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Oil & Gas Separation Book 1 > Oil & Gas Separation Book 1 > Flashcards

Oil & Gas Separation Book 1 Flashcards

1
Q

What are the main components of a typical hydrocarbon reservoir? (3)

A
  • Oil
  • Gas
  • Water
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2
Q

What are the main objectives of a separation system? (2)

A
  • Obtain Oil which is free from gas and water

- Obtain Gas which is free from any liquids

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3
Q

Define the term ‘Oil and gas Separator. (1)

A
  • A pressure vessel which is designed to separate reservoir fluids into liquid and gaseous components
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4
Q

Give examples of other names which are used to describe an Oil & Gas Separator. (5)

A
  • Trap
  • Knock Out Vessel
  • Stage Separator
  • Flash Drum
  • Scrubber
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5
Q

Give the names of the components on a Xmas Tree (6)

A
  • Lower Master Gate Valve
  • Upper Master Gate Valve
  • Kill Wing Valve
  • Swab Valve
  • Flow Wing Valve
  • Choke
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6
Q

Draw a simple line diagram of a Xmas tree and its flow line (P&ID) (1)

A

Draw…

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7
Q

Which valve is immediately downstream of the ‘Choke Valve’ on a Xmas Tree? (1)

and

What is its Function? (1)

A
  • NRV (Non Return Valve)

- To prevent Oil from one well back-flowing into another.

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8
Q
  • What is the function of a pressure low switch on system located on a flow line? (1)
A
  • The pressure switch low (PSL) will warn the operator if the flow line pressure is too low.
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9
Q

What is the function of a pressure high switch on system located on a flow line? (1)

A
  • The pressure switch high (PSH) will warn the operator if the flow line pressure is too high.
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10
Q

Which system are the PSL & PSH on a flow line tied into and why? (2)

A
  • In both instances the pressure switches are tied in to the platform emergency shut-down (ESD) system.
  • To shut-down plant and equipment in a controlled manner if a hazardous situation should arise.
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11
Q

Which valve or valves on the Xmas tree would be activated from the ESD system to shut down the well? (2)

A
  • The upper master gate valve and the flow wing valve.
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12
Q

What are the Lower Master Gate Valve & the Flow Wing Valve also referred to as? (1)

A
  • Surface safety valves.
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13
Q

Why would the ‘set points’ of a PSL and PSH change? (1)

A
  • Because the the oil well will become depleted over time this the pressure drops in the flow line
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14
Q

With regards to pressure switches on a flow line - what could cause a low pressure situation? (4)

A
  • Less flow of the well due to a wax build up or a slug of water entering the bottom of the well.
  • A valve closing on the Xmas Tree due to a problem with the Hydraulics which would keep the SURFACE SAFETY VALVE open while healthy - a hydraulic system problem would cause the valve to close.
  • A large leak in the flow line itself due to flange failure or a rupture in the piping
  • A low pressure problem further downstream
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15
Q

Why would a well ESD system have an override option? (2)

A
  • The well’s surface safety valve cannot be opened up because of the low pressure in the flow line, but, to restore the pressure the well needs to open. In this situation, the ESD system needs to be over ridden in order to open up the well. For this reason all PSLs are fitted with a by pass (override) or override facility. The by pass (override) switch allows the operator to open the surface safety valve when he brings the well on line.
  • Remember: once the well is back on stream the PSL by pass (override) must be deactivated.
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16
Q

What could cause high pressure situation in the flow line? (3)

A
  • The well beginning to flow more oil due to problems with the well itself. These problems may be caused by a slug of gas building up in the tubing, or the choke valve being eroded away as the oil flows across it
  • A valve being closed on the outlet of the flow line. This could be due to operator error when attempting to change over the well from one flow path to another or when putting the well on test
  • A high pressure problem further downstream in the process.
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17
Q

From the tubing of a well, fluids flow through a number of valves and along a flow line. The following valves would be found in this flow path, but they are not in the correct sequence. Place the valves in the right order, starting with the first valve in the Xmas tree. (5)

A

(a) - Lower Master Gate Valve
(b) - Upper Master Gate Valve
(c) - Flow Wing Valve
(d) - Choke Valve
(e) - Non-Return Valve

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18
Q

What is a Separation train? (1)

A
  • A sequence of separator vessels.
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19
Q

What would you find on a flow line after the Xmas tree and before it ties into the main header? (1)

A
  • An isolation (block) valve or DBB
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20
Q

