Safer Exploration & Production Operations Company


Modifications to the LPG Storage and Loading Station


Modifications to the LPG Storage and Loading Station


SEPOC is the Republic of Yemen's leading national Exploration and Production Operations Company. It is the upstream Operator of Yemen's premier Block (18) in the city of Mareb and the largest and second largest producer of gas and oil in the country respectively.

LPG stands for “Liquefied Petroleum Gas” and the term is used to describe two Natural Gas Liquids: propane and butane, or a mix of the two. LPG is stored in a cylindrical tank. The reason why LPG is stored in a spherical tank is liquid form gas is to be highly pressurized to keep it in liquid form. LPG is used for many purposes such as fuel for gas barbecue grills and gas cooktops and ovens, gas fireplaces, and in portable heaters.

SEPOC LPG loading stations are designed for the transfer of dangerous pressurized liquids from stationary to mobile tanks.

Project Name

Modifications to the LPG Storage and Loading Station

Project Main Objective

The purpose of the project is to maintain the LPG storage system and keep its loading station running at maximum production capacity. Moreover, this project comes to meet the set related safety and security maintenance regulations.

Project Methodology

Connecting the company's two systems for storing and loading LPG

What is the two SEPOC LPG storing and loading systems?

1-    The old system was established during the management of the former operator of block 18 (Yemen Hunt Oil Company).t mainly consists of a 6” pipeline that transferred the LPG product extracted from three cryogenic plants (CPU-I, KPU-A & KPU-B) and pumped to 10 horizontal cylindrical vessels (bullets) with a nominal capacity of each (92 m3), three loading pumps and two loading bays with two loading point each, recently the pipeline of the LPG product extracted from the new cryogenic plant CPU-II connected to the old LPG storage.

2-    The new system was established (with new cryogenic plant CPU-II) during the YLNG project, mainly consisting of a 6” LPG pipeline from CPU-II to the storage area, two pressurized embankment mounded bullets with a capacity of 520 m3 gross, two loading pumps, one loading bay with two loading points, new fire water system, F&G system, and safety shutdown system.

Why Modification?:

·       For more Operational flexibility,

·       Storage of LPG in Mounded Bullet provides an intrinsically passive & safe environment and technologically proven safe device.

Tie-in project implementation:

·       SEPOC’s primary objective is the save storage and operation of the trucks’ loading station.

·       Nowadays the storage of dangerous gases becomes a challenging problem. The use of mounded bullets is one of the feasible solutions to the problem. The design aspects of mounded storage vessels are more complicated than conventional above-ground spheres or bullets. Mounded bullets are horizontal pressure vessels that are intended for the pressurized storage of liquefied petroleum gas (LPG) under ambient temperature. In mounded storage facility, a mound of earth or suitable inert material is provided to cover the bullet, which is kept above ground, complete except for nozzles, and manhole covers. Mounded bullets are considered to be a safer option for LPG storage than conventional methods, such as Horton spheres, buried storage, etc. because situations leading to a possible Boiling Liquid Expanding Vapour Explosion (BLEVE) are eliminated. The mound protects the vessel from engulfment by fire, radiation from a fire nearby, acts of sabotage terrorism, and vandalism. Mounded storage is also used in situations where minimization of visual impact is important. The mounds reduce the visual impact of the storage site. As they have a sand cover around them, they can take the impact of external projectiles or flying objects. The dished ends of the bullets are the weakest points of material construction susceptible to catastrophic failures. Hence, they are to be directed away from the process or occupied areas.

·       Based on these factors, the management decision was to implement the tie-in project between the two systems using the existing tie-in streams under the new system battery limit.




Execution Plan:

·       Inspect and replace all corroded lines of the old system inside the area,

·       Installation of insulation gasket at the battery limit of the old system pipelines coming from the plants,

·       Tie-in LPG from the KPU-A & KPU-B cryogenic plants to the new system,

·       Tie in LPG from the CPU-I cryogenic plant to the new system,

·       Tie in the new and existing vapor lines,

·       Tie-in for interconnecting the new and existing loading pumps suction headers,

·       Tie-in for interconnecting the new loading pumps discharge header with existing discharge lines going to the loading bays #1 & #2.


