2013: Advent Oil & Gas: Prospecting and exploration

by on December 4, 2013

Based on our knowledge of oil and gas formation we can make some reasonable guesses as to where they can be found.  The best places to look are sedimentary rock basins, especially those that are close to faults and plate boundaries – but there over 700 major basins and they tend to be pretty big, and by no means all of them have oil!  How can we narrow down the search?

Oil and gas exploration is a fairly major area in itself, and involves a variety of stages from the initial survey to full-scale production.  In the UK, the first stage is getting a licence to in the UK to ‘search and bore for and get’ petroleum, since the UK’s oil and gas reserves are owned by the Crown.  Licenses are usually granted for blocks defined by lines of latitude and longitude.  The license holder pays a yearly rental fee proportional to the area of the block, which increases each time so as to encourage investors to actually explore and drill rather than buying up all the seabed and sitting on it.

Once you have the rights to exploit an area, it’s a sensible idea to have a look at the rocks using a seismic survey.  This is essentially a form of sonar: send a pulse of sound waves through the rock (and water where necessary) and study the echoes.  Originally explosives were used, although these days a high-pressure air gun is preferred.  The echoes are picked up by an array of microphones on the ground or by hydrophones towed behind a ship; these are then analysed by computer and used to generate a model of the bedrock and (hopefully) any oil and gas reserves.

A survey indicating oil or gas is often followed up with exploration wells.  These are similar to normal wells, but rather than being specifically for extraction they are solely for information gathering: they allow investigation of the real rock formations and determine if there really is any oil or gas.  Sometimes exploration wells are drilled outside known oil fields or surveyed areas, in which case they’re called ‘wildcat wells’, but this is a seriously expensive gamble and so is rarely done nowadays.

The next stage is appraisal, which involves more drilling.  Appraisal wells are used to test the characteristics of the oil or gas, such as composition, flow rate, and reservoir extent.  At the end of a successful appraisal stage, the field is at last ready for commercial development!

This probably sounds quite lengthy and convoluted; in reality it’s much worse.  To get from the permit application to the start of development generally takes four to eight years and costs something in the region of $25 million.  After that, the rig needs to be designed, built, and installed at much greater expense… more on which in the next article!

Leave a Reply