Proceeding Simposium Nasional IATMI25 – 28 Juli 2007, UPN “Veteran” Yogyakarta _________________________________________________________________________ RECOVERING GAS FROM LOW PRESSURE GAS WELLS, AN EFFORT TO SUSTAIN GAS PRODUCTION FROM PAGER GAS PLANT By : Ahmad Zainuddin Operations Engineering – Reliability, Engineering and Maintenance Department Sumatera Light North Operations, PT Chevron Pacific Indonesia – Duri, Riau 28884 Telp. (0765) 824816, Fax. (0765) 825977 e-mail: [email protected] ABSTRACT Pager Gas Plant (GP) has three unit Gas Compressor (GC) consists of two unit 2-stage GC (GC #1 and #2) to capture high suction pressure from gas wells and one unit 3-stage GC (GC #3) to capture low suction pressure from associated gas. Since it started operating in 1997, the 3-stage GC had never been used as original design due to insufficient raw associated gas. Even, it was changed to 2-stage (re-staging) in Y- 2000 to cover more gas from gas wells and for spare at once. Pager GP average gas production tends to decline from year-to-year. Having the peak production of 24.6 MMSCFD in 2001, it was rapidly descending to become 20.3, 16.9, 9.3 and 7.7 MMSCFD in 2002, 2003, 2004 and 2005 respectively. The gas wells pressure from surrounding Pager GP area were getting lower, so that we could only run 1 unit of 2-stage GC (GC-1 or GC-2) at Pager GP. It included gas wells of Sidinginan (Sid) #3 & #5 which had line pressure lower than suction pressure made them unable flowing to Pager GP. A solution needed to face the challenges for sustaining gas production from Pager GP. Since there is no additional gas reserves in the future field development, we could only optimize existing facilities. Several initiatives were developed and implemented including: Run one more gas compressor (GC #3) by changing it back to 3-stage GC to recover low pressure gas wells (Sid #3 and #5) and Separating incoming gas line between high and low suction pressure to allow Sid #3 and #5 flowing to GP to be compressed in 3-stage GC. As the result, Pager GP can sustain the gas production and help 2006 average gas production to be 4.3 MMSCFD in which getting incremental 2.3 MMSCFD from placing these initiatives. Keywords : Low Pressure Gas Wells, Re-staging Gas Compressor, Separating Incoming Gas Line INTRODUCTION areas. All CPI-own gas sources including those from the Pager area are used for power generation Declining gas production from Pager Gas through several gas turbines located in Duri and Plant was a major concern for related Sumatera Minas (Figure 1). Light North (SLN) Operations teams in early 2006. Reservoir studies and technical Although the gas is only utilized internally for evaluations indicated that the gas reserves for gas generation of electricity in PT Chevron Pacific wells around the Pager area are fully depleted. An Indonesia (CPI) area, a lack of reliable gas assessment of the feasibility of reopening existing supplies can affect CPI daily operations since gas wells for additional gas volumes was not power is required to run production wells and to favorable since those wells had a low wellhead provide power to CPI Camps and other industrial pressure when they were shut-in. Unfortunately, IATMI 2007-TS-06 When the average gas production declined PAGER GAS PLANT FACILITIES to below 10 MMSCFD. the gas supply suction pressure from associated gas with a to Pager GP was from the Pinang Gas Plant (a capacity of 5 MMSCFD. etc). The three gas compressors (ARIEL PROBLEM ANALYSIS JGH/4) consist of two 2-stage GC (GC #1 and #2) to capture high suction pressure from gas wells During the first three month of 2006. Plant gas transmission line (about 75 km of 