SPE 59028 GAS LIFT WITH NITROGEN INJECTION GENERATED IN SITU Miguel A. Lozada Aguilar, M.del Remedios Arredondo Monarrez, SPE, Pemex, PEP.
Copyright 2000, Society of Petroleum Engineers Inc.
Nitrogen injection generated in situ with membrane
This paper was prepared for presentation at the 2000 SPE International Petroleum Conference and Exhibition in Mexico held in Villahermosa, Mexico, 1–3 February 2000.
technology can be a feasible and profitable alternate
This paper was selected for presentation by an SPE Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Papers presented at SPE meetings are subject to publication review by Editorial Committees of the Society of Petroleum Engineers. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A., fax 01-972-952-9435.
source of gas lift as shown in this study. INTRODUCTION Bellota – Chinchorro is one of the seven producing areas in the Southern Region of Mexico. The current production of this field is 105 000 STB/D of oil and 150
ABSTRACT
MMSCF/D of gas produced from dolomite formations,
Gas lift is a feasible option as an artificial lift system in a
belonging to Jurassic and Cretaceous age.
depleted field. In the Bellota field there is no substructure
The objective of this study are the wells drilled in the
means to install any type of artificial lift system, therefore
Bellota field. Initial production of the bellota field started
the use of nitrogen as a gas lift source is necessary to
in 1982 reaching a peak production of 44 000 STB/D in
keep the Bellota wells producing.
After evaluating
1995. Current production is at 20 000 STB/D, mainly
different options we implemented a nitrogen generated
attributed to natural depletion. Year- to- date production
in situ project using the membrane technology.
from this field is estimated at 140 MMSTB, and it is
This paper analyzed the gas lift process design by using
expected to produce another 50 MMSTB from calculated
nodal analysis and optimum allocation of nitrogen in
total reserves.
each well.
Special emphasis and consideration was
given to this project from an economical, operational,
This field is divided in two different sections. The wells
technical and environmental points of view. It is olso
that will be discussed in this gas lift application belong to
compares
alternatives
the north section. These wells are currently depleted
including the traditional gas lift method using natural gas
below saturation pressure. It is presumed that a gas cap
as a source as well as the use of stored nitrogen from
has been already formed in the top of the reservoir,
storage trucks (Tanks).
Our evaluation of results
since GOR has been decreasing gradually. In addition,
obtained from the different options investigated in this
the reservoir pressure has decline drastically making it
study clearly indicates that this method is a good option
necessary
in this particular situation.
assistance to keep the wells producing.
this
option
with
differents
to provide some form of artificial lift
Those wells that have been converted to gas lift, are deep wells, which have so many disadvantages for any
2
MIGUEL A. LOZADA AGUILAR, M.DEL REMEDIOS ARREDONDO MONARREZ
SPE 59028
artificial lift system. Some electric submergible pumps
for its use in petroleum industry, they have evolved until
have been tested before with poor results, and then, a
now, having 60% of better permeability and 30% of
gas lift system by using nitrogen as source was installed,
better selectivity, besides, a significant reduction on
since no facilities were available to handle natural gas as
consumption energy has been achieved (Figure No.1).
a source for gas lift.
Equipment to be installed on location together with
In the very beginning, storage trucks were used to
membrane unit is the following: two air compressors
deliver nitrogen, but since this method was so
pack, an air – nitrogen compressor pack, flow meter unit
expensive, an in situ nitrogen generation project was
and additional equipment. A brief functional description
implemented, using the membrane technology. In this
for each component is given next to it.
way, it was possible to reduce 50% the total costs in
a).- Two air compressor pack.
three gas lift wells.
This pack has the function of comprise the air, which
In March 21 of 1998, gas lift started in wells Bellota 136,
comes from the atmosphere to be deliver into the next
138 and 158-D using nitrogen generated in situ with
compression stage. Air pressure is increased from
membrane technology as a source.
atmosphere
pressure
to
200
PSIG.
Those
two
compressors handle 5.6 MMSCF/D with 1100 HP of PRINCIPIA
OF
MEMBRANE
EQUIPMENT
FOR
NITROGEN GENERATION
potency. b).- Air – nitrogen compressor pack. This pack has the function to raise the air pressure that
Nitrogen generation through membrane equipment is
comes from the previous stage to be deliver into the
carried out by pumping an air current into membrane,
membrane unit at 400 PSIG, and it has also the function
which due to its especial material design let the air to be
to increase the pressure of nitrogen which comes from
separated into nitrogen and oxygen mainly. This is
membrane unit in two stages, one of them from 400
achieved basically because the oxygen flows faster than
PSIG to 900 PSIG and the other one from 900 PSIG to
nitrogen through it, being expulsed to the atmosphere,
2000 PSIG, to be deliver into the gas line for gas lift
as long as the nitrogen is absorbed into the membrane
purpose.
