Researchers in Kyoto University, Japan, have developed a new technology to release gas trapped in shale formations using carbon dioxide instead of water.
Hydraulic fracturing – otherwise known as fracking – is a technology which, along with horizontal drilling, allows for extracting gas from tight shale formations. A vertical well is first bored to reach the shale deposits, then the drill-bit is slowly turned to create a horizontal well-bore. Into this well-bore a fracking fluid – consisting mainly of water and sand – is pumped at high pressure to fracture the shale and release the gas.
This method – although effective – poses many problems such as reliance on high quantities of water and the need to safely dispose of the returning water, known as ‘produced water’, after fracking is completed. Produced water is contaminated by various, often dangerous, chemicals and is of great environmental concern. Especially since a fracked well can continue producing the flow-back water for 20 to 30 years – many years after the well has ceased to produce any gas.
This is why the Japanese invention is so promising. By injecting carbon dioxide into shale bedrock instead of water, the technology will not have to rely on millions of gallons of fresh water, as well as solving the problem of neutralising the toxic produced water.
Also, the technology is expected to help combat global warming as it will confine CO2 underground.
According to the research team led by Kyoto University Prof. Tsuyoshi Ishida and Assistant Prof. Chen Youqing, CO2 becomes a “supercritical” fluid if it is heated to 31.1 C or more and subjected to pressure of at least 73 atmospheres. A supercritical fluid is very smooth and has properties midway between a liquid and gas.
The research team confirmed that supercritical CO2 injected into shale bedrock fractured the bedrock and created finer cracks more widely than compared to the use of pressurized water.
The research team said it plans to start a large-scale substantiative experiment to verify the technology in autumn, aiming for practical use of the technology within several years.
Source: The Japan News
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