Drilling programmes prosper on back of exploration investment

Paul Boughton

Drilling activity remains robust around the world, with the US, Europe and the Far East attracting major exploration investment. Eugene McCarthy reports.

BP has added two drilling rigs to the deep water Gulf of Mexico, bringing its fleet to a company record nine rigs as it continues to develop its portfolio of assets in the key US offshore basin.

One of the rigs is a new ultra deep water drill ship known as the West Auriga that is under long-term contract to BP from Seadrill, a leading international offshore drilling contractor. The vessel, capable of operating in up to 12,000 feet of water, has begun development drilling work at BP's Thunder Horse field.

The other is a reconstructed drilling rig on BP's Mad Dog oil and gas production platform. It replaces the original rig on the platform that was badly damaged and left inoperable by Hurricane Ike in 2008. With the new, state-of-the art rig, the platform recently resumed development drilling at the massive Mad Dog field complex (Fig. 1).

"The addition of these two new rigs reflects the vital importance of the deep water Gulf of Mexico to the future of BP," said Richard Morrison, regional president of BP's Gulf of Mexico business.

BP currently anticipates investing on average at least US$4 billion (EUR3 billion) in the Gulf of Mexico each year for the next decade. Part of this involves the Atlantis North expansion - the first of seven additional wells to be tied back to the existing Atlantic platform.

Back in Europe, Lundin Norway, a subsidiary of Lundin Petroleum, has announced the flow test rate of the previously announced Gohta discovery of about 4300 barrels of oil per day (bopd). Gohta is Lundin Petroleum's first oil discovery in the Barents Sea, offshore Norway. The well 7120/1-3 operated by Lundin Petroleum was drilled on PL492 approximately 35 km north of the Snohvit field in the Barents Sea. The well proved oil in contact with an overlying gas cap.

The purpose of the well was to prove petroleum in reservoir rocks in Triassic sandstone reservoirs and Permo-Carboniferous carbonate reservoir. In the carbonate reservoir the well found a 25 metre gross gas column above a 75metre gross oil column in karstified and dolomitised limestone. The Triassic sandstone was water bearing.

A drill stem test (DST) was performed to assess the quality of the carbonate reservoir. The DST produced a flow rate of approximately 4300 bopd through a 44/64" choke with a gas/oil ratio of 1040 standard ft3 per barrel. The main flow of the reservoir was stable over 24hours and the pressure build-up lasted 36 hours and did not show any barriers such as faults or significant reservoir characteristics variations. This is the first successful test of Permian carbonates reservoirs on the Norwegian shelf.

The DST result has confirmed good production properties of the reservoir. The preliminary evaluation of the gross recoverable oil and gas resources from the Gohta discovery is estimated at between 105 and 235 million boe of which the oil resources are between 60 and 145 million barrels and the gas resources are between 275 and 545billion ft3 of gas.

In Turkey, TransAtlantic Petroleum has announced that it expects its 2013 year-end exit rate to top 5,000 boed. The company currently has three active rigs in south eastern Turkey and two active rigs in the Thrace Basin in north western Turkey. TransAtlantic says it expects to add one drilling rig in Bulgaria and release one drilling rig in the Thrace Basin in Turkey to maintain a five rig operation going forward.

TransAtlantic recently drilled a horizontal well in the Selmo field (100 per cent working interest) in south eastern Turkey targeting the maximum stratigraphic depth (MSD) zone at a depth of approximately 5,200 feet. The company is currently drilling a second horizontal MSD well, with up to another five in planning.

Also in south eastern Turkey, the company recently drilled the Göksu-5H horizontal well (100 per cent working interest) to the Mardin zone at a total measured depth of 5400 feet.

A further two exploration wells are being drilled in the Molla area. The Tepe-1 (100 per cent working interest) has a targeted depth of 9500 feet in the Mardin and Bedinan formations on an exploration license the company acquired in May 2013. The Ambarcik-2 (50 per cent working interest) has a planned total depth of 9750 feet targeting the Bedinan formation in the Arpatepe license. The company planned to drill at least one vertical well in the Arpatepe field (50 per cent interest) before the end of 2013.

In the Far East, Petrogas subsidiaries Petrogas Island and RHP Salawati Island have commenced drilling at the Zircon-1 exploration well in the offshore area of the Salawati Kepala Burung production sharing contract, West Papua.

Located in water depth of 32 metres, the well is planned to reach a total vertical measured depth of 1205 metres. It is the first of a multi-well high impact drilling programme to be drilled in this offshore area.

The Zircon prospect was high-graded for drilling after the company conducted a 450 km2 3D seismic survey in 2010.

Zircon-1 is located 4.3km south west of the Koi-1 discovery. Koi-1 was drilled in 2000 and the well flowed 980 boe/day and 2.7 million standard ft3/day of gas through a drill stem test from the Miocene Kais limestone.

Baker Hughes extends cutter life and bit runs

Baker Hughes has launched the StayCool multidimensional cutter which helps operators drill to total depth faster and more cost effectively by extending cutter life and footage per run. Used exclusively on the Hughes Christensen Talon platform of premium polycrystalline diamond compact bits, these cutters incorporate a contoured diamond table, wear-resistant diamond materials, and new interface designs.

"Historically, operators would design more cutters into a bit to compensate for cutter wear or damaged cutters, which isn't always the most efficient way to drill," said Scott Donald, vice president of drill bits for Baker Hughes. "The StayCool cutter allows us to offer a bit that maintains the same cutter density but can perform better when cutters are worn."

In challenging environments such as interbedded sandstones and carbonates, bit performance is directly related to cutters and their ability to withstand heat.

Overheated cutters experience abrasive wear faster, which can lead to lower rates of penetration (ROP) and higher mechanical specific energy (MSE) or wasted energy that is not directly transferred into removing rock.

In the Cana Woodford field of Oklahoma, this technology provided customers with a 10 per cent improvement in ROP and a 37 per cent improvement in footage when drilling through hard sands interbedded with hard limestones.

In the Pinedale anticline of Southwestern Wyoming, StayCool cutters are being used to drill through abrasive sandstones interbedded with shale. In this area, the Talon bit with StayCool cutters has improved the distance drilled by 12 per cent in 50 runs totalling 156,000 ft. StayCool cutters have already drilled more than 289,000ft in 89 runs, in five different applications in field tests, and for more than 20 customers throughout the USA.

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