GoM projects to favor electric flowlines, low dosage inhibitors for hydrate prevention
Electrically-heated equipment and Low Dosage Hydrate Inhibitors (LDHI) are likely to become the key flow assurance technologies in the Gulf of Mexico (GoM), Stephen Hamilton, lead flow assurance engineer at Premier Oil said.
More than half of the projects starting up in the Gulf of Mexico over the next two years will be using subsea tiebacks, operating in water depths of over 2,000 metres below the sea level.
The high pressures and low temperatures in deep water environments support the formation of hydrates, making this a crucial development area for flow assurance.
According to Giancarlo Mangiafico, project coordinator at Eni Petroleum, hydrates have often been found in deep waters a year after a well has stopped operating.
This is why choosing the right flow assurance technology is of vital importance.
Although the use of LDHI and electrical risers and flowlines are relatively new technologies, market participants interviewed by Upstream Intelligence said these tools would yield better results and would require lower capital expenditure than thermodynamic inhibitors.
Using electrical current to mechanically heat the pipelines keeps the temperature in the lines above the levels associated with hydrate and wax formation.
While this technology has been around since the 1970’s, it is yet to see wide scale usage offshore in deep waters.
The associated power supply costs have thus far has been the main downside to using electrically heated equipment. Heat loss is greater at lower water depths and there is also an issue with loss of pressure.
However, newer technologies such as direct electrical heating pipe-in-pipe (DEH PIP) and electrical trace heating pipe-in-pipe (ETH PIP) are addressing these problems.
Both methods utilise PIP solution, which essentially means than one pipe is inserted into another larger pipe with insulating material between the two.
In an electrically heated PIP solution electrical wires run along the insulation, thus heating the pipe.
For the trace heating method, three cables are inserted in the pipe and as the cables meet at the connection the sum of their currents amounts to zero, which effectively earths the flow so there is no need for a return cable.
Some estimates place the potential capital expenditure (CAPEX) savings for trace heating PIP technology at 30% for lengths up to 24km.
Technip along with Total are at the forefront of developing the ETH PIP technology. It has already been utilised in the Islay development in the North Sea, albeit only in water depth of 120 metres.
DEH PIP solution is being used by operator BP on the Shah Deniz gas-condensate project in the Caspian Sea. The DEH PIP technology is also designed to reduce the power usage by forcing a single phase current directly to the pipeline.
Similarly to the ETH PIP this solution does not require a return cable as the electric “loop” is earthed directly to the seabed or seawater. Thus both technologies have the capacity to reduce the power usage.
“If you can get the power usage down and avoid using loop-flows you can make dramatic capital expenditure and operational expenditure savings,” a senior flow assurance engineer said.
Low Dosage Hydrate Inhibitors
Another proposed solution for subsea production lines has been using LDHI. Unlike thermodynamic inhibitors (MEG injections), which often require one-to-one chemical to water ratio, LDHI chemical requirements are much lower.
This would enable companies to make cost savings on the chemicals used.
LDHI fall into two categories - kinetic hydrate inhibitors (KHI) and anti-agglomerants. KHI delays hydrates from forming while anti-agglomerants restrict hydrates from reacting to each other by keeping hydrate crystals in slurry that can be flushed out with remaining fluids.
Dr Bahman Tohidi, Director, Centre for Gas Hydrate Research and Centre for Flow Assurance Research at the UK’s Heriot-Watt University, said testing on kinetic inhibitors has yielded very stable results.
“If something works in the lab then there is no reason to believe that it will not work in the field,” he said.
While the understanding of LDHI has increased greatly over the last five years, some key questions remain, such as establishing the precise mechanisms which make inhibitors work and how different system parameters might affect this.
LDHIs are also not very environmentally friendly and this is why they have not been used in other offshore locations, such as the North Sea.
Dr. Tohidi pointed out that the environmental regulations in the Gulf of Mexico are not as stringent and thus LDHI, such as anti-agglomerants, could be a good option for the area.
Despite successful test results in lab and field testing, Tohidi said the industry is conservative and slow to adapt new technologies such as LDHIs. This view was echoed by other market participants when asked about electrically heated equipment.
While the uptake has been slow, industry experts agreed the technologies set out in this article will play a key role in the next phase of subsea flow assurance.
“We are slowly ironing out all the snags,” a senior industry source told Upstream Intelligence.
Co-operation between different developers is increasing, which is likely to accelerate the cost-effectiveness of the technology, the source said.
“This time we don’t have to wait for thirty years until these technologies are perfected,” he said.