What is the assembly of pipework where the different flow lines enter the headers called? (1)

A
  • Manifold
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21
Q

What is the gathering system? (2)

A
  • The system of pipework used to gather reservoir fluids from the wells for further processing. The gathering system comprises of flow lines and headers
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22
Q

In an Oilfield separation system, which substances have to be separated? (3)

A
  • Oil
  • Water
  • Gas
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23
Q

What is the typical density range of crude oil? (2)

A
  • 640kg / m3

to

  • 880kg/ m3
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24
Q

What are other terms for Natural Gas? (2)

A
  • Free Gas

- Solution Gas

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25
Q

Describe ‘Free Gas’ (2)

A
  • Hydrocarbon mixture which exists in a gaseous state at reservoir conditions of temperature and pressure.
  • Remains as a gas when produced under normal conditions.
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26
Q

Describe ‘Solution Gas’ (2)

A
  • Is dissolved in the oil at a certain temperature and pressure.
  • If the pressure is reduced and/or the temperature is increased, the solution gas may be liberated from the oil. When this occurs the gas assumes the characteristics of free gas.
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27
Q

Under what conditions can the density of a Hydrocarbon Gas change?

A
  • The density of the gas depends upon the pressure at which it is confined
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28
Q

What is the density of a typical hydrocarbon Gas at

(a) 50 bar
(b) Atmospheric Pressure

A

(a) 36 kg/m3

(b) 1.6kg/m3

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29
Q

The volume of gas and of oil produced from a reservoir is often expressed as a ratio.

What is this ratio often describes as?

A
  • Gas to Oil Ratio or ‘GOR’
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30
Q

Describe Gas to Oil Ratio. (1)

A
  • GOR is defined as the volume of gas produced per unit volume of oil production.
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31
Q

What are the usual Oilfield units for the GOR? (1)

A
  • Standard cubic metres of gas per standard cubic metres of oil (sm3/sm3)
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32
Q

What other units apart from (sm3 Gas / sm3 Oil) can be found? (1)

A
  • Standard cubic feet of gas per barrel of oil (scf/ bbl).
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33
Q

If the daily production from a field 2560 sm3 of oil and 128000 sm3 of gas what is the field GOR? (1)

Draw the formula (1)

A
  • 128000 sm/3 Gas / 2560 sm/3 of Oil

is:

50 sm/3 Gas per Sm/3 of Oil

Formula:

sm/3 Gas divided by sm/3 of Oil

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34
Q

If the daily production from a field is 4400sm3 of oil and 110,000 sm3 of gas, what is the field GOR? (1)

A
  • 110,000 Gas / 4400 Oil

is 25 sm3 Gas per sm3 of Oil

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35
Q

When water is drawn up from a well, what forms may it be found in? (2)

A
  • Free Water

- Emulsified in the Oil itself

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36
Q

What is the typical density of ‘Produced Water’? (1)

A
  • 1072 kg/ m3.
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37
Q

If the three reservoir fluids of oil, water and gas were to be placed in a closed container and allowed to stand, separation would occur. Describe this separation. (3)

A
  • Water being the most dense would sink to the bottom
  • Oil being less dense than water would sit on top of the water
  • Gas being the least dense would occupy the space on top of the water
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38
Q

Reservoir fluids are being continuously produced and must be continuously separated. This takes place in one or more pressure vessels which are designed to achieve optimum separation as a continuous process. What can this process be described as? (2)

A
  • Two Phase Separation

- Three Phase Separation

39
Q

Describe Two Phase Separation (1)

A
  • In two-phase separation, gas is removed from total liquid (oil plus water)
40
Q

Describe three phase separation (2)

A
  • In three-phase separation, in addition to the removal of gas from liquids, the oil and water are separated from each other.
41
Q

When would the two phase separation method normally be applied? (1)

A
  • Normally be used when the reservoir fluids contain only a small proportion of free water.
42
Q

The total process within the separator can be broken down into four parts, what are these four parts? (4)

A
  • Primary Separation
  • Secondary Separation
  • Mist Extraction
  • Liquid Accumulation
43
Q

Describe Primary Separation (6)

A

As the reservoir fluids enter the vessel an initial separation of gas and liquid takes place. This happens because of:

  • a reduction in velocity
  • a reduction in pressure
  • a change in flow direction
  • Reduction in Velocity:

The velocity of the inlet stream is reduced as the fluids flow from a relatively small diameter pipeline into the large volume separator.