Plant Operations (Gas Processing)

Plant operations operate 4 NGL & 1 LOP extraction plants, residual reinjection gas compressors RGC, LPG storage systems, including LPG loading stations, pressure letdown stations (LDS) systems, residual transferring gas compressor for YLNG feed and utilities systems such, power generators, instrument air compressors and fire fighting systems. Additionally, they provide fuel gas to PEC pressure letdown station and pipe line operations, as well.

Gas processing plants were built at two oil and gas well gathering and separation centers, CPUI & KPU.

LOP and 4 CPU RGCs were built at the end of the eighties, CPUI & 2 RGC plants and KPU 2 NGL extraction plants with 4 RGC plants were built at the beginning of the nineties. The newly built in CPU-II gas processing unit with gas transfer compressor and LDS systems were built in 2009-2012,

Each gas processing plant was designed for processing a 420 mmscftd associated gas from HP separators, passing through a treatment section removing contaminations such entrained moisture, solid particles and liquid droplets, the ready gas for processing is cooling and finally directed to the last separation stage fractionation systems. Process outlet streams are LPG, C5+ and residual gas.

LPG product streams (20000- 25000 bbls/d), through two pipelines, directed to LPG storages and via a 3 x2 loading stations feeding the local market.

C5+ product streams (approx. 7000 bbls/d) either injecting with the produced oils or directed to the blending tank at refinery mixing with high octane imported gasoline, feeding the local market.

Residue gas streams through the RGC injected into CPU, KPU reservoirs, including Al-Raja reservoir, and YLNG feed through the LDS.

Al-Raja field oil and gas wells gathering and LTS separation system, interconnected with KPU facilities, the producing liquids and gas through a pipe line separated in KPU separation systems mixing the gas with KPU gas feeding KPU gas plants, residue from KPU RGC manifold, pipelined to Al-Raja compressor suction for final re-injection   

LOP is an absorption gas processing unit, and considered the first commissioned gas processing unit, but currently not online, could be utilized in the future exploration plans.

CPU Lean Oil plant & RGC's

The lean oil C5+ plant (commissioned in 1988) is an ambient oil plant which can recover approximately 3,000 BPD of LPG and 6,000 BPD of C5+ from the inlet flow of 500 MMSCFD of rich natural gas, this plant also include a 10,000 BPD condensate stabilizer which was added in 1991.

The reinjection gas compressor (RGC’s) consist of two groups, the first group consist of four (16,000 BHP each) gas turbine driven centrifugal compressors with four stages of compression. The 1st stage of each RGC unit is designed to boost 20MMMSCFD of gas from 250 to 660 PSIG. The 2nd stage boost is from 660 to 1060 PSIG and is designed for 60 MMSCFD. The 3rd and the 4th stages boost from 1060 to 1975 to 3500 PSIG and are rated at 150 MMSCFD each. The second group consists of two gas turbine driven centrifugal compressors (25,560 BHP each) with three stages of compression, all three stages are rated of 200MMSCFD; and each compressor compresses the gas from 550 to 3300 PSIG.

There are three recovery compressors (VRC’s) each having 1,500 BHP electric motor which driven a two stage centrifugal compressor, they compress the gas from 2 to 250 PSIG. The capacity of each unit has a first stage capacity of 5.3 MMSCFD and a second stage capacity of 13 MMSCFD.

The facility provides all of its own electric power. There are three 13,000 KW (13 Mega watts) electric generators units driven by 16,000 BHP gas turbine.

