6 - nitrogen pumping

Italfluid Egypt ConfidentialNitrogen Pumping

INTRODUCTION TONITROGENPUMPING


Overview

• Nitrogen characteristics

• Nitrogen pumping unit - Operating instructions and main components

- Operations (Tanks filling, Assembly and Tests, Cool-down, Pumping)

• Main applications in oilfield:- Pressurizations, Replacement/Purging, Gas lift


Nitrogen characteristicsNitrogen:Nitrogen: odourless, colourless, and inert gas, present in nature at elementary

state; indeed it constitutes 78% of the earth atmosphere in wich molecule N2 can be found.

Chemical symbol NAtomic number 7Atomic weight 14,007Fusion temperature -210° CBoilling temperature -196° CGas density 1,251 Kg/m3

Liquid density 808,2 Kg/m3

Critical temperature 126,1°K (-147,1°C)Critical pressure 34,6 bar


• Industrially, nitrogen is prepared through fractioned distillation of liquid air

Nitrogen characteristics

• On the market, nitrogen can be found in:– Gaseous state, stored inside gas-cylinders with pressure of 150-200 bar– Liquid state, stored in boiling state, inside special thermal insulated tanks at

-196°C with pressure of 3 bar


Nitrogen pumping unit

Nitrogen PumpNitrogen Pump

Nitrogen TankNitrogen Tank

Pipes and componentsPipes and components

Operating instructions and main component


Nitrogen pumping unitOperating instructions and main component

Cryogenic unit which pumps liquid nitrogen at very low temperature (-196°C) and pressures up to 10000 psi, and coverts it into a gas (max 70°C) by means of vaporizer

Nitrogen pumpNitrogen pump

Operating instructions:

Main components:

• Engine / Transmission

• Return and suction manifold section - Liquid nitrogen suction line system - Tank’s return line system

• Triplex pump section - Cold ends - Warm end

• Intake manifold section (high pressure line system)

- Liquid nitrogen high pressure line system - Vaporizer - Gaseous nitrogen high pressure line system

• Coolant circuit (water brake)




Engine / TransmissionEngine / Transmission• It supplies the necessary power for the movement of the triplex pump, and to carry out additional functions

• It is directly connected to the waterbrake and different hydraulic pumps

• Hydraulic pumps supply power to the hydraulic engines of the circuits of the triplex pump, centrifugal pump, coolant and lubrication

• It is equipped with air start-up

• The compressor, activated by diesel engine, keeps the pressure of the air circuit around 8 bar

Main components




Return and suction manifold sectionReturn and suction manifold section(Low pressure line system)(Low pressure line system)

• A line is present at the outlet side of the centrifugal pump (centrifugal pump's recirculation) which by-passes the triplex pump for the recirculation of the liquid nitrogen inside the tank during the cool-down phase

• It is connected to the intake line of the nitrogen tank through cryogenic flexible pipes

Liquid nitrogen suction line system:

• It supplies liquid nitrogen to the triplex pump with a pressure of 40-100 psi

• A centrifugal pump (boost pump) is installed on the line, in order to bring the liquid nitrogen from the pressure outgoing from the tank (generally 10-20 psi) to that entering the triplex pump (40-100 psi)

• Nitrogen pumps are usually equipped with a by-pass line of the boost pump

Main components




Return and suction manifold sectionReturn and suction manifold section(Low pressure line system)(Low pressure line system)

• It is connected to the nitrogen tank’s return line through cryogenic flexible pipes

Tank’s return line system:

• It allows the return of non-pumped liquid nitrogen inside the tank

• A quick cool-down line is installed on the line to fill the pump

• A line is installed on the outlet of triplex pump for the recirculation of liquid nitrogen during cool-down phase

Main components




Triplex pump sectionTriplex pump section

Those are pistons that suck liquid nitrogen with low pressure and discharge liquid

nitrogen with high pressure. The cold ends are connected and guided by the warm end

Cold ends:

• It is a 3-piston pump, whose task is to increase the pressure of liquid nitrogen until a maximum operating pressure of 10000 psi

• It is enabled through the hydraulic transmission: the diesel engine enables a pump with variable displacement which convoys the oil under pressure to the engine with fixed displacement

• The speed of the triplex pump (and therefore the nitrogen output) is regulated by changing the displacement of the pump with variable displacement

It is made up by the following parts:

Warm ends:

