UK independent Arenite Petroleum is seeking investors to help it drill a proof-of-concept horizontal well into UK Permian carbonates, as well as test an underlying Carboniferous strata.
The move, which will target two horizons in the Permian carbonates, follows a re-evaluation of historic well and seismic data, which identified a large gas field offshore North Yorkshire.
Arenite, with joint venture partners Europa Oil and Gas, re-analyzed the results of several wells drilled by Total over 40 years ago. Five wells flowed gas at high rates (three of those wells flowed over 15 MMscf/d) but were viewed at the time as sub-economic.
In 1991, Conoco drilled a further well which flowed at 34 MMscf/d and 1230 b/d condensate from fractured Permian carbonates. At the time, companies considered the gas finds small and subsequently relinquished their licenses.
Arenite completed a detailed re-evaluation using advanced seismic imaging techniques, coupled with industry experience in analogue gas fields where horizontal drilling and well completion techniques have redefined commerciality. Arenite says its mapping reveals a huge accumulation in naturally fractured Permian-aged carbonate rocks a few miles offshore with vast underlying Carboniferous potential.
Mike Cooper, Director & Founder at Arenite Petroleum Limited explains: "We name this accumulation the Maxwell gas field. It is a giant gas field which has been hiding in the open, analogous to the realization made many decades ago that a series of small gas discoveries in the Netherlands were indeed part of the giant Groningen gas field, now the largest onshore gas field in northwest Europe. Though the sustainable production rates at the Maxwell gas field are yet to be established, with state-of-the-art drilling, completion and production techniques, Arenite believe commercial deliverability can be achieved. Arenite has presented compelling technical data at recent technical conferences to demonstrate the vast potential."
Cooper says the Carboniferous is known to hold huge potential in both shale gas and tight sandstone strata throughout Northern England, as outlined in a British Geological Society/Department of Energy and Climate Change Bowland Shale gas study.
"Indeed, to the west of Arenite’s acreage, Third Energy produce from naturally fractured Permian carbonates at Ryedale and are planning to test the Carboniferous at Kirby Misperton in 2017," says Cooper.
There is also interest in this type of reservoir from the majors. Oil major BP has started drilling a proof-of-concept well to test the Carboniferous beneath the producing Ravenspurn gas field, in the southern North Sea.
This well is projected to cost ~£100 million to drill, including a long-term test. Drilling at Maxwell will cost a fraction of this sum, says Arenite.
Egdon Resources is planning a 2017-18, well immediately north of Arenite’s acreage on its Resolution discovery, which is one of the structural culminations of the bigger Maxwell gas field.
"Using modern geological techniques, we can explain that the four gas discoveries (wells 41/18-1, 41/20-1, 41/24a-1 & 41/25a-1) made over a large area, form part of a very large gas accumulation stretching over hundreds of square kilometers," says Arenite. "At the time of drilling, these discoveries were interpreted as small accumulations. However, it can now be demonstrated most of these wells flow tested small isolated 'pop-up' fault blocks. Had Conoco drilled a horizontal well away from these anomalous pop-up features, as was their intention before encountering drilling problems, we believe such a well would intersect natural fractures which would have delivered commercial flow rates, proving the extensive accumulation.
"The old exploration wells experienced significant challenges with high formation pressures, which caused drilling problems and yielded anomalous results when flow tested. We now understand that the sequence of rocks these wells drilled through were overpressured due to there being an extensive gas column, producing high pressures at relatively shallow depths. This phenomenon is now well understood and can be managed using appropriate drilling techniques.
"High pressures within the target sequence are also known from potash mining operations in the area. This anomaly is compounded in the offshore Scarborough area by the presence of long gas columns. Whereas the gas industry can overcome the problems drilling from surface using a column of drilling fluid to mitigate the high pressures, drilling underground boreholes within mines does not benefit from such mitigation."
Arenite says it has met and corresponded with The Crown Estate and York Potash (Sirius Minerals) and believes producing this high-pressure gas is the best way to enable safe future offshore mining operations. "The flow rates that have been achieved offshore would almost certainly overwhelm a mining operation. The problem area is east of a series of major geological faults which trap the gas before it gets onshore," it says.
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