Leaving no rock unturned

Elaine Maslin examines new UK government funded seismic shoots and data reprocessing, all free to the industry, which are among initiatives aimed at boosting UK Continental Shelf exploration.

Seismic lines – where last year’s Rockhall Trough and Mid North Sea High seismic lines were shot. Image from OGA.

While exploration has been dwelling at historic lows on the UK Continental Shelf (UKCS), a scheme to open up underexplored areas of the basin could yet turn the trend around.

The UK’s still relatively new Oil and Gas Authority (OGA) was given government funding to shoot seismic over the Mid North Sea High, in the central North Sea, and the north Rockall Trough, west of Scotland, last year, supported by legacy data reprocessing. Both are being used to decide what will be offered in the 29th licensing round, which was due to open early August. Further, the OGA is eyeing yet more new seismic acquisition in areas of western Britain and the East Shetland Platform this year.

Gunther Newcombe, director of exploration and production at the OGA, and a geologist by education, thinks there’s a lot that has been overlooked in the basin. “People call the area [North Sea] mature, even super mature, which is true for some areas. But, some mature areas, like the southern North Sea, still have potential. Carboniferous tight gas has a lot of potential, for example.”

To shine a light on these underexplored areas, the OGA has spent £20 million (US$26 million) of government funding on new 2D seismic data.

The new seismic was shot by WesternGeco, covering 200,000sq km of the UK Continental Shelf. What’s unique is that it, and the 20,000km of legacy data, is being made freely available to the industry – in processed and unprocessed form. Furthermore, some of the legacy data are lines that can no longer be shot again, due to fishing gear now in the area. Some of the 1980s seismic was also shot with dynamite, which offers a good quality clean source but is no longer used.

The shoot used long offset broadband seismic for lower frequency data, something that has been missing in the past, OGA says. Gravity and magnetic data were acquired at the same time. To get the data to the market as fast as possible, onboard processing was carried out from September 2015 to March 2016. By 24 May, some 6000 data packages had been downloaded.

Rockall Trough

The Rockall Trough and Mid North Sea High were chosen because they’re underexplored. Fiona Legate, senior analyst, UK Upstream Oil and Gas, Wood Mackenzie, says only Austria’s OMV, an integrated oil and gas firm, and independent minnow Parkmead, have acreage in the Trough.

According to PGS, the Rockall Tough has fewer than 10 wells per 1000sq km. Newcombe says that only two discoveries have been made in the Rockall area: Dooish, on the edge of the Trough in the northern Irish Rockall Basin; and Benbecula, in the northeast Rockall Basin in the UK sector. Legate says that six exploration wells have been drilled in the Rockhall Trough itself to date, largely in the 1980s and 1990s, and all were dry holes.

Some of the challenges in the Rockall are deeper waters, but also Basalt intrusions, which make mapping of migration complex. “It is deepwater and there has been a lack of data,” Newcombe says. “There was a survey in 2014 by BP with better definition. It was the first shoot in that area. We now have 10,000sq km [in the area and] from that it will be hard to define a prospect to drill. But it can show the play potential in order to do more seismic.”

Mid North Sea High

Unlike the Rockhall Trough, there are quite a few acreage holders, including majors and independents, in the Mid North Sea High. But still, it has been described as “one of the last remaining underexplored areas of the UKCS” by geoscience firm Polarcus, with a possible Devonian-Carboniferous petroleum system that hasn’t been tested and has been hard to image.

Legate says that 23 exploration wells have been drilled in the Mid North Sea High, mostly in the 1960s-1980s. One well had gas shows and another oil shows, she says.

“The Mid North Sea High has in part been explored in the past, but it has lacked good quality data for the industry to create a deeper understanding of the geology,” Newcombe says. Firms have also largely focused on the Permian in the past. “We have new data and reprocessed data, plus the BGS (British Geological Survey) study on the northern North Sea Paleozoic. This will give people greater insight.”

The new data is giving companies the opportunity to look at deeper horizons, he says. The BGS survey on the northern North Sea Paleozoic is also letting people see where plays extend into the onshore, from which they can extrapolate back to the offshore.

Licensing round

The Rockall Trough and Mid North Sea High will feature heavily in the 29th licensing round, a round likely to be light on license commitments, Legate says. Just seven well commitments were featured in the 28th round, which closed right at the start of the oil price crash. With frontier acreage involved, fewer well commitments can be expected this time round. More likely, data reprocessing or shooting seismic surveys could be expected.

This makes it an opportunity, Legate says. “It is an opportunity to pick up acreage cheaply with few commitments. Any work completed would benefit from the low cost base we are seeing, so there is a bit of an opportunity here. What is interesting is the new Innovate License, which gives companies up to nine years,” she says. “Companies also don’t have to prove financial capability. This could attract some of the smaller exploration and production companies to acquire acreage.”

Instead of having different licenses, the Innovate License will have a phased approach with different steps, covering data reprocessing, seismic acquisition, wells, etc. “It is more flexible and pragmatic and gives us more flexibility to mature more of the work programs,” Newcombe says. The bid scoring system is also being updated.

Go west

The next seismic shoot will focus on south west Britain and east of Shetland, which will be backed up by reprocessing legacy data in those areas. Areas to be targeted include Morecambe Bay, the Irish Sea, and the Minches and the East Shetland platform.

“People forget areas, like the Western Approaches,” Newcombe says. “No seismic has been shot for 20 years there. All the Irish area has been covered, but not the British side. They drilled 20 years ago and didn’t find anything massive, so it has been forgotten.” Another forgotten area is western Britain, such as off Morecambe Bay where the Dragon discovery was made on the border with Ireland, he adds.

The Orcadian Basin in the East Shetland Platform could also prove prospective. It’s another area with fewer than 10 wells per 1000sq km, PGS says. “People said it could be really quite prospective, but it’s a different geology to Brent, it’s slightly older, so in the past people kept to what they knew,” Newcombe says. But, he says there’s a similar high in this area to that on which Norway’s massive Johan Sverdrup discovery was made. “[There has been] some taking from Norwegian learnings and looking at the Orcadian High,” he says.

To further spur commercial activity, a £500,000 competition has been launched to encourage geoscientists and engineers to develop interpretations and products potentially using last year’s new seismic data. Wells data from the Outer Moray Firth has also been released to industry.

The industry is also taking matters into its own hands. In the mature areas, a group of operators is working together to organize a “group shoot” seismic campaign. In addition, the BGS, working with industry and government funding, has completed its study of the northern North Sea Paleozoic potential, delivered to its operator sponsors this year. It is due to be released to industry more widely in 2017. This project aims to encourage research deeper and wider than conventional hydrocarbon horizons, covering the Mid North Sea High, Moray Firth and Orcadian Basin and the Irish Sea.

Some £700,000 funding has also been put into the Lyell Centre in Edinburgh, a joint venture between BGS and Heriot-Watt University. Pst-doctoral study in geoscience and reservoir engineering is also being funded.