- The Shall Gas Boom: A Fracking Primer: The shale gas boom has totally transformed the US energy landscape. Shale gas refers to natural gas that is trapped within shale formations. Shales are fine-grained sedimentary rocks that can be rich sources of petroleum and natural gas. Sedimentary rocks are rocks formed by the accumulation of sediments at the Earth’s surface and within bodies of water. Common sedimentary rocks include sandstone, limestone, and shale.