Exploration Hazards
GEOLOGICAL HAZARDS (SFU 2004, Appendix 11 Strong)
Geologic hazards are conditions or active processes that pose a potential threat to petroleum exploration or development, including the long term security of sea-floor installations (e.g., wellheads and pipelines). In many instances, hazards are interrelated (e.g., earthquakes and slope stability) and others can be related to oceanographic conditions (waves and currents, and sediment mobility). Appendix 11 of the Provincial Scientific Report (Strong et al., 2002) presents a detailed review of the important geologic hazards that exist in the region of the Queen Charlotte Basin. These include: bedrock outcrops, geologic faults and associated seismicity, boulder beds, sediment mobility (large bedforms in high wave and current regions), mass wasting (underwater landslides), steep slopes, shallow gas, and dynamic coastal processes.
Earthquakes
The
west coast is the most seismically active (earthquake prone) area of Canada
and this poses a very potential hazard to all aspects of offshore operations.
In order to mitigate these potential effects, it is important that detailed
site surveys of the geological hazards be completed and evaluated by any
eventual regulating body. However, detailed site surveys are not appropriate
until exploration targets have been chosen. These targets will not be chosen
until seismic surveys have been completed in the region. Therefore, this
process cannot be started until after the lifting of the moratoria.
In the meantime , the Geological Survey of Canada plans on producing a seismic hazard chart and map and the Coasts Under Stress project will evaluate the potential hazards from seismic activity to oil and gas operations. This information will then be used to rule out areas that are particularly hazardous and, if the moratoria are lifted, will help to increase the efficiency of the industrial seismic surveys.
Research by Bird (1997) and others indicates that the Queen Charlotte Fault is capable of generating “megathrust” earthquakes up to magnitude 9.0 on the Richter scale (Strong et al. 2002; Cretney et al. 2002; JWEL 2001). Large earthquakes in the close vicinity of the Queen Charlotte Basin could produce severe tsunamis without warning (RSC 2004), and tsunamis generated even thousands of kilometers away could damage offshore facilities in the region (JWEL 2001). While major earthquakes and tsunamis are rare in the Queen Charlottes, uncertainty surrounds the specific hazard level (frequency) of these events (RSC 2004; Rogers 2003; Strong et al. 2002; JWEL 2001). A more pressing concern in the region would be sediment instability (possible underwater landslides) triggered by seismic events that could be catastrophic for several types of offshore drilling and production platforms.
The image in this section shows seismicity (earthquakes), both on a microscale and on a large scale, that have occurred along the Queen Charlotte Fault. The star marks a magnitude 8.1 event. This figure by Bird (1997) comes from Strong et al. 2002, Appendix 8.
ENVIRONMENTAL HAZARDS - (Courtesy Appendix 14 Strong et al,, 2002)
Temperature
Despite the apparent mild temperatures, annually there are approximately twenty frost days in the region. The freezing and icing associated with this is recognized as a particular hazard of operations in the region, but does not pose any unusual conditions to those encountered in similar higher latitude onshore and offshore exploration and production operations elsewhere in BC, Canada and internationally. For example in the Jeanne d’Arc Basin on the east coast (Grand Banks region), the temperature variations are larger and more severe. There the air temperature ranges from –17.3°C to 26.5°C and the surface water temperature ranges from –1.7°C to 15.4°C. In the Jeanne d’Arc Basin the thickness of icing (glaze and frost) is 72 mm (10 year maximum) to 169 mm (100 year maximum). Similarly, spray icing thickness in the region is 316 mm (10 year maximum) and 514 mm (100 year maximum). So, comparatively, the temperatures in the Queen Charlotte region are relatively quite mild.
Wind and Tides
The
strong winds in the Hecate Strait generate considerable waves and swells.
Winds are strongest from October to February and are usually out of the south
or southeast. The actual wave heights are dependent on the fetch, (i.e.,
the proximity to sheltering land), and on the water depth. Pacific Ocean
swells influence much of the lower part of Hecate Strait and the Queen Charlotte
Sound. During storm events the sea state can increase to over 10m. Waves
of 20 – 30 m have been recorded in the strait. Of particular concern is the
rapidity with which the seas can increase, often within hours. Wave heights
in the Jeanne d’Arc Basin of Newfoundland (site of current offshore production)
are very similar to the Hecate Strait. In the Jeanne d’Arc Basin the significant
wave height is 11 – 14 m (1 – 10 year report), and a 100-year value of 17.5m.
The corresponding maximum wave heights are 20.9 – 30.4m (1 – 10 year) and
30.4m (100-year). After the tragedy of the ocean ranger disaster, offshore
platform engineering has improved greatly to withstand extreme wave conditions.
Severe storms, high waves and strong currents can make it difficult to accomplish
operations such as drilling, landing a supply helicopter or loading fuel.
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Wind velocities over the water
in the Hecate Straight.
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SFU (2004) notes that the Queen Charlotte Basin has a strong, complex current and tide regime (RSC 2004; Crawford et al. 2002; Cretney et al. 2002; Strong et al. 2002). Tides in the basin move up to 50 cm/sec, significantly faster than other regions of offshore development such as the Jeanne d’Arc Basin where tides only move up to 8 cm/sec (Strong et al. 2002). Thus, subsea equipment in the Queen Charlotte Basin such as pipelines would be exposed to substantial stress. Currents would also affect the dispersal of pollutants such as drilling muds and oil spills. Pollutants within the water column are expected to dilute and disperse rapidly (Crawford et al. 2002; Cretney et al. 2002), but could travel long distances from discharge points. Models show that pollutants in surface waters such as spilled oil would likely be retained in the basin and eventually reach one of the coastlines (fig. 2.4; Crawford 2003; Crawford et al. 2002; Cretney et al. 2002).
OIL SPILLS AND BLOWOUTS
Another risk during exploration is the possibility of oils spills and blowouts (control being lost over the pressure within the well and petroleum escaping into the environment). The chance of a blowout is higher during exploratory drilling than it is during production. The severity of the damage done to the environment depends on, among other things, what type of hydrocarbons are released, how close to shore they are, and what the winds and tides are like. Once a spill has occurred, only 5-15% of the oil has ever been cleaned up by anthropogenic means.
For more information on oil spills and blowouts, click here.
Some credit from above text to Review of Offshore Oil and Gas Development by Simon Fraser University, 2004 and Appendices 11 and 14 of British Columbia Offshore Hydrocarbon Development: Report of the Scientific Review Panel prepared by Strong, David, Patricia Gallagher and Derek Muggeridge, 2002
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