AUBURN TWP. - In the crook of a hill on a dirt road north of Meshoppen lies Cabot Oil & Gas’s pride and joy: the Bray, a 10-well pad that produced enough natural gas in its first month to supply the city of Philadelphia for a month.
Above ground, orderly rows of green pipes run from 10 wellheads to sand separators and production units. Below ground, Cabot positioned the wells to maximize the amount of surface area of the Marcellus Shale the well taps, spokesman George Stark said.
The techniques used to drill and hydraulically fracture wells on this pad evolved over many decades in oil and gas regions all over the world.
And innovation continues.
It’s possible that techniques used on the Marcellus could one day be used on another.
“The goal is to constantly take this technology and apply it somewhere else,” external affairs coordinator Bill desRosiers said.
The Bray pad has wells that penetrate the upper and lower parts of the Marcellus formation, which can be 300 to 350 feet thick in Susquehanna County. These wells are arranged in a “sawtooth” formation, Stark said, including two upper wells spaced 1,000 feet apart from each other and two lower wells spaced the same distance.
“Downhole spacing, that’s truly what you’re trying to understand,” he said.
Other exploration and production companies are also refining the technology they deploy in Northeast Pennsylvania.
Chief Oil & Gas uses specialized “walking” drilling rigs that can drill multiple wells on a single pad, moving from one surface location to another without having to be disassembled, said spokeswoman Daria Fish.
Chief also uses directional drilling and logging to track geologic formation and characteristics while drilling.
High-strength steel casings and specialized cement are also used to increase well bore integrity and protect fresh water zones, she said. The cement used to seal the spaces between steel casings and the borehole contains special additives to create a tight seal against fluids and shallow sources of gas, she said.
Some new technologies also help address air pollution while boosting revenues for drilling companies. Cabot employed two of these on the Bray pad.
Before Cabot started drilling the wells on that pad, pipeline company Williams had already placed a gas line on site. Instead of diesel fuel, Cabot used gas from this line to power the drilling rig and completion equipment. This saved the company millions, Stark said.
The company also avoided burning excess gas, or flaring, on the wells after fracturing. For the Bray pad, all the gas was “turned in line” after completion, Stark said, meaning it was all funneled into a pipe and harvested for sale.
Among industry outsiders, discussion continues to revolve around two techniques whose combination has reinvigorated oil and gas production in the United States: directional drilling and hydraulic fracturing.
Both have evolved gradually over decades of practice. Both also have early ties to the oil fields of Pennsylvania.
The first use of liquids to fracture a rock to release oil was in “shallow, hard rock wells” in Pennsylvania, New York, Kentucky and West Virginia in the 1860s, according to a history of hydraulic fracturing by Carl T. Montgomery and Michael B. Smith published 2010 in the “Journal of Petroleum Technology,” a publication of the Society of Petroleum Engineers.
These early fracturers used liquid nitroglycerin, a method the authors call “extremely hazardous and often used illegally.” At high pressure, the fluid could reduce the oil-bearing to rubble and enhance oil recovery.
Drillers then experimented with other liquids that would leave cracks in the rock intact, opening a pathway for oil and gas. In-depth study and development of the “Hydrafrac” procedure did not come until 1947, when Stanolind Oil and Gas Corp. injected 1,000 gallons of thickened gasoline (i.e., napalm), down a well in Kansas to stimulate a limestone formation, Montgomery and Smith wrote.
In 1948, Stanolind’s J.B. Clark wrote a paper on the new Hydrafrac technique that has been widely cited as the introduction of hydraulic fracturing to the industry. A news clipping from “The Bradford Era” that year describes a process with some similarities to the hydraulic fracturing done on the Marcellus Shale today:
Forcing jellied gasoline down the hole “splits the rock formations and opens cracks through which oil can flow into the well-hole,” the article states. “Sand suspended in the mush keeps the crack from closing again.”
Decades of study and trial-and-error led to significant changes, according to Montgomery and Smith. Since 1953, hydraulic fracturers have used water as a base fluid and now use thousands of times more fluid than in early 20th century wells. The industry has also tinkered with various acids, brines and surfactants.
To prop open fractures, all different sizes of sand grains, plastic pellets, steel shot and even glass beads have been forced down well bores. Engines also increased in size from an average of 75 hydraulic horsepower to more than 1,500 hydraulic horsepower.
For shale formations such as the Marcellus, hydraulic fracturing in a vertical well isn’t enough on its own. It took combining that technique with horizontal drilling to make the shale economically viable.
The first patent on a drilling in a curved line came in 1891, according to a U.S. Energy Information Administration history of horizontal drilling published in 1993. The first recorded horizontal oil well came in 1929 in Texon, Texas. The second was drilled in 1944 in Venango County, Pa..
Drillers around the world experimented with the technique, but it didn’t catch on until the early 1980s, when improvements in downhole drilling motors and telemetry equipment made it profitable, according to the EIA.
According to the EIA, while drillers eventually found commercial success in the Austin Chalk and Bakken Shale fields of Texas and North Dakota, respectively, it took George P. Mitchell to combine the two techniques in the Barnett Shale in Texas.
Mitchell Energy & Development drilled the first well in the Barnett in 1981. Mitchell then experimented with different methods of drilling and fracturing until it came up with the most cost-effective combination, according to a history of the shale gas boom by Zhongmin Wang and Alan Krupnick of nonprofit research organization Resources for the Future.
“It was the successful development of the Barnett play that jump-started the shale gas boom,” Wang and Krupnick wrote.