to be delivered to the next compression stage. Before
c).- Membrane unit.
the separation process, air composition is 78% of
This pack has the function of separate 5.6 MMSCF/D of
nitrogen, 21% of oxygen and 1% of rear gases;
air to obtain 2 MMSCF/D of nitrogen with 95% to 98% of
Neverdeless just after the separation process, gas
quality. This unit is built up of 36 cylinders, the ones has
mixture will be expulsed into the atmosphere with 40% of
the membrane element inside of them.
oxygen content, and the one that has been absorbed
d).- Flow meter unit.
into the membrane has from 95% to 98% of nitrogen
This unit has the function of measure the amount of
content.
nitrogen that is deliver into the gas line for gas lift.
Membranes are built up from a polymeric thin cap, which
e).- Additional equipment.
has special physical properties that make the separation
This equipment helps in order to let the main equipment
efficiency to have a variation base on: pressure,
accomplish its function. Some of the most important
temperature,
devices are: filter system, coolers, start on compressor,
permeability,
membrane
aria
and
selectivity. Since 1987, when they have been reported
energy plant and fuel storage.
SPE 59028
GAS LIFT WITH NITROGEN INJECTION GENERATED IN SITU
GAS LIFT NETWORK AND WELLS CONVERSION
3
reservoir pressure was low enough, end in the other hand, wells productivity index were high enough to
Those three wells, which will be converted from natural
reach dynamic conditions with only one gas injection
flow to gas lift, were drilled in the same location, thereby
point. Thanks to those conditions mentioned before,
gas lift line construction was cheap and quickly, as
it was possible to shoot the tubing by using puncher
distance from each well was no longer tan 500 FT. It
charges, rather than use workover rigs to pullout
was also necessary to install flow meter and regulation
tubing string and put it back with gas lift valves.
valves for each well. The nitrogen generation equipment
•
Due basically, that there wasn’t any available
was installed in the same location (figure No. 2).
surface control valve for high pressure, it was
In the other hand, in order to make the wells conversion
necessary to install chocks in order to allocate the
cheaper, it was concluded that no workover rigs should
optima amount of gas for each well; thereby it was
be necessary, as operation conditions for each well
necessary to design the right diameter for each one
permitted start the wells on production just by injecting
of them, using Bernulli equation.
gas in one point, that means not to use any upper injection valve. In this way a puncher charge was shot,
ECONOMICAL ANALYSIS
taking in account the equivalent diameter for an specific drop drown from casing pressure to tubing pressure.
a) Assumptions for different scenarios
This was achieved basically, because a high pressure was available in the gas line (2000 PSIG).
In order to asses the feasibility of this project, three scenarios were made in a period of time of five years:
EQUIPMENT DESIGN
1) build up a gas lift network in order to use natural gas as a source, installing compressors in the location to
In order to design the equipment dimensions, it was
increase gas pressure to that one which is
necessary to use three different software: nodal
necessary for each well.
analysis, gas lift design and equal slope method to
2) Inject nitrogen as a gas lift source by using storage trucks.
allocate the amount of gas for each well. Based on the results getting from the equal slope
3) Inject nitrogen as a gas lift source, by generating it with membrane technology, with leasing option.
method and gas lift design software, it was concluded that 2 MMSCF/D of N2 will be necessary to be injected
4) Inject nitrogen as a gas lift source, by generating it
in those three wells, and 1600 PSIG will be required on
with membrane technology, with purchase option.
surface pressure; thereby, according to manufacture
Those assumptions used for this analysis are refereed to
specifications, one equipment for 2 MMSCF/D and 2000
July, 1998 (table No.1).
PSIG was selected for this purpose (figure 3 and 4). •
Gas lift design criteria was to find out the deepest
The economical premises are defined as following:
injection point, thereby, with static conditions was
•
Oil price: It is refereed to July 1998.
possible to start the wells on production with 2000
•
Production race: For comparison purpose, according
PSIG of surface pressure. Injection points were
to allocation of gas for each well, getting from equal
located just above of packers, due basically, that
slope method, it was possible to increase 3725
4
MIGUEL A. LOZADA AGUILAR, M.DEL REMEDIOS ARREDONDO MONARREZ
⇒ Operational cost for membrane purchase is alike
STB/D by injecting 2 MMSCF/D of nitrogen, and •
4125 STB/D by injecting 2 MMSCF/D of natural gas.
to that of comprising costs in gas lift network
Discount rate: It was used that one from Pemex
option, which is equal to 184.2 USD/STB. •
projects, which is 10%. •
SPE 59028
Field depletion: it was taken that one which represents field performance.
