How is it produced?
AFTER A patch of land is cleared, a hole, some 2000-3000 m deep, is dug vertically till it reaches the shale rocks. Steel tubes called casings are inserted and cemented in the hole to isolate the well from the surrounding rocks and aquifers. Now horizontal holes ranging from 1,000-3,000 m are dug to access the rocks at various points. Next step is to fracture the rocks to free the gas trapped within. For this water mixed w with sand and chemicals is pumped into t the ground at high pressure to force it t through the perforations. This creates c cracks in underground rocks. Hydraulic f fracturing of rocks is also called fracking. S Sand holds the cracks open, allowing the g gas to flow into the bore well.
Given the length of horizontal wells, h hydraulic fracturing is often conducted in 10-20 stages, where each stage fo focuses on a limited linear section and m may be repeated numerous times. This multi-stage fracturing requires large volumes of water. A standard singlestage hydraulic fracturing may pump down several hundred cubic metres of water together with proppant and a mixture of chemical additives. In multistages the total volume of water used might reach up to 20,000 cubic metres per well and the amount of proppant up to 4,000 tonnes.
Some of the fracturing fluid injected into the well will return to the surface along with water that occurs naturally in the rocks. This is brought to the surface, collected, treated and reused or disposed of. Along with this, natural gas is also released, which is collected and treated.