When North Sea operator Total was forced to evacuate its Elgin-Franklin asset on March 25, there were predictions that the cause, a very serious gas/condensate leak from a redundant production well, could trigger a major disaster.
Fortunately for the UK offshore industry and especially Total, this has turned out not to be the case.
Nonetheless, it is an extremely serious incident and one that could not have come at a worse time, given the manner in which Brussels is trying to grab control of North Sea safety.
For Total, the task is to stabilise the clearly-damaged G4 well, make it safe, discover the cause or causes and do whatever is necessary to bring the strategically important Elgin-Franklin asset back onstream.
And for the Health & Safety Executive’s Offshore Safety Division, the question to satisfy is, are UK high-pressure/high-temperature fields safe long-term and if not, what must be done to make them safe?
In an exclusive interview with Total E&P UK’s managing director Philippe Guys, Energy was told that E-F was built to the highest standards that prevailed at the time it was engineered in the late 1990s and that this was demonstrated by the safe shut-down and rapid evacuation of the Elgin platform on March 25.
He said the troubled G4 well was among those drilled early on and that it had produced for 10 years prior to last year’s decision to shut it in and carry out an interim decommissioning by using a steel plug to isolate it from the Fulmar sands reservoir.
“On the Elgin platform we have 12 wells of which 11 were drilled in the Elgin formation,” said Guys.
“Out of these 11, three were appraisal wells and were abandoned and never produced.
“The eight remaining wells have been producing since the beginning and G4 was one of these wells.
“A year ago, in February 2011, the well had stopped producing following an abnormal situation in the reservoir.
“It effectively lost its productivity. We decided to plug the well off from the general Elgin reservoir . . . the Fulmar zone.
“The intention was to fully decommission and abandon the well at a later date. This (plugging) was a temporary abandonment of the well.
“The technique of isolating a well from its reservoir is commonly used. You set a deep plug at the appropriate level; plus we have other means of stopping (hydrocarbons) flow like the downhole safety valve.”
The plugging appeared to work, as borne out by routine checks until February 25 when a sudden increase in well annulus pressure was noted.
“That’s when we decided that we would have to intervene quickly in order to stabilise the situation by pumping heavy mud,” said Guys.
Total had the jack-up Rowan Gorilla V in-field at the time, working on the G8 well.
“From the time we stopped the operation on G8 to being able to intervene on G4 was a lapse of less than a week. We started working on G4 on March 4,” he said.
It quickly became evident that gas and liquids were getting into G4 from a formation known as the Hod and which has a reputation for being troublesome in other parts of the North Sea, including at Ekofisk.
One way or another, the outer casing of G4 had been penetrated. However, at the time of writing (late April), it was still not known how the ingress came about.
“It’s too early to know the reason,” said Guys. “We have no evidence right now of any corrosion happening in this well, or any other factor. Something happened to allow Hod penetration of the casing. It could be a leaking joint, it could be cracking, it could be a parted joint. We don’t know.”
Guys said there was also insufficient knowledge of formation stability . . . how the rocks thousands of metres below the seafloor had withstood depletion from the HP/HT reservoir.
Initial reservoir pressure was 1,100Bar and, 10 years on, is now down to around 300-400Bar (more like a normal reservoir), which means a drop in pressure of 700-800Bar. But that is from the producing zone.
“You don’t know that the pressure has dropped uniformly within the reservoir,” said Guys.
He said the formations above (and for that matter below) the Elgin reservoir would still be under high pressure.
“So there is a difference between the formation above and the depleted reservoir,” he said.
“We still have to understand the behaviour of the formation above the producing reservoir and particularly the Hod. It’s a chalk formation and very tight.
“It is very different (to Fulmar) in terms of porosity, permeability and this is why it wasn’t identified as a producing zone.
“When we drilled the Hod before we drilled the Fulmar, it didn’t give any indication of having the potential to produce gas.
“But now we know that something modified the geology to enable this formation to fracture and for the chalk to release the gas it holds.
“Fracturing is used regularly in many tight formations to get the gas out.
“The influence of the depletion on the formation above might be one of the reasons but we don’t know how this might happen in reality. It needs further investigation.”
One of the hopes at Total is that the leakage of gas and liquids up G4 and out into the environment will peter out naturally; for sure there appears to have been a slowing.
THE OPERATION . . . THE OPTIONS
There are two options for dealing with G4 . . . dynamic well kill and drilling relief wells to intercept G4 in the Hod, some 4,000m down.
“We won’t rush to get these things done if we’re not convinced that we can do them safely,” said Guys. “It has to be step by step.”
As has been emphasised at press briefings at various times since March 25, Total is fortunate in that the Elgin platform is undamaged.
Several visits since are enabling the company to build confidence that safe access to the process, utilities, quarters platform can be achieved.
Indeed, as Energy went to print, remedial operations have already started with the first of two wells spudded by the Rowan Gorllia V jack-up with the Sedco 704 standing by to do the same; and a team from Wild Well Control of Houston were making final preparations to carry out the planned dynamic kill (or top kill).
“Since the first day of the incident we’ve been developing the two solutions in parallel and will continue to do so,” said Guys.
As widely reported, a successful dynamic kill could be achieved within just a few weeks from start of preparations, but drilling would take six months.
WWC are working with the intervention vessel Skandi Aker, plus the sixth generation semi-submersible West Phoenix. But for the Elgin emergency, the Aker would by now be en-route to West Africa to carry out routine subsea well interventions on Total assets in the Gulf of Guinea.
Dynamic killing is different from standard killing where, simplistically, a well is filled with mud, in that it uses a combination of mud weight and pumping to counter an ingress of hydrocarbons.
While the well is filling with mud, pumping is used to exert the additional pressure needed through circulation of the mud. It’s a classic way of killing a well.
“These specialists from Wild Well Control haven’t seen any show-stopper for doing the operation,” said Guys.
“Assuming a successful kill, the next step is to permanently abandon the G4 well. That’s the plan. Once the leak is stopped, we need to do a full work-over on the well and then carry out proper abandonment. That would take several weeks, even months, as we were doing on the G8 well.
“But it does not mean that Total can avoid drilling the relief wells. If the top kill is for some reason not working as planned, we need to already be drilling. We would not stop the drilling of any relief well until we are certain that we have control of G4.”
Assuming success with the well kill and follow-on abandonment of G4 and assuming it is not necessary to complete the relief wells, how long might it be before Total can restore production at Elgin?
Guys: “It depends on a lot of factors and it is too early to be talking about restarting production. It depends on the various investigations that will need to be carried and what comes out of those.
“We cannot restart production until we and the authorities are satisfied. How long that will take, I cannot tell you.
“The first priority is to stop the leak safely and as quickly as we can, then the investigations can be carried out; then we can learn from and share the results of the investigations.”
Obviously there could be a prolonged shut-down, especially if the HSE wants a full audit of the entire suite of wells in the Elgin-Franklin area, including satellites Glenelg and West Franklin.
Guys is prepared for this: “We need to be sure we understand what happened and we need to assess from the first to the last wells drilled.
“We are going to look at all our wells and discover what it is we may need to do to make sure that we have a safe enough environment to be able to start production.
“There is no way we can rush.”