It is the section that guides the cold end

Main components




Intake manifold sectionIntake manifold section(High pressure line system)(High pressure line system)

It is constituted by lines outgoing from the triplex pump’s cold ends (intake lines)

Liquid nitrogen high pressure line systemIt is the line section that connects the cold ends to the vaporizer; the nitrogen that flows inside is pressurized but still at liquid state

Main components

It is made up by the following parts:

Gaseous nitrogen high pressure line system

Vaporizer

It is that line section outgoing from the vaporizer; the nitrogen that flows is pressurized and at gaseous state, ready to be pumped; a plug valve (hydraulically actuated) is installed at the end of this line

It is a particular heat exchanger, constituted by a cylindrical chamber filled up by a pipe bundle inside of which liquid nitrogen flows. The coolant fills the chamber and flows around the coiled tubes at a pressure of 80-150 psi. When the liquid nitrogen (-196°C) circulates through the coil, it changes into gaseous state.




Intake manifold sectionIntake manifold section(High pressure line system)(High pressure line system)

Main components

• The temperature of gaseous nitrogen is controlled by the coolant's output and temperature. The gas temperature is kept between 60 and 70°F (15-20°C). The temperature of the coolant’s circuit is controlled manually to keep the vaporizer’s temperature constant between 100 and 120°F (38-49°C).

• The output of the outgoing gas is measured in scfm (standard cubic feet per minute) or in Nm3/min (normal cubic metres per minute)

• A line is present at the cold ends’ outlet which allows the liquid nitrogen, by opening a proper valve (tempering valvetempering valve), to by-pass the vaporizer and convoy liquid nitrogen inside the line (to use only in case of extreme need to rapidly cool the out flowing nitrogen)

• Another line, always mounted at the outlet of the cool ends, allows to re-circulate the liquid nitrogen inside the tanks by opening a specific valve (prime valveprime valve) during the cool-down operation




Coolant circuitCoolant circuit

Main components

It is a water-glycol recirculation system that supplies (through thermal exchange with the vaporizer) the heat needed to cause the evaporation of the liquid nitrogen. The circulation of fluid inside the circuit takes place through a water pump enabled by a hydraulic engine.

The coolant (water-glycol) draws heat from the following sources:

WaterbrakeHydraulic circuit

Lubrication circuits of

triplex pump, etc.

Engine’s cooling circuitIt is a hydraulic brake assembled on an axis of the engine’s power take-off.By sending liquid to the waterbrake, the engine goes under load, and in this way, the engine’s power is converted in heat.

The coolant, flows through the coolant/hydraulic oil heat exchanger, from which it draws heat. In a cold environment, a reverse thermal exchange is possible: the coolant, heated up by the waterbrake, transfers heat to the hydraulic oil; this allows a quicker heating up of the unit.

The exchange between the two circuits takes place through a heat exchanger.Some thermostatic valves regulate the engine’s operating temperature so as to keep it constant within a range of 60-70°C.



1) Registratore a carta2) Temperatura olio triplex3) Pressione olio triplex4) Portata azoto5) Pressione idraulica pompa cilindrata variabile6) Comando velocità pompa triplex7) Pressione sovralim. Pompa cilindrata variabile8) Giri pompa triplex9) Arresto di emergenza motore10) Arresto motore11) Giri motore12) Accensione motore13) Pressione olio motore14) Acceleratore motore15) Pressione aria16) Temperatura acqua motore17) Temperatura coolant18) Pressione motore centrifuga19) Controllo velocità centrifuga20) Pump saver21) Pressione mandata centrifuga22) Temperatura azoto in uscita23) Pressione azoto in uscita24) Pulsante di attivazione valvola pneumatica25) Selettore posizione valvola pneumatica26) Temperatura freno idraulico

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Control panelControl panel




Nitrogen pumping linesNitrogen pumping lines1 - DYNAMOMETER’S PRESSURE VALVE:It regulates the pressure of the liquid flowing to the water-brake

2 - VAPORIZER’S BY-PASS VALVE (TEMPERING VALVE):It opens the vaporizer’s by-pass valve (N.B.: this manoeuvre can considerably and dangerously cool down the outgoing nitrogen’s temperature).

