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Phases of Offshore Oil and Gas

The world needs a fast-paced transition to a no-carbon energy system, which requires a huge re-engineering of the world’s existing energy system. However billions of dollars of investment into oil and gas continues with “growth priorities” being deep-water oil extraction, developing alongside fracking and liquefied fossil gas technologies. 

The pursuit of oil and gas has driven exploration and production into geographically and geologically complex and harsh deep-water environments off the coast of South Africa. Severe weather, currents and greater depths pose risks to the functionality of the equipment/rigs, and their distance from land make it harder for additional rescue personnel to promptly reach the areas in emergency situations. There is always a risk of irreparable damage to entire ecosystems, industrialization of the coastline and also risk that puts lives and the economy on the line as well. Here are the various stages that take place for offshore oil and gas development.

The Mineral and Petroleum Resources Development Act (MPRDA) defines 4 phases of oil & gas development:


  • Average 6 months
  • Key tools used in reconnaissance for subsea oil and natural gas deposits. These seismic surveys use extremely loud shock wave emissions able to travel through the entire water column and penetrate 40kms into the seafloor below, detecting where these deposits might be positioned before mining begins.
  • Air guns are submerged below the water surface, and towed behind a ship. Air gun arrays may consist of up to 48 individual air guns, fired in concert, to create an optimum initial shock wave followed by minimum reverberation of cavitating bubbles.
  • The blasting schedule of the towed multiple air-gun arrays, which produce this high intensity (215-250 dB) sound, means blasts every 10 seconds for 24 hours a day, for months at a time over large areas. Multi-beam bathymetric sonar is often used concurrently.
  • Since sound travels more easily under water than through the air, the blasts from a single seismic survey can travel tens of thousands of square kilometres. Scientists have proven that this noise interrupts the communication, reproduction, navigation and eating habits essential to the survival of marine life, including whales, dolphins, turtles, fish, shellfish and even tiny plankton. These waves of energy also damage eggs, larvae and incite fish and other mobile marine species to migrate away from the affected area. Seismic airgun reconnaissance poses an unacceptable risk of serious harm to marine life at the species and population levels, the full extent of which is often not understood until long after the harm occurs.
  • Given the increasing unprofitability of oil production elsewhere around the globe and our marine environment potentially becoming the next greatest economic source, pressure for output means intensified marine prospecting.
  • Since 2014 and the repeal of legislation seismic surveys no longer require Environmental Impact Assessment (EIA) in South African waters.

For more details about seismic surveys and their environmental impacts, click here.


  • 4-10 years
  • Assessment of quantity, quality, sites and ease of extraction of commercially viable oil/gas petroleum reserve.
  • Infrastructure is developed to access sites. Oil rigs or drill ships and their support vessels are mobilised and conduct pre-drilling activities 
  • Vertical Seismic Profiling is used as a measurement tool to survey the seabed. It involves airguns capable of inducing lethal and sublethal injury[i],[ii], hearing loss [iii],[iv](temporary or permanent), masking of communication, physiological stress[v][vi][vii][viii], acoustic resonance in air cavities, organ rupture, behavioural responses, avoidance of critical habitat areas,  disruption in schooling and migration [ix], disruption of homing or orientation[x]; decreased feeding efficiency[xi];decompression sickness, and mass strandings[xii][xiii]for marine animals.
  • Most commonly activities are on the continental shelf.
  • International companies may explore alone or two or more companies may form joint ventures to explore together with one company being appointed the operator. 
  • Exploratory wells are drilled to discover and map oil/gas reserves. 
  • Average wells drilled per site = 15 wells.
  • During the drilling phase, different drilling bits sizes are used to drill a series of telescoping holes, from the seabed to the total depth of the planned well.
  • Hundreds of square meters of drill cuttings can accumulate meters deep on the seabed during the drilling operation, smothering seafloor life and leading to mortality of deep water corals that are extremely slow growing organisms (hundreds of years old in many cases).
  • The process of drilling releases thousands of gallons of “operational waste”, known as drill muds and cuttings, which are discharged overboard. These muds contain toxic substances like benzene, zinc, arsenic, radioactive materials, heavy metals and other contaminants used to lubricate drill bits and maintain pressure. Pending the level of toxicity, these muds are legally allowed to be released back into the marine environment, impacting the seafloor, benthic community, water column biology.
  • While testing wells, hydrocarbons are sent to a flare boom with a burner to ensure as complete destruction of fluids (including hydrocarbons) as possible. Flaring releases nitrogen oxides (NOx) and volatile organic compounds (VOCs) which can directly harm human health, and cause water quality deterioration, smog, contribute to climate change, and more.
  • This is a phase of high expenditure for oil companies, with no profits.


