Process Description
Process Overview
The Advanced Gas-Oil Separation Process includes three crude oil production wells, High and Low Pressure Production Manifolds, a Test Manifold, a Test Separator, and two parallel gas-oil-water separation trains.
Crude oil from the wells can be routed to any of the three collection manifolds. Crude oil from the two production manifolds is routed to either of the 3-stage separation trains. Crude oil from the test manifold is routed to the test separator to determine a well’s characteristics before placing the well into production service.
Each separation train consists of three 3-phase separators operating at successively lower pressures to separate the crude oil into oil, gas and water streams. Gas released from the 2nd and 3rd Stage separators is compressed and combined with gas from the 1st Stage Separator and sent to treating. Water from each separator is collected and sent to water treating for disposal.
Crude oil from the High Pressure Production Manifold is routed to the 1st Stage Separator. Flashed gas from the 1st Stage Separator combines with compressed flash gas and sent to treating for water removal. Crude oil from the 1st Stage Separator is sent to the 2nd Stage Separator along with oil from the Low Pressure Production Manifold.
Flash gas from the 2nd Stage Separator is combined with compressed flash gas from the 1st Stage Separator and the combined gas is cooled and compressed in two successive stages before combining with the flash gas from the 1st Stage Separator. Condensate from cooling the combined gases is separated before compression in a Suction Knockout Drum. Condensate and crude oil from the 2nd Stage Separator is routed to the 3rd Stage Separator.
Flash gas from the 3rd Stage Separator is cooled and compressed in the 1st Stage of the Gas Compressor. Condensate from cooling the flash gas is separated before compression in a Suction Knockout Drum. The condensate is returned to the 1st Stage Separator by gravity. Crude oil from the 3rd Stage Separator is sent to storage.
Gas from 2nd Stage of the Gas Compressor is cooled and condensate is separated before compression in a Suction Knockout Drum. The condensate is routed to the 2nd Stage Separator.
Wells and Manifolds Section Process Description
Overview
The wells and manifolds section consists of:
– Well #1 and Wellhead
– Well #2 and Wellhead
– Well #3 and Wellhead
– High Pressure Production Manifold
– Low Pressure Production Manifold
– Test Manifold
The purpose of the wells and manifolds section is to:
– Produce and control crude oil from the wells
– Route crude oil to the manifolds
– Route crude oil from the manifolds to GOSP Train A, GOSP Train B and the Test Separator
Wells
Crude oil along with associated gas and water is produced from three wells. Each well is outfitted with an engineered wellhead assembly at the surface which consists of a set of valves to isolate and control the flow from the well. This wellhead assembly is commonly referred to as a “Christmas Tree”. Each wellhead assembly includes an emergency shutdown isolation valve (ESDV) and a production choke valve to manually control the well’s flow and to reduce the line pressure. The pressure at each wellhead is indicated on the instrumentation.
Manifolds
Flow from each well can be routed to any of the three manifolds: the High Pressure Production Manifold, the Low Pressure Production Manifold and the Test Manifold. Crude oil from High Pressure Production Manifold is routed to the First Stage Separators of the A and B separation trains. This is the normal routing when a well is operating at normal pressures. When the wellhead pressure begins declining as it approaches the end of its useful production life, flow from the wellhead can be routed to the Low Pressure Production Manifold and then on to the Second Stage Separators of the A and B separation trains, which operate at lower pressure than the First Stage Separators. This alternate routing increases the crude oil flow rate from the wellhead.
Before a well is put into production service, it is normally analyzed without mixing with another well’s flow by routing the well to the Test Manifold. This manifold supplies the Test Separator so that a well’s production characteristics can be determined. The flow from the Test Manifold to the Test Separator can be finely adjusted using HIC-006.
Test Separator Process Description
Overview
The Test Separator Section Consists of only the Test Separator, D-001. The purpose of this section is to separate the flow from an individual well so its characteristics can be determined without interference from other wells.
Test Separator, D-001
Crude oil from the Test Manifold is brought into one end of the Test Separator, D-001 and enters the upper section of the vessel which contains a baffle to minimize the disturbances from slugs of oil and water entering with the feed. Oil, water and gas in the feed flow under this baffle into the main separation compartment of the Test Separator.
