The Process of Unconventional Natural Gas Production
Hydraulic Fracturing
Hydraulic fracturing produces fractures in the rock formation that stimulate the flow of natural gas or oil, increasing the volumes that can be recovered. Wells may be drilled vertically hundreds to thousands of feet below the land surface and may include horizontal or directional sections extending thousands of feet.
Fractures are created by pumping large quantities of fluids at high pressure down a wellbore and into the target rock formation. Hydraulic fracturing fluid commonly consists of water, proppant and chemical additives that open and enlarge fractures within the rock formation. These fractures can extend several hundred feet away from the wellbore. The proppants - sand, ceramic pellets or other small incompressible particles - hold open the newly created fractures.
Once the injection process is completed, the internal pressure of the rock formation causes fluid to return to the surface through the wellbore. This fluid is known as both "flowback" and "produced water" and may contain the injected chemicals plus naturally occurring materials such as brines, metals, radionuclides, and hydrocarbons. The flowback and produced water is typically stored on site in tanks or pits before treatment, disposal or recycling. In many cases, it is injected underground for disposal. In areas where that is not an option, it may be treated and reused or processed by a wastewater treatment facility and then discharged to surface water.
"Unconventional" Natural Gas Production, Shale Gas Extraction and Hydraulic Fracturing
Hydraulic fracturing is a technique used in "unconventional" gas production. "Unconventional" reservoirs can cost-effectively produce gas only by using a special stimulation technique, like hydraulic fracturing, or other special recovery process and technology. This is often because the gas is highly dispersed in the rock, rather than occurring in a concentrated underground location.
Extracting unconventional gas is relatively new. Coalbed methane production began in the 1980s; shale gas extraction is even more recent. The main enabling technologies, hydraulic fracturing and horizontal drilling, have opened up new areas for oil and gas development, with particular focus on natural gas reservoirs such as shale, coalbed and tight sands.
Shale Gas Extraction. Shale rock formations have become an important source of natural gas in the United States. Shale gas is present in many locations in the contiguous United States, including some areas where oil or gas production has never occurred before.
Production of Coalbed Methane. Coalbed methane (CBM) was first extracted from coal mines as a safety measure to reduce the explosion hazard posed by methane gas in the mines. Today the methane is captured and used as a source of energy. Deeper coal formations might require hydraulic fracturing to release the natural gas.
Tight Sands. Tight sands are gas-bearing, fine-grained sandstones or carbonates with a low permeability. Unless natural fractures are present, almost all tight sand reservoirs require hydraulic fracturing to release gas.