Initial investment: Initial investment was considered in this way: ⇒ For gas lift network option, it was considered to built up 13 miles of gas lift line of 6 in. and 3 in.. ⇒ For
b) Interpretation of economical indicators. Some of the indicators shown here are quite far good for
was
any petroleum project, basically because the high
considered to invest on nitrogen line from
production rate to be expected (table 2). Some
membrane equipment to each well.
comments are summarized as following:
⇒ For
membranes
membrane
leasing
purchase
option,
option,
it
it
was
-
considered to invest on nitrogen line from
all of the four option are excellent, as it is unlikely to
membrane equipment to each well.
reach the same value for discount rate in any bank.
⇒ For storage trucks option for nitrogen injection,
-
Regarding to investment efficiency all the values are quite high, so it means that all the four options are
there wasn’t any investment. •
Giving the risk approach form internal rate of return
profitable.
Operational costs: In order to obtain those costs, it was considered the production increase for each
-
cash flow will be available since the early stages.
option, as well as the total operational costs for each option, getting, in this way the cost for each
Pay back period is very short for every option, so
-
Net present value could be the indicator to be
produced barrel.
considered for making a good decision, since option
⇒ Operational costs for that to build up gas lift
1 and 4 represent the highest values, and they also
network, is an addition of: differential cost
represent an important difference between the
between to buy 2 MMSCF/D of natural gas and
others options.
to sell the same amount of sour gas; leasing of
-
As net present value for option 1 and 4 are quite
compressors to increase gas pressure from gas
similar, best option should be that which has some
line pressure to that which is required to inject in
else benefits; whether environmental, technical or
to the well; and comprising costs to inject sour
operational aspects concerns.
gas
toward
sweeter
station;
which
yield
657.8+48+184.2 = 1249 USD/D. ⇒ Operational cost for that to leasing storage
TECHNICAL, OPERATIONAL AND ENVIRONMENTAL ISSUES
trucks for injecting 2 MMSCF/D of nitrogen is equal to 18,650 USD/D.
•
Technical comparisons:
⇒ Operational cost for leasing membranes to
⇒ According to equal slope method, figure 6 shows
generate 2 MMSCF/D of nitrogen is equal to 11,
how injecting the same amount of gas, whether
275 USD/D
nitrogen or gas at the same depth, it is possible to obtain 400 STB/D more injecting natural gas than nitrogen. The explanation of this is because nitrogen
SPE 59028
GAS LIFT WITH NITROGEN INJECTION GENERATED IN SITU
5
is heavier than natural gas, thereby getting a higher
particular case, anyway, if it was true, it is possible
gradient all along the tubing; therefore, the higher
to use chemical products to avoid this phenomena.
flowing bottom hole pressure, the lower liquid rate based on productivity index ecuation. For this
CONCLUSIONS
specific case a 10% production rate increase could be achieved (figure 5).
•
⇒ In the other hand, shows how the higher nitrogen
it is an unfinished and available source in the atmosphere.
weigth in the annulus, the surface requirements pressure is lower from that with natural gas injection,
•
therefore less potency is required. For this particular case it is expecting to reduce 10% of total costs due
Nitrogen injection as a gas lift source is feasible, as
Nitrogen injection as a gas lift source has a similar profitability as that with natural gas injection.
•
to potency reduction (figure 6).
At this moment with the current conditions on the leasing contract, it is more profitable for PEMEX to buy and install its own plant.
•
Operational and environmental comparisons:
•
⇒ Nitrogen is an unfinished source available in the atmosphere, thereby its use doesn’t have to deal
nitrogen rather than natural gas. •
with hydrocarbon exploitation.
of gas line mileage is achieved. •
supply. ⇒ As nitrogen is an inert gas, safety problems are
Reduction of 10% of production rate is expected as a result of inject nitrogen rather than natural gas.
•
reduced enormously. ⇒ Petrochemical plants can only handle 3% of impurity
There is a significant reduction on risks, as nitrogen is an inert gas, besides of that a significant reduction
⇒ Nitrogen plants can be installed in the most convenient place, as they don’t need natural gas
It is possible to save 10% of potency injecting
Further investigation will be needed to evaluate the nitrogen impurities on corrosion problems.
•
The amount of nitrogen used for gas lift is
as a total amount of gas, thereby nitrogen uses as a
constrained
gas lift source is constrained by the total processed
petrochemical plant, which shouldn’t be no higher
gas. For this particular case the impurity percentage
than 3%.
by
the
total
gas
handled
in
was no higher than 0.5%. ⇒ As it is known nitrogen generated with membrane
REFERENCES
technology has from 5 to 2% of impurities, mainly oxygen. Somewhere during membrane operation,
-
there were some corrosion problems in the process facilities, but unfortunately by that time it was
and Associates Limited. -
necessary to stop membrane operation for budget reasons, without giving the chance to evaluate
concern as this technology is a good option for this
The technology of artificial lift methods – volume 2ª kermit Brown.