Gas flashes and separates into the vapor space at the top of the vessel, while immiscible water and oil separate by gravity and form two liquid layers in the separation compartment. The separation compartment is bounded by another baffle extending from the bottom of the vessel to halfway between the top and bottom of the vessel. Separated water and oil collect on the feed side of this baffle. The water/oil interface level is controlled at halfway up the separation baffle (which, therefore, is one quarter of the height of the vessel) by LIC-002 which adjusts the takeoff flow of water from the bottom of the separation compartment. The flow of water is indicated on FI-005. The design flow is 2.0 MBPD. The water contains small amounts of oil and is taken offsite to remove the oil before disposal.
Separated crude oil floats on the water phase and accumulates and spills over the separation baffle into the collection compartment of the Test Separator. The level of collected oil in this compartment is controlled by LIC-001 which adjusts the flow of oil taken from this compartment to either the 2nd Stage Separator, D-201A, or the 3rd Stage Separator, D-301A. The flow of crude oil is indicated on FI-004. The design flow of oil is 16.2 MBPD. Selection of the destination of the crude oil can be made using HS-008A and HS-008B. Note that the routing of the flash gas from the Test Separator should correspondingly be set using HS-007A and HS-007B (see below).
NOTE
LIC-002 indicates 100% when the water/oil interface level in the separation compartment is at the height of the separation baffle. If the interface level goes higher than 100%, water will flow over the separation baffle and mix with oil on the collection side. In this situation, an additional load of water will be placed on the downstream separator.
D-100 Water and Gas Separation
The separation of water out of the oil is not complete as it takes a very long residence time in the separation compartment for this to occur and also because there is agitation of the liquid phases due to the high rate of initial gas separation in the Test Separator. Larger droplets of water will coalesce and fall to the bottom of the separation compartment more easily than smaller droplets. Given the residence time of oil and water in the separation compartment, small droplets of water will be contained in the crude oil in the collection compartment. Most of this water will be separated in the downstream separators.
Gas that is flashed and desorbed from the crude oil is collected in the vapor space of the Test Separator and flows to the opposite end. The residence time that allows water to separate from the oil also allows entrained gas in the oil to desorb from the oil.
To make sure there are as few droplets of oil and water leaving with the gas, a demisting pad extends from the top of the vessel to the middle of the vessel over the separation compartment. This ensures the vapor must pass through the demisting pad as the level of oil in the separation compartment will be slightly higher than the liquid separation baffle. The demisting pad is made of crinkled wire mesh screen (CWMS). Any entrained droplets of liquid will impact the wires and the droplets will coalesce and drain into the oil phase of the separation compartment.
D-001 Pressurization Control
The pressure in the Test Separator is not controlled directly. Gas leaving the Test Separator can be routed to either the 3rd stage discharge line of Gas Compressor K-101A using HS-007A to test at a high pressure or to the 1st stage discharge line of K-101A using HS-007B to test at a lower pressure. The Test Separator’s pressure will float on either of these lines. Check valves are installed in the lines to prevent back flow of gas to D-001. When changing the gas lineup, the lineup of the separated crude oil using HS-008A or HS-008B must be changed accordingly to ensure controllability of the oil level by LIC-001.
If the pressure in D-001 builds, an automatic vent to the flare system is provided. PIC-005 will open at 1,800 PSIG to avoid overpressuring D-001. Also, D-001 is outfitted with a pressure safety valve (PSV) set at 2,000 PSIG.
In high pressure test mode, D-001 operates at a pressure of 1,627 PSIG and a temperature of 162 DEG F while producing 35.2 MMSCF/D of gas.
Separation Train A Process Description
Overview
To accomplish efficient flashing of the crude oil and compression of the flashed gases, crude oil is depressured in 3 successive three-phase separators, D-101A, D-201A and D-301A. The pressure in each separator depends on the operating conditions of the Gas Compressor K-101A which compresses released gas in the opposite direction of the oil depressurization. Most of the gas is released in the 1st and 2nd Stage Separators, D-101A and D-201A. A smaller amount of gas is released in the 3rd Stage Separator D-301A.
