OTC-26756-MS
A. Jothy, and H. Thiruthonder, NGLTech Sdn. Bhd
Copyright 2016, Offshore Technology Conference
This paper was prepared for presentation at the Offshore Technology Conference Asia held in Kuala Lumpur, Malaysia, 22–25 March 2016.
This paper was selected for presentation by an OTC program committee following review of information contained in an abstract submitted by the author(s). Contents
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Abstract
The LP-ERS process is suitable for implementation on marginal and stranded crude and associated gas
producing fields where associated gas is used as fuel and/or flared. Whilst flaring of associated gas is not
recommended, in many instances this is unavoidable due to various techno-commercial considerations.
Crude and associated gas production facilities typically receive production fluids from wells at relatively
low pressures, ranging from 5 barg to 20 barg. At these pressures, there would be significant quantities
of C4⫹ components that can be extracted as condensates and stabilized with the crude. However,
conventional enhanced recovery systems currently available are bulky and costly, resulting in these
enhanced recovery systems not being implemented for marginal and stranded developments.
The LP-ERS is a proprietary process, particularly developed to address the abovementioned issues, to
extract condensates (C4⫹ components) from low pressure associated gas in a cost effective manner,
without the need for bulky compression, refrigeration and dehydration facilities that are typically required
for conventional enhanced recovery systems. Apart from increasing revenue due to increased volume of
stabilized crude production which is generally in the range of 5% to 25% (depending on wellstream fluid
GOR, etc.), the implementation of the system will also significantly reduce greenhouse gas emissions (by
approximately 20%) and improve the quality of the bulk stabilized crude oil produced.
Introduction and Background
The collapse in oil prices has resulted in the death knell for peak oil production. This is resulting in
increased pressure for marginal field oil producers to drive down their cost of production per barrel.
For marginal and stranded crude and associated gas producing facilities, whilst the crude is the main
source of revenue, associated gas is typically an undesirable by-product. Many technologies are available
for the capture of associated gas like gas reinjection, LNG, Gas to Liquid (GTL), Compressed Natural Gas
(CNG) and Gas to Solid but these technologies require significant capital investment and are very often
not feasible, particularly for marginal fields. As a result, in many facilities and developments, associated
gas is used as fuel for the facility and the balance flared.
Crude and associated gas production facilities typically receive production fluids from wells at relatively low
pressures, ranging from approximately 5 barg to 20 barg. At these low pressures, coupled with the relatively
high temperatures that the wellstream fluid arrives at the processing facilities, the associated gas will be rich
in valuable C4⫹ components that can be extracted as condensates and stabilized with the crude. However,
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Low Pressure Enhanced Liquid Recovery System LP-ERS
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OTC-26756-MS
Description of Concept
The concept uses a simple J-T Valve based dew point control unit (DPCU) that is modified for low
pressure applications (termed LP DPCU) to extract condensates from the low pressure associated gas
stream by the chilling process. The chilling duty for the Gas Chiller of the LP DPCU is derived by
evaporative cooling of inhibited fresh water using the leaned-out (and in the process, dehydrated)
associated gas from the LP DPCU in an Evaporator Column prior to the gas being flared. The cold
condensates extracted from the chilled associated gas at the LP DPCU is then contacted with rich flash
gas from the final stage of the crude stabilization train to strip out light ends (C3- components) from the
condensates and to absorb heavy ends (C4⫹ components) from the rich flash gas. The stripped condensate
is then comingled with crude production and stabilized in the crude stabilization multistage separator train
to meet the product TVP and RVP specifications.
Figure 1—Recovery Process Development
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conventional enhanced recovery systems that are currently available for extraction of C4⫹ components from
gas stream are bulky and costly, resulting in these enhanced recovery systems not being implemented for
marginal and stranded developments. To process low pressure gas, these conventional enhanced recovery
systems, will require booster compression and/or mechanical refrigeration, gas dehydration, etc. which
significantly add to space, weight, complexity and cost of the facility and this makes these systems technocommercially not viable for marginal developments.