  • 20 – 50 years
  • Costs are recovered and profits generated. 
  • Small number of highly skilled jobs. Limited opportunities for local companies and local technical skills, where available.  
  • Conventional oil and gas life cycles are broadly similar, but there are differences:
    • During primary production the oil initially flows to the well under its own natural pressure. When the reservoir pressure decreases and the oil flows more slowly, pumpjacks are deployed to pull the oil up to the surface. With primary production, only around 5 to 30 per cent of the original oil present in the reservoir, on average, can be extracted. To better exploit the reservoir, water is injected under pressure into the side of the reservoir to force the oil toward the well. Thereafter viscous polymers can be added to the mix further pressurising the oil. This polymer is so viscous that the water cannot flow through it. The pressure of the injected water is thus transferred through the polymer to the oil, forcing the oil out of the reservoir. Despite enhanced oil recovery techniques around 40% of the oil remains underground whichever method is used.Oil is easier to process, transport and sell. 
    • For gas extraction it is usually sufficient to employ pumps to suck the gas out and thus achieve the maximum yield. Gas is more expensive to transport, difficult to store and commands a lower price per unit of energy than oil. Cooling natural gas to about -260°F at normal pressure results in the condensation of the gas into liquid form, known as Liquefied Natural Gas (LNG). LNG takes up about one six hundredth the volume of gaseous natural gas and makes it viable to develop gas fields for export over longer distances than is normally possible by pipeline. This cost of significant upfront capital investment means that extraction can only be justified by much larger reserves of gas.
  • If an influx of pressurised oil or gas does occur during drilling, well control is maintained through the rig’s blowout prevention system (BOP). This is a set of hydraulically operated valves and other closure devices (rams) which seal off the well, and route the wellbore fluids to specialised pressure controlling equipment. Trained personnel operating this equipment should minimise the possibility of a blowout, or an uncontrolled flow of fluids from a well. The BOP failed to seal the well during the Deep Water Horizon incident.
  • The frequency at which accidental discharges of crude oil occur in offshore waters suggests that they can be expected during “typical” operations[xiv]. The likelihood of an accidental release of hydrocarbons or blowout increases with the depth of the operations[xv].
  • Deep-sea organisms are slower growing and more long lived than their shallow-water equivalents, prolonging their recovery from impacts. Given the inevitably destructive nature of the activity, the avoidance of significant biodiversity losses isunlikely and may well be irreversible on timescales relevant to management and possibly for many human generations[xvi],[xvii],[xviii].
  • Sediment plumes generated during extraction, discharge of wastes, including drilling fluids / muds, drill cuttings and produced formation water are considered to be a source of major risk to deep-sea ecosystems resulting in, among other effects, the burial and clogging of animals’ feeding apparatus[xix].
The effects of discharges of drill cuttings and fluids


  • 2- 10 years 
  • Once it is no longer cost-effective to extract remaining reserves, the site is decommissioned. This involves the removal of production facilities and the cement plugs inthe well.
  • This is a very costly and risky process. Oil and gas companies may opt not to remove structures.
  • The operating companies are responsible for returning the site to as close to original state as possible. This phase can take decades if environmental monitoring is required.

[i]McCauley, R. D., Fewtrell, J., and Popper, A. N. 2003. High intensity anthropogenic sound damages fish ears. Journal of the Acoustical Society of America.113, 638–642. 

[ii]André, M., Johansson, T., Delory, E., van der Schaar, M., Morell, M. 2007. Foraging on squid, the sperm whale mid-range sonar. Journal of the Marine Biological Association UK87, 59–67. 

[iii]André, M., Johansson, T., Delory, E., van der Schaar, M., Morell, M. 2007. Foraging on squid, the sperm whale mid-range sonar. Journal of the Marine Biological Association UK87, 59–67. 

[iv]McCauley, R. D., Fewtrell, J., and Popper, A. N. 2003. High intensity anthropogenic sound damages fish ears. Journal of the Acoustical Society of America.113, 638–642. 

[v]Buscaino, F., Filiciotto, G., Buffa, G., Bellante, A., Di Stefano, V., Assenza, A., Fazio, F., Caola, G., Mazzola S., 2010, Impact of an acoustic stimulus on the motility and blood parameters in European sea bass (Dicentrarchus labrax L.)and gilthead sea bream (Sparus aurata L.)Marine Environmental Research.69, 136-142.

