What is Shale Gas
Shale gas is a type of natural gas that is called an “unconventional gas.” It is found in the gaps between pieces of shale, a sedimentary rock formed deep underground from deposits of silt and clay. Unlike conventional gas, which can be extracted simply through excavation, unconventional gas is natural gas that required special technologies to extract it.
Shale Gas Drilling
Shale gas drilling technoques differ from conventional techniques due to the low permeability of low porosity characteristerics of the shale rock, necessitating two advances over traditional well designs:
Directional and Horizontal Drilling: Shale gas wells need to maximize he surface of the well bore in contact with the formation in order to increase recovery. To achieve this objective, wells penetrade the formation horizontally (as opposed to vertically) to follow its shape. In addition, the azimuth of the well is intended to be perpendicular to the natural fractures of the formation.
Hydraulic Fracturing (Fracing): Once drilled into, the source rock is further fractured to increase the flow of fluids toward the wellbore. Fractures are induced via the injection of pressurized fluid into the well bore. The rock cracks in multiple places around the horizontal portion of the wellbore, with micro pellets of sand or other materials in solution in the water prevent the fractures from closing back in once the fracing job is completed.
These completion techniques hav raised some potential environmental concerns as fracing requires large amounts of fresh water and heavy truck traffic in and around the drilling areas. If mismanaged, fracing fluid spills or leaks could lead to contamination of surrounding areas with hazadous chemicals in fracing water soultion.