  • Reduction In Pressure:

The pressure is reduced by maintaining a controlled pressure on the vessel lower than that of the inlet stream.

  • Change In Flow Direction

The change in flow direction is accomplished by placing some form of deflector at the inlet to the separator. (We will be looking in more detail at the internal features of separators in the next section).

44
Q

Describe Secondary Separation (10)

A
  • After the initial separation, gas will flow towards the outlet of the vessel. However, it will still contain a certain amount of liquid in the form of droplets. In the secondary separation process these liquid droplets are removed from the gas stream.
  • Liquid droplets which are suspended in the gas stream will tend to fall or ‘settle’ towards the bottom of the vessel. This is simply due to the FORCE OF GRAVITY
  • The ease with which the droplets will settle out of the gas stream and fall into the liquid accumulation section of the separator depends on a number of factors. These include:
  • The size of the droplets
  • The density of the liquid droplet compared to the density of the gas
  • The velocity at which the gas stream is travelling through the separator
  • The turbulence which exists in the flowing gas stream

Of these factors:

  • The difference in density between oil and gas and the droplet size will be determined by the composition of the well stream
  • The velocity of the gas stream is determined by the size of the separator and its throughput
  • Turbulence can be reduced by having device called straightening vanes built into the separator to make the gas flow more streamlined
45
Q

Inside a Separator, how is the velocity of the gas stream flowing through it determined? (1)

A
  • Determined by the size of the separator and its throughput
46
Q

How is the difference in density between oil and gas droplet size determined? (1)

A
  • By the composition of the well stream
47
Q

How is turbulence reduced inside a separator? (2)

A
  • Straightening Vanes

- These make the gas flow more streamlined

48
Q

Describe ‘Mist Extraction’ (3)

A
  • Secondary Separation will not remove VERY small particles (mist) of gas from the gas stream. Therefore a ‘mist extraction’ device is built into the vessel.
  • Mist extraction is accomplished using either an impingement or a centrifugal force mechanism.
  • The most common mist extraction device is the knitted wire mesh pad which is an impingement mechanism.
49
Q

How does a knitted wire mesh mist extraction device operate? (3)

A
  • Placed near to the gas outlet from the vessel
  • As the gas flows past the wire mesh, the droplets flow in a more straight line, striking the wire strands and sticking to them.
  • As more droplets stick to the wire, a film of liquid forms which slowly moves to the lowest point on the wire and falls down eventually as the collection grows larger to the liquid accumulation section of the separator. This is achieved simply with the force of gravity
50
Q

Illustrate the action of a knitted wire mesh pad (mist extractor) (3)

A

Shows the:

  • Flow of gas around the mesh pad
  • Mesh Pad itself
  • Collection of liquids gravitating to the liquid accumulation section
51
Q

With Regards to Mist Extraction, when is a centrifugal force mist extraction method normally used?

A
  • Usually used in vessels where the gas flow is vertically upwards
52
Q

Describe centrifugal force mist extraction (3)

A
  • The gas stream containing liquid mist is made to flow in a circular motion
  • Centrifugal force throws the liquid particles outwards.
  • Causes the particles to collect on the walls of the vessel and gravitate towards the liquid accumulation section of the vessel
53
Q

What is one potential downfall of using centrifugal force mist extraction? (2)

A
  • Centrifugal extraction requires a change in gas flow direction at high velocities
  • This results in large pressure drops which limit the application
54
Q

What is retention time?

A
  • Retention time is the period of time required liquids (oil) must stay in a separator to allow the gas trapped in the oil to rise to the surface and join the gas stream again
55
Q

If reservoir fluids flow into a separator at the rate of 5400 sm3/day and the accumulation section of the separator is 12.5 sm3, please determine the gas to be liberated from the liquid.

A
  • 1 day = 24 hours x 60 min = 1440 min
  • 5400 sm3/day / 1440 min = 3.75 sm3/min
  • 12.5 sm3 / 3.75 sm3/min = 3.33 minutes
56
Q

In three phase separation, how many parts to the separation process are there? name them (5)

A
  • Primary Separation
  • Secondary Separation
  • Mist Extraction
  • Liquid Accumulation
  • Oil & Water Separation
57
Q

What is stage separation? (5)