[vi]Graham A. L., Cooke S. J. (2008). The effects of noise disturbance from various recreational boating activities common to inland waters on the cardiac physiology of a freshwater fish, the largemouth bass(Micropterus salmoides). Aquat. Conserv. 18, 1315–1324.

[vii]Wysocki, L. E., Ladich, F. Dittami, J. 2006. Noise, stress, and cortisol secretion in teleost fishes. Biological Conservation128, 501–8. 

[viii]Santulli A., Modica A., Messina C., Ceffa L., Curatolo A., Rivas G., et al. (1999). Biochemical responses of European seabass (Dicentrarchus labrax L.) to the stress induced by off shore experimental seismic prospecting. Marine Pollution Bulletin. 38, 1105–1114.

[ix]Sarà, G., Dean, J., D’Amato, D., Buscaino, G., Oliveri, A., Genovese, S., et al. 2007. Effect of boat noise on the behaviour of bluefin tuna Thunnus thynnus in the Mediterranean. The Marine Ecology Progress Series. 331, 243–253

[x]Simpson, S. D., Meekan, M. G., Larsen, N. J., McCauley, R. D., Jeffs, A. 2010. Behavioral plasticity in larval reef fish: orientation is influenced by recent acoustic experiences, Behavioral Ecology, 21, 5, 1098–1105.

[xi]Purser J., Radford A. N. (2011). Acoustic noise induces attention shifts and reduces foraging performance in three-spined sticklebacks (Gasterosteus aculeatus). PLoS One, 6, e17478. 

[xii]Hildebrand, J. 2006. Impacts of anthropogenic sound. 101-123 in: Ragen, T.J., Reynolds III, J.E., Perrin, W.F., Reeves, R.R., and Montgomery, S. 2006. Marine Mammal Research: Conservation beyond Crisis. Baltimore: Johns Hopkins.

[xiii]Gordon, J., D. Gillespie, J. Potter, A. Frantzis, M. Simmonds, R. Swift, D. Thompson, 2004. A Review of the Effects of Seismic Survey on Marine Mammals. Marine Technology Society Journal, 4, 14-32.

[xiv]Cordes, E.E., Jones, D.O.B, Schlacher, T.A., Amon, D.J., Bernardino A.F., Brooke, S., Carne,y R, DeLe,o D.M., Dunlop, K.M., Escobar-Brione,s E.G., Gates, A.R., Génio, L., Gobin, J., Henry, L-A., Herrera, S., Hoyt, S., Joye, M., Kark, S., Mestre, N.C., Metaxas, A., Pfeifer, S. Sink, K., Sweetman, A.K. and Witte, U. (2016) Environmental Impacts of the Deep-Water Oil and Gas Industry: A Review to Guide Management Strategies.Front. Environ. Sci. 4:58. doi:10.3389/fenvs.2016.00058 

[xv]Muehlenbachs, L., Cohen, M. A., and Gerarden, T. (2013). The impact of water depth on safety and environmental performance in offshore oil and gas production. Energy Policy 55, 699–705. doi: 10.1016/j.enpol.2012.12.074

[xvi]Amon, D. J., Ziegler, A. F., Dahlgren, T. G., Glover, A. G., Goineau, A., Gooday, A. J., et al. (2016). Insights into the abundance and diversity of abyssal megafauna in a polymetallic-nodule region in the eastern Clarion-Clipperton Zone. Sci. Rep. 6:30492. doi: 10.1038/srep30492

[xvii]Vanreusel, A., Hilario, A., Ribeiro, P. A., Menot, L., and Arbizu, P. M. (2016). Threatened by mining, polymetallic nodules are required to preserve abyssal epifauna. Sci. Rep. 6:26808. doi: 10.1038/srep26808

[xviii]Jones, D. O., Kaiser, S., Sweetman, A. K., Smith, C. R., Menot, L., Vink, A., et al. (2017). Biological responses to disturbance from simulated deep-sea polymetallic nodule mining. PLoS ONE 12:e0171750. doi: 10.1371/journal.pone.0171750

[xix]Niner HJ, Ardron JA, Escobar EG, Gianni M, Jaeckel A, Jones DOB, Levin LA, Smith CR, Thiele T, Turner PJ, Van Dover CL, Watling L and Gjerde KM (2018) Deep-Sea Mining With No Net Loss of Biodiversity—An Impossible Aim. Front. Mar. Sci. 5:53. doi: 10.3389/fmars.2018.0005

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