In search of gas with high-tech tools Energy producers search for new reservoirs on land and at sea
In the search for natural gas deposits at land and on sea, geologists use a similar approach to that used to discover new oil fields. They begin by combing through existing data, such as the results of previous explorations or geological databases. While scrutinising the data, they are looking for certain characteristics which indicate the presence of natural gas. It is often stored in basins which sit above a very thick layer of sedimentation (at least 2,500 metres thick), while porous sandstone and carbonates are also good indicators. Using advanced technology, the scientist can evaluate existing measurement data to create a model of what a promising basin full of natural gas looks like. Only when this extensive analysis indicates evidence of possible gas deposits will geologists begin their investigations, which can often be very expensive.
Gas reservoirs are distributed unequally around the globe, with almost two-thirds of the known natural gas and oil reserves located in the strategic ellipse, an area which stretches from the Middle East to the Caspian Sea region and as far as northern Russia.
Russia has the largest proven natural gas reserves in the world and is also the world’s leading exporter of natural gas. That’s good news for Germany and Western Europe, as the Russian gas is within pipeline distance and can be transported to the European markets safely and efficiently. A fruitful energy partnership with Russia has been in place for more than two decades.
Sound waves can reveal new reservoirs
Sound waves play an important role in searching for new gas deposits. Geologists and physicists use sound waves to discover new reservoirs, even when the gas is under permafrost in Siberia or deep under the Atlantic. Using high-tech tools such as vibrator trucks or air cannons on ships to generate vibrations, they then measure the reflections of the sound from the rock strata with special microphones and then analyse the echo on computers which can calculate the structure of the potential reservoir.
But the only way of being absolutely sure is to drill a test well. This extracts drill cores from underground which the scientists then analyse under the microscope. They have to persevere, as only one in every three or four test wells is successful in finding natural gas.
After a successful test well, the trademark feature of the oil and gas industry, the derrick, appears. For production on land (onshore), gas companies drive a hole into the ground with a derrick, which is lined with steel pipes and concrete and is sealed off with a ‘Christmas tree’ above ground, which prevents gas from leaking from the borehole. If the gas lies under the sea bed (offshore), drilling platforms are usually necessary to access the gas.
During production, the natural pressure of the gas in the reservoir makes sure the raw material flows to the surface, where it is then purified of unwanted elements such as steam or particulate matter. If the natural pressure falls too much because the reservoir is at an advanced stage of production, the technicians install compressors that suck the gas out of the ground, and maximise the yield from the reservoir.
Special production methods for tight gas and shale gas
But it’s not always simple and straightforward to extract the gas from the reservoirs. Tight gas and shale gas do not flow to the surface by themselves, because they are trapped in isolated pores within very dense rock, or, in the case of shale, the gas is still firmly embedded in in the layers of clay where it was formed.
In order to extract this natural gas, water pressure has to be used to crack open the rock. This process is known as hydraulic fracturing, or “fracking”. Chemical additives are used in this process, as well as water and sand, which has made fracking a source of controversy in some parts of Europe.