A
  • The aim of separation is to stabilise the oil for shipment at or near atmospheric pressure meaning a separator would have to be operated at this pressure
  • When the reservoir fluids are extremely high and the GOR is large also - a separator would have to be extremely large.
  • In order to achieve optimum separation with a high pressure/high GOR the separation process is carried out with a number of separators working in series - this is known as stage separation
  • Each separator would operate at a lower pressure than its predecessor.
  • At each stage the gas which is liberated and separated is removed and the liquid passes on to the next vessel in the sequence
58
Q

How does primary separation occur? (4)

A
  • Primary separation occurs at the inlet to the vessel due to:
  • A reduction in pressure
  • A reduction in velocity
  • A change in flow direction
59
Q

What are the 5 parts of secondary separation? (5)

A
  • Gravity settling of liquid droplets from the gas takes place
  • Mist extraction section which removes very small droplets of liquid from the gas
  • Liquid accumulation section of the separator where retention time allows gas bubbles to be liberated from the liquid
  • The oil and water separation section (in a three phase separator).
60
Q

When is stage separation normally used?

A
  • Stage separation is used where there is a large throughput of relatively high gas / oil ratio reservoir fluid and where there is a large total pressure drop to be accommodated.
61
Q

Identify the classification of separators according to configuration (3)

A
  • Horizontal
  • Vertical
  • Spherical
62
Q

Identify the classification of separators according to phases separated (2)

A
  • Two phase separators

- Three phase separators

63
Q

Identify the classification of separators according to Duty (3)

A
  • Bulk Separators
  • Test Separators
  • Clean up Separators
64
Q

What is a bulk separator? (2)

A
  • Bulk separators are used to process most of the fluids passing through a system.
  • They are in continuous use.
65
Q

What is a Test Separator? (1)

A
  • Test separators are used to check the production rates of individual wells
66
Q

What are the main features of a Test Separator?

A
  • Used when taking one well of out of the main process flow stream to check production rates
  • Smaller than bulk vessels, can only handle production from one well at a time
  • Always equipped with meters on each outlet line to measure flow rates of oil, water and gas.
67
Q

Identify the classification of Separators according to position in a train of separators (6)

A
  • First Stage (High Pressure)
  • Second Stage (Medium Pressure)
  • Third Stage (Low Pressure)
68
Q

Draw a complete separation system (6)

A

Draw

69
Q

What is typically used to change the flow direction of the inlet stream required as part of the primary separation process in

(a) Vertical Separator (2)
(b) Horizontal Separator (3)

A

(a)
- By having the inlet nozzle to the vessel constructed at a tangent to the vessel shell.
- Causes the inlet stream to swirl around the inside of the separator under the influence of centrifugal force thus separating large volumes of liquid

(b)

  • A horizontal separator relies on properly shaped and positioned deflector devices
  • Baffle plate for lower GOR
  • Dish deflector would be more suitable for most applications.
70
Q

Draw a diagram showing an ‘Inlet Deflector’ on a Vertical Separator. (4)

A

Shows the:

  • Vessel Shape
  • Gas Stream
  • Liquid Accumulation
  • Tangentially positioned inlet nozzle
71
Q

Draw a diagram showing, on a Horizontal Separator the:

a) Baffle plate inlet deflector (6
(b) Dish deflector (6)

A

Shows the:

  • Vessel shape
  • Gas Stream
  • Liquid Accumulation
  • Nozzle
  • Flow of Gas
  • Correct position of each deflector
72
Q

How can the turbulence in the flowing gas stream be reduced inside a separator?

A
  • Straightening vanes
73
Q

Draw a diagram of ‘Straightening Vanes’ inside a separator (4)

A

Shows the:

  • Flow of turbulent gas
  • Flow of gas after reduced turbulence
  • Vanes themselves
  • Horizontal baffles with curved edge downwards
74
Q

Draw a diagram of a:

a) Two-Phase Vertical Separator (3
(b) Three-Phase Horizontal Separator (4)

A

Shows the:

  • Shape/Configuration of Vessel
  • Nozzles and what goes in/comes out of each nozzle
75
Q

What is a Horizontal Baffle? (3)

A
  • Flat plates located in the separator just above the liquid accumulation section.
  • Help to prevent waves in the liquid which might result in liquid re-entrainment in the gas stream.
  • May also provide the support for some of the other internal features of the separator such as the straightening vanes.
76
Q

What is:

(a) A Vortex Breaker
(b) Why is it used

A
  • Internal pipe with holes fitted to the liquid outlet nozzle inside the separator.
  • If vortex forms, it could drag gas into the outgoing liquid stream, thus defeating the purpose of the vessel.
77
Q

Draw a diagram of a ‘Vortex Breaker’ (3)