8” pipeline) facilities modification was the selected alternative to CDGT. flow line. UPN “Veteran” Yogyakarta _________________________________________________________________________ most of the inactive gas wells no longer have in. The dry produce gas is delivered thru CPI initiatives to enhancing gas production. However. keeping the Central Duri Gas Turbine (CDGT) for fuel. it with the maximum capacity of 10 MMSCFD each was found that the gas production from Pager area and one 3-stage GC (GC #3) to capture low frequently fluctuated. there are no future plans for compressors was chosen to increase gas further development either through infill drilling production from this area. the Sidinginan production decreased or gas from the higher-pressure gas wells could be even “no flow” due to increased backpressure on recovered. condensate and water from to low gas volumes and low suction pressure. original design due to insufficient associated gas Although the overall gas production from volumes from the Sidinginan Gathering Station. GC#3 was reconfigured were not stable. But if Pinang GC was down. while from Pinang field) and Sidinginan gas wells (Sid the Low Pressure GC is about 5 psig. so reactivation would require a power requirements of gas compressor which significant capital cost resulting in negative resulted in fuel cost savings. At that time. the of the other two compressors (GC#1 or GC#2) to production from Sidinginan would increase be shut-down for inspection and overhaul. economics due to the marginal gas reserves of these wells. The suction pressure of booster GC in this plant compresses gas wells High Pressure GC is approximately 50 psig. Another objective of this reconfiguration was to tact production facilities (such as well head hook. gas-producing well streams prior to sending it to From operations point of view. or work-over except for maintenance operation on the existing gas wells. The equipment running far below its rated capacity incoming gas is compressed by the reciprocating creates high compressor cylinder temperatures due gas compressors and then dehydrated to prevent to high gas volumes being recycled to the 1st stage. The Pager Gas Plant is a gas-handling facility other two Gas Compressors were shut-down due to separate natural gas. IATMI 2007-TS-06 . The reconfiguration also allowed one the wells. significantly. Proceeding Simposium Nasional IATMI 25 – 28 Juli 2007. the facilities shown in Figure 3. Based on production forecast modification of Pager Gas Plant including gas and reserve profile. is 25 MMSCFD limited by gas dehydration system and gas compressors design. The other gas wells in the Pager Area the 3-stage GC has never been operated per were shut-in. The maximum gas plant capacity programs. Production Review An alternate solution to increase gas production was to lower the field pressure through Gas production from the Pager Gas Plant modification of existing facilities and equipment. and the Pager Area (Pager GP minus Pinang Since this alternative involved existing assets production) has declined every year since 2001 as without addition of new equipment. Pager GP was relatively stable. hydrate formation and corrosion from condensed The above conditions led us to search for water. Pager GP required only one gas compressor for daily operations. If the production from Pinang to become a 2-stage compressor so that additional increased. #3 and #5). improve adiabatic efficiency thereby reducing up. Figure 2 shows the flow process in since there will be no future gas development Pager Gas Plant. the gas sources In the year 2000. Low = 285 psig . The choice was made to utilize configuration. Figure 6 shows