Locating oil and gas reserves used to be a bit of a game, with a little bit of observation and geological interpretation, and a lot of luck. Sometimes surface features such as oil seeps and pockmarks might have highlighted the presence of hydrocarbons. However, often drills were sunk in areas close to where oil and gas had already been found in the hope that there would be more. Nowadays, exploration depends on highly sophisticated technology, specially trained professionals and a lot of investment.
The first stage to any type of exploration is always a desk study. This will involve using resources, such as maps and drill hole data, which have already been collected to look for areas of interest. Scientists will then recommend which more in-depth surveys should be conducted. A lot of data can be found on free to access websites, such as Geoview of Minview as governments encourage exploration in their area, to enrich the economy and provide jobs. Other factors will also have to be considered, such as if there are any special conservation considerations, including ecologically and historically significant sites. If the site is offshore, the bathymetry of the area is also important as deeper water will raise the cost of extraction drilling and generally be more technically challenging.
- To learn more about how to use Geoview watch this tutorial video
The time taken for the sound waves to return to the surface will depend on the density and thickness of the rock layers (Wikipedia, accessed 16/6/2020).
The next stage of exploration for oil and gas is usually to conduct geophysical surveys. Magnetic and gravity surveys can be used to assist with interpretation; however, often the most information is gleaned from seismic studies. Seismic surveys work a bit like how bats and dolphins use echolocation. Sound waves are set off from a survey ship or Vibroseis truck and these penetrate the rock layers below. Some waves will get reflected at shallow rock boundaries and others will continue to deeper boundaries before being reflected. The reflected waves are recorded by geophones (on land) or hydrophones (on water) and their travel time back to the surface is recorded. This data is used to build a picture of the subsurface.
- For more information and a hands on activity relating to seismic studies read Seismic Acquisition
This type of oil platform is commonly used for offshore drilling in the North Sea (Wikimedia, accessed 16/6/2020).
Once a hydrocarbon prospect has been identified and approval has been granted from the government, exploration drilling can commence. The type of drill rig used will depend on the location of the oil and gas reservoir. Some drill rigs may even be housed on specially designed ships, if they are working in very deep water. During the drilling process core samples are taken for analysis. This provides more information about the rock types, presence (or absence) of oil and gas, permeability of the rocks and other important properties.
- For a hands-on activity have a go at Exploration Drillingor watch the video here.
- For more information on oil formation and exploration watch this short video