controller for liquid level control in the separator. The controller
should have an amplification factor of 10, and integral constant of 1E10, and
a derivative constant of 0. It should hold the level at 25% of the vessel
height (Hint: OLGA uses the term HOL to indicate fraction of vessel volume).

• Add a vertical two-phase separator. OLGA asks for a “train” variable, which
in this case is gas, since the geometry we defined downstream of the
separator is the gas outlet. Use 3-inch valves for the oil level control valve
and emergency drain valve. The backpressure for the two valves should be
300 and 200 psia respectively. Use a CD of 1 for the valves. The “high-
high” level is set at 40% of the volume, while the low level switch is set at
15% of the volume. The emergency dump reset is at 50% of the volume.

• Add trend plot variables for gas flow at the separator gas outlet (GG), liquid
level in the separator (LIQLV), oil mass flow at the separator normal oil drain
and the emergency oil drain (GNODHL and GEODHL). Also add the
controller output (CONTR) for the liquid level controller, which will give the
opening of the oil level control valve.


Run the simulation for 15 hours and observe the liquid level in the separator and the
liquid flow out of the separator to see if the level controller is working correctly.
Check the controller output for the level controller to determine if the sizing of the
liquid drain valve is reasonable.

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