UK Deepwater Drilling - Implications of the Gulf of Mexico Oil Spill - Energy and Climate Change Contents

2  Challenges of Deepwater Drilling

4. Deepwater drilling depths are sometimes defined as greater than around 400m, while water depths of greater than 1500m are defined as "ultra-deepwater". Mr Malcolm Webb, Chief Executive of the industry association Oil and Gas UK, told us:

I don't think there is an agreed industry definition of what constitutes deepwater [...] When we started in the North Sea over 40 years ago, depths of 100 or 200 feet [30-60m] would have been regarded as deepwater, and as our abilities and technologies have moved forward so the definition of what is "deep" has moved with it.[1]

5. Compared to conventional offshore drilling methods, deepwater presents unique technical challenges related to greater water depths, higher pressures, manipulating the extra long riser pipe connecting the wellhead to the rig (over 1,500m in the case of the Deepwater Horizon), extreme temperature gradients and added costs. We found it interesting to note Mr Webb's observation that the intervention in the well at the seafloor switches from divers to Remotely Operated Vehicles (ROVs) at "about 500 feet [150m]",[2] as this seems to be an obvious threshold for deepwater operations.

6. The pressure in the well is controlled by ensuring that the pressure of the drilling fluid (known as mud) in the well bore—known as the bottomhole pressure—is sufficient to oppose the pressure from the oil, gas and water in the reservoir (known as the formation pressure or the pore pressure). This prevents fluids from the reservoir entering the well. Dr Tony Hayward, BP's former Group Chief Executive, informed us "the pressure on the drill pipe and the volume of [drilling] mud [...] are the two most important parameters that are monitored and measured on a continuous basis".[3] If the formation pressure is greater than the bottomhole pressure oil and gas would enter the wellbore, and would lead to a blowout if uncontrolled. The drilling fluid engineer monitors the formation pressure and increases the density of drilling mud to balance the pressure and keep the well bore stable. These active pressure control systems are the first line of defence against losing control of the well.

7. Mr Webb told us: "deep water brings some particular risks with it".[4] Deepwater is characterised by young rock formations that differ from shallow-water or onshore exploration. This is exemplified by the narrow gap between the pressure of the oil and gas in the reservoir and the typically small changes in pressure required to fracture the rock around it (known as a low fracture gradient, this is typically low under deepwater). Small increases in formation pressure can therefore cause rock fractures to occur, destabilising the borehole and potentially leading to an influx of gas and oil (known as a kick) which if uncontrolled could lead to a blowout. This inclination for fractures to occur is caused by an increased weight pressing down on the oil and gas bearing rock formation (known as overburden). This can necessitate using lighter drilling fluid, which could potentially make it more difficult to control the well, and a lighter cement mixture (used when fixing the pipe casing into the borehole), potentially making the well more vulnerable to the formation of channels around the casing up which gas could flow.

8. Deepwater environments also present the combination of low temperatures, high seabed pressures, gas and water that cause "gas hydrates" to form. Gas hydrates are cages of frozen water molecules with gas trapped inside and have a tendency to bond with metal, resulting in blockages (as occurred during BP's "top hat" operation to kill the Macondo well).

9. Even though the incident in the Gulf of Mexico took place in deepwater, Mr Webb told us: "The depth of water is not the critical element here".[5] Mr Roland Festor, Managing Director of Total Exploration and Production UK, argued that: "Macondo has fundamentally nothing to do with deepwater".[6] This is because, once the blowout had occurred—while the depth of the water made the response to the incident more difficult—it was the fact that it was a high-pressure, high-temperature (HPHT) well that made it more challenging to control.

