Oceans, caught between devil and the deep blue sea… (Pun intended!) – XIII

Offshore oil drilling basics:

On January 4 this year, the Trump administration in U.S.unveiled a five-year blueprint to expand offshore drilling and gas leasing in nearly all U.S. waters. The plan, which would span 2019 to 2024, would also let the government auction off permanently protected areas.  This announcement was a significant counter-blow to the environmental movement, especially to the marine ecologists and it opened a Pandora’s Box for debate over this issue.   

So, what does all this mean?  And how is this connected with marine pollution?  One of the main sources of oil spills into oceans is from offshore oil drilling.  Offshore drilling is a mechanical process where a well-bore is drilled into the seabed.  This bore is used to explore and subsequently extract fossil fuels and natural gases, which lie in rock formations beneath the sea-floor. Offshore oil production process involves environmental risks, most notably oil spills from oil tankers or pipelines transporting oil from the platform to onshore facilities, and from leaks and accidents on the platform.  Produced water (water that comes out as a by-product along with the oil and gas and that is highly saline and may include dissolved or in-separated hydrocarbons) is also another environmental issue.  On the other hand, there is a school of thought, especially from oil industry itself, which claims that offshore oil drilling can offer advantages to the marine environment.   However, before diving deep into this debate, it is essential to understand what offshore drilling is.  

Let us start with UNCLOS or The United Nations Convention on the Law of the Sea.  UNCLOS defines the rights and responsibilities of nations concerning their use of the world’s oceans, establishing guidelines for businesses, the environment, and the management of marine natural resources.  UNCLOS has prescribed a sea zone called as “exclusive economic zone” (EEZ), over which a country has exclusive rights for exploration and use of marine resources, including energy production from water and wind in that region.


World map with countries and their exclusive economic zones

Accordingly, EEZ is an area adjacent to the territorial sea, extending seaward to a distance of 200 nautical miles (370 km) from its coastal baseline.  For India therefore, for example, the coastlines are not the actual boundaries of India. Indian border is 370 kilometers away from the coast and inside the seawaters as shown in the adjacent figure.  This area around the country is called the “exclusive economic zone” (EEZ).  And therefore India has exclusive rights regarding the exploration and use of marine resources including fisheries, tourism, oil and other mineral exploration, energy production like the wave and tidal energy, wind energy and so on.

India EEZ boundariesAs shown in the figure India’s total EEZ area is 2,305,143 km2.  Out of this area, 1,641,514 km2 is around mainland and Lakshadweep and 663,629 Sq.km around Andaman and Nicobar Islands.    However, India is currently seeking from UN to extend its EEZ to 560 kilometers, since maybe there are possibilities of finding substantial oil reserves below the ocean beds of Indian Ocean. 

Now let us understand another term related to offshore drilling, called “continental shelf.”  “Continental shelf” has slightly different meanings in the geographical and legal parlance.

Geographically speaking, a continental shelf is merely the parts of continents that extend underwater to the shelf break. As the edge of a continent gently extends underwater, it eventually hits a drop-off point that is called the shelf break. At this point, the land begins a sharp decline, which is known as the continental slope. This slope leads to the dark, cold depths of the ocean floor. Refer below figure:


Because the average depth of water over a continental shelf is between 100 to 200 meters, these shallow waters are well-lit and warm, creating the perfect environment for plant life to flourish. In fact, all of the ocean’s plants are found on these shelves, as well as copious amounts of algae. This abundant plant life attracts all types of sea creatures, and while only 10 percent of the ocean is found on continental shelves, these warm waters house most of the ecosystems.

The legal definition, which is used by the United Nations Convention, defines the term as submerged land that extends to 200 nautical miles (370 Kilometers) from a continent’s coastline.  In other words as per UN convention, Continental Shelf is nothing but the area of the exclusive economic zone.  Refer below figure:


Accordingly, continental shelves or exclusive economic zones contain most valuable resources, such as oil and gas and minerals. Most of the world’s petroleum is trapped at a depth of between 500 and 25,000 feet (152 and 7,620 meters). This fuel is usually trapped under dirt and rock on the seafloor. All of this oil began as tiny plants and animals called plankton, which died in the ancient seas between 10 and 600 million years ago. This decaying matter drifted to the bottom of the ocean and, over time, was covered with sand and mud. In this oxygen-free environment, a kind of slow cooking process took place. Millions of years of heat and pressure eventually transformed this organic material into vast deposits of liquid, gas and solid petroleum, all capped in traps under thick layers of rock. 

Hydrocarbon reservoirs

As stated at the beginning, offshore drilling is a mechanical process which extracts these entrapped fuels and gases.  Today’s oil rigs are amazingly massive structures. Some are almost floating cities, employing and housing hundreds of people. Other enormous production facilities sit atop undersea towers that descend as far as 4,000 feet (1,219 meters) into the depths — taller than the world’s most ambitious skyscrapers. To sustain their fossil fuel dependency, humans have built some of the most massive floating structures on Earth.

Global offshore oil production (including lease condensate and hydrocarbon gas liquids) in 2015 was at the highest level since 2010 and accounted for nearly 30% of total global oil production. More than 27 million barrels of oil were produced offshore in 2015 in more than 50 different countries.  Below graph depicts total oil produced Vs. oil produced from offshore wells. 


In next article, we will see an environmental side of offshore oil drilling. 


  1. Division for ocean affairs and the law of the sea, United Nations
  2. Marineregions
  3. Whatarethe7continents
  4. National Geographic
  5. Wikipedia
  6. Encyclopedia online

Milind Joshi


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