By Taylor Kuykendall
The relatively new drilling techniques used to tap the Marcellus shale that have drawn the ire of environmentalists and raised the eyebrows of property owners are the same methods that make Marcellus shale wells profitable.
While horizontal drilling and hydraulic fracturing processes are not new to the industry, they have only been recently scrutinized by the general public. Michael Hohn, state geologist and director of the West Virginia Geological Survey, said what’s new with the Marcellus shale is the scope of fracturing.
“Almost any organic-rich shale has to be fractured in some way,” Hohn said. “That is an old process. People have been fracturing for a while. Whether it is setting off an explosive down in the well or what they are doing now with these large, hydraulic fracks.”
Because natural gas is held in the porous areas of the shale, drillers must stimulate the release of the gas. This is done either through hydraulic fracturing or explosive fracturing. The most common method is hydraulic fracture, or hydrofracking.
During the hydrofracking process, water, sand and various chemicals are pumped into the ground to create enough pressure to fracture the shale. The resulting fractures allow the gas to escape from pockets formed in the shale.
Some of the gas is released immediately, while other gas molecules adsorbed in various materials are released.
“The result is the gas comes out of the well relatively slowly,” Hohn said. “Not only because the few pathways to get to the well are very small, it’s also because it doesn’t want to leave the walls of the voids down there because it is attracted to them.”
Because of this phenomenon, some gas wells may continue to produce a steady stream of natural gas for years.
Sand is used as a “proppant.” It essentially keeps the newly fractured shale from collapsing and allows faster collection of the gas.
The process was first used in the United States in 1947 and has been used in applications outside of the oil and gas industry as well. The majority of natural gas wells in the United States utilize hydraulic fracturing to boost the rate of gas capture to economically feasible levels.
Environmental concerns related to fracking include concerns about groundwater quality, surface contamination and possible induced seismic activity. Further, the long-term effects of fracking have not been fully studied.
A study by the Environmental Protection Agency on the process of hydraulic fracturing is expected to be released in 2012.
Hohn said the industry is careful to limit fracture to the shale and not impact surrounding rock formations.
“The purpose of the fracturing is to just fracture the Devonian shale,” Hohn said. “The companies are trying to maximize the fracturing of the shale but not any of the rocks above or below.”
He said what might happen that isn’t planned is what is being studied now.
Traditional drilling involved digging a well straight into the ground and tapping into gas immediately below the well.
Now, drillers can drill down to the gas-bearing formation, and then turn the drill horizontally and continue drilling between 4,000 feet and 5,000 feet sideways. This increases the amount of gas that can be extracted from a single well.
Additionally, drillers can also drill multiple horizontal wells from a single site. Drillers could potentially replace more than 20 wells, each on their own site, with multiple horizontal wells drilled from a single site.
Natural fractures occurring in the shale are typically vertical. By drilling horizontally, the wells are more likely to intersect natural fracture patterns to take advantage of fracture networks in the shale, increasing the volume of gas extracted from a single site.
Horizontal wells and vertical wells utilize fracturing to release natural gas deposits in the Marcellus shale.
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