UK Deepwater Drilling Activity

10. The majority of wells drilled on the UK Continental Shelf (UKCS) are in water-depths of less than 100m, but oil and gas exploration companies have increasingly been drilling in deeper waters as reserves in more accessible areas run dry. Mr Webb told us: "the deepest well so far drilled in the UK Continental Shelf was at 6,000 feet [over 1,800m] of water".[7] According to DECC statistics on existing production installations in the West of Shetland (WoS) Basin, BP has a platform on the Clair field, and two processing ships in the Foinhaven and Schiehallion Fields. The Clair began production in 2005, and has a water-depth of around 140m. The Foinhaven has a water depth of between 400-600m and the Schiehallion 350-450m. We heard from Paul King, Managing Director of Transocean's North Sea Division, that: "The Paul B Lloyd [a Transocean rig] is working for BP west of Shetlands at the moment in up to 3,000 feet [over 900m] of water".[8] The Tormore and Laggan fields are being explored by Total and lie in 630m of water.[9] Total is also searching 1,600m underwater in the Tobermory field, north of the Clair field. Chevron is exploring the Rosebank-Lochnagar fields in 1,115m of water.[10] In comparison, the Deepwater Horizon was drilling in ultra-deepwater at a depth of 1,544m.

Operations on the UK Continental Shelf

11. The Macondo Well in the Gulf of Mexico was being drilled into a high-pressure, high-temperature (HPHT) "over-pressurised" oil and gas reservoir. Over-pressurised wells are hazardous as the fluid in the reservoir can escape rapidly. Total pointed out that while they have operational experience of such fields in the Central North Sea, the geological conditions encountered WoS are very different and "no significant overpressure" has been encountered in that area to date. [11] Dr Hayward told us: "there is nowhere where we are drilling in deepwater [in the UKCS] and the reservoirs have high pressures and temperatures".[12]

12. DECC figures estimate that the deepwater oil and gas resource (which includes estimates for future discoveries) of the West of Shetland and the less well explored West of Scotland account for 15-17.5% of UK total resources. However, the resource estimates for the West of Scotland (located north of the Outer Hebrides) area are highly uncertain.[13]

13. As part of Total's development of the Laggan-Tormore area (600m in depth) in the WoS, a new gas pipeline system is being built that will connect these discoveries to the UK mainland. The new system has been "oversized" with the expectation that further exploration and development in the coming decades (including prospects that in isolation could not justify the cost of this infrastructure) will take advantage of the excess capacity. This development has started with the construction of a new gas plant in Sullom Voe, the Shetland Island's oil and gas terminal. Total hope that discoveries such as Tobermory, located eight blocks north of the Clair field and in 1,600m of water, will create opportunities for new fields and infrastructure that "would further protect the UK's security of supply".[14]

14. DONG Energy is one of the largest acreage holders in the WoS region and a partner in Total's recently sanctioned Laggan-Tormore gas development. DONG Energy is not currently drilling as operator in UK territorial waters, but drilled the WoS Glenlivet gas field in 2009 and has interests in a further six discoveries.[15]

15. On 1 October 2010 the Government gave the go-ahead for the first deepwater drilling off Britain since the Gulf of Mexico incident. This consent was given to Chevron to drill in the Lagavulin Prospect located in the West of Shetland area at a depth of just over 1,500m (comparable to the Macondo Well). Chevron and its partners plan to drill an exploration well in the prospect with an expected duration of six months. In accordance with UK regulation, an Environmental Statement for the well has been in the public domain since March 2010.[16] Chevron has drilled 18 deepwater wells in the WoS since 1987 without serious incident, and is also exploring the Rosebank-Lochnagar fields in 1,115m of water.[17]

1   Q 4 Back

2   Q 12  Back

3   Q 116 (Hayward) Back

4   Q 3  Back

5   Q 1  Back

6   Q 239  Back

7   Q 5 Back

8   Q 69 Back

9   Ev 77 Back

10   Chevron Business Portfolio, Back

11   Ev 77 Back

12   Q 114 Back

13   Ev 596 Back

14   Ev 77 Back

15   Ev 632 Back

16   Ev 591 Back

17   Ev 591 Back

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Prepared 6 January 2011