Recommended resources
The freely available resources this lesson will direct you to.
Hello, and welcome to the first lesson. This module begins with the plant as a whole before moving into instrumentation functions and safe work. If you can follow where the fluids go, it becomes much easier to understand why a pressure transmitter, level instrument, or shutdown valve is installed at a particular point.
Today you will trace a typical well stream from its inlet to the plant through separation, treatment, possible storage, and export. The important habit is to follow each resulting stream—gas, oil, and produced water—rather than imagine that everything stays in one pipe. Allow about 40 minutes, including the short video and selected reading.
Start with the mixture, not the equipment names
A producing well may deliver gas, crude oil or condensate, water, and sometimes sand or other contaminants together. A wellhead provides the connection and valves at the well; a flowline carries production toward the facility. Where several wells feed a plant, a gathering system and manifold route their flows into the appropriate processing train. Wells need not all enter at the same pressure: some may join a later, lower-pressure separation stage.
A block flow diagram shows the major equipment and the direction of material flow. It is a map of what happens to the stream, not a complete account of every pipe, valve, or instrument. At each block, ask two questions: What enters? and What distinct streams leave? A separator, for example, does not simply pass the inlet mixture onward. It gives gas and liquids different routes.
Watch this short facility overview, then use the supplied diagram to follow its streams.
Offshore Oil and Gas Production Facilities - Process Flow
Watch “Offshore Oil and Gas Production Facilities - Process Flow” from School of Engineering 101 for a narrated trace of the process diagram used below.
Watch the equipment overview to identify the wellheads, separators, compressors, dehydration unit, pumps, and metering systems. In the separation path, notice that liquid continues to lower-pressure vessels while gas leaves from their tops. Then follow the crude route and the gas route to export. The closing comparison explains where the illustrated high- and low-pressure wells join.
Follow the separation stages
Begin at the left of the diagram. The highest-pressure wells enter the HHP separator; the illustrated HP and LP wells join at their respective lower-pressure separators. Do not assume every well visits every vessel. Instead, select one inlet and trace its route.
For a stream entering the HHP separator, some gas leaves from the vessel’s upper outlet. Its remaining liquid passes to the HP separator, then to the LP separator, and finally to the surge vessel. At successive stages, the liquid is exposed to lower pressure, allowing more gas to come out in a controlled way. The pressures printed on this particular diagram—about 60, 15, 3, and 0.4 barg—help you recognize that progression. They are example values, not required operating pressures for all plants.
A production separator may also split oil from produced water. Gravity helps: gas collects above the liquids, while water tends to settle beneath oil. The pictured diagram does not draw a produced-water outlet or water-treatment train. That is a limitation of this simplified drawing, not evidence that the well stream contains no water. In a fuller plant diagram, follow separated water to its own treatment and approved disposal or reinjection route.
The gas outlets take another path. In the illustrated compressor arrangement, gas from the LP separator enters the first compressor stage; gas from the HP separator joins at the second; and gas from the HHP separator joins at the third. Compression raises gas pressure so it can continue through treatment and toward export. Thus, a gas parcel leaving the LP separator and one leaving the HHP separator do not necessarily pass through the same number of compressor stages.
There is a useful distinction at the surge vessel, too. Its purpose here is to buffer the outgoing liquid flow before pumping. Despite its ability to hold liquid temporarily, it is not the crude storage tank implied by the broader term “storage.”
Complete the routes: treatment, storage, and export
The drawing makes the main paths visible, but a real facility may need additional treatment and may place storage elsewhere. Read the selected handbook passages to put those possibilities in context.
[PDF] oil and gas production handbook | abb
Read selected parts of ABB’s Oil and gas production handbook to compare a general production overview with the particular facility pictured above. Concentrate on where streams split, what treatment accomplishes, and which storage arrangements are optional.
In “2 Process overview” (PDF pp. 7–8), inspect Figure 1, “Oil and Gas production overview,” then read the figure explanation on p. 8. In “2.2 Main Process Sections,” read “2.2.1 Wellheads” (pp. 13–14), starting at the wellhead description; then “2.2.2 Manifolds/gathering” (pp. 14–15), from the gathering-line description. Continue with “2.2.3 Separation” (pp. 15–16), from the separation overview; “2.2.4 Gas compression” (p. 16), from the gas-path explanation; and “2.2.5 Metering, storage and export” (pp. 16–17), from the export overview. For the branches missing from our diagram, turn to “4.2.7 Water treatment” (p. 44) and read from the water-treatment account. Finally, in “4.4.2 Storage” (p. 54), read from the storage alternatives.
After separation, treatment makes each product suitable for its next destination. On the pictured gas route, compressed gas passes through glycol dehydration to remove moisture, then through gas metering toward the gas export pipeline. Other gas compositions or delivery specifications may call for further contaminant removal. Neither the exact equipment nor its order is identical at every facility.
On the liquid route, the diagram shows liquid leaving the surge vessel, passing through a crude transfer pump, then a liquid metering system, and entering a crude export pipeline. The pump supplies pressure for transfer; metering measures the quantity exported. Elsewhere, crude may need further water removal or other conditioning before it meets its export requirements.
Storage is a possible stage, not a universal vessel between the pump and export line. Some facilities store treated crude in tanks or offshore storage before loading it into a tanker. Others, like the example drawing, send it by pipeline to a terminal, where storage may be located. Gas is commonly exported by pipeline rather than held in a large tank at the production facility. When tracing a drawing, place storage where that drawing actually shows it; when describing a typical process, state that its location and presence depend on the facility.
A compact way to retain the full picture is to account for all three destinations:
| Stream after separation | Typical further path |
|---|---|
| Gas | Compression as needed, gas treatment, metering, then pipeline export |
| Crude oil or condensate | Further liquid treatment if needed, pumping and metering, then pipeline export or storage and loading |
| Produced water | Water treatment, then disposal or reinjection under the facility’s requirements |
Key takeaways
A well stream enters through a wellhead and gathering route, then separation divides it into streams with different purposes. Track the gas, liquid hydrocarbon, and produced water separately. Gas may need compression and dehydration before export; crude may need further treatment and pumping; produced water has its own treatment route. Metering records exported product, while storage may be on site, at a terminal, or absent from a particular export path.
In the next lesson, you will revisit these same plant areas from an instrumentation perspective: what must be measured, controlled, safeguarded, and monitored to keep the streams moving as intended.