The countercurrent pressurization and condensation of the flashed gases from the 2nd and 3rd Stage Separators allows hydrocarbons such as butane and pentane and heavier to be mostly recovered in the product crude oil while methane and ethane are mostly recovered in the product gas. Propane distributes significantly into both the oil and gas products.
The gas from D-101A is not compressed; it is combined with the net compressed gas from the 3rd Stage of K-101A and sent off to the Dehydration Unit. The gas from D-201 is compressed in the 2nd and 3rd Stages of K-101A along with gas from the 1st Stage of K-101A. The gas from D-101A is compressed in the 1st Stage of K-101A.
The gas flowing to each stage of K-101A is cooled with cooling water. Any condensed liquids are removed in a Suction Knockout (K.O.) Drum. The liquid collected in each K.O. Drum is sent to an oil separator with a suitable pressure.
Oil from the High Pressure Production Manifold is routed to the 1st Stage Separator D-101A using HIC-004A. The operating principle of D-101A is exactly the same as the Test Separator, D-001. Gas that is flashed from D-101A is routed to the discharge of the 3rd stage line of Gas Compressor D-101A to be taken off to the Dehydration Unit. Separated water from D-101A is taken off for treatment. Separated crude oil is taken off to the 2nd Stage Separator D-201A.
Oil from the 1st Stage Separator D-101A is combined with condensate from the 3rd Stage K.O. Drum D-102A, with oil from the Low Pressure Production Manifold and with oil from the Test Separator D-001 operating in the high pressure test configuration (note: the oil lines from the Test Separator are not shown on schematic page 4 to reduce clutter). This combined stream is flashed in 2nd Stage Separator D-201A. Flash gas from D-201A is taken off to the 2nd Stage of K-101A via its Suction Cooler E-201A (not shown on schematic page 4) and 2nd Stage K.O. Drum D-202A. Separated water from D-201A is taken off for treatment. Separated crude oil is taken off to the 3rd Stage Separator D-301A.
Oil from the 2nd Stage Separator D-201A is combined with condensate streams from both the 1st and 2nd Stage K.O. Drums, D-202A and D-302A, and with oil from the Test Separator D-001 operating in the low pressure test configuration (note: the oil lines from the Test Separator are not shown on schematic page 4 to reduce clutter). The combined stream is flashed in 3rd Stage Separator D-301A. Flash gas from D-301A is taken off to the 1st Stage of K-101A via its Suction Cooler E-301A (not shown on schematic page 4) and 3rd Stage K.O. Drum D-302A. Separated water from D-301A is taken off for treatment. Separated crude oil is taken off to storage.
1st Stage Separator, D-101A
Crude oil from the High Pressure Production Manifold is flashed in 1st Stage Separator D-101A. The flow rate of the feed from the manifold is manually adjusted using HIC-004A. D-101A operates at 1,631 PSIG and a temperature of 163 DEG F. Flash gas from D-101A is routed to the 3rd Stage discharge line of Gas Compressor K-101A which operates at 1,624 PSIG under the control of PIC-101A which adjusts the combined flow of flash gas from D-101A and the net compressed gas from the 3rd Stage of Gas Compressor K-101A. A check valve prevents reverse flow from the discharge of K-101A to D-101A.
Oil, water and gas are separated in D-101A using the same operating principles as the Test Separator D-001 (see above). The level of the collected water is controlled by the oil/water interface level controller LIC-103A which adjusts the water flow taken off to battery limit for oil recovery prior to disposal. The flow of water is indicated on FI-105A. Design water flow is 3.6 MBPD when the Test Separator is in operation and 5.5 MBPD when it is out of operation.
The level of the collected oil in D-101A is controlled by LIC-101A which controls the flow of oil to the 2nd Stage Separator D-201A. The flow of oil out is indicated on FI-104A. The design flow is 30.4 MBPD with the Test Separator in operation and 46.8 MBPD when it is out of operation.
In the event the pressure in D-101A builds, an automatic vent to the flare system is provided. PIC-104A will open at 1,800 PSIG to avoid overpressuring D-101A. Also, D-101A is outfitted with a pressure safety valve (PSV) set at 2,000 PSIG.