this change before GC#3 by reactivating the 1st stage of this GC since and after the modification. it would return back to the separator needed to be reactivated to process the original 3-stage design. It is also important to valves were required for the 1st stage GC #3 monitor the compressor’s discharge temperature (~US $60M) and they were available as spare since that directly affects the life of piston rings parts in CPI warehouse stock. new configuration. New compressor load and ratio (Figure 5). Pager GP GC#3 were changed to become: sustained gas production to achieve an average • Suction pressure: 4. High = 270 psig could not be avoided due to decreasing well-head • Discharge pressure: pressures. There were no significant costs for 2000 software to identify the required compressor executing this modification. Some block The two inlet lines with different valves were adjusted to be normally open or pressures require two compressors with different normally close as required by the new suction pressures. High = 475 psig quarter of 2006. only the low pressure separator was operated for processing all gas coming to the plant. High = 475 psig This low suction pressure setting is to accommodate incoming gas from low pressure gas CONCLUSION wells of Sidinginan. UPN “Veteran” Yogyakarta _________________________________________________________________________ Based on this observation. to achieve optimum operation conditions with the For automatic safety shutdown systems. it was • Suction pressure: concluded that Sidinginan gas wells could not Low = 40 psig . optimization of existing IATMI 2007-TS-06 . Also as shown in the it has the lowest allowable inlet pressure. The production Low = 20 psig . GC #1 and GC #2 were 1. Sikladi. In this case. High = 15 psig 2. Sidinginan gas. High = 270 psig to Pager GP. Previously. we limited execution time was related to start-up of the the temperature to about 300°F which is below the compressor unit which required less than 2 weeks maximum allowable temperature of 320°F. To address safety concerns IMPLEMENTATION related to changing the plant flow process. Separating the incoming gas line This higher suction pressure setting is to between high pressure (from Pinang) and low accommodate higher pressure gas coming from pressure (from Sidinginan) gas streams was a other fields (Ubi. When there are no more reserves for future set as follows: field development. modification to plant operations. Proceeding Simposium Nasional IATMI 25 – 28 Juli 2007. Menggala and Pinang). performance is performed through use of RCS.3 MMSCFD in 2006 which is an increase of Low = 3 psig . Once process flow diagram. solution to allow increased gas flow from both The last step involved a minor sources at the same time. High = 72 psig was relatively stable for several months after • 2nd inter-stage pressure: modification although a slight production decline Low = 110 psig . Figure 4 shows the gas production • Discharge pressure: profile from Sidinginan and Pinang GP in the first Low = 285 psig . a new SOP (Standard Operating Procedure) was The first step to implement the idea is to developed by Plant Operators to ensure the develop a restaging design for GC #3 to become a equipment and system would be operated in a safe 3-stage compressor. the high pressure horizontal GC#3 is restaged. High = 145 psig balance the line pressure from Pinang GP which • Inter-stage pressure: made these low pressure gas wells unable to flow Low = 110 psig . Simulation of gas compressor and controlled condition. As a comparison. Most of project and compressor valves. the PLC control system shutdown settings for After implementing the change.3 MMSCFD