Drilling the well Wellbore drilling and casing construction
Editor's Note: This is the third 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.
The drilling of a well is undoubtedly the most recognizable process of the natural gas industry. The tall drilling rig rising high above the ground has essentially become the logo and the face of the industry in the Marcellus Shale. While the purpose of a drilling rig is quite simple, the process, itself, is anything but.
"The drilling of a well is designed by a team of engineers far in advance of any operations on the ground," said Rory Sweeney of Chesapeake Energy. "The design - as part of our overall development strategy - tells us where the well needs to go to be the most productive, how the well is built and how we ensure safe and environmentally conscious operations. The whole process is mapped and blueprinted."
"We use a very careful and well planned process to safely access the methane in the formation and produce it to the surface for all the advantages that affordable natural gas provides, including use for heating, electricity production, as a feedstock for plastics and other synthetic materials, a transportation fuel and many other uses. A lot of work goes into ensuring we capture all of the gas we produce and send it to market."
However, before the drilling rig even arrives at the well pad, a variety of preparations and precautions must take place. The pad is constructed with three-foot berms that encircle it. The construction team also builds a concrete base with a shallow round hole in the center called a cellar through which each well begins its construction.
"A conductor rig is then brought in," Sweeney continued. "This small rig installs a conductor casing, which is roughly 24 inches in diameter. That casing is installed to roughly 60 feet, then cemented into place. The reason we use the smaller conductor rigs as opposed to a full-sized drilling rig is because they are much more mobile and can move from pad to pad relatively quickly."
After the conductor rig has completed its task, more protection is added to the site to protect against spills.
"We set up a host of environmental controls prior to any drilling," Sweeney said. "We set up our liner, put berms around the edges and lay down additional matting on top of that."
Mobile housing units are brought onto the pad for the site supervisors, geologists and specialists. The arrival of rig trucks, each carrying a section of the drilling rig, signals the beginning of the "rigging up" process.
Rigging up involves raising the rig tower, or the derrick, making the connections necessary for fluid treatment and includes bringing in drill pipe, casing equipment, drill bits, containment tanks, power generators, fuel and additives for drilling mud, which is stored on location. The entire rigging up process can take roughly three to four days.
"Finally, we're ready to start drilling," Sweeney said. "The type of drilling we use is decided by what kind of fluid we use to circulate the drill cuttings to the top of the wellbore. We'll start by drilling using a freshwater-based fluid and drill between 500 to 1,000 feet down through the freshwater aquifer. We'll then install the surface casing and cement it into place to seal off the freshwater zone."
Casing is the process of lining the drilling hole, or the wellbore, with steel casing. It's then cemented by pumping cement down the casing and then up the outside of the casing until it surrounds the well casing all the way to the surface, thus protecting the wellbore and the earth around it.
Sweeney said that special thixotropic cement is used for the casing, which is designed so that it solidifies rapidly.
After the surface casing is installed, the drillbit is lowered back into the hole to drill to roughly 2,000 feet down, though the exact depth varies based on the specific geology of the area. Freshwater-based fluid is used in this portion of the well, and the returning "drill cuttings" are then run through a shaker, which separates larger rock fragments from the liquid by shaking them out of the solution and depositing them into a steel container. The solids are then dried before they are removed from the location. Smaller cuttings particles are removed from the fluid using a combination of centrifuges and settling tanks, and the fluid is recycled back down the wellbore to continue drilling. Ingredients can be added to adjust the attributes of the fluid, such as weight and viscosity.
"Throughout the drilling process, drill pipe needs to be added to extend the drill string to the bottom of the wellbore," he continued. "Each section of pipe is 30 feet long, and they are attached together by screwing in more sections as the wellbore gets longer. The drill string is connected to a motor suspended above the rig floor, known as a top drive, that also pumps the drilling fluid down through the drill string. It is raised and lowered by the draw works, which are large winches that can range between 500 and 2,000 horsepower.