A proprietary compact, self-contained process unit that is specifically tailored for enhanced stabilized crude
recovery from production facilities operating at low pressures in the range of 5 barg to approximately 20 barg
or more, known as Low Pressure Enhanced Recovery System (LP-ERS) has been developed. This system
maximizes the recovery of C4⫹ components from the associated gas and stabilizes the recovered condensate
and crude to meet the typical final product specification, True Vapor Pressure (TVP) and Reid Vapor Pressure
(RVP), of typically 12 psia and 10 psia respectively. This is achieved with the added benefit of significantly
reducing the greenhouse gases (CO2) emissions due to burning associated gas as fuel or flaring.
The LP-ERS operates at rather low pressure whilst maintains the good performance of increasing
stabilized crude production depending on the production rate, fluid compositions and Gas Oil Ratio
(GOR) of the production fluid. The low pressure feature of the system makes the implementation of this
technology more economically viable through the elimination of booster compression and/or refrigeration
system, dehydration, etc. thus reducing the size, weight and overall capital cost.
The system configuration is simple, compact and easily retrofitted on existing facilities. The system has
minimal moving parts and easily operable thus providing high system availability and maintainability.
Furthermore, the system is designed to enable continuous production with the existing system while the
LP-ERS is off-line for maintenance.
OTC-26756-MS
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Detailed Description of Technology
Figure 2 shows the typical configuration of the LP-ERS. The process consists of 3 main unit operations:
1. Low Pressure Dew Point Control Unit (LP DPCU)
2. Flash Gas/Condensate Contactor
3. Chilled Water Generation System
Figure 2—Typical Configuration of LP-ERS
Low Pressure Dew Point Control Unit (LP DPCU)
The following figure illustrates the dewpoint control and condensate recovery from associated gas at low
pressure. The main components of the LP DPCU comprises of the following:
●
●
●
●
Gas Chiller
Gas/Gas Heat Exchanger
Low Temperature Separator
J-T Valve
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The condensates extracted not only increases the stabilized crude volumes but also improves the crude
quality by increasing its API Gravity and reducing its viscosity. Also, the extraction of the C4⫹
components from the associated gas improves the quality of the gas as the gas product will be leaner. In
situations where the associated gas is used as fuel gas or flared, the CO2 (greenhouse gas) emissions are
reduced by an average of approximately 20%.
The system configuration is simple, compact and easily retrofitted on existing facilities as the system
requires minimal external utilities. The system has minimal moving parts and easily operable thus
providing high system reliability and availability with low maintenance requirements. Furthermore, the
system is designed to enable continuous production with the existing system while the LP-ERS is off-line
for maintenance.
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OTC-26756-MS
Figure 3—Schematic of Conventional and LP-ERS J-T Valve System
The following figure shows the phase envelope of the associated gas stream with the benefit of locating
the J-T Valve downstream of the Low Temperature Separator when the gas pressure is low. Based on the
figure below, it is shown that the LP-ERS cooling yields higher condensate recovery (Quality line of 0.35)
as compared to the Conventional J-T Valve system (Quality line of 0.15). Using the conventional
configuration, only 2344 bpd of condensate is recovered whereas LP-ERS J-T Valve System recovers
2771 bpd of condensate.
Figure 4 —Phase Envelope with Quality Line
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The associated gas stream is chilled with Gas Chiller and it is then routed to the Gas-Gas Heat
Exchanger. A closed loop Chilled Water system which supplies inhibited chilled water at approximately
12°C to the Gas Chiller. From the Gas-Gas Heat Exchanger, the fluid is routed to the Low Temperature
Separator for gas-liquid separation. The gas from the Low Temperature Separator is routed to the J-T
Valve to letdown the gas pressure (and thus further chill the gas) prior to being fed to the Gas-Gas Heat
Exchanger.
Unlike conventional J-T Valve system where the J-T Valve is located upstream of the Low Temperature Separator, LP-ERS locates the J-T Valve downstream of the Low Temperature Separator. This
configuration maximizes liquid drop-out from the associated gas stream for low operating pressure
system. In addition, it avoids the need for hydrate inhibitor injection facilities as the operating temperatures are well above hydrate formation temperature.
OTC-26756-MS
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Figure 5—Schematic of Flash Gas/Condensate Contactor
Chilled Water Generation (CWG) System
The cooling duty required for the LP DPCU of the LP-ERS is supplied by the CWG System. In
conventional system, to achieve the required cooling duty on the DPCU, the gas is either boosted in
pressure to facilitate adequate J-T cooling or a mechanical refrigeration package is installed to provide the
required cooling duty. Both options require additional facilities which are bulky and heavy, resulting in
a costly system.