from these initiatives as illustrated • 1st inter-stage pressure: in production curve in Figure 7. V. M. Proceeding Simposium Nasional IATMI 25 – 28 Juli 2007. T. the incremental return of adding gas production through this kind of surface Long. “Operator & Technician his guidance to execute this project and Mr. and Stewart. “Enhancing facilities modification is very significant Compressor Productivity”. for ___________.. GPAC 18th considering the low initial cost and short Annual Operations/Maintenance duration for project execution. Publishing Company. PT Chevron Pacific Indonesia. 2. “Compressor Manual”. Certification – Production Operation Aprianto S. “Surface Production improve performance of equipment and Operation Volume 2: Design of Gas- increases profit through recovery of additional Handling Systems and Facilities”. UPN “Veteran” Yogyakarta _________________________________________________________________________ surface facilities can help sustain gas REFERENCES production.. Restaging a gas compressor can substantially Arnold. Mawardi Z. 3. Human Resource Learning data related to sub-surface matters. Chevron ACKNOWLEDGEMENTS Corporation. Alberta. 1999. 1998 The author thanks to Mr. In summary. K. Houston. for his contribution to give advice and Module 6A”.. B. & Development... 2006 ___________. Gulf low pressure gas. 2007 IATMI 2007-TS-06 . Conference. and Hardeveld.. 43Km 26”-36.3 Km To Kota Pinang PAGER GP Sikladi Tanggul Tinggi Duri So.3 1ST STG 2ND STG 3RD STG Glycol Contactor 104 PSI DISCH BOTTLE DISCH BOTTLE DISCH BOTTLE COOLER COOLER COOLER LC Still Column GLYCOL FILTER FLASH TANK OUTLET To CDGT METER CHARCOAL DRY GAS 0 375 F FILTER GLYCOL PUMP REBOILER Red : Gas Line TO PIT Purple : Glycol TO FLARE Note : Comp 3 only 2 Stg operated FIGURE 2.5Km P.Balam Seruni Sintong Se.5Km Butun Libo GP Station & Metering Station Waduk 10”-19Km 16” Doral Mindal Se-Libo Minas GT Minas m Lindai 24”-28.So 12”-12Km Sabak Rangau Hiu Aman N.75 Km Dumai AND SHIPPING PUMPS 10”10Km Rantau Bais Buaya So.4Km Bangko Ujung Tanjung Oil Wharves & Antara Nella Metering Station Singa 6”-6.5 Km Dusun Waduk Mandar 30” Loopline-36.1Km 8”-8. PAGER GAS PLANT – FLOW PROCESS IATMI 2007-TS-06 .9Km Talas Ayu Rintis North Booster 24”-7.6Km 8”-36. Zamrud Rumbai A GA Pekanbaru S FIGURE 1. Rupat 10”-30.9Km 6K ”-1 24 MINAS STORAGE TANKS Kotabatak 12”-18Km AND PUMP STATION Ninik 12”-14Km Beruk N.5Km Libo Pusaka Kelabu 10”-32.Sebanga Pukat Pematang Pinggir Pedada Pudu Bow Sebanga 30”-36.3Km 16”-11.5Km Pakning Kopar Petani 12”-5Km Central Duri GT Pak Jorang 18”-11.2Km Benar Genting 30 “. Langgak Kotagaro Zamrud Osam Suram 24”-78.Menggala Se.46.9Km Tanjung Medan 6”-3.9Km DUMAI STORAGE TANKS 8”-1.120Km Idris Bungsu Kasikan AS 12”-13Km 8”-14Km AM 12”-19Km 16”-20Km Beruk ER Paitan Terantam Petapahan So.9 Km Akar Pager Pemburu Telinga 8”-21. Tilan Palem 36 “. Batang Balam 12”-12Km Kerang Mutiara Mangga Sintong Candi Tunas Ubi 6” No.1 DISCH BOTTLE DISCH BOTTLE SIDINGINAN HIGH PRESS PCV SEPERATOR COOLER COOLER UBI SUCT BOTTLE SUCT BOTTLE LOW PRESS SIKLADI SEPERATOR PINANG PCV COMP . Proceeding Simposium Nasional IATMI 25 – 28 Juli 2007. CPI GAS SYSTEM Flow Process PRE COOLER SUCT BOTTLE SUCT BOTTLE Gas Well 1ST STG 2ND STG 104 PSI COMP .Menggala Gulamo Lincak MCTN Field Kulin Petani GP 6”-8.54.46Km 30 “.2 1ST STG 2ND STG MENGGALA 104 PSI DISCH BOTTLE DISCH BOTTLE COOLER COOLER SLUG CATCHER SLUG CATCHER Mist Pad SUCT BOTTLE SUCT BOTTLE SUCT BOTTLE Bubble Cup COMP . UPN “Veteran” Yogyakarta _________________________________________________________________________ N Pinang Damar 6”-6. Jingga Hitam Pungut Intan Sebanga GP Benua Sangsam Tandun Penasa 12”-9.897Km 24”-26.7 Km Putih 