A

Shows:

  • Separator shape
  • Pipe with holes fitted to the liquid outlet nozzle
  • The flow of liquids towards it
78
Q

What is a Weir? (3)

A
  • Vertical baffles placed in the liquid accumulation section of the separator.
  • In a three-phase vessel they separate the oil accumulation area from the water accumulation part
  • May also be used to isolate a section of the oil accumulation part of the separator to provide a calm area for level control equipment to operate in.
79
Q

What are the six internal features of separators (6)

A
  • Inlet deflectors
  • Straightening Vanes
  • Mist Extractors
  • Horizontal Baffles
  • Vortex Breakers
  • Weirs
80
Q

Draw a detailed digram of a Three Phase Horizontal Separator (6)

A

Shows the:

  • Shape of the Vessel
  • Inlets & Outlets
  • 5 Required Internals
  • Oil, Water, Gas Separation
  • Flow of Oil, Gas & Water
  • Section Separated by Weirs
81
Q

Draw a detailed diagram of a two phase separator (

A

Shows the:

  • Shape of the Vessel
  • Inlets & Outlets
  • 5 Required Internals
  • Oil, Gas Separation
  • Flow of Oil, Gas & Water
  • Vortex Breaker as one of the 5 internals
82
Q

Name some other devices which can be found in separators apart from the 6 most common (2)

A
  • Water Jets

- Coalescing Plates

83
Q

What is a water jet inside a separator? (2)

A
  • Nozzles inside the separator with an external connection which a high pressure water supply can be connected to.
  • Accumulated solids such as sand can be stirred up with this high pressure jet prior to it draining from the separator
84
Q

What is a coalescing plate inside a separator? (2)

A
  • A type of mist extractor consisting of a series of parallel plates on which small droplets of liquid mist collect and join (Coalesce) to form larger ones.
  • Straightening Vanes also act as coalescers
85
Q

Give the names of 2 external components of a separator (2)

A
  • Pressure Gauge

- Sight Glass

86
Q

What is a Bourdon tube? (4)

A
  • Oval shaped tube bent into ‘C’ shape inside a pressure gauge
  • One end fixed and open to pressure to be measured, the other is sealed and free to move
  • Free end connected to linkages to a pointer which moves around a scale
  • Pressure applied, tube changes from oval to circular shape and thus straightens out
  • The tube when it tries to straighten moves the linkages which then moves the pointer
87
Q

Draw a detailed diagram of the internals of a pressure gauge (7)

A

Shows the:

  • Bourdon Tube
  • Pointer
  • Movement of Pointer
  • Scale
  • Linkages
  • Motion of Tube Straghtening
  • Linkages moving pointer
88
Q

What is:

a) A sight glass (2
(b) The function of a Sight Glass

A

(a) - A vertical glass or plastic tube connected to a vessel by piping
(b) - The liquid level in the tube will be the same as that in the vessel and thus showing the Operator the volume of liquid in the vessel

89
Q

What type of sight glass is used for higher pressure systems? (1)

A
  • A reflex sight glass
90
Q

What is a reflex sight glass? (

A
  • Special metal column with a recess machined in one side.
  • Tempered glass window fits over the recess and is held in place by ‘U’ bolts and a housing.
  • The glass window forms a pressure tight seal with the column.
  • The glass slab of the window is smooth on the outside but has triangular grooves cut in its inside face. This feature helps to give a clear indication of the interface between liquid and gas.
  • Light rays entering the glass above the liquid level strike the grooves which are in contact with gas - making the outside of the glass where there is no liquid look lighter. When the light rays enter the glass where the grooves are in contact with liquid, some of the light is absorbed thus making is easier to see where the liquid level is.
91
Q

Draw a diagram showing how light is reflected and absorbed in a reflex sight glass (3)

A

Shows:

  • Arrows showing light being deflected off the triangular grooves on the internal section of glass
  • Arrows showing light being absorbed into the triangular grooves on the internal section of glass
  • The triangular section of glass itself
92
Q

What are sight glasses fitted to a Separator using? (1)

A
  • Ball check valve
93
Q

How does a ball check valve operate? (

A
  • The ball within the valve remains stationary under normal operating conditions
  • It allows the normal flow of liquid or gas through the valve as the level moves up or down.
  • If the glass should break, there would be a rush of fluid through the valve, forcing the ball tightly against its seat, stopping the loss of fluid.

Oil & Gas Separation Book 1 (1 decks)

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