2nd Stage Separator, D-201A
Crude oil from D-101A is combined with crude oil from the Low Pressure Production Manifold, with crude oil from the Test Separator D-001 operating in high pressure test mode, and with condensate from the 3rd Stage Suction K.O. Drum D-102A. This combined stream is flashed in 2nd Stage Separator D-201A. D-201A operates at 375 PSIG and 152 DEG F. Flash gas from D-201A is routed to the inlet of 2nd Stage Suction Cooler E-201A before being compressed in the 2nd Stage of Gas Compressor K-101A. A check valve prevents reverse flow from the inlet of E-201A to D-201A.
Oil, water and gas are separated in D-201A using the same operating principles as the Test Separator D-001 (see above). The level of the collected water is controlled by the oil/water interface level controller LIC-203A which adjusts the water flow taken off to battery limit for oil recovery prior to disposal. The flow of water is indicated on FI-205A. Design water flow is 0.3 MBPD.
The level of the collected oil in D-201A is controlled by LIC-201A which controls the flow of oil to the 3rd Stage Separator D-301A. The flow of oil out is indicated on FI-204A. The design flow is 37.6 MBPD.
In the event the pressure in D-201A builds, an automatic vent to the flare system is provided. PIC-204B will open at 450 PSIG to avoid overpressuring D-201A. Also, D-201A is outfitted with a pressure safety valve (PSV) set at 490 PSIG.
3rd Stage Separator, D-301A
Crude oil from D-201A is combined with crude oil from the Test Separator D-001 operating in low pressure test mode, and with condensate from the 1st and 2nd Stage Suction K.O. Drums, D-302A and D-202A. This combined stream is flashed in 3rd Stage Separator D-301A. D-301A operates at 71 PSIG and a temperature of 140 DEG F. Flash gas from D-301A is routed to the inlet of 1st Stage Suction Cooler E-301A before being compressed in the 1st Stage of Gas Compressor K-101A. A check valve prevents reverse flow from the inlet of E-301A to D-301A.
Oil, water and gas are separated in D-301A using the same operating principles as the Test Separator D-001 (see above). The level of the collected water is controlled by the oil/water interface level controller LIC-303A which adjusts the water flow taken off to battery limit for oil recovery prior to disposal. The flow of water is indicated on FI-305A. Design water flow is 0.2 MBPD.
The level of the collected oil in D-301A is controlled by LIC-301A which controls the flow of oil to storage facilities. The flow of oil out is indicated on FI-304A. The design flow is 35.2 MBPD.
In the event the pressure in D-301A builds, an automatic vent to the flare system is provided. PIC-304B will open at 90 PSIG to avoid overpressuring D-301A. Also, D-301A is outfitted with a pressure safety valve (PSV) set at 490 PSIG.
1st Stage Suction Cooler, E-301A
Prior to compression, the flash gas from 3rd Stage Separator D-301A cooled in 1st Stage Suction Cooler E-301A which uses cooling water to cool and partially condense the gas from 140 DEG F to 75 DEG F using TIC-302A. E-301A will also cool any gas recycled from the discharge of the 1st Stage of K-101A.
1st Stage Gas Compression, K-101A
K-101A is an electric motor driven, three-stage centrifugal compressor. The 1st Stage of Gas Compressor K-101A takes suction from the top of D-302A and compresses the gas to 419 PSIG and 249 DEG F. The design flow of gas is 7.7 MMSCF/D. A minimum flow controller FIC-301A will open a recycle line from the discharge of the 1st Stage back to the 1st Stage Suction Cooler E-301A in case the gas flow drops below 6.0 MMSCF/D. The net gas flow out from the 1st Stage of K-101A to E-201A is adjusted by PIC-302A.
2nd Stage Suction Cooler, E-201A
The 2nd Stage of K-101A compresses flash gas from 2nd Stage Separator D-201A, any flash gas from the Test Separator D-001 while operating in low pressure testing mode, and net gas from the 1st Stage of K-101A. Prior to compression, the mixed gases are cooled in 2nd Stage Suction Cooler E-201A which uses cooling water to cool and partially condense the gas from 152 DEG F to 75 DEG F using TIC-202A. E-201A will also cool any gas recycled from the discharge of the 3rd Stage of K-101A.