3 - HIGH PRESSURE NITROGEN RECIRCULATION VALVE (PRIME VALVE): It opens the recirculation line, from the cold ends' outlets to the tank's return line

5 - NITROGEN TANK RETURN VALVE

8 - QUICK COOL-DOWN VALVE

10 - BOOST PUMP BY-PASS VALVE

6 - TRIPLEX BY-PASS VALVE

7 - CENTRIFUGAL VALVE

9 - NITROGEN INTAKE VALVE

13 - PLUG VALVE HYDRAULIC ACTUATED

11 - BOOST PUMP

12 - VAPORIZER

4 - NITROGEN RECIRCULATION VALVE

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Nitrogen tankNitrogen tank


• They are equipped with instruments (cryogenic valves, gauges) and with a very sturdy frame which has a protection role during transports and loading/unloading operations.

• The tanks are used to store and transport nitrogen, which is conveniently kept in refrigerated liquid state (at -196°C)

• The generally used tanks have a capacity of about 8000 liters (about 2000 gal)

• They are made up by an internal stainless steel shell, which contains the liquid. The shell is covered by an interspace which is filled with insulating material (perlite) in which vacuum is created. The external shell is carbon steel made



Nitrogen tankNitrogen tank(Components)(Components)


1 – LEVEL INDICATOR:It indicates the level of the liquid nitrogen inside the tank2 – PRESSURE GAUGE:It indicates the tank’s internal pressure3 – GASEOUS PHASE VALVE:It opens the inlet of the differential-meter connected to the gaseous phase

5 – EQUALIZER VALVE:It connects the “liquid phase valve and the gaseous phase valve

8 – SAFETY VALVE 3 barSafety valves that open up when the pressure reaches 3-6 bar

10 – RELIEF EXCLUSION VALVEIt stops the exhaust of pressure through a relief valve

6 – VACUUM BREAK DISC:Disc located on the tank’s exterior surface and kept in position by the vacuum inside the interspace of the same tank7 – VACUUM PUMP’S FITTING

9 – TRANSPORT RELIEF VALVEValve that must be always kept operating during transport or parking while it must be closed during operations; it opens up when the internal pressure reaches 1.7 bar

13 – CHECK VALVE

11 – BLEED-OFF VALVEvalve used to manually exhaust the internal pressure12 – OVER FLOW VALVEIt must always be kept open during fill up operations. it indicates the filling up level of about 80% of tank when the liquid overflows

4 – LIQUID PHASE VALVE:It opens the inlet of the differential-meter connected to the liquid phase

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Nitrogen tankNitrogen tank(Components)(Components)


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8816 – RETURN SHUT-OFF VALVE:Valve on the tank’s return line that must be kept open during operations

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17 – INTAKE SHUT-OFF VALVE:Valve on the pump’s intake line that must be kept open during operations

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14 – FILTER

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15 – INTAKE VALVE

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18 – SAFETY VALVE 10 bar:Valves located on the lines, which open up when the pressure reaches 10 bar.

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19 – REAR FILLING VALVE:Valve for the shut-off of the rear tank’s filling

line

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20 – DRAINING VALVE:Valve that allows to exhaust the line’s pressure prior to remove the flexiblegrinding wheel.

202021 – PRESSURIZATION VALVE:Valve that, once open, convoys liquid nitrogen to the vaporizer

212122 – VAPORIZER

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Pipes and componentsPipes and components• Pumping line’s components (pup joints, valves, tee, elbows, cross-over, etc.) must be manufactured for 10000 psi w.p., and they must have “weco fig. 1502” connections

• Pumping line’s connections must be welded or integrated (threaded connections don’t admit)

The following components are always required in pumping lines

N° 2 Plug valves:1 – Immediately after the pump2 – At the end of line

• Low pressure flexible pipes (suction and return lines) must be cryogenic and equipped with CGA 1”1/2 connections

N° 1 Check valve N° 1 Bleed-off valve

Pipes and ComponentsPipes and Components


Nitrogen pumping unitOperations

• Tanks filling:Tanks filling: Filling operation is different depending on tank’s temperature (tank is “cold” if it contains liquid nitrogen, instead tank is “hot” if it is empty)

• Assembly and test:Assembly and test: Pressure test must be performed with fresh water. In case of absence of triplex liquid pump, fill the line with fresh water and pressurize with nitrogen

• Cool-down:Cool-down: This operation is necessary to cool all pump’s components in which liquid nitrogen will flow, and to favour the filling of boost-pump’s intake lines

• Pumping:Pumping: It is forbidden to exceed operative parameters


Main applications in oilfieldThe main operations that are carried out with a nitrogen pumping unit are:

