Why shale rock is different

Workers on site Eagle Ford

Shale is a fine-grained sedimentary rock that belongs to a category of rocks known as mudstones. Shale is distinguished from other mudstones because it is fissile and layered—or laminated. Shale splits easily into relatively thin sheets due to this lamination, allowing oil and gas trapped beneath the shale rock to be extracted using modern fracturing techniques that open passageways between the laminations.

Shale is a common type of rock and is found in most countries, and the rapid increase in US shale production therefore created hope for the extraction of gas from shale deposits in other countries. In recent years, major international oil companies have explored opportunities for producing shale gas in China, Argentina and Poland.

However, preconditions for shale gas production are not so good in most countries outside the US, since they lack the infrastructure, availability of subcontractors for drilling and production as well as and public regulation of shale gas production.

Horizontal drilling for Shale gas

Oil and gas explorers in the US have been aware of large deposits of shale gas and oil since the 1940s, but until recently were unable to extract such resources in a cost-effective manner.

Advances in technological capability such as horizontal drilling and hydraulic fracturing have now made it possible to extract the gas and oil deposits in economic quantities directly from the source rocks.

The wells are first drilled vertically, and then horizontally 1,500 to 3,500 metres through the source rock layers. Then the work on fracturing the source rock starts. After installing and perforating the production pipe at multiple stages, a mixture of  sand and water with some chemicals is pumped down the bore hole. Fissures are then created in the source rock by injecting the water and sand at high pressure.

When pumping operations are completed, the fissures are kept open by the sand that was pumped in during the fracturing process. When the well is commissioned, the gas or oil will flow through the sand in the new fissures and further into the well bore and up to the surface.