Unlocking Unconventional Oil and Gas

In the basement of Alderson Hall, in a lab painted butter yellow and crimson with soaring, utilitarian square concrete pillars, amongst a hodgepodge of machine room detritus and laboratory equipment, is a non-descript apparatus that does something extraordinary. It makes a rock behave as if it isn't there.

Specifically, the rock responds as if, instead of being in a room in the basement of the petroleum engineering building at Mines, it’s in its ancestral home – perhaps thousands of feet from the surface, hot and under tremendous pressure. In the conditions under which it has spent millennia, the rock is stressed and sometimes pushed to the breaking point. How? Mines Petroleum Engineering Professor Azra Tutuncu, or one of her students, uses the machine to squeeze, heat and perhaps shake the rock. The machine sits on rocking, gel-insulated feet to make sure it doesn't shake the building or break the floor.

Tutuncu wants to understand the rock’s properties, and find out under what conditions, and how, the rock will crack. This is important because, far away on the desolate sagebrush steppes of Wyoming, or under the undulating grasslands of the Great Plains, the vast rock formation from which this sample came is saturated with gas. Gas that can only be extracted by breaking that rock.   

To figure out the best, most efficient and most environmentally sound way to do so, Mines is the go-to university in the U.S. Its Unconventional Natural Gas and Oil Institute (UNGI), which Tutuncu directs, helps Mines fill a role only an academic institution can provide. It fosters unconventional research collaborations, provides students training available virtually nowhere else in America, and partners as an honest broker with industry and government to help train effective government regulators.

“UNGI’s role is to be a leader in research, where we can collaborate with the worldwide oil industry, state and government agencies, and other academic organizations,” Tutuncu said, “ and to unlock these resources appropriately in an environmentally friendly and economically viable fashion.”

 

When Drilling Got Harder

For many years, all that was necessary to harvest oil and gas was to pluck the low-hanging fruit of formations from which the oil sometimes literally gushed from the ground. And, if you believe the movies, under the fountainous deluge, the drillers always danced for joy. But in the last few decades those conventional reservoirs, from which oil and gas easily flowed, began to run out.

Meanwhile, an enterprising driller named George Mitchell began looking in the 1980s at a formation called the Barnett Shale – with an eye toward how to crack it. Shales are dense sedimentary rocks produced from compressed silt or mud. They may hold hydrocarbons abundantly in the pores of the rock, but the pore spaces are not very permeable. These shales often form the upper and lower seals on conventional petroleum reservoirs.

Drillers had noted for years that when they bored through the shale, they would encounter occasional pockets of gas. But the rock as a whole was far too impermeable to yield the gas trapped inside it. Mitchell knew the formation could produce a huge quantity of gas if only he could figure out how to make the rock release it in an economically feasible way. But how? Mitchell and his engineers solved their problem by using an existing technique, in new and improved ways, on the recalcitrant shale. The technique was hydraulic fracturing.  Later the process of horizontal drilling – a critical advancement – came into use.

To drill horizontally, engineers drill down into the gas-bearing rock and then gradually turn the bit horizontally into the rock layer that contains the hydrocarbons they're after. A well horizontally drilled into the reservoir formation vastly increases the surface area of a well exposed to the oil-or-gas- bearing rock. In the case of a 100-foot-thick layer and a one-foot-diameter well, they theoretically can go from 160 square feet to 3,207 square feet of exposed petroleum-yielding rock. By drilling multiple horizontal wells in multiple directions from one well pad, they multiply the effect.

Why hydraulic fracturing? One great way to make tight shale give up petroleum is to make your own escape route for the gas by infiltrating it with fissures. “With most of those formations,” said Jennifer Miskimins, associate professor of petroleum engineering at Mines, “unless you crack them a little bit, they're not going to flow at all.”

By injecting fluid under high pressure into a well, petroleum engineers break the rock all around it. They also mix sand or tiny beads of kiln-fired clay called “proppant” with their fracturing fluid. The mixture varies greatly in color and texture; beakers of it can resemble charcoal-grey instant dried yeast or tan, dry tapioca pearls. When these micro-ball-bearings infiltrate the fissures as the rock breaks, they help prop the cracks open.

Because the well bore is horizontal at depth, the well can be fractured sequentially dozens of times – the number is increasing as petroleum engineers become more experienced. With the horizontal bore, the multiple wells possible from one pad, and the fracturing process, it's now possible for one well pad to replace what would have formerly required 957. A well pad that, in the past, would have allowed access to 160 acres of the productive rock can now access 153,207 acres.

This vast improvement in the surface area of petroleum-bearing rock from which drillers can extract gas – along with increasing gas prices – enabled unconventional gas to become economically viable. And as more and more drilling companies, large and small, have rushed to share in the bonanza, unconventional gas production has soared. A map of shale basins under development today looks vastly different and more colorful than maps of just a few years ago.

“You will be amazed at some of the very giant shale basins we are dealing with in the last two to three years that were not even on the map in 2005,” said Tutuncu. Presently about 30 percent of U.S. natural gas production comes from unconventional sources, but by 2035, said Tutuncu, it will be beyond 50 percent.