• PressurizationPressurization

• Replacement / PurgingReplacement / Purging

• Gas liftGas liftNitrogen is pumped in the well through CT or production tubing, to make easier the spontaneous well production, lightening the liquid column in the well

Pressurizations with nitrogen can be requested for different operations, such as stuffing due to change of lever or shots, fixing of packers, rebalancing of pressures above and below a valve prior to anti-creep levelling it, etc... Prior to start pumping, make sure that pressure is present inside the well and as a consequence, apply the same pressure on the treatment line prior to open the valves

Nitrogen can be pumped in pipelines and tanks that contained corrosive or inflammable liquids, to restore inert atmosphere

• Acidizing / FracturingAcidizing / FracturingNitrogen is pumped in the well to squeeze acid. After the reaction between acid and formation, nitrogen makes easier the reaction’s fill removal


Pressurizations / ReplacementPressurizations / Replacement

Main applications in oilfieldComputation criterion

1. Identify the volume to pressurize or relocate2. Once the final pressurization/replacement

pressure is known (at the head or bottom of the well), calculate the average end replacement/pressurization pressure: (BHP+WHP)/2.

The bottom hole pressure, once the Well head pressure (or pumping) is known, can be calculated by using specific sheets of the well site manual (“Pressure at a given depth for a nitrogen column”), intersecting the well head pressure column with the depth line (TVD).

N.B. if the bottom hole pressure is known, by using the same tables, it is possible to calculate the well head /pumping pressure




3. Calculate the average temperature: (BHT+WHT)/2. In case that the temperature at the bottom of the well is unknown, calculate it by using an average geo-thermal gradient equal to 0.03°C per depth metre (TVD)

4. By using the specific tables of the Wellsite manual (“M³ of nitrogen per M³ of space” or “scf of nitrogen per barrel of space” according to the units of measurement used), intersecting the just calculated column of the average temperature with the average pressure line, it is possible to obtain the volume factor

5. Calculate the quantity of nitrogen required for the specific work, multiplying the volume factor by the volume calculated in point 1

6. Once the pumping flowrate has been defined, calculate the time need for pressurization, by dividing the quantity of nitrogen calculated in point 5 by the same flowrate




N.B.:N.B.: To calculate the nitrogen needed for the operation, never forget to consider the quantity of nitrogen lost during the pump's cool down (approximately 10000 scf = 283 Nm3).

IMPORTANT:IMPORTANT: In case the string or pipe has already an initial pressure, calculate the relative quantity of nitrogen (using the above procedure) and subtract it to the one calculated in point 5


EXEMPLESExemple 1: Pressurization of a surface pipe

The following example can be applied for horizontal (or characterized by small inclination differences) pipeline; it is the case for example of coiled tubing on reels to displace and possibly pressurize after the hydraulic testing phase and prior to descend into the well

Let’s consider a horizontal pipe closed at the two edges, whose characteristics are:

Internal diameter = Internal diameter = 8”8”

Length = Length = 20 km20 km

Temperature = Temperature = 20° C20° C

Questions:Questions:

1. How much nitrogen is required to pressurize the pipe up to 1750 psi?2. How much time do I need to perform the operation, assuming to pump a constant output of 1000 scf/min?



Answers:Answers:

1. The volume available is: 20000 (m) x 3.28084 (conversion factor m/ft) = 65617 ft (length in feet of the pipe) 8 (in) x 0.08333 (conversion factor in/ft) = 0.66664 ft (diameter of pipe)

(0.66664 / 2)² x 3.1416 = 0.34904 ft² (area of pipe’s section) 0.34904 (ft2) x 65617 (ft) = 22903 ft³ (pipe’s volume) 22903 (ft³) x 0,17811 (conversion factor ft3/bbl) = 4079.3 bbl

Considering that the pipe is horizontal, the average end replacement/pressurization pressure is exactly 1750 psi. After calculating the volume in barrels, let’s look at the table of the Wellsite Manual that indicates the volume factor in scf per barrel of space. In our case, at the intersection of line 1750 psi with the column indicated with 20°C, we find the value: 670 670 x 4079.3 (bbl) = 2733131 scf2733131 scf (remember to consider the 10000 scf needed for the pump’s cool down)

2. The time needed to perform the operation will be: 2733131 (scf) / 1000 (scf/min) = 2733 min (≈ 45 hours and 33 minutes)2733 min (≈ 45 hours and 33 minutes)



Let’s consider the same pipe of the previous example, but let’s assume that is initially pressurized with nitrogen at 1000 psi and that there are 1000 bbl of water at its interior.

