Apr 13, 2009

Production System on Offshore Platform

Many permanent offshore platforms have full oil production facilities onboard. It is the facility which performs processing of production fluids from oil wells in order to separate out key components and prepare them for export. Typical production fluids are a mixture of various hydrocarbons and are valuable in this natural form.

The production systems consist of the following :

On-boarding System Oil Production Separation/Dehydration Oil Export Well Cleanup and Unloading Gas Compression System (i.e. Surge, LP, MP and HP Compression System) Gas Reinjection System

The on-boarding system is designed to receive subsea wells production from the Drill Centers. HP Separators are designed as two-phase separator to separate out gas and liquids of the well fluids for further gas and oil processing downstream.

Oil from the HP Separators will be routed to a series of vessels for stabilization and dehydration prior to export.

The MP Separator is provided to remove gas and water from the crude oil. Separated crude is routed through

the Oil Heater to enable the oil to achieve the required RVP, before being transferred to the LP Separator and

then the Oil Treater for dehydration to meet 0.5 BS&W. The treated oil will be routed to the Surge Vessel,

which is provided (as a buffer) to hold up surge volume for the Oil Booster and Export Pumps. Oil Booster

Pumps will then boost the crude oil pressure for the dry oil from Surge Vessel to be transferred to the Crude Oil

Export. Crude Oil Export Pumps are designed to deliver the dry metered oil to onshore during normal

operations via pipeline or tanker.

Process Flow Diagram of Typical Platform Separation Process

The Well Cleanup Separator is provided to handle well unloading fluids and containing drilling and completion

fluids with spent acids.

The stages of compression (i.e. Surge, LP, MP and HP Compression Systems) are to be provided to satisfy the

demand of gas gathering from various separators, fuel supply to fuel consumers and gas reinjection.

The Gas Reinjection Manifold will gather gas discharges from HP Compression System for reinjecting back to

the reservoir.

Oil and Gas Processing (Oil Section)

Figure 1: Typical PFD of Oil and Gas Processing

The typical process flow diagram (PFD) of oil and gas processing for most of fixed or floating offshore production. Two sections consists crude oil stabilisation and associated gas compression.

Crude oil stabilisation section is processing the crude oil with export oil specification. The common export oil specification are true vapour pressure (TVP 100 kPa @ 50ºC) or reid vapour pressure (RVP 7psia @60ºF) and water content; basic sediment and water (BS&W) maximum at 0.5 vol%.

Typical arrangement of crude oil separation and stabilisation are; 3 Staage Separator (HP-MP-LP Separators) and Electrostatic Coalescer. An Inlet Heater is required at upstream of HP Separator. The outlet temperature is above emulsion breaking temperature to increase oil and water separation. The HP Separator separates oil, water and gas with 3-5 minutes residence time. The recommanded operating pressure for separators are: 10 bara (HP), 4.5 bara (MP) and 1.5 bara (LP)

Figure 2: Horinzontal 3-Phase Seaprator

The HP Separator, 3 phases (oil, water and gas) separation, horinzontal vessel with wier. Separation of oil from water relies on specific gravity. The gas goes to compression train, the water goes to Produced Water System, and the oil goes to Interstage Heater.

Interstage Heater further is heating oil to above wax dissolve temperature 75ºC. The oil send to MP Separator for further oil, water and gas separation. The oil send to LP Separator.

LP Seaparator stabilises oil as per requirement of TVP. The LP Separator may operates as 2 phase or 3 phase separation due to low water content in oil.

The oil from the LP separator is pumped via a low shear pump to the coalescer. The coalescer removes remaining water content in oil.

The BS&W and salt content of the oil is managed by the removal of produced water at each stage of the process and by the coalescer. The stabilised and dried crude then flows to the production tanks, via a crude cooler.

Posted by boonlee's blog at 6:16 AM Labels: Process technical