6”=3Km Topi Pinggir So.7Km Bekasap GP Pelita Pematang Duri GT Cucut 16”-27Km Duri Rokiri DURI STORAGE TANKS So Bagan Belada Bekasap Cebakan AND PUMP STATION Gatam Obor Bek. Topaz Beruk Ne. TOTAL GAS PRODUCTION FROM PAGER GAS PLANT AND PAGER AREA Total Gas Production Pinang and Sidinginan 5.500 3. Gas production due to 1. Sidinginan (not include Pinang) 10.500 Increase Sid.000 0 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 Jan-07 Month Total Pager Gas Plant Gas Production Total Pager Area Gas Production FIGURE 3. Gas prod.000 Pinang GC down Sid. GAS PRODUCTION PROFILE FROM PINANG AND SIDINGINAN IATMI 2007-TS-06 .000 3. 500 decrease while increasing Pinang 0 01-Jan-06 11-Jan-06 21-Jan-06 31-Jan-06 10-Feb-06 20-Feb-06 02-Mar-06 12-Mar-06 22-Mar-06 Month Pinang Gas Sidinginan Gas FIGURE 4.000 MSCFD Gas Production from Ubi.500 Re-POP Increase production Sidinginan #3 from Pinang gas wells 4.000 Pinang GC shut down due to pigging job 1. 15. Menggala. Sikladi.500 Pinang GC shut down for montly inspection 2. Proceeding Simposium Nasional IATMI 25 – 28 Juli 2007.000 4. Menggala.000 Pinang.000 MSCFD 2.000 30.000 5. Sidinginan 20. UPN “Veteran” Yogyakarta _________________________________________________________________________ Total Gas Production 35. Ubi.000 Gas Production from 25.000 Sikladi. Proceeding Simposium Nasional IATMI 25 – 28 Juli 2007. RECIPROCATING GAS COMPRESSOR SIMULATION IATMI 2007-TS-06 . UPN “Veteran” Yogyakarta _________________________________________________________________________ PAGER GAS COMPRESSOR 400 psi HP Line LP Line GC #1 150 psi 50 psi V3 V2 V1 400 psi GC #2 400 psi 150 psi 50 psi V3 V2 V1 400 psi GC #3 400 psi 150 psi 45 psi 5 psi V4 V3 V1 V1 GC #1 and GC# 2 GC #3 2 StageCompressor 3 Stage Compressor FIGURE 5. UPN “Veteran” Yogyakarta _________________________________________________________________________ Simplified Process Flow Diagram Gas Flow to Gas Compressor Pager Gas Plant (BEFORE) GAS GAS GAS COMP # 3 COMP # 2 COMP # 1 PCV to control suction pressure of Comp # 3 ( 3 – 15 psi ) NC NO NO NC NO HIGH Press. 5 PINANG GP FIGURE 6A. Separator NC LOW Press. Proceeding Simposium Nasional IATMI 25 – 28 Juli 2007. SIMPLIFIED PFD GAS FLOW TO GAS COMPRESSOR (BEFORE) Simplified Process Flow Diagram Gas Flow to Gas Compressor #3 From Low Pressure Gas Wells GAS GAS GAS COMP # 3 COMP # 2 COMP # 1 PCV to control suction pressure of Comp # 3 ( 3 – 15 psi ) NC NO HIGH Press. Separator NC = Gas flow to Gas Comp # 3 NC = Normally Close Valve NO = Normally Open Valve NO NO PAGAR GS SID # 3. 5 PINANG GP FIGURE 6B. Separator NC PCV to control suction pressure of GC # 1. SIMPLIFIED PFD GAS FLOW TO GAS COMPRESSOR #3 FROM LOW PRESSURE GAS WELL (AFTER) IATMI 2007-TS-06 .3 (set @ 40 psi minimum ) LOW Press. Separator NO = Gas flow to Gas Comp # 3 NC = Normally Close Valve NO = Normally Open Valve NC PAGAR GS SID # 3.2. 000 MMSCFD 2.500 2. Proceeding Simposium Nasional IATMI 25 – 28 Juli 2007.271 MMSCFD (Before) 1.000 0.500 3.000 1.500 Re-stage and Separate 4. UPN “Veteran” Yogyakarta _________________________________________________________________________ SIDINGINAN #3 AND #5 GAS PRODUCTION Before and After Modification at Pager Gas Plant 4.545 MMSCFD (After) 2.500 0.000 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 /2 /2 /2 /2 /2 /2 /2 /2 /2 /2 /2 /2 /2 /2 /2 /2 /2 /2 5 5 5 6 6 7 7 8 8 9 9 0 0 0 1 1 2 2 /0 /0 /0 /0 /0 /0 /0 /0 /0 /0 /0 /1 /1 /1 /1 /1 /1 /1 01 15 29 12 26 10 24 07 21 04 18 02 16 30 13 27 11 25 DATE Actual Production Average Production FIGURE 7.000 Incoming Gas Line on 29 May 2006 3.500 0. LOW PRESSURE GAS WELLS PRODUCTION IATMI 2007-TS-06 .
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