Questions:Questions:

1. How much nitrogen is required to pressurize the pipe up at 1750 psi?2. How much time do I need to perform the operation, assuming to pump a capacity of

2000scf/min for the first 4 hours and 1000 scf/min for the remaining time?



Answers:Answers:1. The available volume is given by the pipe's capacity minus the volume occupied by the water (since it is a fluid that cannot be compressed): 4079.3 – 1000 = 3079.3 bbl The pipe is horizontal, and the average end replacement/pressurization pressure is exactly 1750 psi. After calculating the volume in barrels, let’s look at the table of the Wellsite Manual that indicates the volume factor in scf per barrel of space. In our case, at the intersection of line 1750 psi with the column indicated with 20°C, we find the value: 670 => 670 x 3079.3 = 2063131 scf This volume is the one needed to pressurize the pipe up to 1750 psi, in case the initial pressure

inside it, is null; since the initial pressure is actually equal to 1000 psi, the nitrogen volume already present inside the pipe must be subtracted:

391 x 3079.3 = 1204006 scf The volume of nitrogen needed is therefore: 2063131 – 1204006 = 859125 scf859125 scf

2. The time needed to perform the operation is: 2000 (scf/min) x 240 (min) = 480000 scf (nitrogen volume pumped in the first 4 hours = 240 minutes) 859125 - 480000 = 379125 scf (nitrogen volume left to pump) 379125 (scf) / 1000 (scf/min) = 379 min (6 hours and 19 min) (time needed to pump the remaining volume of nitrogen at the capacity of 1000 scf/min) The total pumping time will be therefore: 240 (min) + 379 (min) = 619 min (10 hours and 19 619 min (10 hours and 19

minutes)minutes)


EXEMPLESExemple 3: Replacement of the fluid being formed

The following example concerns the replacement of a column of liquid being formed, using nitrogen; this situation can occur in case of treatment in matrix (e.g. acidification) with bull-heading pumping or anyhow to re-start a well, by filling the nitrogen column to decrease hydrostatics.

Let’s consider a vertical well, constituted as shown in the figure

Tubing = Tubing = 3”1/23”1/2 , , 10.2 lb/ft10.2 lb/ft Casing = Casing = 7” 7” , , 29 lb/ft29 lb/ft

Tubing shoe = Tubing shoe = 2500 m2500 m Packer = Packer = 2500 m2500 m

Top of perforations = Top of perforations = 2600 m2600 m BHP = BHP = 3200 psi at 2600 m3200 psi at 2600 m

WHT = WHT = 20° C20° C BHT = BHT = 140° C140° C

Question:Question:

How much nitrogen is required to relocate the fluid contained in the wellthrough shots?


EXEMPLESExemple 3: Replacement of the fluid being formed

Answer:Answer:Since up to 2600 metres must be relocated (top of shots), the volume to consider is given by the sum of the

tubing’s capacity plus the casing volume from the packer to the top of perforations:* 8.29 x 2500 x 3.28084 / 1000 = 67.99 bbl (tubing’s internal volume)* 37.148 x (2600-2500) x 3.28084 / 1000 = 12.19 bbl (casing's internal volume)

The volume to relocate is therefore: 67.99 + 12.19 = 80.18 bbl

Once the pressure at the bottom of the well has been calculated (3200 psi), using the tables of the Wellsite Manual we find the value of the well head pressure which is about 2450 psi. Therefore:

* (3200 + 2450) / 2 = 2825 psi (average pressure)The surface temperature is 27°C, while the bottom temperature is of 133°C. From which:* (140 + 20) \ 2 = 80°C (average temperature)

Once the average temperature and pressure values have been calculated, the relative volume factoris calculated using the table of the wellsite manual, which is 814

By multiplying the volume factor calculated by the total volume to relocate:814 x 80.18 = 65267 scf65267 scf

Add 10000 scf for cool-down


QUESTIONS ?QUESTIONS ?

6 - nitrogen pumping

Documents

unitoperating instructions

ccritical pressure

main componentreturn

main applications

main componentcryogenic

bar liquid state

suction manifold sectionreturn

gaseous state