by Al Pickett, special contributor
Things are never as simple as they seem. And sometimes when you think you understand something, you find that there’s another stage that calls for fresh scrutiny.
As Frank Zamora pointed out recently, many in the industry believe that nearly 50 percent of the perforated clusters in hydraulically fractured wells go untreated, meaning the entire fracture stage is not being stimulated and consequently production volumes are not being optimized.
“I believe those claims are accurate,” he stated.
Zamora is senior vice president of technology and engineering for FTS International, which bills itself as the largest private well-completion service company in North America. He works at the company’s research and development center in Houston, where FTS International, formerly known as Frac Tech, is developing new technology to improve the results of hydraulic fracturing.
It is well documented how horizontal drilling and hydraulic fracturing have revolutionized the oil and gas industry, but now service companies, including FTS International, are working to develop a better understanding of the stimulation process and thereby improve well performance.
Zamora said he sees several trends in hydraulic fracturing, including the use of diverting technology to maximize reservoir volume and optimize refrac designs.
“I have been doing this for 38 years, and times are exciting now,” he stated. “Technology has evolved so much, and we are so much more efficient. We know more about the formation. We can mix and match with different formations, which is important because everything is so formation dependent.”
FTS International created the NuFlo system, building on methodology that has been proven to increase production in new wells and refracturing applications. After half of the fracture stage is stimulated, the NuFlo temporary diverting agent is employed. It is designed to effectively divert fracturing fluid into new fractures.
“The fluid carrying the proppant goes to the path of least resistance,” Zamora explained. “So we developed a material to plug the dominant fractures, allowing the fluid to divert to other untreated fractures.”
The NuFlo diverting agent is a degradable plastic that disintegrates with time and temperature, sometimes as quickly as 24 hours in bottomhole temperatures of 250 to 280 degrees, according to Zamora. He said each of the dissolvable diverting agents is composed of various particle sizes that temporarily block existing fractures and help develop new fractures to increase stimulated reservoir volume.
“It allows us to put the frac across all of the stage and develop all of the perforations,” he added. “It has improved frac efficiencies.”
Although Zamora said FTS International doesn’t have any specific numbers to quantify the impact that the NuFlo diverting agent has on a well’s production volume, he did observe that their customers “say it has improved production, and the well in which they have used it is the best well in the field.”
He said it is difficult to quantify its results because the results are so field dependent. FTS International has used it in the Marcellus, Woodford, and Eagle Ford plays.
“The technology is not patented,” Zamora pointed out. “It is a 20-year-old technology, but it has proven to be very successful.”
FTS International has not yet used the NuFlo diverting agent in the Permian Basin, but Zamora said it has a customer who plans to use it soon in the Delaware Basin on the far west side of the Permian Basin in doing refrac designs.
“We can go back into a well that is two or three years old and is already showing the decline curve, and we can get it back to a better rate,” he explained. “We can go back in a well that has been producing with a 4,000- to 5,000-foot lateral that has been perfed from toe to heel. There may be a tremendous amount of oil still in place. You want to place the proppant back in the interval, but you want to try to keep it from going in the same fractures that have already been stimulated. The (diverting) material is so small that it is not rate dependent. If you have enough differential pressure, you can push it to other parts of the lateral.”
The trend, according to Zamora, is more frac stages and shorter intervals. He said the NuFlo diverting agent can help the operator fracture new rock by blocking existing perforations.
If a diverting agent can substantially increase production in a new well, one can easily see how it would also be beneficial in refracturing a well whose production is on the decline.
“Refrac’ing is in the early stages,” Zamora observed, “but people are bullish on refrac’ing and are optimistic about its production potential. The refrac market might be the next boom. There are still tremendous opportunities out there. We just need a little help from the oil gods. We can plug old fractures, meaning we will be fracturing new rock with the refrac. Of course, trying to reopen existing fractures is less expensive than drilling a new well.”
He predicted that refracturing existing gas wells will really take off when—and if—the natural gas price improves.
If refracturing existing wells will significantly increase production volumes, Zamora’s prediction could soon become reality.
Reducing Need for Fresh Water
Another trend that Zamora has observed is the ability to take 100 percent of the produced water and reuse it in the next fracture job, thus reducing the need for fresh water.
Although FTS International doesn’t filter out suspended solids in produced water, it has developed a system that allows it to use the produced TDS (total dissolved solids) water. That helps to meet the industry’s challenge of reducing the amount of fresh water required for well completion operations.
The company’s Aquacor suite of fluids helps customers control the effects of produced and recycled water on the fracturing systems. The Aquacor LB Fracturing Fluid is a guar-based crosslinked system designed for use with recycled water with a high boron content and low to moderately high temperatures. It employs XLD-2, which attaches to the borate particles in the water without reducing the overall stability of the crosslinked fluid, according to Zamora.
Among the benefits to the Aquacor fluid systems that he lists are controlling surface crosslink viscosity caused by boron, minimizing surface treating pressure, and reducing fresh water use, increasing the industry’s environmental stewardship. He said it facilitates the reuse of water with up to 100 ppm (parts per million) of borate.
Zamora said the Aquacor fluid systems are being used extensively in the Mid-Continent and Permian Basin. That is especially important on the New Mexico side of the Delaware Basin, he emphasized, where the produced water has a “high hardness” but fresh water for use in fracturing oil and gas wells is in short supply. He said the water in the Delaware Basin doesn’t have a lot of iron in it, but a scale inhibitor can be added if necessary to the produced water that is being reused as a frac fluid.
“That is a tremendous savings for our customers,” he continued. “They don’t have to buy fresh water and truck it in. The produced water is coming from the same formation, and the customer has already captured it. They can blend it on the fly and compensate with fresh water if they need to.”
He said some companies are treating for biocides when they filter the suspended solids, pulling the bacteria out to prevent future H2S issues.
PolyLite Fracturing Fluid
FTS International has also developed what it calls PolyLite fracturing fluid, which is a simplified low-polymer system that provides a cost-effective alternative to conventional fracturing fluids.
Zamora said PolyLite fracturing fluid is a borate-based crosslinked system that offers stability at polymer loadings up to 40 percent lower than typical crosslinked systems.
“It stabilizes the system, taking the polymer from 15 to 20 pounds per gallon of water to 12 pounds,” he point out. “And we are trying to get to 10 pounds and still have good suspension. Its low-viscosity and high-elasticity design is formulated to minimize treatment costs and optimize fracture conductivity.”
He added that it can also be effectively mixed in many brine waters.
The latest technological developments by FTS International and other well completion service companies are designed to optimize production, reduce costs, and be environmentally friendly. The results would have inconceivable just a decade ago.
Al Pickett is a freelance writer in Abilene and author of four books. He also owns the West Central Texas Oil Activity Index, a daily and weekly oil and gas reporting service. For more information, email firstname.lastname@example.org.