The patent pending NGLTech’s LP-ERS uses a novel system to generate chilled water which operates
in a closed loop system. Similar to cooling tower’s concept, where air is used to facilitate evaporative
cooling of water, the LP-ERS utilizes superheated gas (instead of air) from the LP DPCU as the
evaporative medium. Superheated gas from the Gas/Gas Heat Exchanger of the LP DPCU is routed to the
bottom of the Evaporator Column to be in contact with warm water from the Gas Chiller of the LP DPCU
which is routed to the top of the column.
The Evaporator Column can be housed with trayed, structured, random packing with internals suitable
to promote vapor liquid contact. A liquid hold-up boot is required to provide sufficient liquid residence
time for vapor liquid separation and to provide adequate surge volume for the downstream pump.
The following gives the schematic flow diagram of the Chilled Water Generation System:
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Flash Gas/Condensate Contactor
Cold condensate from the Low Temperature Separator of the LP DPCU is let down in pressure and then
routed to the top of the Flash Gas/Condensate Contactor where it is cross contacted with warm flash gas
from LP Separator of the crude stabilization train. The Flash Gas/Condensate Contactor inlet stream and
operating conditions are set in such a way that C3- components in the condensate stream are minimized
and absorption of C4⫹ components from the flash gas stream to the condensate stream is maximized.
Depending on the crude quality and production rate, crude may be spiked into the condensate stream to
enhance the absorption of C4⫹ components from the flash gas stream. This will maximize the recovery
of stabilized liquids whilst minimizing flash gas generation on the downstream final stage (LP Separator).
Condensate that has been stripped off with C3- components are then routed to the LP Separator for
stabilization. The operating conditions of the LP Separator is set in such a way that the crude and
condensate product is stabilized to meet a TVP specification of less than 12 psia and an RVP specification
of less than 10 psia.
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OTC-26756-MS
Case Study
Example case study that follows demonstrates how the LP-ERS process can be used on existing facilities
that produce and process crude and associated gas. The LP-ERS’s performance is benchmarked against
typical conventional oil/condensate stabilization system.
Typically composition of associated gas routed to flare consist of methane, ethane, propane and butanes
(i.e. C4- components). It also contains significant quantities of pentanes and heavier hydrocarbon
components (i.e. C5⫹ components) which can be recovered as condensates whilst meeting the product
vapor pressure specifications. Figure 7 and 8 below shows the conventional processing facility and
processing facility with implemented LP-ERS respectively. The full wellstream fluid arrives at the inlet
to the facility at approximately 13 barg and 60°C for this case study.
Figure 7—Typical Crude Stabilization Unit (Base Case)
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Figure 6 —Schematic Diagram of the CWG system
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Presentation of Data and Result
Below is a brief tabulation on comparison of crude recovery and CO2 emission for the base case and for
the case using the LP-ERS.
Table 1—Production Comparison
Production Years
Base Case (bbl/day)
Incremental with the LP-ERS (bbl/day)
% Incremental Recovery
449
566
1191
256
6.0%
7.6%
18.3%
32.0%
2015
7500
2016
7500
2017
6500
2018
800
Total Crude Recovered over 4 Production Years
898,630 Barrels
Table 2—CO2 Reduction
Production
Years
2015
2016
2017
2018
Total Gas
(mmscfd)
Total Cont
Flare (mmscfd)
Molar Flow
(kgmol/h)
CO2 Produced
without ERS
(metric tonnes/yrs)
CO2 Produced
with ERS
(metric tonnes/yrs)
CO2 Reduction
(metric tonnes/yrs)
% CO2
Emission
Reduction
7.13
11.25
32.50
8.00
6.05
9.81
29.95
7.09
345.46
553.22
1627.93
397.15
234,114
338,941
883,531
212,880
179,651
270,283
737,693
181,249
54,463
68,659
145,838
31,631
23%
20%
17%
15%
Table 3—Comparison of Crude Properties
Crude Properties
Crude Stabilization Unit
Low Pressure Enhanced Recovery System (LP-ERS)
TVP
RVP
API
Viscosity
12 psia
8.5 psia
36
1.25
12 psia
10 psia
39.5
0.86
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Figure 8 —Processing Facility with Implemented LP-ERS
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OTC-26756-MS
Based on the above tabulations the following conclusions are drawn:
●
●
Shrinkage of actual gas volumes being flared due to the extraction of C4⫹ components
Leaning the gas to the flare due to the extraction of the heavier ends from the associated gas
stream.
