Aker BP first ever to use new well stimulation method offshore

The first successful “Single-Trip Multi-Frac” campaign has been executed on the Valhall field. This specific method of well stimulation has never been done offshore before.

The method significantly reduces the cost of the well because less time is needed for use of vessels and equipment. Stian Ø. Jørgensen, head of the the Well Intervention and Stimulation Alliance in Aker BP, says:

“The traditional method takes two-three days to fracture a single zone of the reservoir. With ‘Single-Trip Multi-Frac’, we can now do two zones in a day. We also see a potential for doing this more efficiently.”

Tommy Sigmundstad, SVP Drilling and Well in Aker BP, says:

“The new method will make implementation of several projects possible. It provides more flexibility; we spend less time per well, and it decreases the unit cost of the operations. In turn, this results in a reduced price for the stimulation and we can bring the well on stream earlier compared with the conventional stimulation method that has been used. Therefore, we see a substantial upside through use of this stimulation method.”

The Valhall field has always needed stimulation to maximise production from the wells. This is because the field consists of chalk formations with low flow rates. A stimulation vessel and coiled tubing are needed for this operation.

The actual stimulation takes place by creating fractures in the reservoir, by high pressure pumping in sand mixed with a fluid system into the reservoir. The process is called fracturing and contributes to improve flow. Several zones in the reservoir must be fractured, and with the normal method, the coiled tubing is pulled out completely for each zone – an extensive and time-consuming process.

Jørgensen explains:

“What’s new about ‘Single-Trip Multi-Frac’ is that several zones can be fractured with just one trip down into the well. This is done with the aid of a sleeve installed in the completion that can be opened and closed down in the well.”

This allows to pump sand mixed with a fluid system into the well, while the coiled tubing remains in the hole the entire time. When one zone has been fractured, you close and move on to the next zone.

A total of four zones were stimulated using the new method during the ‘Single-Trip Multi-Frac’ campaign on the G10 well at the Valhall field centre in November. Three of the zones were stimulated on just one trip down in the well. The same method was also successfully applied on the first well on Valhall Flank West.

Valhall has produced one billion barrels since the field opened in 1982. The ambition is to produce another billion barrels. The ‘Single-Trip Multi-Frac’ method is well-known on land, including for production of shale oil in the US. Putting this method to use in new and more complex conditions 3 500 metres down in the well was no easy task. Aker BP and its partners NCS Multistage, Stimwell Services and Schlumberger have worked almost five years to solve the challenges. Jørgensen says: 

“When you want to develop pioneering technology or methods, you have to dare to fail. That’s how you finally end up with a good and proven result.”

Jørgensen says that a lot of important lessons have been learned in the process, with regards to equipment and the fluid system involved in the operation. He says:

“The biggest challenge has been that the coiled tubing has become stuck and we have not been able to break loose. We have worked quite a lot on understanding the ‘energy regime’ in the well. We have also optimised the tool at the end of the coiled tubing and worked intensively with the fluid system to reduce the risk of getting stuck.”

Jørgensen emphasises that Aker BP will continue to stimulate wells in the traditional manner in reservoirs where this is considered to be the best method.