What makes unconventional shale gas even more attractive is this country’s potential reserves, which worldwide rank second only to China. For those interested in energy independence for the United States, this makes shale gas an attractive option. “In the U.S. we're on the screaming decline for [conventional] natural gas,” Miskimins said. Just a few years ago, permits were being issued to California ports for importing liquefied natural gas from abroad. Now, she said, shale reservoirs make up about 50 percent of what's produced on a daily basis in the U.S.

 

Leading the Pack

From the beginning, Mines has led and continues to lead the way in researching and improving unconventional oil and gas extraction methods. “Mines was looking at unconventional reservoirs before anyone called them unconventional,” Miskimins said. Mines has studied the geology of the Piceance and Green River Basins of Wyoming and the Niobrara play around Chugwater, Wyo., for decades, she added.

Hydraulic fracturing of gas shale is a unique niche for Mines, according to Miskimins. The university’s research focuses on:

  • understanding the mechanical behavior of rocks and how they respond to various sensing – often seismic or acoustic – methods that petroleum companies use to gauge them
  • creating models that accurately simulate how reservoirs will fracture and behave over time
  • or simply trying to understand the geology of the shale beds.

           

To capitalize on this expertise two years ago, Mines Vice President of Research John Poate asked Miskimins and John Curtis, Mines professor of geology and head of the Potential Gas Committee, to form an institute specifically focused on unconventional reservoirs. This was the seed of UNGI, aimed at bringing bright minds from different departments on campus together to look at big ideas and projects in unconventional oil and gas.

Today UNGI promotes communication and new research consortia among faculty in many different departments. UNGI presently includes 41 Mines faculty and more than 30 graduate students, and one of the first consortia to emerge from this group, the UNGI Coupled Integrated Multiscale Measurement and Modeling effort, involves faculty from nine different departments, five Department of Energy national laboratories, and several independent and major oil companies.

In addition, UNGI plans to be an impartial resource for the public, industry and government in addressing the environmental concerns associated with hydraulic fracturing, researching claims of damage or contamination and seeking ways to improve the process, reducing or eliminating contamination, and saving water. Presently, ground and surface water contamination by fracturing fluid is the largest perceived risk, but habitat destruction by well pads and the sheer quantity of water required for hydraulic fracturing are additional concerns. In 2010, for instance, 10,500,000 gallons of water were required to fracture one well 5,000 feet long in 20 to 25 fracturing stages.

“The public has every right to be concerned about this,” Tutuncu said. “That is why we are looking into the scientific and engineering facts behind hydraulic fracturing and how can we reduce environmental impacts and save water.”

Tutuncu's own rock-shaking-and-breaking project in the basement lab has environmental aims at heart. Better understanding the properties of the rock a company will fracture helps the company minimize the water and chemicals they will need to get the job done. Her setup will also allow her team to directly introduce different fracturing fluids into the sample and measure the response. One method they will test is to use a simple solution of salt and water with no other chemicals, Tutuncu said. Because shale usually demands extremely high water pressure to break, increasing the salt concentration makes the rock more breakable, so the process requires less water – and only a trace amount of chemicals may be needed to do it.

The core cells at the heart of the setup were specially designed and ordered by Tutuncu to radically improve on existing methods for testing. There is no experimental setup anywhere else in the world with the same capabilities to implement the real reservoir conditions. A single, accurately shaped cylindrical core sample can be tested inside, rather than an unrealistically sized and shaped series of blocks typical of current testing methods. Because shale is thinly layered, the stresses are very different in different directions of the rock, and therefore the size and shape of the samples matter too.

 

Sharing the Knowledge

UNGI also plans to reach out and help other countries begin investigating their reservoirs. The sudden interest in unconventional petroleum fields has caused some countries to realize they are sitting on top of an unexpected windfall. “Argentina, which was not even in the oil play at all in the past,” Tutuncu said, “is unexpectedly number three in terms of total recoverable unconventional shale gas reserves.”

Argentina will need help to exploit those reserves. Scientists at Mines are curious to compare the characteristics of their shale with our country’s to understand if the techniques we use on our basins are transferrable to theirs. UNGI hosts visiting scholars from many countries and likewise fosters research into the similarities between various U.S. basins and world shale plays to speed production in those countries.

The Mines Petroleum Engineering Department offers three-week, condensed “Super School” training classes every summer on the fundamentals of petroleum engineering for oil and gas company employees with non-petroleum-engineering backgrounds.

In addition, the department and UNGI – in partnership with ExxonMobil and GE Oil & Gas, the University of Texas at Austin, and Penn State University – have initiated a public service effort to train government regulators and policymakers in the areas of shale reservoir drilling, completion, hydraulic fracturing and production.

Michael Parker, a technical advisor in the Safety, Health and Environment group of Exxon-Mobil Production Company, said that public confidence in oil and gas extraction is built through strong, sound regulation enforcement, and one of the publicly perceived weaknesses in the industry has been a lack of good regulation.

Exxon-Mobil and GE Oil & Gas saw that they had the ability to improve competence among new regulators by providing a short course that would teach those with biology or environmental science backgrounds the fundamentals of the business they will regulate. But they knew they weren't the ones to do it. That's when they turned to Mines. “We know what we want, we're just not quite sure how to get there,” Parker said, “and that's the void they're filling for us very effectively.”

This article appears in the 2012-13 issue of Energy and the Earth magazine.