One of the exciting new developments in the production of both oil and natural is the ever-changing, always-evolving “Frac Frontier.” Hydraulic fracturing, the practice of pumping fluid and sand at high pressure to increase the flow of the hydrocarbons to the surface, has been credited, along with horizontal drilling, with bringing about the dramatic increase in the nation’s oil and gas production.
But the industry, from university researchers to frac service companies, is working feverishly to develop even more efficient ways in terms of time and money to improve frac’ing operations.
“Even though hydraulic fracturing is still just pumping sand and fluid in the ground, it is not quite that simple,” pointed out Mukul M. Sharma, professor and “Tex” Moncrief Chair for the Department of Petroleum, Geosystems, and Chemical Engineering at the University of Texas in Austin. “There are a lot of changes taking place that can impact efficiency, cost, well production, higher EUR (estimated ultimate recovery), and being environmentally responsible.”
Dr. Dan Hill, chairman of the Department of Petroleum Engineering at Texas A&M, said his faculty members are working on laboratory measurements of proppant conductivity in shale, including the measurements of the proppants under stress, the most effective size of proppant, and the non-uniform distribution of the proppants.
“We are even testing the shale with no proppants to determine how to get more conductivity just opening natural fractures,” Hill explained. “There are a lot questions to be answered to determine how much conductivity is optimal and how good wells are created.”
He said Texas A&M professors are also paying a lot of attention to predicting the long-term performance of these multi-stage frac’d shale wells.
“It is a difficult question to understand and predict the decline curve of these wells,” added Hill. “The question is how do I do things better? This is a young technology. Some of the work is fundamental, such as core scale measurement on a nano-scale structure that is so small it is only 10 methane molecules wide. We are doing basic measurements on how molecules move around. Right now, practitioners in the field are doing what they think works best.”
He said this is an exciting time for his department.
“It really is a new world,” he emphasized. “We are working to build a better understanding of the basic matrix of these shales that have low permeability and can’t perform like sandstone.”
Research is not limited to universities, either. FTS International, formerly known as Frac Tech Services, is opening a new corporate technology center in Houston where Shawn Stroman, the vice president of engineering for FTS International, said his staff will be working on developing new fluids and proppants.
“Our goal is to add value to our clients,” he emphasized. “The ultimate goal is to increase the amount of rock contact. There is a lot to understand, from fracture interaction to stresses, mineralogy, and natural fractures. It is different from formation to formation, but not all rocks are homogeneous in one formation, either.”
Although some developments by companies such as FTS International are proprietary, Sharma said the technological advancements in hydraulic fracturing can be broken down into three or four areas, including fluids, proppants, and frac design.
Changes in fluids
Sharma said there are plenty of developments on the fluid side.
“More and more, we realize the need to use more brackish water, especially in West Texas and South Texas, where there is a shortage of fresh water,” he explained. “We are developing polymers as friction reducers that can tolerate high-salinity [80,000 or higher parts per million] brine. Some companies are using CO2, nitrogen, and LPG [liquid petroleum gas], or a combination of them, as energized fluids instead of [in place of] water. Of course, that is more expensive than water.”
The advantage of a gel hydrocarbon-based fluid is that it can flow back as a hydrocarbon gas and can be recovered as liquid and put into the sales line, according to Sharma. He noted, however, that there are always concerns about safety when using anything flammable.
“There is also new hardware, mixing water and proppants where the fluids can handle temperatures from a minus temperature to a plus 200 degrees,” he added.
Another new development, according to Sharma, is the use of hybrid fracs in which a cross-linked gel is used first, followed by a slick water pad with proppants that provides a more viscous fluid.
Stroman said FTS International has developed its proprietary Diamond hydraulic fracturing fluid that is an alternative to guar-based fluids, which have long been a staple of the industry. The guar bean, which is used in many products, comes from India and Pakistan. A dramatic increase in the cost of guar last year caused FTS International to develop its Diamond fluid.
“It is used where you are trying to put higher amounts of proppants in place,” he explained. “It is designed to improve efficiency and increase viscosity.”
Since guar is a gum-gelling agent, Stroman said it leaves about four percent soluble residue.
“The goal is to have a clean proppant pack,” he continued. “Our Diamond product leaves less than one percent soluble fines.”
Improved proppants
FTS International has also introduced Spearprop™, a resin-coated 100 mesh sand that is much stronger than 100 mesh raw sand that is used extensively by the industry.
“Spearprop™ is much stronger and can handle higher closure pressure,” Stroman stated. “Spearprop™ is also designed to withstand the sandblast when you shoot perforations to clean out the hole. We can work with customers to develop proppants to meet their specific needs. Spearprop™ was first developed for a customer in the Haynesville Shale.”
Sharma added that the industry is working on developing new lighter-weight, higher-crush-resistant proppants.