2nd Stage Suction K.O. Drum, D-202A
2nd Stage Suction K.O. Drum D-202A separates the condensate formed in E-201A so it does not damage the compressor. D-202A operates at 75 DEG F and 373 PSIG. The level of collected condensate is controlled by LIC-202A which adjusts the flow of condensate to the 3rd Stage Separator D-301A. The pressure of D-202A is not controlled; it will seek its own pressure depending on the conditions of the other compression stages and the amount of flash gas it is supplied. A demister pad is installed in the upper part of D-202A to remove any entrained droplets of liquid from the exiting gas.
2nd Stage Gas Compression, K-101A
The 2nd Stage of Gas Compressor K-101A takes suction from the top of D-202A and compresses the gas to 888 PSIG and 166 DEG F. The design flow of gas is 34.7 MMSCF/D. A minimum flow controller FIC-201A will open a recycle line from the discharge of the 3rd Stage back to the 2nd Stage Suction Cooler E-201A in case the gas flow drops below 22.5 MMSCF/D. All of the gas from the discharge of the 2nd Stage of K-101A is sent to the 3rd Stage Suction Cooler E-101A.
3rd Stage Suction Cooler E-301A
The 3rd Stage of K-101A compresses gas from the discharge of the 2nd Stage of K-101A. Prior to compression, the warm gas is cooled in 3rd Stage Suction Cooler E-101A which uses cooling water to cool and partially condense the gas from 166 DEG F to 90 DEG F using TIC-102A.
3rd Stage Suction K.O. Drum D-102A
3rd Stage Suction K.O. Drum D-102A separates the condensate formed in E-101A so it does not damage the compressor. D-102A operates at 90 DEG F and 759 PSIG. The level of collected condensate is controlled by LIC-102A which adjusts the flow of condensate to the 2nd Stage Separator D-201A. The pressure of D-102A is not controlled; it will seek its own pressure depending on the conditions of the other compression stages and the amount of gas flowing from the 2nd Stage of K-101A. A demister pad is installed in the upper part of D-102A to remove any entrained droplets of liquid from the exiting gas.
3rd Stage Gas Compression – K-101A
The 3rd Stage of Gas Compressor K-101A takes suction from the top of D-102A and compresses the gas to 1635 PSIG and 174 DEG F. The design flow of gas is 34.7 MMSCF/D. A recycle line is taken off the discharge of the 3rd Stage of K-101A back to the 2nd Stage Suction Cooler E-201A under control of FIC-201A as described above. The net gas from the discharge of K-101A passes through a check valve and then combines with flash gases from the 1st Stage Separator D-101A and the Test Separator D-001 operating in high pressure test mode. The combined gases are passed onto the Dehydration Unit under control of PIC-101A which normally operates with a setpoint of 1624 PSIG.
Instrumentation
Wells And Manifolds Section
The choke valves on the Wellheads #1, #2 and #3 are manually controlled with HIC-001, HIC-002 and HIC-003, respectively. The emergency shutdown valves are under control of the interlocks associated with each well (see section on interlocks). Each well is lined up to one of the three manifolds using switches. Well #1 uses switches HS-001A, HS-001B and HS-001C. The switches for Wells #2 and #3 are similarly tagged to the well number. The flow from each well should only be lined up to one of the manifolds at a time. The control system will not prevent lining up a well to more than one manifold.
Test Separator Section
The oil level of the Test Separator D-001 is controlled by LIC-001. The destination of the oil is determined by using switches HS-008A and HS-008B. HS-008A lines up oil to the 2nd Stage Separator D-201A while HS-008B lines up oil to the 3rd Stage Separator D-301A. The oil flow is indicated on FI-004. The water/oil interface level of D-001 is controlled by LIC-002.
The produced water flow is indicated on FI-005.
The pressure of the gas produced in D-001 is indicated on PI-004 and its temperature is indicated on TI-004. Gas can be lined up to the 3rd Stage discharge line of Gas Compressor K-101A using HS-007A or to the 1st Stage discharge line of K-101A (E-201A inlet) using HS-007B. The produced gas flow from D-001 is indicated on FI-006.