"Rig crewmembers make connections by screwing each section of pipe onto the end of the drill string, which is held in place by a clamp on the rig floor. When the drill string needs to be taken out of the hole, the pipe sections are taken apart in sets of two or three and racked back on the rig derrick."
This occurs whenever another layer of casing needs to be installed or if tools at the end of the drill string need to be changed or serviced. At 2,000 feet down, the drill string is removed and the intermediate layer of casing is installed and cemented into place. The intermediate casing is cemented back to the surface to provide another layer of protection for the freshwater zone. A different drillbit is attached to the end of the drill string so that air can be used as the drilling fluid, and the bit drills vertically to roughly 7,000 feet.
"This continues to the kickoff point, which is where we'll begin to make our turn to drill horizontally," Sweeney said. "We'll then switch to a synthetic-oil-based fluid that looks similar to vegetable oil and change to a poly-crystalline diamond compact bit.
"We'll also add a directional motor, which has a one to three degree bend," he said. "The motor can turn the well bore 12 degrees per 100 feet, which is so gradual that it doesn't create any undue strain on the drill pipe or casing. It takes approximately 750 feet of drilling to make a 90 degree turn and begin drilling horizontally into the target zone: the Marcellus shale."
Of course, keeping track of where the drilling operation is below ground is extremely important, but impossible to see from above the ground without the help of technology.
"We have measurement-while-drilling tools, similar to navigational equipment used by NASA, that allows us to know where the drill bit is below the surface within a few feet so we can keep track of where we are underground and follow the blueprint set by the engineers from the very beginning," Sweeney said. "We have directional tools in place that give us complete control of the motor. The shale we're drilling through isn't flat, so these tools allow us to turn up, down, left and right to stay within the targeted shale interval.
"When this process is complete, we remove the pipe and drillbit, install production casing from the bottom of the well all way to the surface and cement it in place."
Next, depending on the operation, the rig is either moved to the next well on the pad or disassembled and taken away. If it remains on the pad, the rig is moved by skids to the next well about 15 feet away, the equipment is reconnected, and the process begins again.
"It takes roughly 15 to 30 days to drill a well," Sweeney said. "Around 22 to 24 people will man a rig, and wells are typically drilled approximately 11,000 to 16,000 feet from beginning to end. We also have onsite geologists, known as mud loggers, who will analyze the cuttings that come up when drilling. This serves as a double check for our geology department on where we are below ground and to gather additional information on the shallow geology."
Throughout the entire drilling process, a primary focus is employee and environmental safety.
"We constantly have spill-prevention measures in place and equipment on site to prevent environmental releases," Sweeney noted. "Tanks need to be cleaned, the rig is kept power washed; if a rig hand isn't busy doing his various duties, he's cleaning."
"Everyone on site is required to wear proper safety gear, including protective eyewear, steel-toed boots and reflective, fire-resistant clothing," he continued. "Additionally, blowout preventers are installed on each well once the surface casing is installed. Blowout preventers are redundant safety devices that can seal the well bore if the crew encounters any issues with down-hole pressure.
Drilling operations also have preparations in place for all kinds of weather possibilities, from fans and constant hydration in the heat to heaters and wind blocking fabric in the cold to slip precautions in rain and snow.
While the process remains the same, there are actually three different types of drilling rigs used, which can range from 118 to 165 feet tall, according to Sweeney.
"Tier One rigs are the most advanced rigs and are powered by AC electricity with electronic controls," he said. "Tier Two rigs are DC-electric rigs with conventional controls, and Tier Three rigs are hydraulic rigs with conventional controls."
It's been known for some time that natural gas beneath the Appalachian Mountains existed, but until recently the technology needed to economically produce it kept it from being extensively explored. Today, in only a month or less, the obstacles that separated people from decades' worth of natural gas can be conquered, allowing the resource to benefit the nation with cheaper, local, American natural gas.
Johnny Williams can be reached at (570) 265-1639; email: firstname.lastname@example.org.
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.