A few months ago, I was opportuned to spend some time at Seplat petroleum development company (SPDC) in the southern part of Nigeria. I had studied chemical engineering for about three years but I hadn't acquired any field experience or a real world opportunity to put all I had been taught into practice. So when this chance came I gladly took it with open arms. I will be sharing a little of the knowledge I gained while working at an oil and gas integrated facility.
I was posted to different facilities at different times but I will talk more on the flowstation and the liquid treatment facility located at Amukpe, Delta State Nigeria.
THE FLOWSTATION
A flowstation is usually the first stop for hydrocarbon fluids coming from crude oil and gas wells. It's purpose is to separate the hydrocarbon into liquid and vapour phases, reduces turbulence and pass on the liquid to the next facility.
The capacities of Flow stations are classified as;
Single bank station
Double bank station
Single bank stations are designed to flow thirty thousand barrels (30000bbls) of crude oil daily while double bank stations flow sixty thousand barrels (60000bbls) of crude oil daily.
FLOWSTATION PROCESS OVERVIEW
Hydrocarbon enters the flowstation from the oil and gas wells through inlet pipes which have been bulked based on like pressures so as to ensure proper flow of the hydrocarbon. The well alignment process ensures that oil and gas wells of widely dissimilar pressures do not flow together as this would lead to problems on the flow pipelines as the principle of survival of the fittest would have to come into play (i.e hydrocarbon with higher pressures will flow leaving those of lower pressures behind).
The hydrocarbon enters the inlet manifold which houses ligament valves meant for the control of the direction of the flow of the oil and gas wells into different headers.
There headers include;
(1)The Test header
(2)The Low Pressure header
(3)The High Pressure header
The headers are protected with relief valves which are located at one end of the the inlet manifold.
The different headers direct the flow of hydrocarbon into different separators which are;
(1)The High Pressure (HP) Separator
(2)The Low Pressure (LP) Separator
(3)The High Pressure/ Low Pressure Separator which can serve as either a HP or LP separator depending on the configuration.
(4)The Test Separator.
The hydrocarbon flows into the high pressure separator which has a static pressure of 3.5 bars.
The HP separator’s static pressure is maintained by BPCVs (back pressure control valves) which receive signals from pressure controllers. These pressure controllers have a set point of 3.5bars hence they detect and send signals to the back pressure control valves to either open up to vent out gas or close up to hold in more gas depending on the pressures of the oil and gas wells flowing into the separator.
The High pressure separator is a two phase separator. This means that it separates hydrocarbon into liquid and gas phases. The high pressure separator helps to also step down the pressure of the hydrocarbon which it separates. The liquid from the HP separator flows into the LP separator through the help of a dump valve.
The LP separator has a static pressure set at 1.8bars. This static pressure is also maintained by the BPCVs and the LP vessel, also being a two phase separator separates the hydrocarbon into liquid and gaseous phases.
Note that all the gas separated by the HP & LP separators are sent to an Associated Gas Compression Station (AGCS) which compresses the gas and sends it back to the oil and gas wells to help the upward flow of weak or dormant wells through the process of gas lifting.
The liquid separated by both the HP & LP separators is then sent to the liquid treatment facility for further separation and treatment.
THE ROBERT-SHAW PANEL
The Robert-Shaw Panel, also referred to as the fail safe panel is the heart of the flowstation as it ensures that the entire process is running in safe mode in critical conditions
The RS panel is connected to all vessels in the flowstation and works in conjunction with all pressure and level controllers to sound alarms when each of these set points have been exceeded or have not been met.
The RS panel switches the flowstation to full manual mode when any maintenance jobs are being carried out.
THE KNOCKOUT VESSEL
The knockout vessel serves as a receptacle to take in all gaseous discharges that are being sent to the flare tip in the facility.
It takes in gas from process and relief valves and ensures that liquid doesn’t get to the flare tip. This is possible as it is connected to the saver pit and any liquid that enters the knockout vessel flows by gravity to the saver pit.
LIQUID TREATMENT FACILITY
The liquid treatment facility is a facility which serves to receive hydrocarbon from the flowstation, separate the hydrocarbon on the basis of crude oil, water and gas by the help of 3 phase separators which further helps to lower the BS&W (Basic sediment and water) of the hydrocarbon and inject the produced water down to disposal/injection wells by the help of injection pumps.
The liquid treatment facility at SPDC receives hydrocarbon from all Seplat oil and gas fields within the Delta state axis (Oben, Sapele and Amukpe) and helps to further separate the hydrocarbon components to produced a much drier crude oil product.
LIQUID TREATMENT FACILITY (LTF) PROCESS OVERVIEW
Hydrocarbon from the flowstations at Oben, Sapele and Amukpe(Seplat oil and gas fields in Delta State, Nigeria) which have all been injected with demulsifiers all flow into the LTF at its inlets manifold header where they all comingle and enter into the 3 phase separators.
The 3 phase separators help to separate the hydrocarbon based on crude oil, water and gas phases by taking residence times into consideration to create good interface levels between the oil and water.
The 3 phase separator sends out oil through an oil outlet to the export pumps which send the crude oil down to the Rapele gathering manifold which then diverts the crude oil flow to either the Forcados oil terminal or the Warri Refining and Petrochemical Company (WRPC).
Produced water from the 3 phase separator is sent to the mono pumps which help to further pump the water into the produced water treatment (PWT) package.
The 1st stage of the PWT package is the de-oiler. The de-oiler sends any oil separated from the water through an oil reject line back into the 1st stage separators. The water flows into the de-sander. The water flowing through the oil reject line is injected with water clarifiers to clean the water, reduce turbidity and recover oil from produced water.
The water enters the de-sander where any solid particles accompanying the water are removed. The produced water flows into the bag filters which help to filter out any particles that accompany the produced water.
The produced water then flows downstream to surge tanks. In the surge tanks, the water enters one surge tank and lets the water settle. It then flows into another surge tank through an equalizing line.
The produced water is then pumped into disposal wells by water injection pumps.
A lot of other processes occur before crude oil is gotten in its final and retail form. Such processes include subjecting the crude oil to fractional distillation in fractionating columns. That process is another entire exciting part of chemical engineering.
I hope this post was able to enlighten those that were in the dark about this industrial process. All images and texts are original works of 