There has been "significant progress" towards plans to stop a gas leak on an offshore platform, the operator has said.
All 238 staff were evacuated from the Elgin platform, around 150 miles off Aberdeen, when it began leaking gas more than two weeks ago.
About 200,000 cubic metres of gas are escaping from the platform each day, coming out from a rock formation below the sea. It is then escaping into the air from a leak on the platform at the top of the well, about 80ft above sea level.
Oil and gas company Total said preparatory work for the planned drilling of both a primary and back-up relief well continued this week with two flights to the platform to assess the situation.
Total employees and specialists from Wild Well Control, a specialised well intervention company, have now travelled to the platform three times.
A spokeswoman said: "During these two visits this week, additional valuable information was gathered to prepare for the well control operation and to carry out essential cleaning of key areas around the wellhead, where waxy deposits had accumulated."
She added that two rigs are being mobilised for the drilling of the relief wells.
The Sedco 714, which is expected to start drilling first, has been outside the Elgin exclusion zone since April 8, while site surveys for its exact location are completed.
The second rig, the Rowan Gorilla V is closing down operations on the nearby West Franklin field before repositioning itself to drill the second relief well.
Two further vessels are being mobilised to support the drilling, with the West Phoenix, a semi-submersible drilling rig, on stand-by outside the two nautical-mile exclusion zone, and Skandi Aker, a light intervention vessel, is in Peterhead harbour being fitted with dedicated equipment to support the operations.
The drilling of a relief well is one option being explored by the company, while the other, to pump heavy mud into the well, is also being considered.
Experts have said drilling a relief well could take months, while blocking the leaking well would involve people re-boarding the platform.
No final decision has been taken on the course of action but the spokeswoman said the operation to stop the leak is "progressing according to plan".
Earlier this week the Scottish Government said taste testing of fish from the area close to the gas leak in the North Sea had shown they are "untainted".
A research vessel collected fish, water and sediment from the edge of the two-mile exclusion zone around the platform last weekend.
The first stage of testing of the fish samples involved a panel of specially trained sensory testers at Marine Scotland Science in Aberdeen, who can detect the taint of hydrocarbon contamination.
They concluded that the samples contained no trace of hydrocarbons.
However, full chemical testing of all environmental samples is still being carried out.
Environment Secretary Richard Lochhead said: "The environmental impact of this gas leak has been minimal so far. However, it's important we take precautions and analyse all available data. Therefore, it's reassuring that sensory testing of the fish samples gathered by the Alba na Mara (vessel) have found they are untainted by hydrocarbons.
"Full chemical analysis work, including water and sediment samples, is ongoing and will provide further clarification on any impact.
"We will continue our monitoring activities for the duration of this incident so we can assess any impact on the marine environment and respond as needed."