“We are also working on new technology in which an electrically conducting proppant can provide diagnostic information,” he added. “It can tell you where the proppant has gone by logging the well after it is frac’d.”
He said that new technology has not yet been implemented in the field.
New frac designs
When multi-stage fracs began becoming popular, companies would simply take the length of the lateral and divide by a certain number, thus putting a frac every 50 or 100 feet, for example. Later, however, utilizing the information provided by logs, service companies were able to provide indices to more accurately put the frac stage at optimal locations, based on the “sweet spot” of hydrocarbons or the brittleness of the rock.
Now, work is being done to take that a step further with other frac techniques in order to contact as much rock as possible.
Sharma said that in 2009 he first proposed the “Texas Two-Step,” which is a new way of sequencing fractures. Most wells are frac’d from toe to heel, according to Sharma, sequentially coming up the well bore. He said he suggested fracturing Stage 1 and Stage 2, and then doing fracture No. 3 between the first two, and then continuing that two-step process.
He said some people thought he was crazy, but “it provides a better orientation of fracturing.”
“Halliburton had built a sliding sleeve, which can be cemented in, allowing fractures to be in whatever sequence you want,” Sharma explained. “We are working with Halliburton, and the first implementation in the field will be this year.”
Another new frac technique is called zipper frac, which Texas Tech officials have patented. Stroman said zipper fracs can be employed in two laterals that can be anywhere from 250 to more than 1,000 feet apart.
“You can frac two wells with one crew,” he explained. “You do Stage 1 in the first well, then close it like a zipper, unhook, and frac Stage 1 in the second well. You continue to alternate each stage in each well. It causes an incremental increase in fracture interaction.”
Sharma added that zipper fracs have been primarily used when multiple wells have been drilled off the same pad in the Eagle Ford and Bakken Shale formations, often resulting in better wells.
Stroman said that zipper frac’ing techniques have been incorporated in the majority of the active oil and gas fields in the United States.
He noted that FTS once did a simultaneous fracture, when it frac’d two laterals with two different crews at the same time.
“We did it out of necessity because the Corps of Engineers gave us just one week to frac wells along the Trinity River (in Fort Worth),” he recalled. “So we brought in two crews and frac’d both wells at the same time. They made some of the best wells in the Barnett Shale. The ultimate goal is to initiate as much rock contact as possible.
“Ultimately, zipper frac’ing of horizontal wells seems to be the preferred approach over simo-frac’ing,” Stroman said. “This technique incorporates two fracturing fleets and is applied with much the same idea as zipper frac’ing, and that is to stimulate as much of the reservoir as possible. Each stage of each well is completed at the same time. Often the logistics and planning of multiple fracture fleets can be an issue, hence the reason zipper fracturing is more popular.”
Environmental issues
Water management is a major issue in frac’ing, too, especially in areas where fresh water is limited.
Stroman said some of FTS International’s clients in the Marcellus Shale in the Northeast have gone to basically a closed loop system in which they can treat the flowback and produced water, then reuse it for additional well completions, essentially using the same water over and over again. The ability to reuse produced water helps minimize fresh water use in oilfield operations.
“We have also put the finishing touch on our new Aquacor™ water management system’s mobile water purification unit,” he said. “We began Beta testing it in the Barnett Shale in February. Once we are comfortable that the unit is performing optimally in our field tests, we plan to deploy it for operations in various basins, including the Marcellus Shale. Operators in the Northeast often experience flowback water that is difficult to recycle and reuse. Plus, water disposal options tend to be more limited in that area.”
Aquacor™ can treat vast quantities of water, as much as 15,000 to 16,000 barrels a day, according to Stroman. He said the ability to provide its own water treatment unit also gives FTS International integrated services.
In another effort to provide a more environmentally clean service, FTS is currently testing systems for converting some of its mobile pressure pumping units to run partially on natural gas, Stroman said. The bifuel units will run on both diesel and natural gas. Cutting diesel use in favor of natural gas lowers costs and is more environmentally friendly.
Stroman added that FTS did its first test in the Haynesville a year ago using gas from an adjacent well. “We continued testing for about six months with one of our customers in the Haynesville Shale,” he said. “We learned a lot from that test and went back to the drawing board to research and refine our company’s best options for deploying bifuel units in the field. We have evaluated and tested several different systems from competing manufacturers and expect to start deploying some units for bifuel operations by mid-2013.
“Our goal is to have many of our pumping units be bifuel, meaning they can run off either diesel or natural gas,” he said. “That decreases the need for diesel, but using natural gas, of course, is not always an option.”
Universities and frac service companies are developing products and techniques meant to save time and money, as well as increase production.
“Every aspect of the business is under study,” observed Texas A&M’s Hill, “from fluids to proppants to environmental aspects. All factors are inter-related. It is also pretty apparent that there is a people side to this grand scale of activity. It is putting tremendous pressure on enrollment in our [petroleum engineering] program.”