Hydraulic fracturing: Well completion and fracture stimulation
Editor's Note: This is the fourth part in a six-part series giving a step-by-step look at the process that a natural-gas company conducts to produce natural gas from the Marcellus Shale. The series is a collaboration with Chesapeake Energy and the company's methods of operations are not meant to reflect the operations of other natural gas companies.
Ever since the natural-gas industry began production from the Marcellus Shale, the process of hydraulic fracturing, also known as fracking, has been the focus of public controversy. However, through the use of rigorous and robust safety measures, Chesapeake Energy has used the common and proven technique to successfully produce the natural gas that would otherwise be impossible to reach.
"The fracturing process is highly engineered and technical," Rory Sweeney of Chesapeake said. "Every part of it is planned from the very beginning and engineers develop a gameplan that the completions team follows. There's a variety of advanced equipment needed for the process and the site layout is painstakingly designed to facilitate the most efficient and safe operations. Before the equipment is put into place, though, the team holds a safety meeting to prepare. Then, again, after the equipment is positioned, the team holds another safety meeting to prepare for the completion operation itself."
One of the most important pieces of equipment, which serves as the headquarters of the site, is the data van.
"The data van is where the onsite completions team carefully keeps track of every bit of information about the fracture," Sweeney said. "The proposed pumping schedule is uploaded there to ensure the job runs as close to design as possible. Staff on- and off-site use the information collected to monitor pressure, fracture length, fluid use, equipment performance and other functions."
The well, which is capped after drilling and before the completions crew arrives, and the surrounding geology is protected by the several layers of steel casing and cement that were installed during the drilling process. The wellbore is pressure tested prior to fracking to ensure the integrity of the well.
"The next step is perforating," Sweeney said. "A 'perf gun' is lowered down the well bore, and it will create a set of small, directional perforations roughly the size of a quarter in the production casing near the end of the horizontal section of the well."
Above ground, a blender truck mixes the fracturing fluid, which is typically around 94 percent water, 5 percent sand and 1 percent chemical additives.
The additives include an acid to neutralize pH, clean any cement that remains inside the wellbore from the casing process and dissolve any rock that may also be in the wellbore from the perforation process. A disinfectant is also used in the fluid, which eliminates any potential bacteria and sterilizes the wellbore. A corrosion inhibitor eliminates rust; a friction reducer reduces the fluid's surface tension in the wellbore; an iron-control agent prevents iron from settling out of the fluid; and a scale inhibitor prevents mineral buildup on the interior wall of the casing.
"The fluid is then sent into the low-pressure side of the treater manifold, which distributes it to pumps. The pressurized fluid is then pumped through iron piping into the high-pressure side of the manifold," Sweeney said. "From there, it is pumped down the wellbore through the perforations in the casing and into the target formation. It takes advantage of natural zones of weakness in the shale, expanding them enough to release the gas trapped within the rock."
This is one of the first points where the actual completion operation can be compared to job design. If the fracture doesn't occur within a reasonable pressure compared to what was expected in the design, the operation shut down to investigate possible causes. If everything is going according to plan, the operation continues.
"The sand following the fluid and props the fractures open. By this time, the additives are effectively neutralized. A plug is installed at the end of the set of perforations, thus ending the first stage of the completion. The process is repeated several more times down the length of the horizontal portion of the wellbore, creating perhaps a dozen stages in total. The well is pressure tested after every stage to confirm its integrity."
Each stage of requires roughly 350,000 to 650,000 gallons of fracturing fluid and can take between one and a half to four hours to complete. The number of personnel and equipment can vary as well, ranging from 40 to 55 people on site and approximately seven to 32 frac tanks, four sand storage containers, two blenders, 14 to 16 pumps, additive storage tanks, a vacuum truck, the data van and various miscellaneous equipment.
However, throughout the entire fracturing process, the focus on environmental and personal safety remains the same.
"Protective equipment such as hardhats, safety glasses, steel-toed boots and reflective, fire-resistant clothing is required," Sweeney said. "Prior to stepping onsite, there is a Job Safety Assessment that focuses on safety awareness. There is always an onsite security guard to admit authorized personnel and to keep a headcount of individuals onsite so that everyone can be accounted for at all times.
"Additionally, there are environmental-protection measures such as containment berms around the pad, plastic mats under the work area and containment measures under anything that may pose the risk of a potential leak, such as vehicles and fluid connections," he continued. "The bolts of the wellhead are checked and personnel make sure everything is secure. They also monitor offset wells on location and make sure the operations are not causing any impacts to those wells."
However, it's not only the other wells on location that need to be checked.
"We also keep track of any old, abandoned wells in the area that we've previously identified and made sure (they) were addressed before any work began at our site," Sweeney said.
When the final plug of the fracturing process is installed, the crew and equipment leaves the location and the well is prepared for a long, quiet life of producing natural gas.
"Without hydraulic fracturing, it would not be possible to economically produce natural gas from shale formations," Sweeney said. "This process promotes the movement of the gas to the wellbore so it can be produced and transported to market for a variety of beneficial uses, from heating and energy production to manufacturing of plastics and synthetic fabrics."
Johnny Williams can be reached at (570) 265-1639; email:email@example.com.
This story also appears in the latest Northeast Driller, which is available today. To read select stories from the Northeast Driller, visit www.northeastdriller.com.