HYDRAULIC FRACTURING

WHAT IS HYDRAULIC FRACTURING
Hydraulic fracturing is the process of drilling for natural gas and oil underneath the ground. Water mixed with other components is pumped into the ground to create cracks (also referred to as fissures or fractures) to release the gas into wells that have been built for collection.

Groundwater protection remains a main goal and paramount to the success of and well operation. The well’s design, the casing, and the inherent risk associated with the hydraulic fracturing process itself all factor into new shale gas well development. Over the years, this technology has been used safely and successfully in over one million wells. Regulators together with operators have mitigated many of environmental risks. Shale gas, or natural gas, producers most often will leave a small wellhead behind on the property along with several storage tanks, and a metering system to measure shale gas production.

Schematic description of hydraulic fracturing for shale gas. (Wikipedia)

METHOD

A hydraulic fracture is formed by pumping the fracturing fluid into the wellbore at a rate sufficient to increase pressure downhole at the target zone (determined by the location of the well casing perforations) to exceed that of the fracture gradient (pressure gradient) of the rock.
The fracture gradient is defined as the pressure increase per unit of the depth due to its density and it is usually measured in pounds per square inch per foot or bars per meter. The rock cracks and the fracture fluid continue further into the rock, extending the crack still further, and so on.

Fractures are localized because pressure drop off with frictional loss attributed to the distance from the well. Operators typically try to maintain "fracture width", or slow its decline, following treatment by introducing into the injected fluid a proppant – a material such as grains of sand, ceramic, or other particulates, that prevent the fractures from closing when the injection is stopped and the pressure of the fluid is removed. Consideration of prop pant strengths and prevention of prop pant failure becomes more important at greater depths where pressure and stresses on fractures are higher. The propped fracture is permeable enough to allow the flow of formation fluids to the well. Formation fluids include gas, oil, salt water and fluids introduced to the formation during completion of the well during fracturing.

ENVIRONMENTAL IMPACT

Hydraulic fracturing has raised environmental concerns and is challenging the adequacy of existing regulatory regimes. These concerns have included ground water contamination, risks to air quality, migration of gases and hydraulic fracturing chemicals to the surface, mishandling of waste, and the health effects of all these, as well as its contribution to raised atmospheric CO₂ levels by enabling the extraction of previously-sequestered hydrocarbons. Because hydraulic fracturing originated in the United States, its history is more extensive there than in other regions. Most environmental impact studies have therefore taken place there.