KPU Facilities

The KPU is located in the Kamil field which is about 25 km east of the CPU; The KPU facility handles more than 1,100 MMSCFD of gas in the production separators. 
The KPU has two 420 MMSCFD cryogenic plants. 
Most of the gas from the production separators is processed in the two cryogenic plants prior to YLNG gas delivery. Otherwise it will go to injection wells through the injection manifolds.
The KPU has two cryogenic plants the design of the two KPU cryogenic plants are identical to the CPU cryogenic plant. Each cryogenic plant has two NUOVO PIGNONE Frame 5 turbines powering 3 stages of recompression.

There are four generators (2750 kW each), 800 kW diesel generator, water wells, living quarters, sewage treatment plant and necessary facilities

Al-Raja Plant

Al Raja plant is located about 20 KMs east of KPU facilities (Kamil Processing Unit). It was constructed in 1992 with one stage -an Avon compressor driven by a Rolls Royce turbine receiving 400MMCFD residue gas from KPU via a 16” pipeline with a pressure of 3000 psi which was compressed to 5500 psi before being injected into the field via the injection manifold into injection wells AR#1,2,4,9,1015,16&19, Asaeeda#1 and DAW#1.

Al-Raja is accommodated with auxiliary utilities of two caterpillar gas power generators one MW each, two Ingersoll-Rand air compressors, a fuel gas heater, a utility water system, and accommodation.

Production test separator and manifold receiving 400 MMSCFD (million standard cubic feet per day) condensate from wells and send it to KPU via 20” pipeline to slug catcher in KPU with the pressure of 1500 psi. Each production well is choked from approximately 3500 psi to 1600 psi and goes through a gas heater to compensate for temperature drop due to pressure drop before going to the production manifold.

Al Raja facility expanded in 1999 with: -

Two stages NUOVO PIGNONE compressor driven by a NUOVO PIGNONE Frame 5 turbine, two low-temperature separators associated with heat exchangers, two caterpillars gas-powered generators one MW each, and new MCC.

Injection & production manifolds expanded & five injection wells AR#21,25,28,30&31 drilled & production wells as well.

Condensate is divided into two ways in the production manifold;

1-     To low-pressure manifold with the pressure of 1400 psi & into a 20” pipeline direct to KPU slug catcher with a quantity of approximately 400 MMSCFD to be processed there.

2-     To high-pressure manifold with a pressure of 2200 psi & 400 MMSCFD to low-temperature separators (LTS) with 200 MMSCFD each. Pressure & temperature dropped by JT v/v from 2200 psi & 120Fo to 1600 psi & 70 Fo, enter the separator & separation process takes place inside LTS (T=70 Fo, 1600 psi).

The liquid is drawn from Low-temperature separation) LTS (underneath through a 6” pipeline to production 20” pipeline (20,000 BBD in early days and depleted by years to around 1000 BBD in 2015) going to KPU slug catcher. 

Residue gas is taken from TS’s top and goes to 1st stage scrubber, to the suction of the LP compressor. The gas is compressed to 3000 psi, going to 1st stage gas/air coolers (10 fans), to 2ed stage scrubber, and the suction of the HP compressor. The gas was compressed to 5500 psi and sent to 2ed stage coolers to be cooled to 130-140 Fo before going to the injection manifold.

In sept-2010 the Avon compressor stopped due to a lack of gas during the g gas diversion to the YLNG project.

Novo Pignone K-3451 compressor discharge to injection manifold decreased to around 4900 psi due to Avon K-3351 compressor stop.

Novo Pignone K-3451 compressor stopped on 17/4/2015 no more injections due to a lack of gas from KPU due to diversion to YLNG.

In July 2015 a modification was carried out to the residue gas 16” pipeline coming from KPU in which a 12” line connected from the 16” line to the outlet line of LTS’s going to N.P K-3451 suction to enable CPUII operating.

K-3451 N.P compressor recently has been running with gas feed either from CPUII or KPU residue gas with a flow rate of 390 MMSCFD, 1350 psi suction pressure, and 4500 psi discharge pressure injecting to AR#1,2,10,16,19,28 &30 injection wells. Most injection & production wells are closed due to ongoing circumstances.