In terms of new technology within the subsea processing area, Pazflor is currently Total’s number one project in the world-----------www.africaoilgasreport.com

When you drill into a reservoir of oil, you do not just get what you came for. You also get sand and water. Conventionally this mixture of the desirable and undesirable is pumped out of the well, out of the sea and the constituents separated either on a floating platform or on land.
FMC Technologies in Norway is developing units that will do this on the ocean bed and will deploy the process on the Pazflor field in deepwater Angola.
There are two benefits of separating gas from the oil-water mix on the sea floor. First, it makes the whole process more efficient. The gas will flow freely up to the surface because it is so light and the oil-water mix can be pumped out using much less energy than if it had gas with it. Secondly the unit lowers the pressure at the seafloor, creating a greater difference in pressure with the reservoir below, which means that more oil can be extracted. So not only is it easier to get the oil out - but more oil can be extracted too.
Pazflor is in Angola’s Block 17. Total, the operator of the block, signed a $1 billion contract with FMC Technologies in 2008 for the subsea production system - which made it the most expensive subsea engineering, procurement, fabrication and supply (EPES) project at that time.
“In terms of new technology within the subsea processing area, Pazflor is currently Total’s number one project in the world,” says Gilles Barnay, Total’s manager of the subsea part of the project. “It is a world technology first for subsea separation applied to such a large scale development.”
Currently, the project is at the engineering stage. Engineers in Norway are finalising the details based on Pazflor’s specifications. If the project is carried out according to schedule, the field will come online in the second half on 2011, making it the fourth field in the block after Girassol, Dalia and Rosa. Production of Pazflor, which will have 49 wells, is estimated at 200,000 barrels per day. This will push total production in Block 17 to over 700,000 bpd.
Gravity is the science of the subsea separation unit. Gas is lighter than liquid, so when you put them in a vessel the gas will rise to the top and the liquid sink to the bottom. The gas will escape through a pipe at the top, and the oil- water mix will be pumped out the bottom.
Of course, what actually happens is not that simple. The whole mixture needs some extra help for the separation process to happen more efficiently. As soon as the gas-liquid mix enters the unit, for example, an inlet device helps to channel the gas one way and the liquid the other.
The separation technology here has been used for decades on topside installations, while the inlet devices see continuous development by FMC subsidiary CDS. The main difference with the subsea hardware is that it must be able to withstand the incredible pressure of being about a kilometre underwater. The casing must be much more robust. The steel walls will be about 10cm thick.
In fact, it is not just the outside pressure that is a challenge. The pressure inside can in some cases be higher. The separator needs to be collapse-proof, but also explode-proof.
One of the major challenges is how to install the whole system at such incredible depths, and how to make it such that each piece can he removed if necessary. Even though the separator is made in a way that should mean that it can work for 20 years without any maintenance, there needs to be a contingency plan for repairs.
The system will be installed in three stages. First, the foundations will go down, which have suction piles that go into the mushy seabed. Then the rest of the station is put into place. Finally, the separator is descended from a ship above.
To ensure high system availability each of six pumps will be regularly retrieved, typically every third year for preventive maintenance, so there will be maintenance work going on every year. Since two spare pump modules are supplied and a pump can be replaced in 24 hours, this will not slow down production.
Since subsea separation results in more oil, it is obviously a great advantage in a world where there is increased sensitivity about dwindling hydrocarbons resources.
But there is a key reason why subsea separation is only at its infancy: It is only now that the accompanying subsea technology - such as pumps, separators and instrumentation - has achieved enough operational experience to make giant projects like Pazflor operationally feasible. It takes a long time for technology: to be qualified for operation at the seabed. Subsea pumps, and the accompanying high-voltage power transmission, are now more reliable and have been developed for deeper and deeper waters.
The Pazflor project will be realised using a hybrid pump that has been specially developed for the job. Because most of Pazflor’s oil is very viscous, not all of the gas will be removed from it in the separator, so the pumps need to be gas tolerant.
FMC are pioneers in subsea separation. So far they have only built and implemented one project, at the Norwegian Tordis field, which was installed at the end of 2007. Instead of separating gas and liquid, the ‘Tordis project separated water and sand from the oil. the Tordis subsea separation and boosting system, together with topside modifications, will result in the production of an extra 35 million barrels from the field.
Pazflor is FMC’s biggest project. It will build three of the yellow cigar- shaped separation units, which will each be about 25m high and have a capacity to separate 110,000 barrels per day. The separators will eventually be built in Arles, France, the subsea pumps in Bergen, Norway, the umbilical in the US. The whole system will be assembled in Norway and tested before being sailed to Angola.
One of Pazflor’s distinctive features is that in three of its four reservoirs the oil is heavy and viscous, and the pressure is low. This means that without some help would be almost impossible to extract the oil. The separation unit will lower the pressure at the wellhead so that the pres sure difference with the reservoir is sufficient for the oil to flow up. And since the gas is being separated from the liquid, less energy is needed to pump it all out.
The pressure of the system is controlled by a Christmas tree at the well- head, and by the gas flow pipe coming out of the separator. Water will be injected into the reservoir to maintain the pressure there.

So far FMC has made a model of the separator and tested it at low pressure and with model oil chosen to be as close as possible to Pazflor’s crude. It has also been tested for sand- handling, to ensure that sand does not accumulate in the system. High pressure tests are being conducted in Solaize, France, with real crude.
FMC engineers believe that Pazflor will introduce new technology for many other fields around the world, where a separation unit is seen as the best solution for making low pressure reservoirs productive. They also see an increasing need for Tordis-type solutions, where the water is separated form the oil in units on the seabed.
“There are an enormous amount of fields that are producing so much water they simply cannot separate and treat it topside,” they say. “There is so much water that the water-production facilities are at the limit of their capacities, and thereby limits the oil production. If you remove the water subsea, you will be able to produce a lot more oil. It is likely in the future that many more fields will use sub- sea separation systems since they increase the total oil recovery.”
FMC is currently bidding for other projects based on similar technology at other fields around the world: “The basic driver is to produce more oil and produce it more efficiently,” says Gruehagen
Gilles Barnay of Total adds that the Pazflor project has been extremely challenging: “A lot of work has gone on in the preparation, from conceptual studies to the qualification of equipment. We have done lots of testing.”
Total are very excited about the technology’s potential: “It opens new possibilities in our portfolio to develop such difficult reservoirs,” he adds.