If you have an ACS member number, please enter it here so we can link this account to your membership. (optional)

ACS values your privacy. By submitting your information, you are gaining access to C&EN and subscribing to our weekly newsletter. We use the information you provide to make your reading experience better, and we will never sell your data to third party members.



Proppant Progress

A workhorse for oil and gas extraction sees material advances amid growing demand

by Melody M. Bomgardner
September 5, 2011 | A version of this story appeared in Volume 89, Issue 36

Wedged In
Credit: Momentive
Curable resins make proppant grains stick together to prop up a gas well fracture.
Hydraulic Fracturing Schematic
Credit: Momentive
Curable resins make proppant grains stick together to prop up a gas well fracture.

The stars have aligned for a product that is used deep in the earth. Hydraulic fracturing methods for natural gas recovery, which took off in 2007, have increased demand for proppants—grainy materials that increase the flow of natural gas and oil by propping up fissures in rock.

Suppliers of proppants and the resins used to coat them have been rapidly expanding capacity to keep up with the demand. Several types of companies are supplying the proppant market, including resin makers such as Georgia-Pacific Chemicals and Momentive Specialty Chemicals, industrial minerals firms, ceramics producers, and even nanotech start-ups. Many of them are using chemistry to make proppants that increase the flow of gas and oil while holding up against extreme pressures and temperatures.

In the oftentimes heated discussions about the materials used in hydraulic fracturing, or fracking, proppants have not received the attention that fracturing fluids have attracted. The fluids—a mixture of water and chemicals including thickeners, friction reducers, surfactants, salts, and acids—are used to suspend and carry large quantities of proppants into the far reaches of a gas or oil well.

Great Grains
Credit: Momentive
Proppants can be coated with curable resins (left three panels) or precured resins (right).
Various of Momentive’s coated proppants for oil and gas drilling/hydraulic fracturing.
Credit: Momentive
Proppants can be coated with curable resins (left three panels) or precured resins (right).

In the fracking process, the fluid-proppant mixture is pumped at high pressure into shale deposits, often a mile or more beneath the surface. The pressure causes fractures to open in the rock. Once the pumping stops, the fluid flows back out of the well, but the proppant grains stay behind to hold the fractures open and let the gas or oil seep out. This task has grown more challenging as drillers have increased the depth and horizontal reach of their wells.

Proppants can be materials as simple as silica sand, mined from ancient sandstone deposits of smooth, spherical quartz grains in places like Saskatchewan and Wisconsin and sieved into different sizes. But as drillers have gone after reserves that are more difficult to access, they are turning to tougher, resin-coated sand; stronger, more precisely sized ceramic proppants; and even new ceramic forms based on nanotechnology.

“The combination of horizontal drilling and fracturing of unconventional resources has been nothing short of a paradigm shift in the amount of proppant used,” observes Brian D. Olmen, president of Kelrik, a consultancy that specializes in minerals used in the energy industry. According to the American Petroleum Institute, up to 80% of natural gas wells drilled in the next decade will require hydraulic fracturing.

The amount of proppant used in a well depends on the number of stages, or fracturing points, that will have material pumped into them along the horizontal length of the well. Wells routinely reach more than a half-mile laterally and have 10 to 20 stages or more, each taking an average of 300,000 lb of proppant. That can quickly add up to 3 million to 10 million lb, Olmen says.

In the Marcellus Shale wells of Pennsylvania and West Virginia, drillers may use 10 million to 20 million lb of proppants in wells that reach 1.5 miles down and another 1.5 miles across, says Jerry Borges, vice president of Momentive’s oil-field technology business. He points out that 20 million lb is equal to 100 railcars of sand, and all of it goes down a wellbore pipe only 5.5 to 7 inches in diameter.

Not all proppants are appropriate for all wells. “The specific site and drilling operation dictate the kind of proppant best suited for the job,” explains Michael R. Roberts, a vice president at Georgia-Pacific Chemicals, which sells coating resins to proppant makers. “For instance, noncoated sand may work in shallow drilling operations, but coating provides needed resistance to the increased underground pressure at greater drill depths.” Resin-coated sand is less likely to be crushed and release well-clogging fine particles.

Of the proppants used in 2010, more than 88% were sand or sand coated with resin. Demand for resin-coated sand has been growing compared with other types of proppants, with volumes increasing more than 25% annually for the past five years, according to Olmen.

The other 12% of demand was mainly for ceramic proppants, which are more spherical, have stronger crush and heat resistance, and can provide higher flow capacity compared with sand, particularly at temperatures and pressures that, in some wells, can exceed 300 °F and 10,000 psi.

Not surprisingly, companies that specialize in resins for coated proppants are expanding production. Georgia-Pacific is increasing capacity at its Lufkin, Texas, facility. The company does not disclose the chemistry of its resins, but like Momentive, it is known for manufacturing phenol-formaldehyde and urea-formaldehyde resins used to make plywood and other construction materials.

For its part, Momentive is quickly ramping up production of specialty curable resin coatings at its Brady, Texas, facility. “We developed the curable resins not only to strengthen the sand but to make it stick together,” Borges says. The curing occurs under the high temperature and pressure of the well. “When the curable-resin-coated proppant gets stuffed into that crack, it bonds together and becomes like a rock—it’s a very high permeability pipeline that stays intact because it is held together with the resins we use,” he explains.

Meanwhile, leading ceramic proppant maker Carbo Ceramics has completed a fourth manufacturing line at its plant in Toomsboro, Ga., and added resin-coated proppants to its portfolio.

Carbo is a public company, and its second-quarter results give some insight into growth in the industry. The firm saw revenues increase 34% to $150 million, compared with last year’s second quarter, because of increased sales volumes and prices of its proppants. The average selling price of 1 lb of ceramic proppant was 36 cents, up 11% from the prior year. Carbo told investors it will have 1.75 billion lb of capacity by the end of 2011.

At nanotech start-up Oxane Materials, the ceramic proppants cost more per pound, but on the other hand, they weigh less. Oxane was spun off from Rice University, where researchers exploited the overlap between nanotechnology innovations and their Houston location, in the heart of the gas and oil drilling industry.

Oxane founder Andrew R. Barron, a materials science professor at Rice, says traditional proppants are strong, but also heavy, and they do not flow all the way to the end of the rock fracture. His team makes lighter spheres using nanotechnology. “One of my students worked out how to make hollow ceramic beads, like very small Ping-Pong balls.” The hollow sphere of aluminum oxide was “incredibly strong,” Barron says. In addition, every sphere in each batch was exactly the same size.

Barron realized the particles could be used as proppants, and Oxane was spun off in 2002. The company bought a plant in Van Buren, Ark., and has been making its OxFrac proppants. These proppants are suited for West Texas wet gas wells, which contain both gas and oil. The company has announced plans to expand.

Olmen says proppant makers must stay on top of changes in demand as drilling expands into areas such as the Eagle Ford Shale formation in South and East Texas and the Bakken formation in Montana and North Dakota, which contain both gas and oil and require coarser proppants.

Momentive’s Borges says his company is already adapting. “We are working on new chemistries, mostly for oil-field development. It takes a lot of resin know-how and applications know-how to make a resin perform at the various temperatures and depths we operate in.” 


This article has been sent to the following recipient:

Chemistry matters. Join us to get the news you need.