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The Technology:
Map it, Drill it, Frac it
By Cheryl Hudak
Almost anyone in the natural gas industry will agree that producing natural gas today is a three-part journey. As unconventional resources play increasingly critical roles in meeting U.S. energy needs, fracture stimulation (or hydraulic fracturing) has become the third leg of the long journey from exploration to production. It brings home the gas.
Hydraulic fracturing, commonly known as “fracing,” is a completion technique used by engineers to create a crack or fracture in rock that contains oil or gas, propping open the rock to let hydrocarbons flow out and up through the wellbore.
In 2007, about 50% of the total U.S. natural gas production came from unconventional resource plays such as tight sand, gas shale and coalbed methane. As one of the nation’s top unconventional operators, Chesapeake uses hydraulic fracturing techniques on approximately 99% of its wells.
Festooned with red pipes, the University 19-9 #2 is the star of the show
during fracture stimulation in West Texas. An army of pumper trucks,
mixing tanks and storage units for water and sand converge on the site
during the four to five days it takes to frac the well.
“Often, completions are the key to discovering new plays,” explained Jeff Fisher, Senior Vice President – Production. “There have been a lot of bypassed rocks, known depositions considered uneconomic. New completion techniques have opened up opportunities that previously didn’t exist.”
According to Fisher, Chesapeake has fraced most wells in the hard rock plays where it operates for many years. The difference is today the company combines fracing with horizontal drilling.
“That’s changed the game,” he said. “At one time, fracture stimulation was done to enhance well productivity. Today, in our shale plays, it’s required to have any production at all.”
The technique is used in newly completed wells to increase drainage rates and maximize field development. It is also used for already-producing wells in developed or mature fields to get the most out of existing infrastructure and maintain production rates.
The entire fracing process is highly complicated and can take up to four or five days to complete. It also requires enormous planning and expense.
“The coordination required to frac a well is unbelievable,” Fisher said. “I think fracture stimulation is perhaps the most intense operation in natural gas development. It is a carefully choreographed part of the business, as we have to coordinate fluids, pumps and sand, and monitor every aspect of the job to make necessary adjustments.”
The process is further complicated by the fact not all wells, locations or geology respond to fracture stimulation in the same way.
“Not all shales are the same,” Fisher explained. “For instance, the Haynesville Shale in Louisiana is hotter, deeper and over-pressured – very challenging from an operational perspective. Of course, that high pressure means it is a very productive play, but it does require higher pressure equipment.”
Regardless of location, depth or geology, every frac job is performed by experienced crews from companies that specialize in the procedure. It is an expensive finale to the development process, often adding $500,000 to over $1 million to each well’s cost. Without it, however, shale gas drilling would be fruitless.
Chesapeake is considered a leader in the use of hydraulic fracturing techniques.
“We’re doing a lot of the same things other unconventional operators do,” Fisher said, “but more of it and in more places; so we can transfer the technology from play to play. We understand that and use it more effectively to optimize each play. We are constantly learning and reapplying new information.
“Our Reservoir Technology Center helps incorporate rock sciences into our activities. We are learning more and more about fluid sensitivities and rock mechanics, and modeling through computer programs that simulate the effects of fracing. These help us understand the many variables and economic elements involved.
“We’re also learning where in a thick formation the well should land – top, middle or bottom of the formation – for maximum results. This helps us guide the wellbore exactly where we want it to be. It’s another way our core lab provides a great advantage.”
Chesapeake production teams are experimenting with microseismic technology, which allows them to monitor and see – in real time – the rock, as it cracks during the hydraulic fracturing process.
“We’ve always tried to understand exactly what happens when we do fracture stimulation,” Fisher noted. “But we can’t actually see it occur, where it is, and how effectively it opened up the reservoir. Microseismic technology may in the future give us the ability to adjust the fracturing process on the fly. Today, we can record fracs with seismic data, which provides us better information on how the fracing process went on any specific well.”
Such information leads to innovation as operators gain experience in the powerful pairing of horizontal drilling with fracture stimulation. One such innovation is simulfracing, where more than one well is fraced at the same time. This technique offers better diversion of fluids and more complex fracturing than isolated fracs. Production is often enhanced and the operation is more efficient and cost effective as well.
While the fracture stimulation process may appear to use large amounts of water, those quantities are less imposing when compared with total water usages in an area. For example, Chesapeake drilling and completion activities at projected peak development in the Marcellus Shale will account for less than 0.06% of that region’s entire water consumption.
A typical Chesapeake well in the Barnett Shale uses about 3 million gallons of water for drilling and completion – usually just once during its projected 20-30 year lifespan. In comparison, a golf course uses about 3 million gallons of water every 10 days. The amount of water used per well varies with each area and well; but in every case, frac fluids and water are disposed of at permitted facilities or treated for re-use.
Environmental issues are of critical importance in every location where the company operates. The company meets or exceeds oil and gas regulations throughout its operations. Each hydraulic fracturing project is designed, conducted and monitored to mitigate environmental impact while maximizing natural gas production.
Natural barriers also play a role in protecting ground water. With most freshwater aquifers located less than 1,000 feet below the earth’s surface and fracturing operations conducted at levels between 4,000 and 12,000 feet below ground level, there are thousands of feet (often between one and three miles) of natural geologic barriers between Chesapeake’s productive shale formations and freshwater zones.
Simplified steps in hydraulic fracturing
1. Water, sand and additives are pumped at extremely high pressure down the wellbore.
2. The liquid goes through perforated sections of the wellbore and into the surrounding formation, fracturing the rock and injecting sand or proppants into the cracks.
3. Experts continually monitor and gauge pressures, fluids and proppants, studying how the sand reacts when it hits the bottom of the wellbore, slowly increasing the density of sand to water as the frac progresses.
4. This process may be repeated multiple times, in “stages” to reach maximum areas of the wellbore. When this is done, the wellbore is temporarily plugged between each stage to maintain the highest water pressure possible and get maximum fracturing results in the rock.
5. The frac plugs are drilled or removed from the wellbore and the well is tested for results.
6. The water pressure is reduced and fluids are returned up the wellbore for disposal or treatment and re-use, leaving the sand in place to prop open the cracks and allow the gas to flow.