A Train 1st Stage Separator Section
The produced oil level of the 1st Stage Separator D-101A is controlled by LIC-101A. Oil flow is indicated on FI-104A.
The water/oil interface level of D-101A is controlled by LIC-103A. The produced water flow is indicated on FI-105A.
PIC-104A is an emergency vent to flare that will open if the pressure of D-101A rises above 1,800 PSIG. It is designed to open before the pressure safety valve PSV-101A opens (setpoint = 2,000 PSIG). It can also be used to depressure D-101A at shutdown.
A Train 2nd Stage Separator Section
The produced oil level of the 2nd Stage Separator D-201A is controlled by LIC-201A. Oil flow is indicated on FI-204A.
The water/oil interface level of D-201A is controlled by LIC-203A. The produced water flow is indicated on FI-205A.
PIC-201A is an emergency vent to flare that will open if the pressure of D-201A rises above 450 PSIG. It is designed to open before the pressure safety valve PSV-201A opens (setpoint = 490 PSIG). It can also be used to depressure D-201A at shutdown.
A Train 3rd Stage Separator Section
The produced oil level of the 3rd Stage Separator D-301A is controlled by LIC-301A. Oil flow is indicated on FI-304A.
The water/oil interface level of D-301A is controlled by LIC-303A. The produced water flow is indicated on FI-305A.
PIC-301A is an emergency vent to flare that will open if the pressure of D-301A rises above 90 PSIG. It is designed to open before the pressure safety valve PSV-301A opens (setpoint = 490 PSIG). It can also be used to depressure D-301A at shutdown.
A Train 1st Stage Compression Section
TIC-302A controls the outlet temperature of 1st Stage Suction Cooler E-301A by adjusting the cooling water flow through E-301A.
The condensate level in 1st Stage Suction K.O. Drum D-302A is controlled by LIC-302A which controls the flow of condensed liquid to the 3rd Stage Separator D-301A. LHH-302A is a trip sensor for the interlock system of K-101A. The pressure of D-302A is controlled by PIC-302A which adjusts the net flow out of the 1st Stage of Gas Compressor K-101A to the 2nd Stage Suction Cooler E-201A.
A Train 2nd Stage Compression Section
TIC-202A controls the outlet temperature of 2nd Stage Suction Cooler E-201A by adjusting the cooling water flow through E-201A.
The condensate level in 2nd Stage Suction K.O. Drum D-202A is controlled by LIC-202A which controls the flow of condensed liquid to the 3rd Stage Separator D-301A. LHH-202A is a trip sensor for the interlock system of K-101A. The pressure of D-202A is indicated on PI-202A.
FIC-201A is designed to keep a minimum flow through the 2nd and 3rd Stages of K-101A. At design conditions FIC-201A’s output is 0% because the gas flow is above the minimum. This control keeps K-101A’s 2nd and 3rd Stages out of surge conditions. Surge can lead to damage of the Gas Compressor as gas rapidly reverses within the compressor, leading to heat-up and excessive vibration. The outlet temperature of the 2nd Stage is indicated on TI-203A. THH-203A is the trip sensor for the interlock system of K-101A. The differential pressure across the 2nd Stage of K-101A is indicated on PDI-201A.
A Train 3rd Stage Compression Section
TIC-102A controls the outlet temperature of 3rd Stage Suction Cooler E-101A by adjusting the cooling water flow through E-101A.
The condensate level in 3rd Stage Suction K.O. Drum D-102A is controlled by LIC-102A which controls the flow of condensed liquid to the 2nd Stage Separator D-201A. LHH-102A is a trip sensor for the interlock system of K-101A. The pressure of D-102A is indicated on PI-102A.
The outlet temperature of the 3rd Stage is indicated on TI-103A. THH-103A is the trip sensor for the interlock system of K-101A. The differential pressure across the 3rd Stage of K-101A is indicated on PDI-101A. HK-101A is a switch to start and stop the motor of K-101A.
The pressure of the total gas flow produced by flashing and compression is controlled by PIC-101A which adjusts the flow to the Gas Dehydration Unit. The total gas flow is indicated on FI-101A.