-
oxygen impact on this problem, specially because sour gas is produced in those wells. So this is a big
Nodal analysis software, “PIPESIM”, Baker Jardine
Gas lift optimitation and design software – GLOPCealc.
-
Temas selectos sobre bombeo neumático continuo. Colegio de Ingenieros Petroleros de México.
6
-
MIGUEL A. LOZADA AGUILAR, M.DEL REMEDIOS ARREDONDO MONARREZ
Optimización de la distribución de gas en la red de bombeo
neumático
del
campo
Cunduacán
–
Oxiacaque, AIPM, Miguel Angel Lozada Aguilar y Maria del Remedios Arredondo M. -
Technical and operational manual of membrane plants.
SPE 59028
SPE 59028
GAS LIFT WITH NITROGEN INJECTION GENERATED IN SITU
MEMBRANE DIAGRAM
NITROGEN
WASTE OXYGEN VENT
FIBER
AIR FEED
Figure 1
FIELD MEMBRANE DIAGRAM
FLOW LINE
PROCESS FACILITIES BELLOTA 138 WELL
MEMBRANE EQUIPMENT
COMPRESSOR COMPRESSOR COMPRESSOR
NITROGEN LINE
Figure 2
MEM BRA NE
BELLOTA 158-D WELL
GAS METER
BELLOTA 136 WELL
7
8
MIGUEL A. LOZADA AGUILAR, M.DEL REMEDIOS ARREDONDO MONARREZ
SPE 59028
WELL PERFORMANCE WITH NITROGEN INJECTION
1800
Iny.P.=1437 PSIG Iny. P.=1380 PSIG
1400 1200 Iny.P.=1671PSIG
1000
BELLOTA 136 800 BELLOTA 138
600
BELLOTA 158-D
400 200 0
0
0.2
0.4
0.6
1
0.8
NITROGEN INJECTION RATE (MMSCF/D )
Figure 3
EQUAL SLOPE METHOD CHARACATERISTIC CURVE FOR THREE WELLS WITH NITROGEN INJECTION 4500 4100
4000
Liquid rate(STB/D)
LIQUID RATE (STB/D)
1600
3500 3000 2500 2000 1500 1000 500 0 0
0.25
0.5
0.75
1
1.25
1.5
1.75
Nitrogen injection rate (MMSCF/D)
Figure 4
2
2.25
2.5
SPE 59028
GAS LIFT WITH NITROGEN INJECTION GENERATED IN SITU
9
EQUAL SLOPE METHOD
LIQUID RATE (STB/D)
NATURAL GAS VS. NITROGEN INJECTION COMPARISON 5000 4500
NATURAL GAS
4500
NITROGEN
4100
4000 3500 3000 2500 2000 1500 1000 500 0 0
0.25
0.5
0.75
1
1.25
1.5
1.75
2
2.25
2.5
GAS INJECTION RATE (MMSCF/D)
Figure 5
SURFACE REQUIREMENTS PRESSURE
NATURAL GAS VS. NITROGEN COMPARISON 1500 2000 2500 D e p t h( m )
3000 3500 4000 4500 5000 NITROGEN
NATURAL GAS
5500 700
950
1200
1450
Pressure (Psi)
Figure 6
1700
1950
10
MIGUEL A. LOZADA AGUILAR, M.DEL REMEDIOS ARREDONDO MONARREZ
SPE 59028
BASIS FOR ECONOMICAL ANALYSIS
OPTION
1
2
3
4
CONCEPT
GAS LIFT NETWORK
PRICE PER BARREL (USD)
FIELD OPERATIONAL PRODUCTION DISCOUNT CAPITAL INCREASE RATE (%) INVESTMENT COSTS (USD/STB) DEPLETI ON (%) (STB/D) (USD)
10
4125
10
NITROGEN INJ. WITH STORAGE TRUCKS
10
3725
10
MEMBRANE LEASING
10
3725
10
3725
10
1’253,000
0.3028
10
5.0006
10
150,000
3.027
10
1’710,960
0.049
10
0
MEMBRANE PURCHASE 10
Table 1
PROFITABILITY INDICATORS OPTION
1
CONCEPT
GAS LIFT NETWORK
NET PRESENT VALUE (DLS)
INVESTMENT EFFICIENCY INTERNAL PROFITABILIRATE OF EFFICIENCY R A T E ( % ) TY RATE RETURN (%) (%)
PAY OUT TIME (YEARS)
44’380,058
36
82
1155
900
0.0865
21’221,890
10,000
347
678’996,700
539’353,083
1.47 x 10
2
NITROGEN INJECTION WITH STORAGES TRUCKS
3
MEMBRANE LEASING
29,481,607
198
116
6310
4995
0. 0158
MEMBRANE PURCHASE
40’575,592
25
74
780
0.03
0.1281
4
-7
Table 2
