The activity in the Oil and Gas sector can be broadly divided into three sectors: An upstream, midstream and downstream sector. The upstream sector is the part of the Oil and Gas industry involved with finding oil fields and bringing oil up to the ground. Upstream activities include exploratory
work, such as the search for underground (or underwater) Oil and Gas reservoirs, and the initial drilling, followed by the production phase, which is the actual extraction of oil from the ground. A whole range of
different structures (platforms) are used offshore for drilling and production operations, depending on size and water depth. For depths more than 2000 meters, the most used platforms are the semi-submersible platforms (for drilling and production), rig vessel (for drilling only) and FPSO (Floating, Production, Storage and Offloading) for oil production, storage and transfer of oil
illustrates the three types of platforms cited above.
(a) Drill Rig 5 FPSO
(c) Semi-submersible
Offshore platforms used in Oil and Gas
In addition to oil prospecting, water, gas and sediments are also present in the oil reservoir, meaning
2
that when the petroleum comes up to surface it is a mixture of three fluids: Oil, gas and water.
1.2 illustrates a typical Oil and Gas reservoir, in which the presence of oil, gas and water can be
observed.
Typical Oil and Gas reservoir
It is thus recognized that for the processing of the three types of fluid (oil, water and gas), a set of equipment should be required to process them. This processing will usually depend on economic
viability criteria, which will require simpler processing units, based on decantation, use of separating vessels and other physico-chemical processes, or even more complex processes including oil
treatment, gas, and treatment of water for disposal or re-injection into the wells, and normally recent Oil
and Gas platform use the complex process configuration [7]. Although there is a wide range of sizes
and layouts, most production facilities have many of the same processing systems illustrated in the
Oil and Gas Production Overview [8]
the mixture oil, gas and water coming from the production manifolds enter in different
separation stages, which the main objective is to separate the mixture (oil, gas and water), originating
three different process: Water treatment, oil treatmenent and gas treatment.
Until a few years ago it has been a common practice in oil fields to flare associated petroleum gas
resulting from the initial treatment of crude oil. To minimize this practice, the Oil and Gas Industry has
decided to process the gas, and for this reason has historically employed two options, gas re-injection
and monetization, to use the associated gas; these options are only extensively used in a few
economically developed oil producing countries
When the gas leaves the separators, it has generally lost so much pressure that it must be
recompressed to be transported. The compression process includes a large section of associated
equipment such as compressors, scrubbers (to remove liquid droplets) and heat exchangers, lube oil
treatment, etc. The compressors act as the main important device in this process [10].
Figure illustrates a typical part of gas compression Piping and Instrument Diagram (PID) in which a
typical compression process is shown containing some of the traditional instruments used in a
compression of gas 2. Incoming gas is first cooled in a heat exchanger, It then passes through the
scrubber to remove liquids and goes into the compressor. The anti-surge loop and the surge valve
(ASV 101) allow the gas to recirculate.
Figure : Illustrative gas compression PID [11]
1.2 Literature Review
The literature review of this work is divided into two subsections. In the first subsection the work
concerning the centrifugal compressor is reviewed, with a special highlight to its relation with the Oil
and Gas Industry. The second subsection explores the study of the RAMS (Reliability, Availability,
Mantainability and Safety) analysis, by reviewing its application in the industry, with a special attention
2Note that several instruments are not shown for simplicity
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to its application in the Oil and Gas Industry as well as some attention to works related to the gas
compressors.