Overall, the combined effect results in a reduction of greenhouse emissions due to flaring by
approximately average of 20%.
Conclusions
The LP-ERS process detailed in this document introduces a novel process configuration which will
potentially increase the stabilized liquid yield from an oil and gas processing facility to as much as 25%
improvement in cumulatively recovery. The process is configured in such a way that C4⫹ components
extracted from the associated gas stream at low pressure are absorbed into the crude stream whilst the C3
and lighter components in the stabilized crude product stream is minimized or eliminated.
Features and Benefits of the LP-ERS
●
●
●
●
●
●
Cost Effective Low Pressure System
The LP-ERS allows extraction of condensates (C4⫹ components) from the associated gas stream
at lower pressure (as low as 7 barg) relative to conventional enhanced recovery system, thus
avoiding the need for booster compression, gas dehydration and mechanical refrigeration, etc.
Increases Recovery and Revenue
Increases stabilized crude production in the range of 5% to 25% over typical conventional systems
depending on the production rate, GOR and fluid compositions.
Reduced Green House Gas Emissions
Improves gas quality by removal of heavy ends (C4⫹ components) in cases where the gas is used
as fuel gas or flared, reduces the CO2 emission by an average of approximately 20%.
Improved Bulk Stabilized Crude Quality
Extracted condensates (C5⫹ components) from the associated gas stream, when stabilized with
crude increases the API gravity and reduces the viscosity of the crude, thus improving the quality
of the bulk crude.
High System Availability & Low Operating Cost
The system has minimal moving parts and low complexity, making the system easy to operate with
minimal and easy maintenance, thus providing high system availability and low operating cost.
Self-Contained System and Easy Retrofit
Being essentially a self-contained system, the process can be implemented with potentially
minimal modifications to existing facilities.
Applications
The LP-ERS process is suitable for implementation on marginal and stranded crude and associated gas
producing fields where associated gas is used as fuel and/or flared. Whilst flaring of associated gas is not
recommended, in many instances this is unavoidable due to various techno-commercial considerations.
The LP-ERS is a system that is particularly suited these facilities and apart from the increased revenue
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1. The LP-ERS recovers significant quantities of heavy ends from associated gas stream. The
increased stabilized crude production ranging from an incremental production of 6% to 32%
depending on the production rate, GOR and fluid compositions.
2. The crude properties such as API and viscosity has improved by 9.72% and 31.2% respectively.
3. The LP-ERS reduces greenhouse gas emission as the heavy ends are stripped of the gas by:
OTC-26756-MS
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accrued due to extraction of condensates from the associated gas, it significantly reduces GHG emissions,
thus reducing the environmental impact associated with the development.
Nomenclature
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
Chilled Fresh Water
Compressed Natural Gas
Dew Point Control Unit
Floating Production Storage and Offloading
Floating Storage Unit
Greenhouse Gases
Gas Oil Ratio
Gas to Liquid
High Pressure
Joule-Thompson
Liquefied Natural Gas
Low Pressure
Low Pressure Enhanced Recovery System
Liquefied Petroleum Gas
Reid Vapor Pressure
True Vapor Pressure
References
1. NGLTech Sdn Bhd. (2009). Patent No. Patent No. 1: OPEN LOOP HEAVY OIL ABSORPTION PROCESS
(OLHOA). Malaysia.
2. NGLTech Sdn Bhd. (2011). Patent No. Patent No.5 : HIGH RECOVERY CRUDE & CONDENSATE STABILIZATION. Malaysia.
3. NGLTech Sdn Bhd. (2012). Patent No. Patent No.6 Jointly Owned with PETRONAS: SLUG & SAND HANDLING
AND SEPARATOR WITH INTEGRATED POLISHING SCRUBBER (Sep-iSYS™). Malaysia.
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CFW
CNG
DPCU
FPSO
FSU
GHG
GOR
GTL
HP
JT
LNG
LP
LP-ERS
LPG
RVP
TVP